Patent Publication Number: US-9898016-B2

Title: Variable product agrochemicals application management

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority from, U.S. patent application Ser. No. 13/027,435, filed Feb. 15, 2011, entitled “VARIABLE PRODUCT AGROCHEMICALS APPLICATION MANAGEMENT,” which is incorporated herein by reference in its entirety and claims the benefit of U.S. Provisional Application No. 61/388,414, filed Sep. 30, 2010, entitled “VARIABLE PRODUCT AGROCHEMICALS APPLICATION MANAGEMENT.” 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     SUMMARY 
     Embodiments of our technology are defined by the claims below, not this summary. A high-level overview of various aspects of our technology are provided here for that reason, to provide an overview of the disclosure, and to introduce a selection of concepts that are further described below in the detailed-description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in isolation to determine the scope of the claimed subject matter. In brief and at a high level, this disclosure describes, among other things, ways to assist a grower in developing and implementing strategies for agrochemical application. 
     In brief, embodiments of the technologies described herein provide ways to facilitate variable-product agrochemicals application. In one embodiment, a field (or area of land) is delineated and mapped into zones of ground, that are suitable for receiving a certain agrochemical, based on characteristics of the ground within the zones. For example, the agrochemical might be a fertilizer and the zones might represent areas of the field that are vulnerable to fertilizer loss due to soil characteristics. Using information about the delineated zones, appropriate mixture ratios or rates of fertilizer to be applied to areas of the field are determined. For example, areas within zones of land susceptible to fertilizer loss might be determined to receive specially adapted or enhanced efficiency fertilizer, while areas within zones of ground that are not susceptible to fertilizer loss might be determined to receive a conventional fertilizer. The determined fertilizer application sources, mixture ratios, and rates, which we refer to as the “fertilizer product,” can be presented as a schedule or listing or visually as a geographically referenced map of the field, showing which areas of the field are to receive the determined fertilizer products. This map, or other information representing the determined fertilizer products can also be transferred in an appropriate form to a controller of a fertilizer applicator, thereby enabling fertilizer to be applied to the field consistent with the determined ratios and rates of the fertilizer products. Additionally, the map, or other information representing the determined fertilizer products, may be stored for record keeping or used for reporting, evaluating application strategies, or other analysis. For example, the map may be used as an overlay onto a map showing crop yields within the field. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein: 
         FIGS. 1A and 1B  depict aspects of an illustrative operating environment suitable for practicing an embodiment of our technology; 
         FIG. 1C  depicts an area of land suitable for receiving fertilizer application in accordance with embodiments of the present invention; 
         FIG. 2A  depicts areas of land suitable for receiving fertilizer application, an example mapping of fertilizer-application cells, and fertilizer application by a fertilizer applicator in accordance with embodiments of the present invention; 
         FIGS. 2B-2E  depict areas of land suitable for receiving fertilizer application and an example mapping of fertilizer-application cells in accordance with embodiments of the present invention; 
         FIG. 3  depicts an illustrative process flow-diagram that illustrates an embodiment of facilitating a method of ultimately applying variable-product fertilizer to an application area; 
         FIG. 4  depicts a method by which the present invention may be used in order to apply fertilizer to an application area. 
         FIG. 5  depicts a method by which the present invention may be used in order to apply fertilizer to an application area. 
         FIG. 6  depicts a method by which the present invention may be used in order to determine attribute values; 
         FIGS. 7A-7C  depict methods by which the present invention may be used in order to delineate a zone; 
         FIG. 8  depicts a method by which the present invention may be used in order to partition an application area into application cells; and 
         FIG. 9  depicts a method by which the present invention may be used in order to determine a fertilizer product for applying to an application cell. 
     
    
    
     DETAILED DESCRIPTION 
     The subject matter of the present technology is described with specificity herein to meet statutory requirements. However, the description itself is not intended to define the technology, which is what the claims do. Rather, the claimed subject matter might be embodied in other ways to include different steps or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the term “step” or other generic term might be used herein to connote different components or methods employed, the terms should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described. 
     Acronyms and Shorthand Notations 
     Throughout the description of the present invention, several acronyms, shorthand notations, and terms are used to aid the understanding of certain concepts pertaining to the associated system and services. These acronyms, shorthand notations, and terms are solely intended for the purpose of providing an easy methodology of communicating the ideas expressed herein and are in no way meant to limit the scope of the present invention. The table below does not include a full definition. A full definition of any term can only be gleaned by giving consideration to the full breadth of this patent. 
     Sometimes, we use different terms to refer to similar or the same things. We do not necessarily mean to implicate a difference, per se; but are constrained by certain statutory requirements that apply to patents and patent applications. For example, claims must use proper antecedent basis. Sometimes satisfying that rule can lead to wordiness, whereas using a different word helps make referring to prior terms easier. Thus we might use different words in that regard. The following is a list of these terms: 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 DEM 
                 Digital Elevation Model 
               
               
                 TWI 
                 Topographic Wetness Index 
               
               
                 Agrochemical 
                 A substance able to be applied to an application 
               
               
                   
                 area, and which may be solid, liquid, gaseous, or a 
               
               
                   
                 combination of one or more solid, liquid, or gaseous 
               
               
                   
                 substances including, for example, fertilizers, 
               
               
                   
                 herbicides, pesticides, other crop protection 
               
               
                   
                 chemicals, erosion control or other surface control 
               
               
                   
                 substances, conditioners, nutrients, minerals, 
               
               
                   
                 neutralizers, soil additives, amendments, or similar 
               
               
                   
                 substances. 
               
               
                 Fertilizer, 
                 A type of agrochemical for application to an 
               
               
                 Fertilizer Source 
                 application area. It is contemplated that in some 
               
               
                   
                 embodiments, the term “fertilizer” includes any 
               
               
                   
                 agrochemical of combination of agrochemicals. 
               
               
                 Application Area 
                 An area of land suitable for receiving an application 
               
               
                   
                 of an agrochemical, and which might include one or 
               
               
                   
                 more fields, pastures, orchards, courts, golf courses, 
               
               
                   
                 yards, lawns, planting or cultivating beds, lots, or 
               
               
                   
                 similar areas of land, or a portion of such an area. 
               
               
                 Discrete Land 
                 A discrete portion of land located within an 
               
               
                 Unit 
                 application area associated with one or more 
               
               
                   
                 attribute values. 
               
               
                 Location Point 
                 A location in an application area that has an 
               
               
                   
                 associated attribute value corresponding to a 
               
               
                   
                 degree of expression of an attribute at that 
               
               
                   
                 location. For example, location points may 
               
               
                   
                 represent locations in an application area 
               
               
                   
                 corresponding to measurements of an attribute, 
               
               
                   
                 such as soil pH-level measurements, vegetation, soil 
               
               
                   
                 structure, or other attributes, and may be uniformly 
               
               
                   
                 spatially distributed or located wherever attribute 
               
               
                   
                 data, such as field measurements of attributes, are 
               
               
                   
                 available. They may be more densely located 
               
               
                   
                 around areas where an attribute has a greater 
               
               
                   
                 variance and may be more spread apart in areas 
               
               
                   
                 where the attribute varies less. 
               
               
                 Attribute Value 
                 An attribute value corresponds to a degree of 
               
               
                   
                 expression of an attribute present at a location 
               
               
                   
                 point or within a discrete land unit of an application 
               
               
                   
                 area. An attribute value may be expressed as 
               
               
                   
                 numerical quantity (e.g., “6” or “20%”) or as a 
               
               
                   
                 classification (e.g. “acidic” or “sandy”), and may be 
               
               
                   
                 derived from a measurement of an attribute at a 
               
               
                   
                 single point within a discrete land unit or may be an 
               
               
                   
                 average, median, or similar representative value of 
               
               
                   
                 the degree of expression of an attribute possessed 
               
               
                   
                 by a discrete land unit. An attribute value also may 
               
               
                   
                 be represented as an index value, which 
               
               
                   
                 corresponds to an index that represents degrees of 
               
               
                   
                 expression of an attribute. A set of attribute values, 
               
               
                   
                 corresponding to a plurality of discrete land units or 
               
               
                   
                 location points in an application area, may be 
               
               
                   
                 characterized or represented as an attribute grid, 
               
               
                   
                 with each point on the grid corresponding to a 
               
               
                   
                 location of a discrete land unit or location point 
               
               
                   
                 having an associated attribute value. 
               
               
                 Attribute Zone 
                 An area of land in an application area that has 
               
               
                   
                 similar attribute values. For example, in one 
               
               
                   
                 embodiment, zones are made up of substantially 
               
               
                   
                 contiguous discrete land units having substantially 
               
               
                   
                 similar attribute values or having attribute values 
               
               
                   
                 corresponding to the same attribute classification, 
               
               
                   
                 such as “acid” or “alkaline. 
               
               
                 Application-Area 
                 Application-area information includes attribute 
               
               
                 Information 
                 information corresponding to characteristics of the 
               
               
                   
                 application area. In some embodiments this 
               
               
                   
                 includes attribute values that are geographically 
               
               
                   
                 referenced within the application-area or 
               
               
                   
                 associated with location information. Application- 
               
               
                   
                 area information may further include other 
               
               
                   
                 geographic information of application area such as 
               
               
                   
                 its geographic location, proximity to streams, roads, 
               
               
                   
                 wetlands, or similar features. Application-area 
               
               
                   
                 information can, in some embodiments, also 
               
               
                   
                 comprise one or more sets of measured or 
               
               
                   
                 determinable values of a characteristic or attribute 
               
               
                   
                 at locations in an application area. For example, for 
               
               
                   
                 the attribute of soil acidity or alkalinity, application- 
               
               
                   
                 area information might include a set of attribute 
               
               
                   
                 values representing the location and measured soil 
               
               
                   
                 pH-levels of various location points in the 
               
               
                   
                 application area. 
               
               
                 Fertilizer Product, 
                 A determined fertilizer or agrochemical application 
               
               
                 Agrochemical 
                 for an application cell. A fertilizer (or agrochemical) 
               
               
                 product 
                 product can include the source(s) or type(s) of 
               
               
                   
                 fertilizer, and can also include the quantity or 
               
               
                   
                 volume of fertilizer, application rate, and fertilizer- 
               
               
                   
                 mixture information such as a proportion of mixed 
               
               
                   
                 fertilizer types. 
               
               
                   
                 In one embodiment, a fertilizer product is 
               
               
                   
                 determined for each application cell in an 
               
               
                   
                 application area. A fertilizer product, or a set of 
               
               
                   
                 fertilizer products for multiple application cells, may 
               
               
                   
                 be formatted as a schedule showing application 
               
               
                   
                 levels, rates, mixture ratios, quantities, total 
               
               
                   
                 amounts, or sources. 
               
               
                 Application Cell 
                 A portion of ground that will receive a certain 
               
               
                   
                 product of fertilizer. The boundaries of an 
               
               
                   
                 application cell may be determined by the physical 
               
               
                   
                 reach or other limitations of a fertilizer applicator, 
               
               
                   
                 user preferences, or by other application 
               
               
                   
                 parameters, in one embodiment. 
               
               
                 Application Strip 
                 A row of partitioned application cells of uniform 
               
               
                   
                 width. An application strip represents an area of 
               
               
                   
                 ground covered by a single pass of a fertilizer 
               
               
                   
                 applicator. By way of example, applying fertilizer to 
               
               
                   
                 an application area may be accomplished by a 
               
               
                   
                 series of back-and-forth passes over the application 
               
               
                   
                 area, to ensure the entire application area receives 
               
               
                   
                 fertilizer. 
               
               
                 Fertilizer- 
                 Parameters, which in some embodiments are used, 
               
               
                 Application 
                 along with the application-area information to 
               
               
                 Parameters 
                 determine the fertilizer-application information, 
               
               
                   
                 which will be used for apply fertilizer to each 
               
               
                   
                 application cell. Fertilizer-application parameters 
               
               
                   
                 comprise information such as (1) indications of 
               
               
                   
                 fertilizer-applicator equipment which might affect 
               
               
                   
                 the application cell size; (2) user application 
               
               
                   
                 preferences such as a risk-avoidance level for 
               
               
                   
                 known risk areas, fertilizer-application products, 
               
               
                   
                 preferred fertilizer types, user-specified buffer 
               
               
                   
                 areas, and application-cell size (3) available fertilizer 
               
               
                   
                 types; (4) rates and ratios of fertilizer types to 
               
               
                   
                 apply for given application-area characteristics; (5) 
               
               
                   
                 attribute thresholds or index thresholds; (6) 
               
               
                   
                 information about the type of crop that will be 
               
               
                   
                 grown in the application cell; (7) historical data such 
               
               
                   
                 as previous parameters, previous application rates 
               
               
                   
                 and ratios, and past crop yields; (8) economic 
               
               
                   
                 parameters such as the cost of the fertilizer or cost- 
               
               
                   
                 benefit analyses of the cost for applying a particular 
               
               
                   
                 fertilizer to an application cell verses the expected 
               
               
                   
                 gain from an improved crop-yield from that cell; (9) 
               
               
                   
                 government regulations (which, for example, might 
               
               
                   
                 limit the amount or location of certain types of 
               
               
                   
                 fertilizer sources that can be applied); and (10) local 
               
               
                   
                 geographic information (such as a nearby stream or 
               
               
                   
                 wetlands that might affect which fertilizer is to be 
               
               
                   
                 applied to adjacent application cells. 
               
               
                 Equipment 
                 Equipment parameters are a subset of fertilizer- 
               
               
                 Parameters 
                 application parameters and include parameters 
               
               
                   
                 relating to the fertilizer-applicator equipment and 
               
               
                   
                 other parameters affecting the physical limitations 
               
               
                   
                 of applying fertilizer. For example, equipment 
               
               
                   
                 parameters may include the reach or coverage-area 
               
               
                   
                 of an applicator for given types of fertilizer or 
               
               
                   
                 information which can be used to determine an 
               
               
                   
                 applicator&#39;s reach or coverage-width, such as a 
               
               
                   
                 model number of a fertilizer applicator. 
               
               
                 Fertilizer- 
                 Information including the results of the process for 
               
               
                 Application 
                 determining a fertilizer product to apply to an 
               
               
                 Information 
                 application cell based on application-area 
               
               
                   
                 information and, in one embodiment, fertilizer- 
               
               
                   
                 application parameters. Fertilizer-application 
               
               
                   
                 information can include information specifying a 
               
               
                   
                 product of fertilizer to apply in an application cell 
               
               
                   
                 such as the source(s) or type(s) of fertilizer, the 
               
               
                   
                 quantity of fertilizer, application rate, and fertilizer- 
               
               
                   
                 mixture information such as a proportion of mixed 
               
               
                   
                 fertilizer types. 
               
               
                   
                 In one embodiment, fertilizer-application 
               
               
                   
                 information also specifies location information for 
               
               
                   
                 the application cell; in one embodiment it also 
               
               
                   
                 includes other information such as the results of 
               
               
                   
                 additional analysis performed using fertilizer 
               
               
                   
                 application information. 
               
               
                 Fertilizer Product, 
                 A determined fertilizer or agrochemical application 
               
               
                 Agrochemical 
                 for an application cell. A fertilizer (or agrochemical) 
               
               
                 product 
                 product can include the source(s) or type(s) of 
               
               
                   
                 fertilizer, and can also include the quantity or 
               
               
                   
                 volume of fertilizer, application rate, and fertilizer- 
               
               
                   
                 mixture information such as a proportion of mixed 
               
               
                   
                 fertilizer types. 
               
               
                   
                 In one embodiment, a fertilizer product is 
               
               
                   
                 determined for each application cell in an 
               
               
                   
                 application area. A fertilizer product, or a set of 
               
               
                   
                 fertilizer products for multiple application cells, may 
               
               
                   
                 be formatted as a schedule showing application 
               
               
                   
                 levels, rates, mixture rations, quantities, total 
               
               
                   
                 amounts, or sources. 
               
               
                 Fertilizer 
                 A collection of information specifying fertilizer- 
               
               
                 Application 
                 application information, including the determined 
               
               
                 Schedule 
                 fertilizer (or agrochemical) product to be applied for 
               
               
                   
                 each application cell, of a set of application cells, in 
               
               
                   
                 an application area. The schedule can include, in 
               
               
                   
                 one embodiment, information specifying for each 
               
               
                   
                 application cell, a product of fertilizer to apply, or a 
               
               
                   
                 quantity and fertilizer type or types, rate and a 
               
               
                   
                 mixture ratio, if a mixture of fertilizer types is to be 
               
               
                   
                 applied. 
               
               
                 Attribute 
                 An Attribute Threshold or attribute-value threshold 
               
               
                 Threshold 
                 is used to determine fertilizer product to be applied 
               
               
                   
                 based on attribute value(s) of zones within 
               
               
                   
                 application cells. For example, Topographic 
               
               
                   
                 Wetness Index (“TWI”) attribute values that do not 
               
               
                   
                 exceed a given TWI threshold might be ignored, 
               
               
                   
                 thus preventing these lower levels from 
               
               
                   
                 determining fertilizer-application rates and ratios. 
               
               
                   
                 An attribute threshold or characteristic-threshold 
               
               
                   
                 might also be in the form of multiple thresholds, 
               
               
                   
                 forming a bracket or range of characteristic values, 
               
               
                   
                 such as considering only attribute values falling 
               
               
                   
                 below a first value and above a second value. 
               
               
                 Risk-Avoidance 
                 A risk-avoidance level is a fertilizer-application 
               
               
                 Level 
                 parameter which is useable to scale or adjust 
               
               
                   
                 fertilizer product application. In one embodiment, a 
               
               
                   
                 risk avoidance level is used to adjust a 
               
               
                   
                 corresponding attribute threshold. 
               
               
                   
               
            
           
         
       
     
     Our technology may be embodied as, among other things: a method, system, or set of instructions embodied on one or more computer-readable media. Accordingly, the embodiments may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware. In one embodiment, the present invention takes the form of a computer-program product that includes computer-useable instructions embodied on one or more computer-readable media. 
     Computer-readable media include both volatile and nonvolatile media, removable and nonremovable media, and contemplates media readable by a database, a switch, and various other network devices. By way of example, and not limitation, computer-readable media comprise media implemented in any method or technology for storing information. Examples of stored information include computer-useable instructions, data structures, program modules, and other data representations. Media examples include, but are not limited to information-delivery media, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile discs (DVD), holographic media or other optical disc storage, magnetic cassettes, magnetic tape, magnetic disk storage, and other magnetic storage devices. These technologies can store data momentarily, temporarily, or permanently. 
     Illustrative uses of our technology, as will be greatly expanded upon below, might be, for example, to automate and facilitate decision making and actions undertaken by a person in the selection and application of fertilizer. For example, using our technology, a grower would be empowered to quickly identify vulnerable portions of a fertilizer-application area, such as a field, and readily determine a precise fertilizer-application strategy for addressing these vulnerabilities. In another example using our technology, a grower would be empowered to automatically selectively apply specialized fertilizer on a portion of an application area and apply less expensive conventional fertilizers for another portion of the field. In another example using our technology, a grower is empowered to quickly determine a fertilizer-application strategy based on the expected economic benefit derived from applying one fertilizer type verses another type over small portions of a field and automatically apply fertilizer according to the strategy. In another example using our technology, a grower would be empowered to automatically control application of fertilizer by a fertilizer-applicator, based on soil characteristics of the application area, grower-selection of fertilizer-application strategies, or other parameters. In another example using our technology, a grower would be empowered to purchase or prepare only the quantities of specialty fertilizers that are needed, and apply those specialty fertilizers only at locations where it would be helpful. In another example using our technology, a grower would be empowered to view a table or map of recommended fertilizer-application dosages, geographically referenced to locations in a field. The table or map might further assist in decision making and planning by including past fertilizer-application information, information about past crop-yields, or characteristics of the field. Our technologies would also empower a fertilizer-retailer to provide a customer with a fertilizer-application strategy customized to the customer&#39;s needs or application location. Our technology can also provide increased fertilizer-use efficiency and decreased environmental fertilizer loss, facilitate compliance with government regulations, or facilitate record-keeping of geographically referenced records of fertilizer-application history. These examples illustrate only various aspects of using our technology and are not intended to define or limit our technology. 
     The claims are drawn to instructions embodied on computer readable media for facilitating a method of ultimately applying variable-products of agrochemicals, such as a fertilizer, to a fertilizer-application area (“application area”), such as a field. The fertilizer sources or types can include conventional fertilizer (such as urea), enhanced-efficiency fertilizer (such as a fertilizer adapted for minimizing release wet areas), and other fertilizer sources. Enhanced-efficiency fertilizer (“enhanced fertilizer”) includes slow-release fertilizer, fertilizer having properties to minimize release in wet areas, resist or impede environmental loss, and other specialty fertilizer. Examples of enhanced fertilizer include ESN® by Agrium, Inc., Agrotain® by Agrotain International, Inc, NFusion® by Georgia-Pacific, and N-Serve® by Dow AgroSciences. Examples of conventional fertilizers include urea, manure, and chemical salts such as potassium nitrate, calcium phosphate, or ammonium sulfate. It is also contemplated, that in some embodiments fertilizer sources might include agrochemicals such as crop protection chemicals such as herbicides, pesticides, erosion control or other surface control substances, conditioners, nutrients, minerals, neutralizers, soil additives, amendments, or any other solid, liquid, or gaseous, or combination of solid, liquid, or gaseous substances which may be applied to an application area. 
     Some embodiments of the present invention determine a fertilizer and quantity of the fertilizer to be applied to discrete portions or cells of an application area, based on characteristics of the application area and fertilizer-application parameters. The fertilizer might include a single fertilizer type or a mixture of fertilizer types. The term “single fertilizer type” is not intended to convey a homogeneous substance, necessarily, but rather a single fertilizer source. For example UAN (urea ammonium nitrate) would be considered a single fertilizer type, although it is made up of urea, ammonium nitrate, and water. A mixture of fertilizer types includes a mixture of single-fertilizer types, such as a combination of different conventional types or enhanced types or a combination of conventional and enhanced fertilizer types. 
     At a high level in one embodiment, the method starts with determining attribute values that are associated with land or soil characteristics in an application area. Based on these attribute values and various agrochemical-application parameters (“application parameters”), the application area is divided into a number of application cells, which are portions of land that will receive a certain product of fertilizer. 
     The boundaries of an application cell (or at least its width) are determined by the physical reach or other limitations of a fertilizer applicator (such as a multi-bin spreader), user preferences, and by other application parameters, in one embodiment. The fertilizer-application parameters are also used, along with the application-area attribute values to determine the fertilizer-application information, which will be used to apply fertilizer to each cell. Fertilizer-application information includes an identification of type or types of fertilizer to apply to a cell, a rate and/or quantity of each fertilizer type to apply, and a ratio of fertilizer types to apply (when multiple types are to be used). 
     The fertilizer-application parameters include items such as: (1) indications of fertilizer-applicator equipment (e.g., the type of applicator, which fertilizer sources and how many fertilizer sources it can apply), its application reach (which affects the application cell size); (2) user application preferences including application rates and ratios, which in one embodiment are specified as a quantity per unit land area (e.g., 200 lbs/acre), risk-avoidance level, which is useable to scale or adjust fertilizer application rates, and other preferences, (3) available types of fertilizer; (4) rates and ratios of fertilizer types to apply for given application-area characteristics, which may also include rates if conventional fertilizer were to be used or rates if enhanced efficiency fertilizer were used; (5) attribute thresholds (explained below); (6) the type of crop that will be grown in the application cell; (7) historical data such as previous parameters, previous application rates/ratios, and past crop yields; (8) economic parameters such as the cost of the fertilizer or cost-benefit analyses of the cost for applying a particular fertilizer to an application cell verses the expected gain from an improved crop-yield from that cell; (9) government regulations (which might limit the amount or location of certain types of fertilizer sources that can be applied); and (10) geographic information (such as a nearby stream or wetlands that might affect which fertilizer is to be applied to adjacent application cells. 
     The attribute thresholds are used to determine which fertilizer type to apply based on the attribute value or index value. For example, Topographic Wetness Index (“TWI”) values that do not exceed a given TWI threshold might be ignored, thus preventing these lower levels from determining fertilizer-application rates and ratios. An attribute threshold or characteristic-threshold might also be in the form of multiple thresholds, forming a bracket or range of characteristic values, such as considering only attribute values falling below a first value and above a second value. 
     The determined fertilizer-application information can be represented as an association or mapping (such as a geographic map or a table) of application cells that are associated with information about: (1) what fertilizer type(s) to apply, (2) the quantity of fertilizer to apply, and (3) the ratio of fertilizer types to each other when a mixture of fertilizers is desired. This information can be formatted automatically for use by a controller of a fertilizer applicator and may be presented to a user as a visual representation, such as a table or geographically referenced map of the application area. 
     In one embodiment, the application-area characteristics are characterized as attribute values per discrete portions of land in the application area. In another embodiment, application-area characteristics are characterized as attribute values at a plurality of location points in an application area with each location point having an associated attribute value. In another embodiment, the application-area characteristics are characterized as attribute values per portions of a grid that logically overlays the application area. The values can also be associated with the indices of the grid, where an index represents a location point in an application area. For example, a soil pH-index could indicate soil pH-values at location points throughout an application area. Another exemplary index is the Topographic Wetness Index (TWI), which indicates a likelihood for accumulation of water at a given location point or within a given discrete unit of land within the application area. The TWI can be a factor in deciding where to apply a type of fertilizer; e.g., an enhanced fertilizer verses a conventional fertilizer based on the likelihood that a conventional fertilizer will be more susceptible to environmental loss if it is applied to a given application cell. 
     At a lower level in one embodiment, the method first determines at least one attribute-index or set of attribute values over an application area and then delineates zones based on similar attribute or index values or attribute values (or index values) within the same class or range. For example, contiguous areas having similar TWI values or TWI values falling within the same range will be delineated as one zone. An attribute zone might fall entirely within an application cell or might span multiple cells. 
     The system logically partitions the application area into application cells based on fertilizer-application parameters including applicator-equipment parameters, user preferences, and the size of the application area, and the location of the zones, in one embodiment. Each cell encompasses at least part of at least one zone, thereby associating information about that zone and its attribute values with the cell. For example, a given cell might include part of a zone having a high TWI value and part of a zone having a low TWI value. In one embodiment, the output of the partitioning step yields the application cells (including their size and location), information about the attribute zones within each application cell, and any fertilizer-application parameters relevant to the application cells. 
     Fertilizer-application information, which includes the type(s), rate, and ratios of fertilizer to be applied, for each application cell is also determined. As mentioned, the output of the partitioning step includes the size and location of the application cells, and, for each cell, information about the attribute zones within that cell and may also include fertilizer-application parameters relevant to that cell, in one embodiment. Thus, the output of the partitioning step provides the input for the step of determining the fertilizer-application information. Specifically, the fertilizer-application information is determined, for each cell, based on (1) the fertilizer-application parameters relevant to that cell and (2) information related to the zones within that cell. By way of example, if a given application cell contained only one attribute zone, which had a high TWI value, then the fertilizer-application information for that cell would specify that it should receive an enhanced fertilizer (unless other application parameters specified otherwise). 
     The fertilizer-application information might indicate that only one fertilizer source is to be applied to an entire cell. Alternatively, a mixture should be applied. The decision to apply a mixture is determined by an application parameter known as a mixed-types indicator. This is a parameter that specifies whether or not to use a mixed ratio of fertilizer types in an application cell. If the mixed-types indicator specifies that a mixed ratio of types can be applied where necessary, then the decision of whether to use a mixture and the specific mixture ratio are determined based on the attribute zones within the application cell and the proportion of area of the application cell that each zone occupies, in one embodiment. Thus, for example, assume that a cell includes two zones: one zone that has a low TWI value and occupies 60% of the application-cell area, and another that has a high TWI value and occupies the remaining 40% of the application-cell area. If the mixed-types indicator indicates that using a mixture is permissible, then a mixture of fertilizer types will be used in one embodiment because two zones having different characteristics are within the application cell. Furthermore, in one embodiment the mixture ratio of fertilizer types to apply is determined based on the proportional areas occupied by each zone. Here, the ratio might be 60% conventional fertilizer to 40% enhanced fertilizer. 
     On the other hand, if the mixed-types indicator indicates that only a single type is to be applied, then in one embodiment, a determination of which type to apply must be performed. This determination could be based on the attribute value of the zone occupying the greatest area within the application cell. So, in the above example where 60% of the application cell includes a zone having a low TWI value, the decision of which source to apply would be based on that zone&#39;s characteristic. Since it is characterized as having a low TWI value, a conventional fertilizer type would be applied (unless other application parameters dictated otherwise). 
     Turning now to  FIGS. 1A and 1B , an exemplary operating environment  100  is shown suitable for practicing an embodiment of the invention. We show certain items in block-diagram form more for being able to reference something consistent with the nature of a patent than to imply that a certain component is or is not part of a certain device. Functionality matters more, which we describe. Similarly, although some items are depicted in the singular form, plural items are contemplated as well (e.g., what is shown as one data store might really be multiple data-stores distributed across multiple locations). But showing every variation of each item might obscure the invention. Thus for readability, we show and reference items in the singular (while fully contemplating, where applicable, the plural). 
     As shown in  FIG. 1A , Environment  100  includes agrochemical or fertilizer application-area  110 , (“application-area  110 ”) which might include one or more fields, pastures, orchards, courts, golf courses, yards, lawns, planting or cultivating beds, lots, or similar areas of land, or a portion of such an area suitable for receiving an application of an agrochemical. Although the term “fertilizer application area is shown in  FIG. 1A  and other figures, it is contemplated that in some embodiments, the term “fertilizer application area” refers to an area of land suitable for receiving any agrochemical. Thus application-area  110  represents an area of land suitable for receiving an application of agrochemical, and is made up of a portion of land; for example, as shown in exemplary environment  100 , application-area  110  is a small portion of land in the State of Missouri  115 . Despite being referred to as “application-area,” it is not a requirement that all portions of application-area  110  necessarily receive fertilizer. For example, it is contemplated that in some scenarios, portions of land within application-area  110 , for example buffer areas, will not receive fertilizer. 
     Fertilizer application-area  110  includes characteristics  112 , which comprise features, geography, terrain, composition, or nature of various locations in application-area  110 . For example, characteristics  112  might include the elevation, slope, soil structure, wetness, soil pH-level, soil organic matter, texture, residue, permeability, apparent electrical conductivity (ECa), vegetation, presence and quantity of a substances in the soil, average daily exposure to sunlight, average rainfall, temperature, or any other characteristic that might be relevant to fertilizer application. 
       FIG. 1B  illustrates another aspect of exemplary operating environment  100 .  FIG. 1B  shows data store  162  that stores fertilizer-application related information. This information includes application-area information  120  and fertilizer-application parameters  130 . This information may also include historical information  140  and fertilizer application information  150 , in some embodiments. In some embodiments, data store  162  comprises networked storage or distributed storage including storage on servers located in the cloud. Thus, it is contemplated that for some embodiments, the information stored in data store  162  is not stored in the same physical location. For example, in one embodiment, one part of data store  162  includes one or more USB thumb drives or similar portable data storage media. Additionally, information stored in data store  162  can be searched, queried, analyzed using computing device  164  and user interface  168 . For example in one embodiment, a grower could input a query, through user interface  168 , of past fertilizer-application schedules for an entire application area or for a portion of an application area, search for only those portions of an application area that have previously received enhanced fertilizer, or specify information in data store  162  to be shown on a geographic map of an application area, such as showing a map of a current fertilizer-application schedule with information depicting a cost-benefit analysis for each application cell. 
     Application-area information  120  includes attribute information corresponding to characteristics  112 , which in some embodiments includes attribute values that are geographically referenced within application-area  110  or associated with location information. Application-area information  120  may further include other geographic information of application area  110  such as its geographic location, proximity to streams, roads, wetlands, or similar features. In some embodiments, application-area information  120  comprises one or more sets of measured or determinable values of a characteristic at locations in an application area. For example, for the attribute of soil pH, application-area information  120  might include a set of attribute values representing the location and measured soil pH-levels of various location points in the application area. Similarly, for the attribute of elevation, application-area information  120  might include a Digital Elevation Model (DEM) of the application area. In one embodiment, application area information  120  includes information representing characteristics  112 , characterized as values per portions of a grid that logically overlays the application area. Each attribute value can also be associated with the indices of the grid, where an index represents a location point in the application area and each point has a corresponding value representing a degree of expression of a particular characteristic, in one embodiment. 
     Application-area information  120  might include data provided by a user, a geographic information system database (e.g., GIS) or similar database, or field records, in one embodiment, and may also include additional information determined from this data. For example, application-area information corresponding to slope can be determined from other application area information such as elevation. Similarly, a Topographic Wetness Index can be determined from other application-area information such as a DEM and other spatial input variables representing characteristics  112  of application area  110 . 
     Fertilizer-application parameters  130  comprise information used for determining a fertilizer application based on application-area information  120 . This includes information such as (1) indications of fertilizer-applicator equipment (e.g., the type applicator, which fertilizer sources and how many fertilizer sources it can apply, its application reach, which affects the application cell size); (2) user application preferences such as a risk-avoidance level for known risk areas, fertilizer-application rates or quantities, preferred fertilizer types, user-specified buffer areas, and application-cell size, for example; (3) available fertilizer types; (4) rates and ratios of fertilizer types to apply for given application-area characteristics; (5) attribute thresholds or index thresholds; (6) information about the type of crop that will be grown in the application cell; (7) historical data such as previous parameters, previous application rates and ratios, and past crop yields; (8) economic parameters such as the cost of the fertilizer or cost-benefit analyses of the cost for applying a particular fertilizer to an application cell verses the expected gain from an improved crop-yield from that cell; (9) government regulations (which, for example, might limit the quantity, application rate, or location of certain types of fertilizer sources that can be applied); and (10) local geographic information (such as a nearby stream or wetlands that might affect which fertilizer is to be applied to adjacent application cells. 
     Equipment parameters  132  is a subset of fertilizer-application parameters  130  and includes parameters relating to the fertilizer-applicator equipment and other parameters affecting the physical limitations of applying fertilizer. For example, equipment parameters  132  may include the reach or coverage-area of an applicator for given types of fertilizer or information which can be used to determine an applicator&#39;s reach or coverage-width, such as a model number of a fertilizer applicator. In one embodiment, equipment parameters  132  is used to determine application-cell width during the logical partitioning of application cells. 
     Historical information  140  includes historical data relating to the application area such as previous fertilizer-applications or determined fertilizer-application products, crops and crop yields, and soil characteristics. In some embodiments, information from historic information  140  may be included in application parameters  130 . For example in one embodiment, some of fertilizer-application parameters  130  are based on data from historical information  140  such as previous application rates, user settings, or past crop yields resulting from a previously implemented fertilizer-application strategy. Historical information  140  can also include additional information such as previous analyses of fertilizer application strategies, meteorological records for an application area, or changes in crop yields over time, usable for analyzing fertilizer-application scenarios and facilitating determining a current fertilizer-application strategy. By way of example, a grower could view a geographically referenced map of a current fertilizer application strategy for a field and also view information from historical information  140 , such as locations and success rates of previous crop yields, overlaid onto the map. 
     Fertilizer-application information  150  is received from computing device  164  and stored in data store  162 . Fertilizer-application information  150  includes the results of the process for determining a fertilizer to apply to an application cell based on application-area information  120  and fertilizer-application parameters  130 . This includes information specifying a product of fertilizer to apply in an application cell. Fertilizer product includes the type or types of fertilizer, and can also include quantity of fertilizer, application rate, and fertilizer-mixture information such as a proportion of mixed fertilizer types. In one embodiment, fertilizer-application information  150  may also specify location information for the application cell. Location information defines the application cell&#39;s location either relative to other application cells or the boundary or corner of an application area, as latitude and longitude, or as another geographically referenced location. In one embodiment, fertilizer-application information  150  includes a fertilizer-application schedule, which specifies a fertilizer product for each application cell. 
     Fertilizer-application information  150  is used for generating applicator-controller information  184 , which is discussed below. In some embodiments, fertilizer-application information  150  also can be used to produce charts, tables, or geographically referenced maps showing fertilizer application products for an application area, thereby enabling a grower to see or modify a fertilizer application strategy for the application area. Fertilizer-application information  150  also includes results of additional analysis performed using fertilizer-application information  150 , in one embodiment. For example in one embodiment, fertilizer-application information  150  includes a geographically referenced mapping of fertilizer-application products for each application cell in an application area, and associated economic information such as the cost of the fertilizer-application product for each application cell or a cost-benefit analysis comparing fertilizer cost verses an expected crop yield or expected profit for each application cell. In time, fertilizer-application information  150  becomes part of historical information  140 . 
     Environment  100  also illustratively shows computing device  164  that is communicatively coupled to data store  162 , user interface  168 , and applicator data store  182 . Computing device  164  processes application-area information  120  and fertilizer-application parameters  130  to produce fertilizer-application information  150 . Computing device  164  also processes other information in data store  162  for subsequent analysis, in some embodiments. Computing device  164  includes one or more processors operable to receive instructions and process them accordingly, and may be embodied as a single computing device or multiple computing devices communicatively coupled to each other. Therefore it is not a requirement that user interface  168  be physically attached to computing device  164 , as shown in  FIG. 1B . In one embodiment processing actions performed by computing device  164  are distributed among multiple locations such as a local client and one or more remote servers. By way of example, processing used for determining application-area information  120  based on characteristics  112  might be performed by a local client computer, while processing to create instructions for applicator-controller  180  based on fertilizer-application information  150  and processing involved in fertilizer-application analysis such as cost-benefit analyses and regulatory-compliance, may be performed on a remote server. In another embodiment, computing device  164  is a computer, such as a desktop computer, laptop, or tablet computer with user interface  168  including a display and a keyboard, mouse, touchpad, or similar user input means. Example embodiments of computing device  164  include a desktop computer, a cloud-computer or distributed computing architecture, a portable computing device such as a laptop, tablet, ultra-mobile P.C., mobile phone, a navigational device, or dashboard-computer mounted in a vehicle such as a tractor or fertilizer applicator. 
     User interface  168  is used for displaying information and parameters stored in data store  162  including fertilizer-application information  150 , which in some embodiments, may be in the form of one or more tables, charts, or geographically referenced maps. User interface  168  can also receive information from a user such as fertilizer-application parameters  130 , application-area information  120 , or historical information  140 . In one embodiment, user interface  168  is capable of receiving user input regarding which attributes of application-area information  120  and which fertilizer-application parameters  130  should be considered or ignored for determining fertilizer-application information  150 . User interface  168  can also receive user queries for the information in data store  162  or user requests for analysis performed on information in data store  162 . For example, user interface  168  could display a geographically referenced map of fertilizer application information  150  for application area  110  and enable a user to input a request to see historic crop-yield information superimposed onto the map. In one embodiment, user interface  168  comprises multiple user interfaces, which may be distributed in different locations and may receive information from or provide information to more than a single user. 
       FIG. 1  also depicts an example fertilizer applicator  188 . Fertilizer applicator  188  applies fertilizer to an application area and, in one embodiment, can take the form of a multi-bin fertilizer spreader which is attached to a vehicle or pulled by a vehicle, such as a tractor. Applicator  188  can take the form of other embodiments such as liquid-tanks, injection system, or an any applicator capable of applying a fertilizer product, which may be a solid, liquid, gas or combination of solid, liquid, or gas. The application of fertilizer by fertilizer applicator  188  is controlled by applicator controller  180 . Applicator controller  180  controls the type and quantity of fertilizer released over portions of an application area. Fertilizer applicator  188  includes or is communicatively coupled to applicator controller  180 . Applicator controller  180  controls fertilizer application using applicator controller-information  184 . Applicator controller  180  is communicatively coupled to data store  162 , and includes a processor, such as a microcontroller, for processing applicator controller information  184  to control applicator  188 . In one embodiment the communicative coupling between applicator controller  180  and data store  162  comprises inserting a thumb drive including applicator controller information  184  a thumb-drive reader communicatively coupled to applicator controller  180 . In one embodiment, applicator controller  180  also communicates feedback data about a fertilizer-application session, such as date, environmental conditions, or any modifications occurring to the application schedule, to data store  162 . 
     Applicator-controller information  184  includes instructions usable by applicator controller  180  to direct the application of fertilizer by applicator  188 , over portions of the application area  110 . Applicator-controller information  184  is generated or determined by computing device  164  based on fertilizer-application information  150  and fertilizer-application parameters  130 . 
       FIG. 1C  illustrates an example fertilizer application area  210 , which could be made up of one or more fields, pastures, orchards, courts, golf courses, yards, lawns, planting or cultivating beds, lots, or similar areas of land  215 , or a portion of such an area of land, suitable for growing an agricultural product, plant, or grass, or an area of land that is suitable for receiving any agrochemical. In one embodiment, application area  210  includes a plurality of discrete land units  216 . Each discrete land unit  216  represents a discrete portion of land  215  located within application area  210 . 
     Each discrete land unit  216  is associated with attribute value  222  corresponding to a degree of expression of an attribute possessed by the discrete land unit. An attribute value  222  may be expressed as numerical quantity (e.g., “6”), or as a classification (e.g. 
     “acidic”). An attribute value  222  may be derived from a measurement of an attribute at a single point within a discrete land unit  216  or may be an average, median, or similar representative value of the degree of expression of an attribute possessed by discrete land unit  216 . By way of example, for an attribute corresponding to elevation, a discrete land unit  216  might have an associated attribute value  222  of 735-feet above sea level. This attribute value  222  could represent a single point of elevation within the discrete land unit  216 , or an average or median of elevation points within discrete land unit  216 . A discrete land unit  216  may be associated with multiple attribute values  222 , each corresponding to a different attribute. Moreover, the area of land  215  occupied by a discrete land unit  216  might depend on the associated attribute. For example, an attribute value for elevation taken from a DEM may specify a resolution such as 10 m, corresponding to discrete land units having a 10 square-meter area of land  215 . Thus, the area of land  215  occupied by a discrete land unit  216  could be a large area, a small area, or even a single point, so long as an associated attribute value represented the attribute for that area. 
       FIG. 1C  also shows example zones  225 . A zone represents an area of land  215  in application area  210  that has similar attribute values  222 . In one embodiment, zones  225  are made up of substantially contiguous discrete land units  216  having substantially similar attribute values  222 . In another embodiment, a zone  225  is made up of substantially contiguous discrete land units  216  having attribute values  222  corresponding to the same attribute classification, such as “acid” or “alkaline.” By way of example, consider two adjacently located discrete land units  216  having an associated attribute value  222  for soil pH-levels of 6.9 and 7.1 respectively. In one embodiment, the two discrete land units might be included within the same zone  225 , because the two land units are adjacent to each other and their associated attribute values of 6.9 and 7.1 are substantially similar—i.e. both are very close to a neutral pH level. But in an embodiment where zones are made up of discrete land units having associated attribute values  222  corresponding to the same attribute class, the two discrete land units in this example might not be in the same zone because soil pH-levels of 6.9 and 7.1 correspond to different classes (e.g., 6.9 is acidic and 7.1 is alkaline). The example application area  210  of  FIG. 1C  shows three zones  225 : a first zone made up of discrete land units having associated attribute values equal to 0 or 1; a second zone made up of discrete land units having associated attribute values equal to 4 or 5; and a third zone made up of discrete land units having associated attribute values equal to 8 or 9. 
     Turning to  FIG. 2A , application area  210  is shown logically partitioned into one or more application cells  255 . An application cell  255  represents a portion of application area  210  that will receive a certain product of agrochemical. Each application cell  255  encompasses at least part of a zone  225 . 
     Application cell  255  dimensions can vary based on fertilizer-application parameters  130 , including equipment parameters  132  and user preferences, the size of application area  210 , and the locations of zones  255 . For example, in one embodiment, the width of application cells  255  is based on equipment parameters specifying the physical reach or coverage area of the fertilizer applicator to be used to apply fertilizer. In this embodiment, the dimensions of application cells  255  may be uniform for all application cells in the application area  210 , or only one dimension, such as the width of application cells  255 , may be uniform for all application cells. In the embodiment shown in  FIG. 2A , only the width of the application cells  255  is a fixed dimension, based on physical limitations of the fertilizer applicator; the length of each application cell  255  varies based on the locations of zones  225 . For example, application cells  2551  through  2555 , shown on the left side of application-area  210 , each encompass land of a different proportion of zones  225 . Application cell  2551  and  2555  each encompass only land of a single zone  225 . Application cells  2552 ,  2553 , and  2554  encompass different proportions of different zones  225 . One reason for varying cell length based on zones, as will be further described in connection to  FIG. 4 , is that the product of fertilizer determined to be applied for an application cell is based in part on the zones falling within the application cell. 
     In some embodiments, a row of partitioned application cells  255  of uniform width comprises an application strip  257 . An application strip  257  represents an area of land covered by a single pass of a fertilizer applicator, such as fertilizer applicator  288 . By way of example, applying fertilizer to an application area may be accomplished by a series of back-and-forth passes over the application area, to ensure the entire application area receives fertilizer. This is similar to mowing grass in a yard, where a lawnmower mows a series of adjacent paths back and forth over the yard. The width of grass cut by the mower, for each back-and-forth pass, is fixed and depends on the radius of the lawn-mower blade. Similarly, in the embodiment shown in  FIG. 2A , the width of application strip  257 , and therefore the application cells  255  within application strip  257 , is a uniform width, which is determined based on the physical limitations of fertilizer applicator  288 . Accordingly, fertilizer applicator  288  can therefore apply fertilizer to application area  210  by following a back-and-forth path  289  over application area  210 , with each pass defining an application strip  257  of one or more application cells  255 . In other embodiments, application cells  255  can exist independently of an application strip, depending on the applicator technology to be used for applying fertilizer. 
       FIG. 2B  depicts another embodiment of attribute zones for the same application area shown in  FIG. 2A .  FIG. 2B  shows the same application area  210 , made up of the same plurality of discrete land units  216 , each having the same associated attribute values  222 . But the boundaries of zones  226  shown in  FIG. 2B  are defined by the outer perimeters of the discrete land units  216  within each zone. In this embodiment, zones  226  are delineated by merging together substantially contiguous discrete land units  216  that have similar associated attribute values  222 .  FIG. 2B  is provided to convey that regardless of how the boundaries of the attribute zones are determined, attribute zones include areas of land  215  having substantially similar attribute values  222  or attribute values  222  belonging to the same attribute classification. 
       FIG. 2C  depicts an application area  210 , which includes example location points  217 . Location points  217  are similar to discrete land units  216 , in that each location point  217  has an associated attribute value  222  corresponding to a degree of expression of an attribute at that location point. Location points  217  may represent locations in an application area corresponding to measurements of an attribute, such as soil pH-level measurements, vegetation, soil structure, residue cover, depth to impermeable layer, or other attributes. These locations may be uniformly spatially distributed or located wherever attribute data, such as field measurements of attributes, are available. In some embodiments, location points  217  may be more densely located around areas where an attribute has a greater variance and may be more spread apart in areas where the attribute varies less. As shown in  FIG. 2C , example zones  227  comprise an area of land  215  in application area  210  that has similar attribute values. In this embodiment, a zone  227  encompasses substantially adjacently located location points  217  associated with substantially similar attribute values  222 . In another embodiment, zones  227  might include substantially adjacently located location points  217  associated with attribute values  222  of the same attribute class, such as “acid” or “alkaline.” 
       FIG. 2D  shows one embodiment having an application area  210  made up of a plurality of discrete land units  216 . The application area  210  of  FIG. 2D  also includes a drainage basin  212 . In this embodiment, each discrete land unit  216  has an associated attribute value  223 , which may be an index value that corresponds to an index that represents degrees of expression of an attribute.  FIG. 2D  depicts an example Topographic Wetness Index (TWI). Index legend  290  shows TWI values grouped by index classifications ranging from index values less than 10.4, correspond to an “extremely dry” class, to index values greater than 19.0 corresponding to an “extremely wet” class. Application area  210  also includes four zones  225 ; each zone includes discrete land units with associated index-values of the same index classification. Specifically, zone  2251  and zone  2254  are made of discrete land units  216  with associated attribute values  223  corresponding to dry classes of the TWI (i.e., index values less than 13.8); zone  2252  includes discrete land units  216  having associated attribute values  223  corresponding to the moderate class; and zone  2253  is made up of discrete land units  216  with associated attribute values  223  corresponding to the wet classes of the TWI. Zone  2253  may be expected to include land having wetter TWI values because zone  2253  surrounds drainage basin  212 . In the embodiment shown in  FIG. 2D , zones  2251 ,  2252 ,  2253 , and  2254  are delineated based on having attribute-values belonging to the same attribute or index classification, rather than attribute values that are substantially similar to each other. Similarly, in an embodiment using attribute values that are not index values, zones may be delineated to include attribute values belonging to the same classification, rather than attribute values that are substantially similar to each other. 
     In some embodiments, a set of attribute values corresponding to a plurality of discrete land units  216  (or location points) located in an application area  210  is characterized or represented as an attribute grid, with each point on the grid corresponding to a location of a discrete land unit or location point having an associated attribute value. Likewise, in some embodiments a set of index values corresponding to a plurality of discrete land units  216  (or location points) located in an application area  210  can be characterized and represented as an index grid, with each point on the grid corresponding to a location of a discrete land unit or location point having an associated index value. 
       FIG. 2E  illustrates two similar views of an application area  210 . Both views show the same three example application strips superimposed over application area  210 : application strip  260 , which is made up of application cells  255 , and application strips  261  and  262 . For clarity, only three example application strips are shown in application area  210 ; although typically application cells or strips will cover the entire application area  210 , it is not a requirement to do so. The right-hand view also depicts wetness-index values within the application strips. The wetness-index values are omitted on the left-hand view, for clarity.  FIG. 2E  also shows a fertilizer-application legend  295 , which indicates a fertilizer product to be applied to application strips or cells shown in  FIG. 2E , and an index-legend  291 , which provides a visual representation of index values for the wetness attribute. 
     Application strip  260  represents a variable-product fertilizer application consistent with an embodiment of the invention. Application strip  260  is made up of a plurality of uniformly sized application cells  255 . In the embodiment shown in  FIG. 2E , each application cell has a uniform dimension. Each application cell  255  of application strip  260  has been evaluated to determine an appropriate product of fertilizer to be applied to the cell, based on wetness index values associated with the discrete land units or location points (not shown) enclosed by each application cell  255 . 
     For example, according to fertilizer-application legend  295 , application cell  281  is coded for receiving a conventional fertilizer type. A conventional fertilizer type might be applied to an application cell that encompassed land having drier TWI values because the fertilizer would be less susceptible to leaching, evaporation, or environmental loss mechanisms, than it would if it were applied to land having wetter TWI values. Indeed, the right-hand view of application cell  281  shows that the land encompassed by application cell  281  includes attribute values corresponding to the drier side of index-legend  291 . Similarly, application cell  282 , which encompasses land with attribute values corresponding to the wetter side of index legend  291 , is coded for receiving an enhanced fertilizer type. As previously described, an enhanced fertilizer type may be less susceptible to environmental loss mechanisms and is thus appropriate for application to areas having wetter TWI values. Application cell  283 , which encompasses land with both dry and wet TWI values, is coded for receiving a mixture of enhanced and conventional fertilizer types. As used herein the term coded, as in “application cell  281  is coded to receive a conventional fertilizer type” is intended to mean that a particular fertilizer type is associated with an application cell. 
     In contrast to application strip  260 , application strips  261  and  262  are shown designated for receiving a non-variable or single fertilizer source. These strips may also receive a fixed application rate. In other words, each strip receives only one fertilizer type, at a given fixed-application rate. Strips  261  and  262  are representative of the prior art of fertilizer application technology. Despite encompassing land with varying attribute values, strip  261  receives only an enhanced-type fertilizer and strip  262  receives only conventional-type fertilizer. As a result, areas having wetter TWI values within strip  262 , may lead to greater loss of the conventional fertilizer by leaching or by other environmental loss mechanisms; similarly areas having drier TWI values within strip  261  may not require the more costly enhanced efficiency fertilizer. 
     Turning now to  FIG. 3 , an exemplary embodiment is provided showing an overview of a process of facilitating fertilizer application on an application area  310 . For purposes of explanation, the process, which is referenced generally by the numeral  300 , is shown broken down into 6 stages. Each stage of process  300  represents a different step or series of steps performed, and thereby provides a visual reference of what transpires, for one embodiment. 
     At a stage 1, fertilizer application area  310  is shown with land characteristics  312 . In the example of  FIG. 3 , land characteristics  312  represent antecedent soil moisture, which may be characterized as attribute values representing TWI. Stage  1  only shows one example land characteristic  312  for clarity, but application area  310  can have multiple land characteristics, and it is contemplated that the example process of  FIG. 3  can be performed on other attributes of application area  310 . Furthermore in some embodiments, more than one characteristic or combinations of characteristics such as slope and depth to impermeability may be used to determine attribute values that are then used to delineate attribute zones. 
     As previously explained, in some embodiments, an application area such as application area  310  may be considered to be made up of a plurality of discrete land units, or may include a plurality of location points, with each discrete land unit or location point associated with a location, which can be a geographically referenced location or a relative location, and an attribute value, which represents a degree of expression of an attribute or characteristic at that location in an application area. At a stage  2 , attribute values have been determined for a plurality of discrete land units within application area  310 . In the embodiment shown, a set of determined attribute values are represented as an attribute grid  316 , with each square in the grid corresponding to a location of a discrete land unit with an associated attribute value. 
     Once attribute values are determined, zones of land with similar attribute values are delineated. A stage  3  depicts delineated zones including an example zone  325  in application area  310 . As will be explained, a zone is delineated based on attribute values associated with the discrete land units of application area  310 . At a stage  4 , application area  310  is logically partitioned into application cells, such as example application cell  355 . In this embodiment, the partitioned application cells have a uniform dimension. In other embodiments, application cell location and dimensions may vary based on the locations of zones. As will be explained, application-cell dimensions may be determined based on fertilizer-application parameters and the attribute zones. The process of logically partitioning an application area into one or more application cells is sometimes referred to as “fish-netting” since each application cell can resemble a single mesh of a fishnet. 
     Once an application area is logically partitioned into application cells, a fertilizer product is determined for each application cell. A stage  5  of process  300  illustrates logically partitioned application cells, of application area  310 , associated with a fertilizer product, as indicated by a shading of each application cell. As will be explained, a fertilizer product is determined based on attribute values of zones within each application cell and based on fertilizer application parameters, in one embodiment. The fertilizer product may specify a quantity and type or mixture of fertilizer types to be applied. Each application cell is coded for receiving the determined fertilizer product. For example, in the embodiment shown, according to legend  395 , application cell  381  is to receive a conventional fertilizer type; application cell  382  is to receive an enhanced fertilizer type; and application cell  383  is to receive a mixed ratio of fertilizer types, for a given rate, respectively. The determination of which specific fertilizer types and quantities used for a mixture of fertilizer types is discussed in more detail with respect to  FIG. 9 . 
     Stage  5  of process  300  also provides an exemplary map  350  of application area  310  showing each application cell geographically referenced within application area  310 , and each cell further indicating a fertilizer product to be applied within the cell. As will be explained, the output of the fertilizer-product determination step shown in stage  5 , is a set of fertilizer application-information, which may be visually depicted as a map, table, schedule, or association of information. Fertilizer application-information includes information for a set of application cells within application area  310 , an associated location for each application cell, and an associated product of fertilizer for each cell to receive. Additional information can be associated with each cell, in some embodiments. Thus, the fertilizer application-information can be used to generate a map such as map  350  shown in stage  5  of process  300 . Such a map may be used to facilitate analysis of fertilizer application strategies and may be combined with other information useful for facilitating analysis or record keeping. For example, other embodiments of map  350  might also depict additional information including attribute zones, geographic features of the application area, attributes, crop information such as past crop yields geographically referenced within the application area, economic data such as the incremental cost of fertilizer for each cell or a listing of the total cost and quantities of fertilizer needed for the application, regulatory data, and other information. 
     A stage  6  of process  300  shows generated fertilizer-applicator controller information  384 . In stage  6 , the fertilizer-application information determined in stage  5  is used to generate applicator-controller information operable to direct a fertilizer applicator to apply fertilizer consistent with the determined product for each application cell. 
       FIG. 3  is intended to provide an overview of one embodiment; additional stages may exist in other embodiments. For example, the results of stage  5  may be used for reporting and record keeping, as we described next in connection to  FIGS. 4 and 5 , at steps  440  and  540 , respectively. 
       FIG. 4  and  FIG. 5  illustratively provide high-level flow diagrams of embodiments of a method of ultimately applying a variable-product fertilizer to an application area.  FIG. 6  through  FIG. 9  illustratively provide lower-level flow diagrams of embodiments of the steps of the method embodiments depicted in the flow diagrams of  FIG. 4  and  FIG. 5 .  FIGS. 6 . through  9  correspond to some of the steps depicted in  FIG. 4  and  FIG. 5 . The methods depicted in the flow charts of  FIGS. 4 through 9  are suitable for operation in example operating environment provided in  FIG. 1 . A computing device, such as computing device  164  of  FIG. 1  is used to perform or facilitate performing each step. 
     Turning now to  FIG. 4 , a flow diagram is provided illustrating an exemplary method according to one embodiment, shown as  400 . The method of flow diagram  400  is suitable for operation in the exemplary operating environment of  FIG. 1 . At step  600 , attribute values are determined, based on application-area information. Further details of step  600  are provided in connection to  FIG. 6 . But as will be explained, an attribute value is determined for a plurality of location points or discrete land units in an application area, based on application-area information corresponding to the location point or discrete land unit. An attribute value thus represents a quantized degree of expression of an attribute, that when associated with a location point or discrete land unit, represents the expression of an attribute at that location. Application-area information includes information, which may be provided by a user or accessed from a data store, relating to one or more sets of measured or determinable values associated with the presence of a characteristic, at locations in an application area. For example, a DEM includes information representing elevation associated with geographically referenced locations. Thus, a DEM corresponding to an application area will include values representing elevation at a plurality of locations in the application area. Therefore, in one embodiment, the DEM information functions as a set of attribute values. Accordingly, the attribute values for the elevation attribute may thus be determined by determining a portion of a DEM that corresponds to the application area. 
     An attribute value may express a numerical quantity, such as 735 feet above sea level, or a category or classification of an attribute, such as “acidic.” An attribute value also may be determined from another attribute value. For example, attribute values for slope may be determined from attribute values for elevation. In some embodiments, the set of attribute values may be characterized as a grid, which logically overlays an application area, such that the points on the grid correspond to an attribute value at that location. In some embodiments, a plurality of attribute sets or grids may be used to determine fertilizer application. Therefore in these embodiments, multiple sets or grids of attribute values, corresponding to multiple attributes, may be determined at step  600 . 
     The output of step  600  includes application-area information specifying a set of attribute values, each associated with a location point or discrete land unit in an application area. At a step  700 , this information is used to delineate attribute zones of ground, within the application area, encompassing location points or discrete land units with similar associated attribute values. Each location within an application will fall within a zone. For example, if a zone for the soil pH-level attribute is delineated to include those discrete land units having associated attribute values (i.e., soil pH-levels, in this example) corresponding to “acid,” then the remaining discrete land units of the application area will fall within a separate zone corresponding to “non-acid” or “alkaline and neutral” soil pH-levels. Further details of step  700  are provided in connection to  FIGS. 7A through 7C . 
     At a step  800 , the application area is partitioned into one or more application cells. As previously explained, an application cell represents a portion of land that will receive a certain product of fertilizer. Further details of partitioning step  800  are provided in connection to  FIG. 8 . As will be explained, the dimensions of the partitioned application cells are based on fertilizer-application parameters, the locations of attribute zones, or both. Fertilizer-application parameters include fertilizer-applicator equipment parameters that can determine the width of an application cell based on the reach of the fertilizer applicator used to apply fertilizer. The equipment parameters can also determine a minimum application cell length, based on limitations of the fertilizer applicator to change fertilizer products as it traverses the application area. In an exemplary embodiment, the width of each application cell will be uniform, but the length will vary based on the location of zones in the application area. In this embodiment, a row of application cells comprises an application strip, which represents one traverse of the application area by a fertilizer applicator. As will be explained in connection to  FIG. 8 , in one embodiment, application cell length may be determined based on the locations of zones, in order to minimize variance of zones in an application cell, as the cell length increases. 
     Because every location in an application area will fall within a zone determined in step  700 , each application cell will encompass at least a part of a zone. As a consequence, associated with each application cell is zone information about each zone, zones, or zone portions enclosed by the application cell. This information includes the area of the application cell occupied by a zone or a portion of a zone and the zone attribute and attribute values associated with the zone. 
     At a step  900 , a fertilizer product, for application within each application cell, is determined. The zone information associated with each application cell may be used with fertilizer-application parameters to determine a product of fertilizer to apply to each application cell. As previously explained, a fertilizer product can specify a quantity and type or mixture of fertilizer types to be applied, as well as a rate, in one embodiment. The zone information associated with each application cell, in partitioning step  800 , includes attribute values associated with a zone that can be used to determine a fertilizer type appropriate for the zone. For example a zone having attribute values indicating wetness may be designated to receive an enhanced-type fertilizer. As will be explained, in one embodiment, the fertilizer product determined for an application cell is based on the area of the application cell occupied by a zone or a portion of a zone. For example, in this embodiment an application cell occupied entirely by a portion of a wet zone, might be determined to receive an enhanced-type fertilizer, depending on other fertilizer application parameters. But an application cell that encloses multiple zones or portions of zones might receive a mixture of fertilizer types, wherein the mixture ratio is proportional to the area occupied by each zone or zone portion within the application cell. In another embodiment, the attribute values of location points or discrete land units enclosed by an application cell are used to determine a fertilizer product. Each application cell is coded for receiving a determined fertilizer product corresponding to that cell. 
     The output of step  900  is fertilizer-application information. In one embodiment, this comprises a set of application cells, each associated with information indicating cell location in an application area and a product of fertilizer to be applied to the cell. In one embodiment, the application cells are associated with geographically referenced location information. Additional information relating to attribute-values and information from the fertilizer-application parameters may also be associated with each cell. Further details of step  900  are provided in connection to  FIG. 9 . 
     At a step  480 , application controller information for a fertilizer applicator is generated. Specifically, the fertilizer-application information outputted from step  900  is used to generate computer instructions for operating a fertilizer-applicator controller to control fertilizer application by a fertilizer applicator consistent with the fertilizer product determined in step  900 . Fertilizer-application parameters include information relating to a fertilizer applicator or a controller used by the applicator, for example, a model number, controller identification, or similar information usable for determining a controller and generating instructions executable by the controller for applying fertilizer. In one embodiment, this includes a table or library of instructions for controlling application by the fertilizer applicator. 
     In one embodiment, fertilizer-application information is used to create a shape file, which graphically indicates the locations of application cells in an application area and the determined fertilizer product for each cell. The determined fertilizer product may be indicated by color, shading, or a similar visual reference, as shown in stage  5  of  FIG. 3  or the left-hand side of  FIG. 2E , for example. Using a library of instructions for a controller, the shape file is then converted to an appropriate file format for execution by the controller. 
     The fertilizer application is location dependent; each cell is associated with a location in the application area. Accordingly, in one embodiment, controller instructions include a fertilizer product to apply for a given application cell and an associated location information, which may define the boundaries (or merely the cell length) of that application cell. In an embodiment having uniformly sized application cells, controller instructions may correspond to a listing of fertilizer products such that a controller applies a product specified on the list for a certain duration or distance. In one embodiment, location information may be present via the fertilizer applicator and the applicator controller may receive location information in real-time (or near real-time) to determine an immediate product of fertilizer to apply based on that received location. 
     Continuing with  FIG. 4 , at a step  440  the results of step  900 , including the fertilizer-application information, may be stored for record keeping or used for subsequent analysis, in one embodiment. Stored information becomes part of a set of historical information, over time, which can be used in future fertilizer-application sessions or analysis, in some embodiments. Analysis may also be performed using the fertilizer-application information from step  900 . By way of example, fertilizer application information may be used to generate a table or listing of fertilizer application products for each cell or geographic map of the application area showing each application cell associated with a determined product of fertilizer to be applied to that cell. Fertilizer products to be applied to each cell may be indicated by color-coding, shading, text, outlining, or similar means. In one embodiment, fertilizer application parameters, such as user-provided information, date or time information, regulatory information, fertilizer costs, near-by geographical features, or crop-related information is included on the map or automatically placed with the map into a report that details recommended variable-product fertilizer (or agrochemical) application. This information may, in one embodiment, be stored in a file, viewed, and printed. In another embodiment, a user may export a map showing fertilizer application as a shape file or similar format, which then can be used as a map layer with other information such as crop-yield maps. In another embodiment, a table or geographic map indicating fertilizer products for each application cell is generated with information indicating economic information such as the cost of fertilizer for each cell or the total fertilizer cost, an estimated differential crop yield resulting from applying one determined product vs. another determined product of fertilizer for an application cell, expected profit from crops or a cost-benefit analysis, which compares the cost of applying a determined product of fertilizer vs. the estimated crop yield or profit corresponding to an application of the determined product of fertilizer, for an application cell. In other embodiments, additional information may be included on a geographic map or table indicating fertilizer products for each application cell, such as: attributes of the application area, as shown in the right-hand side of  FIG. 2E ; historical information representing past fertilizer applications or past crop yields; an indication where user-preference deviates from determined fertilizer products for each application cell; an identification of total fertilizer quantities, brands, types, rates, or mixture ratios; applicator equipment information; or government regulations. Such additional information may be geographically referenced on the map where appropriate, in some embodiments. By way of example, consider an application cell that would otherwise be determined to require a certain product of fertilizer, but because of a fertilizer application parameter such as a government regulation or user-specified buffer, a different product of fertilizer has been determined. Information representing this can be represented on the map, and geographically referenced to the application cell or cells to which it applies. In one embodiment, an asterisk may be placed on a cell and below the map the asterisk may correspond to information affecting that cell&#39;s determined product of fertilizer, such as a message indicating that the fertilizer product determined for the cell is affected by a user-designated buffer. Other combinations of information, representing fertilizer-application information including the determined product of fertilizer, historical information, and application area information, may be visually presented on a user interface as a geographically referenced map of an application area suitable for use by a grower, fertilizer distributor, or user to facilitate determining or analyzing a fertilizer application strategy. 
       FIG. 5  is a flow diagram illustrating an exemplary method according to one embodiment, shown as  500 . The method of flow diagram  500  is suitable for operation in the exemplary operating environment of  FIG. 1 . At step  601 , attribute values are determined, based on application-area information. Further details of step  601  are provided in connection to  FIG. 6 . But as will be explained, an attribute value is determined for a plurality of location points or discrete land units in an application area, based on application-area information corresponding to the location point or discrete land unit. In one embodiment, the attribute values are index values. An index value represents a quantized degree of expression of a characteristic or attribute scaled or applied to an index that when associated with a location point or discrete land unit, represents the expression of a characteristic or attribute at that location according to an index of characteristic or attribute values. Application-area information includes information, which may be provided by a user or accessed from a data store, relating to one or more sets of measured or determinable values associated with the presence of a characteristic, at locations in an application area. For example, a DEM includes information representing elevation associated with geographic locations. Thus, a DEM corresponding to an application area will include values representing elevation at a plurality of locations in the application area, and may thus constitute a set of attribute-values for elevation. In one embodiment, as will be explained, this DEM information may be used to determine a Topographic Wetness Index for the application area. 
     An index value, like an attribute value, may express a numerical quantity, such as a TWI of 18.7, or a category or classification of a characteristic or attribute, such as “extremely wet.” An index value also may be determined from another index value or an attribute value. For example, index values for wetness may be determined from attribute values for elevation, as will be explained in connection to  FIG. 6 . A set of index values represents an attribute or characteristic. In some embodiments, the set of index values may be characterized as an index grid, which logically overlays an application area, such that the points on the grid correspond to an index value at that location. Such a grid of index values may be represented as a raster, in some embodiments. In some embodiments, a plurality of indices or grids may be used to determine fertilizer application. Therefore in these embodiments, multiple indices or grids of index values, corresponding to multiple characteristics or attributes, may be determined at step  601 . 
     The output of step  601  includes application-area information specifying a set of attribute values or index values, each associated with a location point or discrete land unit in an application area. At a step  701 , this information is used to delineate zones of ground, within the application area, encompassing location points or discrete land units with similar associated attribute values. Each location within an application will fall within a zone. For example, if a zone for the wetness index is delineated to include those discrete land units having associated wetness-index values less than or equal to 14, then the remaining discrete land units of the application area will fall within a separate zone having wetness-index values greater than 14. Further details of step  701  are provided in connection to  FIGS. 7A through 7C . 
     At a step  801 , one or more nonoverlapping application cells, within the application area, are defined. In one embodiment, the application area is partitioned into one or more application cells. In another embodiment, an application-cell boundaries are determined based on the delineated zones of step  701  and relevant fertilizer application parameters, as will be explained. In this embodiment, application cells are geographically positioned within the application area, based on the location of zones, dimensions of the application area, or fertilizer-application parameters. 
     As previously explained, an application cell represents a portion of land that will receive a certain product of fertilizer. Further details of step  801  are provided in connection to  FIG. 8 . As will be explained, in various embodiments, the dimensions of the defined application cells are based on fertilizer-application parameters, which can include equipment parameters or user-defined cell dimensions, the locations of attribute zones, or a combination of fertilizer-application parameters and the locations of attribute zones. Fertilizer-application parameters include fertilizer-applicator equipment parameters that can determine the width of an application cell based, for example, on the reach or coverage area of the fertilizer applicator used to apply fertilizer. The equipment parameters can also determine a minimum application-cell length, based on limitations of the fertilizer applicator to alter fertilizer products as it traverses the application area. In an exemplary embodiment, the width of each application cell will be uniform, but the length will vary based on the location of zones in the application area. In this embodiment, a row of application cells comprises an application strip, which represents one traverse of the application area by a fertilizer applicator. As will be explained in connection to  FIG. 8 , in one embodiment, application cell length may be determined based on the locations of zones, in order to minimize variance of zones in an application cell, as the cell length increases. 
     Because every location in an application area will fall within a zone determined in step  701 , each application cell will encompass at least a part of a zone. As a consequence, associated with each application cell is zone information about each zone, zones, or zone portions enclosed by the application cell. This information includes the area of the application cell occupied by a zone or a portion of a zone and the zone attributes, indices, and index values associated with the zone. 
     At a step  901 , a schedule specifying fertilizer-application information for each application cell is determined. The schedule can include, in one embodiment, information specifying for each application cell, a product of fertilizer to apply, or a quantity or rate and fertilizer type or types, and a mixture ratio, if a mixture of fertilizer types is to be applied. The zone information associated with each application cell may be used with fertilizer-application parameters to determine the fertilizer-schedule information of each application cell. The zone information associated with each application cell, in step  801 , includes attribute or index values associated with a zone that can be used to determine a fertilizer type appropriate for the zone. For example a zone having attribute or index values indicating wetness may be designated to receive an enhanced-type fertilizer. As will be explained, in one embodiment, a fertilizer product determined for an application cell is based on the area of the application cell occupied by a zone or a portion of a zone. For example, in this embodiment an application cell occupied entirely by a portion of a wet zone, might be determined to receive an enhanced-type fertilizer, depending on other fertilizer-application parameters. But an application cell that encloses multiple zones or portions of zones might receive a mixture of fertilizer types, wherein the mixture ratio is proportional to the area occupied by each zone or zone portion within the application cell. In another embodiment, the attribute or index values of location points or discrete land units enclosed by an application cell are used to determine a fertilizer-application schedule indicating a determined fertilizer product for each application cell. 
     The output of step  901  includes fertilizer-application information. In one embodiment, this comprises a schedule of information relating to a set of application cells, with each cell associated with information indicating location in an application area and a product of fertilizer to be applied to the cell. Additional information relating to attribute-values and information from the fertilizer-application parameters may also be associated with each cell. Further details of step  901  are provided in connection to  FIG. 9 . 
     At a step  580 , application controller information for a fertilizer applicator is generated. Specifically, the fertilizer-application information outputted from step  901  is used to generate computer instructions for operating a fertilizer-applicator controller to direct fertilizer application by a fertilizer applicator consistent with the fertilizer schedule determined in step  901 . Fertilizer-application parameters can include information relating to a fertilizer applicator or a controller used by the applicator, for example, a model number, controller identification, or similar information usable for determining a controller and generating instructions executable by the controller for applying fertilizer. In one embodiment, this includes a table or library of instructions for controlling application by the fertilizer applicator. 
     In one embodiment, fertilizer-application information is used to create a shape file, which graphically indicates the locations of application cells in an application area and the determined fertilizer product for each cell. The determined fertilizer product may be indicated by color, shading, or similar visual reference, as shown in Stage  5  of  FIG. 3  or the left-hand side of  FIG. 2E , for example. Using a library of instructions for a controller, the shape file is then converted to an appropriate file format for execution by the controller. 
     The fertilizer (or agrochemical) application is location dependent; each cell is associated with a location in the application area. Accordingly, in one embodiment, controller instructions include an product of fertilizer to apply for a given application cell and an associated location information, which may define the boundaries (or merely the cell length) of that application cell. In an embodiment having uniformly sized application cells, controller instructions may correspond to a listing of fertilizer products such that a controller applies a product specified on the list for a certain duration or distance. In one embodiment, location information may be present via the fertilizer applicator and the applicator controller may receive location information in real-time (or near real-time) to determine an immediate product of fertilizer to apply based on that received location. 
     At a step  540  the schedule of step  901 , including the fertilizer-application information, may used for subsequent analysis, in one embodiment. The fertilizer-application information may also be stored, and overtime become part of a set of historical information, which can be used in future fertilizer application sessions or analysis, in some embodiments. Analysis may also be performed using the schedule or other fertilizer application information from step  901 . By way of example, fertilizer application information may be used to generate a table or listing of fertilizer application products for each cell or geographic map of the application area showing each application cell associated with a product of fertilizer to be applied to that cell. Fertilizer products to be applied to each cell may be indicated by color-coding, shading, text, outlining, or similar means. In one embodiment, fertilizer application parameters, such as user-provided information, date or time information, regulatory information, fertilizer costs, near-by geographical features, or crop-related information are included on the map or automatically placed with the map into a report that details recommended variable-product fertilizer (or agrochemical) application. This information may, in one embodiment, be stored in a file, viewed, and printed. In another embodiment, a user may export a map showing fertilizer application as a shape file or similar format, which then can be used as a map layer with other information such as crop-yield maps. In another embodiment, a table or geographic map indicating fertilizer products for each application cell is generated with information indicating economic information such as the cost of fertilizer for each cell or the total fertilizer cost, an estimated differential crop-yield resulting from applying one determined product vs. another determined product of fertilizer for an application cell, expected profit from crops or a cost-benefit analysis, which compares the cost of applying a determined product of fertilizer vs. the estimated crop yield or profit corresponding to an application of the determined product of fertilizer, for an application cell. In other embodiments, additional information may be included on a geographic map or table indicating a fertilizer product for each application cell, such as: attributes or characteristics of the application area, as shown in the right-hand side of  FIG. 2E ; historical information representing past fertilizer applications or past crop yields; an indication where user-preference deviates from determined fertilizer products for each application cell; an identification of total fertilizer quantities, brands, types, rates, or mixture ratios; applicator equipment information; or government regulations. Such additional information may be geographically referenced on the map where appropriate, in some embodiments. By way of example, consider an application cell that would otherwise be determined to require a certain product of fertilizer, but because of a fertilizer application parameter such as a government regulation or user-specified buffer, a different product of fertilizer has been determined. Information representing this can be represented on the map, and geographically referenced to the application cell or cells to which it applies. In one embodiment, an asterisk may be placed on a cell and below the map the asterisk may correspond to information affecting that cells determined product of fertilizer, such as a message indicating that the fertilizer product determined for the cell is affected by a user-designated buffer. Other combinations of information, representing fertilizer-application information including the determined product of fertilizer, historical information, and application area information, may be visually presented on a user interface as a geographically referenced map of an application area suitable for use by a grower, fertilizer distributor, or user to facilitate determining or analyzing a fertilizer application strategy. 
     Turning now to  FIG. 6 , a flow diagram is shown illustrating an exemplary method of determining attribute values or index values, according to an embodiment, shown as  600 . At a step  610  application area information is received. As explained previously, application-area information generally comprises attribute-related information associated with location information, which may be geographically-referenced or relatively-referenced location information, such as locations based on the boundaries of the application area, a common point of reference, or other local locations. Application area information may be received directly from a user or from a data store, either locally or online. Application area information may be received within a defined input-window, at any time, or as needed, including subsequently to determining a grid or set of attribute values or index values, such as in cases where attribute values or index values are determined based on other attribute values or index values. In one embodiment, a user provides field records, measurements, lab data, or similar information directly via a user interface. In another embodiment, application area information is received from a data store, where it may be accessed according to location information related to the application area. For example, in one embodiment, application area information is accessed from a GIS or similar database, using information related to the geographical location of the application area, such as coordinates specifying its boundaries. 
     At a step  620 , a set or grid of attribute values is determined. Alternatively, in one embodiment, a set or grid of index values is determined. Application-area information may be received already as a set of attribute-related information associated with location points or discrete land units in the application area. For example, application-area information may be received as a heatmap, raster, table, or similar format that associates values of an expression of a characteristic to locations in an application area. Thus the received application-area information already may be in a format suitable for use as a grid or set of attribute values. In some embodiments, it is not necessary to determine a grid of attribute values or index values as described in connection to step  620 . Rather in some embodiments, the application area information, received in step  610 , already specifies one or more sets of attribute values or index values sufficient for delineating zones. In other embodiments, a set or sets of attribute values may be further processed to determine other attribute values used for delineating attribute zones. For example, a set of attribute values corresponding to elevation and a set of attribute values corresponding to residue cover may be used together to determine a set of attribute values representing TWI for the application area. 
     In some embodiments, attribute values may be processed to be become index-values. In some embodiments, attribute values or index values may be determined from this received set of attribute-related information associated with location points or discrete land units in the application area. By way of example, received DEM information for an application area includes elevation information associated with the locations discrete land units, specified by the resolution of the DEM. This information is suitable for use as a set or grid of attributes for elevation, or it may be subsequently processed for determining wetness-index values associated with each discrete land unit. In another example, received field data, such as measurements of application area characteristics, may already include location information associated with each measurement value, which may be used as an attribute or index value. 
     Alternatively, in some embodiments a grid or set of attribute values, or index values, for an application area must be determined by identifying discrete land units and their locations or identifying location points, determining a value representing an attribute at the location point or location of the discrete land unit, and associating that attribute value with the location point or discrete land unit. A discrete land unit size may be specified by a user or by the application-area information. For example DEM information includes a resolution, which is indicative of the size of discrete land units having the elevation attribute. For example, a 10 m DEM has an elevation value associated with each 10 meter-square area. If multiple attribute values are present in a discrete land unit, an average, median, or otherwise representative value may be used as the attribute value. Alternatively, the discrete land unit may be subdivided into smaller discrete land units, such that each discrete land unit is associated with one of the attribute values. 
     In one embodiment, an attribute or index to be used for determining a set of attribute values or index values may be specified by fertilizer-application parameters. In one embodiment, fertilizer-application parameters include an attribute preference received from a user. The user may select the attribute or index via a user interface or may indicate a preference or selection related to fertilizer application that inherently specifies an attribute. In one embodiment, a previously selected or previously considered attribute is used as a default selection. In one embodiment, the user may be prompted to make a selection, or a user may be presented with previously considered attributes. In one embodiment, an attribute is determined based on available application-area information. For example, where application area information only corresponds to acidity or alkalinity, a soil pH-level attribute would be used. In another embodiment, fertilizer-application parameters relating to available fertilizer inventory, fertilizer costs, or regulations are used to determine an attribute. In the case where multiple attributes are possible, a user may be presented with a list to select from, via a user interface. Alternatively, attributes may correspond to a priority, ranking preferred attributes. 
       FIG. 6  illustratively provides an exemplary embodiment for determining a grid of attribute values, or index values, in step  620 . In this embodiment, a Topographic Wetness Index grid is determined. At a step  625  DEM information corresponding to an application area is determined. The DEM information may be part of a library or GIS database, in one embodiment, and accessible via a data store. A user specifies the DEM information that corresponds to the application area via a user interface, in one embodiment, by defining a boundary of an area in the DEM corresponding to the application area. In one variation of this embodiment, a user interface may be designed or provided using ArcMap. The interface can permit a user to view an aerial depiction of land, such as a satellite or aerial image, that includes the application area, and enable the user to draw a boundary around the application area. Upon completing drawing a boundary around the application area, the user can click a button to automatically determine DEM information corresponding to the area enclosed by the user-defined boundary. A further variation of this embodiment adds a buffer area around the user-defined boundary. In another embodiment, a user may provide coordinates of the boundary of an application area or specify an application area with known coordinates usable for identifying corresponding DEM information. In one embodiment, DEM information corresponding to an application area is determined automatically from available application area information. In one embodiment, a user is also prompted to specify the type or resolution of DEM information to be used for the DEM. The DEM information provides elevation values for discrete areas of ground. For example, a 10-meter DEM provides an elevation for each 10-meter-square area of ground. Thus each 10-meter-square area of ground represents a discrete land unit, and the elevation represents an associated attribute value. 
     At step  635 , step  645 , and step  655 , processing is performed on the DEM information to determine flow direction grid, a flow accumulation grid, and a slope grid, respectively. A flow direction grid created in step  635  is a raster dataset representing flow direction from each discrete land unit to its steepest downslope neighbor. The output of step  635  is an integer raster with values ranging from 1 to 255. At step  645  a flow accumulation grid is created. A flow direction grid is a raster dataset representing accumulated flow to each discrete land unit, as determined by accumulating the weight for all discrete land units that flow into each downslope discrete land unit. Discrete land units having undefined flow direction may only receive flow; they will not contribute to any downstream flow. At step  655  a slope grid is created, which identifies the rate of maximum change in z-value for each discrete land unit. 
     A step  660  determines whether to use additional application-area variables for determining TWI values. These include variables for predicting relative spatial variability in wetness such as vegetation, soil structure, depth to impermeable layer, and residue cover. The decision to use these variables may be specified by the fertilizer application parameters, or may be made automatically when application-area information corresponding to these variables is available. At a step  665 , the additional variables are determined. In one embodiment, these variables include an attribute value associated with a location point or discrete land unit and may be determined as described in connection to step  620 , above. 
     At a step  670 , a TWI grid is created. TWI is used to quantify hydrological processes. For example, as previously explained, TWI can provide a likelihood of accumulation of water within a region. In one embodiment, TWI combines local upslope contributing area and slope information and is defined as: 
                     TABLE 2                  In(A s /tanβ)                    
where A s  is the flow accumulation or upslope contributing area per unit grid-cell width (m 2 /m) and tan β is the land slope in degrees.
 
     In one embodiment, the processes corresponding to steps  625 ,  635 ,  645 ,  655 , and  670 , discussed above, may be carried out using computer-readable instructions written in Visual Basic or Python and using a library of GIS software functions such as ArcGIS developed and released by Environmental Systems Research Institute (ESRI) of Redlands, Calif. Thus for example, at step  625 , a DEM area corresponding to an application area is determined from a user-defined boundary of the application area according to the following instructions: 
                             TABLE 3                          # Process: Clip...           gp.Clip_management(rasdata, Rectanglea, clipdata, rasdata)           InFlowD = “NORMAL”           InType = “DEGREE”                        
At step  635 , a flow direction grid is created according to the following instructions:
 
                             TABLE 4                          #Process: FlowDirection           gp.FlowDirection_sa(clipdata, flowd, InFlowD)                        
At step  645 , a flow accumulation grid is created according to the following instructions:
 
                             TABLE 5                          # Process: Flow Accumulation           gp.FlowAccumulation_sa(flowd, flowa)                        
At step  655 , a slope grid is created according to the following instructions:
 
                             TABLE 6                          # Process: Slope           gp.Slope_sa(clipdata, fslope, InType)           RadDeg = “57.296”           #Process Slope and multiple it by a conversion unit           gp.Divide_sa(fslope, RadDeg, fslopedeg)           #Process Contributing slope           gp.Con_sa(flowa, 100, conta)           #Constant values           Input_raster_or_constant_value_2 = “100”           Input_raster_or_constant_value_plus = “1”           # Process Contributing Area           gp.Plus_sa(flowa, Input_raster_or_constant_value_plus, flowa2)           gp.Times_sa(flowa2, Input_raster_or_constant_value_2, conta)                        
And at step  670 , a TWI grid is created according to the following instructions:
 
     
       
         
           
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
             
            
               
                   
                 # Topographic Wetness Index 
               
               
                   
                 oTan = outtan” 
               
               
                   
                 dTan = “dtan” 
               
               
                   
                 topowi = “wetindex” 
               
               
                   
                 Inttopowi = “Int_twi” 
               
               
                   
                 twiclass = “ wi_class” 
               
               
                   
                 gridpoly = “ wipoly.shp” 
               
               
                   
                 tabclass = “ UPDATED_TABLE” 
               
               
                   
                 recltab = “ wirec” 
               
               
                   
                 # Process Tangent 
               
               
                   
                 gp.Tan_sa(fslopedeg, oTan) 
               
               
                   
                 # Process Divides 
               
               
                   
                 gp.Divide_sa(conta, oTan, dTan) 
               
               
                   
                 # Process TWI 
               
               
                   
                 gp.Ln_sa(dTan, topowi) 
               
               
                   
                 # Processing Topographic Wetness Index to an Integer” 
               
               
                   
                 gp.Int_sa(topowi, Inttopowi) 
               
               
                   
                 # Reclass data 
               
               
                   
                 gp.ReclassByASCIIFile_sa(Inttopowi, rec_2_txt, recltab, “DATA”) 
               
               
                   
                   
               
            
           
         
       
     
       FIGS. 7A, 7B, and 7C  illustratively provide exemplary methods for delineating zones according to embodiments of the present invention, and are shown as  710 ,  720 , and  730  respectively. Generally as shown in methods  710 ,  720 , and  730 , attribute zones or index zones are delineated based on a received set of attribute values or index values, which in some embodiments may be received as a grid of attribute values or index values. Although the steps of methods  710 ,  720 , and  730  may illustratively depict using attribute values or index values, it is understood that, at least in methods  710 ,  720 , and  730 , an attribute value may be used in place of an index value, and vice versa. This is not to say that an attribute value equals an index value, which is not necessarily true. Similarly, attribute values or index values may be received in the form of a grid or a set of values, including a table of values and a raster data set. Thus, for example, steps  712 ,  722 , and  732  may receive attribute values or index values, as either a set of values or as a grid. 
     In some embodiments, multiple iterations of methods  710 ,  720 , or  730  will be performed resulting in a set of attribute zones or index zones, with each member of the set corresponding to all of the zones for a particular attribute or index, such as all of the TWI zones or all of the zones for soil-pH level. 
     Turning now to  FIG. 7A , at a step  712 , a grid of attribute values is received. Attribute values may be received from a step of determining attribute values or index values, such as step  600  of  FIG. 4  or step  601  of  FIG. 5 ; received from a user via a user interface, or received from a data store of application-area information. In one embodiment, the grid of attribute values received in step  712  comprises a raster dataset. At a step  714 , polygon shape files are created based on the grid of attribute values. A polygon shape file is a graphic representation of an attribute value associated with a discrete land unit; each shape file has a polygon value corresponding to an attribute value. By way of example, a set of attribute values for an application area may be graphically represented as a geographically referenced raster-image, heat map, or similar visual depiction of discrete land units that are color coded, shaded, or marked to represent attribute values. This graphical representation may be converted to an image format, in one embodiment, such that information is stored as a bitmap-type image. The output of step  714  thus comprises a set of polygon shape files, with each shape file having a polygon value corresponding to the received set of attribute values. 
     At a step  716 , adjacently positioned, substantially similar shape files are merged together to form an attribute zone. In one embodiment, polygon values of adjacent shape files are compared, and where adjacent shape files are found to be identical or within a certain threshold indicating substantial similarity or classification, the shape files are merged. In one embodiment, this threshold is determined from a fertilizer-application parameter, which might include threshold information received from a user. In another embodiment, a threshold is determined based on the range of values of the received index values or attribute values; for example, a threshold may be determined based on a standard deviation of index values or attribute values. In still another embodiment, image processing is performed on adjacent shape files to identify and merge adjacent shape files having similar color or shading. The output of step  716  includes one or more delineated zones representing areas of similar characteristics; embodiments can include one or more shape files corresponding to each zone, or a data structure of zone-boundary locations and associated attribute values or a classification of attributes of each zone. 
     In one embodiment, the processes corresponding to steps  714  and  716  may be carried out using computer-readable instructions written in Visual Basic or Python and using a library of GIS software functions. Accordingly, at step  714 , polygon shape files are created from a grid of attribute values according to the following instructions: 
                     TABLE 8                  # Convert the TWI Raster data to a polygon shapefile       rasterfId = “VALUE”       gp.RasterToPolygon_conversion(recltab,  gridpoly,  “SIMPLIFY”,       rasterfId)       wipoly_Dissolve_shp = “wipolydis.shp”       wipoly_shp = “wipolydis.shp”                    
And at step  716 , adjacent shape files representing substantially similar characteristics are merged together to form one or more zones according to the following instructions:
 
     
       
         
           
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
             
            
               
                   
                 gp.Dissolve_management(wipoly_shp, wipoly_Dissolve_shp, 
               
               
                   
                 “GRIDCODE”, “”, “MULTI_PART”) 
               
               
                   
                   
               
            
           
         
       
     
     Turning to  FIG. 7B , another method for delineating zones according to embodiments of the present invention is illustratively provided. At a step  722 , attribute values are received. Attribute values may be received as a set or grid of attribute values from a step of determining attribute values or index values, such as step  600  of  FIG. 4  or step  601  of  FIG. 5 ; received from a user via a user interface, or received from a data store of application-area information. At a step  724 , discrete land units associated with the received attribute values are identified. Processing for delineating a zone is performed on discrete land units, in the embodiment provided by  FIG. 7B , thus step  724  identifies the discrete land units associated with each received attribute value. At a step  726 , adjacently positioned discrete land units associated with identical attribute values are merged to form subzones. The output of step  726  includes one or more subzones made up of discrete land units that have the same attribute value. Thus each created subzone becomes associated with the attribute value of its component discrete land units. In one embodiment, the subzones determined in step  726  are used as delineated zones. 
     At a step  728 , adjacently positioned subzones that have substantially similar attribute values are merged together to form a delineated attribute zone. A threshold may be used to indicate substantial similarity. In one embodiment, this threshold is determined from a fertilizer-application parameter, which might include threshold information received from a user. In another embodiment, a threshold is determined based on the range of values of the received index values or attribute values, for example, a threshold may be determined based on a standard deviation of index values or attribute values. In another embodiment, a cluster analysis of values of subzones may be performed to determine zones based on clusters of subzones. 
     In another embodiment, subzones associated with attribute values corresponding to the same attribute classification are merged together to form a delineated attribute zone. By way of example, for the soil pH-level attribute, subzones associated with pH-levels less than 7 might be merged into a zone corresponding to “acidic,” since the attribute values associated with each subzone correspond to the same attribute classification, (i.e., “acidic”). This embodiment contemplates a scenario where substantially similar attribute values or index values represent different attribute or index classifications, and thus are not included in the same zone. By way of example using the pH-level attribute again, attribute values of 6.9 and 7.1 might be considered substantially similar, in that both values are close to a neutral pH-level, and therefore according to the previously described embodiment, their associated discrete land units (or location points) would be included in the same zone. But because an attribute value of 6.9 is considered acidic and an attribute value of 7.1 is considered basic or alkaline, under this embodiment, the discrete land units associated with the two attribute values might fall into different zones. This embodiment also contemplates a scenario where zones are formed based on attribute values of discrete land units (or location points) falling into ranges of attribute values. For example, in one embodiment, a TWI can be divided into 7 ranges: (1) less than 10.4, (2) 10.4-12.1, (3) 12.1-13.8, (4) 13.8-15.6, (5) 15.6-17.3, (6) 17.3-19, and (7) greater than 19, corresponding to the following classifications: extremely dry, very dry, dry, moderate, wet, very wet, and extremely wet, respectively. 
     Turning to  FIG. 7C , another method for delineating zones according to embodiments of the present invention is illustratively provided. At a step  732 , attribute values are received. Attribute values, which may be in the form of index values, may be received as a set or grid of attribute values from a step of determining attribute values, such as step  601  of  FIG. 5 ; received from a user via a user interface, or received from a data store of application area information. In another embodiment, instead of receiving attribute values, index values may be received at step  732 . At a step  734 , location points associated with the received attribute values (or index values, in one embodiment) are identified. Processing for delineating a zone is performed based on the location points in the embodiment provided by  FIG. 7C , thus step  734  identifies the location points associated with each received attribute value. 
     At a step  736 , adjacently located location points associated with identical attribute values (or index values, in one embodiment) are enclosed to create subzones. In one embodiment, a subzone boundary is delineated between location points associated with non-identical attribute values (or index values). In one embodiment, the boundary may be positioned at a location evenly spaced between location points associated with different attribute values (or index values). The output of step  736  includes one or more subzones enclosing location points that are associated with identical attribute values (or index values). Thus each created subzone becomes associated with the index value (or attribute value) of its enclosed location points. In one embodiment, the subzones determined in step  736  are used as delineated zones. 
     At a step  738 , adjacently positioned subzones that have substantially similar attribute values (or index values) are merged together to form a delineated attribute or index zone. A threshold may be used to indicate substantial similarity. In one embodiment, this threshold is determined from a fertilizer-application parameter, which might include threshold information received from a user. In another embodiment, a threshold is determined based on the range of values of the received index values or attribute values, for example, a threshold may be determined based on a standard deviation of index values or attribute values. In another embodiment, a cluster analysis of values of subzones may be performed to determine zones based on clusters of subzones. 
     In another embodiment, described above in connection to  FIG. 7B , subzones associated with index values corresponding to the same index classification, or subzones associated with attribute values corresponding to the same attribute classification are merged together to form a delineated index zone or attribute zone, respectively. 
     Each zone may be considered to be associated with an attribute value or an index value representative of the attribute values or index values associated with the discrete land units or location points within the zone. Embodiments of the representative value include an average value, a median value, or a value otherwise representative of the attribute values or index values associated with each discrete land unit or location point in the zone. 
       FIG. 8  is a flow diagram illustrating an exemplary method for partitioning or dividing an application area into application cells according to an embodiment, shown as  800 . As previously described, application-cell dimensions may be determined based on fertilizer-application parameters, including user preferences and equipment parameters that may specify the physical reach or other limitations of a fertilizer applicator, the size of the application area and the locations of zones. 
     At step  810 , fertilizer-application parameters are determined. Examples of fertilizer-application parameters are discussed previously in connection to  FIG. 1 . Fertilizer-application parameters may be received from a user via a user interface, from a data store, or both. In one embodiment, a set of fertilizer-application parameters is determined based on application-area information, historical information, or both. By way of example, determined attribute values may correspond to a certain fertilizer type or application methodology. In one embodiment, application parameters are determined by a series of questions, text fields, or selections completed by a user through a user interface. This embodiment might prompt the user to provide information relevant to determining application parameters including, for example information about the user&#39;s applicator or equipment, fertilizer inventories, other user preferences, storage locations of data related to fertilizer application, such as the location or path to the location of application-area information and historical information, including past user settings or preferences. One embodiment might prompt the user for this information using a user interface and a series of questions, similar to a user interface and series of questions provided by income tax software. Moreover, a user&#39;s entries may be saved and reused during subsequent sessions. In one embodiment, application parameters may be downloaded from one or more servers, as needed. For example, in one embodiment, information including updated information, related to federal and state regulations, current fertilizer prices or crop futures, or recommended application rates or ratios is retrieved as needed from a data store. In one embodiment, a set of application parameters may be provided by an applicator manufacturer or a fertilizer retailer. In one embodiment, fertilizer application parameters includes a TWI threshold, which may be provided by a user or determined using TWI-related application area information and historical information including differential yield performance (i.e., past yield from enhanced fertilizer minus a past yield from conventional fertilizer). The TWI threshold can be determined to insure a positive yield differential. 
     In some embodiment, fertilizer application parameters include a risk-avoidance level, which is usable to scale or adjust fertilizer application products. For example, the risk-avoidance level parameter can be applied to an attribute threshold to slide the threshold up or down, thereby altering the determined fertilizer product to be applied. More specifically, suppose application parameters include an attribute threshold for TWI representing a TWI value of 17.3 or more. This threshold could indicate that an attribute zone is designated to receive an enhanced fertilizer is only if the attribute value (a TWI value, here) representative of the zone is 17.3 or more. Suppose further that a user, wishing to avoid the risk of loss of conventional fertilizer due to environmental loss mechanisms, provides a high risk avoidance level (or indicates a low tolerance for risk), which could be specified by the user as a number or percentage representing risk the user is willing to take, as a category of risk like low, medium, or high, a slider bar ranging from low to high risk, or a question to the user. This provided risk-avoidance level may be used to adjust the TWI threshold down to a lower level, which would result in zones having corresponding attribute values lower than 17.3, but higher than the newly adjusted TWI threshold, being designated for receiving enhanced fertilizer. In other words, zones that are wet, but below the original TWI threshold may still receive an enhanced fertilizer application. 
     In some embodiments, fertilizer application parameters includes one or more buffers, which indicate areas of land that will not receive fertilizer, such as areas of land adjacent to wells or water resources. The buffers or parameters used to determine buffers may be provided by a user or determined automatically from application-area information, such as information about water resources within the application area. 
     At a step  820 , the application area is divided into application cells. As previously described, in connection to step  800  of  FIG. 4  and step  801  of  FIG. 5 , an application area may be partitioned into one or more application cells, or the boundaries for one or more application cells may be defined within an application area. A set of fertilizer-application parameters includes a subset of equipment parameters that may determine the dimensions of an application cell based, for example, on the reach or coverage area of a fertilizer applicator used to apply fertilizer. In one embodiment, dimensions of an application cell are based only on equipment parameters, and each application cell has a uniform dimension. A minimum discrete cell length may be determined based on equipment parameters related to limitations of an applicator&#39;s capability to vary fertilizer application. This length represents the smallest amount of distance that the applicator can effectively vary application of different fertilizer products, while traversing an application area, or the smallest amount of distance that must be traversed in order to differentiate an applied fertilizer product. 
     In one embodiment, the width of each application cell will be uniform, based on equipment parameters, but the length will vary based on equipment parameters and the location of zones in the application area. In this embodiment, a row of application cells comprises an application strip, which represents one traverse of the application area by a fertilizer applicator. A cell length may be determined based on the minimum discrete cell length discussed above and zones or portions of zones falling into the minimum discrete cell length, in order to minimize variance of zones in an application cell, as the cell length increases. Specifically, an application cell&#39;s length may be extended based on the location of zones relative to the application cell. Fertilizer-application products are ultimately determined based on attributes, in one embodiment, which the zones represent. For a given cell, portions of zones falling in the cell may vary, thus fertilizer product will vary for each cell. Accordingly, cell length may be determined to maximize the area of a cell that minimizes the variance in zones or portions of zones within the cell. Put another way, beyond the minimum discrete length, the cell length should continue so long as the proportion of areas occupied by a zone, zones, or portions of a zone or zones within the cell is substantially constant, in one embodiment. For example, application strip  257  illustrated in  FIG. 2A , includes application cells  255  of varying cell length, based on the location of zones, in order to minimize zone-variance in each application cell. 
     Each cell encompasses at least part of at least one zone, thereby associating information about the zone and its associated attribute values with the cell. In one embodiment, the output of step  820  includes information about each application cell, including application cell size and location, and the associated zone and zone-attribute information. At a step  830 , application parameters are associated with application cells. The information provided by step  830  may be used to determine a fertilizer product for each application cell. The information provided by step  830  includes information specifying each application cell and information associated with each cell including zone and zone-attribute information, and any fertilizer-application parameters relevant to determining a fertilizer product for each cell. By way of example, an application parameter specifying a buffer along one side of an application area may be associated with application cells located on that side of the application area. In one embodiment, the output of step  830  may include a data structure of application cells and associated zone and zone-attribute information, and relevant fertilizer-application parameters. 
     Turning now to  FIG. 9 , a flow diagram is shown illustrating an exemplary method for determining a fertilizer product for each application cell, shown as  900 . As previously described, a fertilizer product can include the type or types of fertilizer, fertilizer application rate or quantity, and fertilizer-mixture information such as a proportion of mixed fertilizer types. In one embodiment, fertilizer products may be determined based on attribute values associated with zones or portions of zones falling within each application cell and based on fertilizer-application parameters. In one embodiment, the attribute values (or index values) of location points or discrete land units enclosed by an application cell are used to determine fertilizer product. As described above in connection to  FIG. 8 , the information provided by step  830  may be used to determine a fertilizer product for each application cell. In one embodiment, this information includes information associating each application cell with zone and zone-attribute information for the zones or portions of zones in the cell and relevant fertilizer-application parameters. 
     At a step  910 , a decision is made regarding whether to apply a TWI threshold. An attribute threshold or attribute-value threshold, such as a TWI threshold, may be included in a set of fertilizer application parameters determined in step  810 , of  FIG. 8 . An attribute threshold is used to determine which fertilizer type or types to apply based on the attribute value or index value associated with a zone, in one embodiment. In another embodiment, an attribute threshold may be used to determine which fertilizer type or types to apply based on the attribute value or index value that are enclosed by an application cell. Attribute values not satisfying the threshold may be ignored, altered, zeroed out, or effectively considered to have a different attribute value. By way of example, consider a TWI threshold requiring a TWI value of 17.3 or more for an enhanced-type fertilizer, and another application parameter specifying that an enhanced-type fertilizer is to be applied to zones having associated TWI values of greater than 15.6, which corresponds to wet, very wet, and extremely wet antecedent soil-moisture conditions. A zone having an associated TWI value of 16 would be considered for receiving an enhanced-type fertilizer, without the TWI threshold. But with the TWI threshold applied, the zone would not be considered for receiving an enhanced-type fertilizer. 
     The decision to apply a TWI threshold in step  910  is determined based on a wetness-index threshold included in the set of determined fertilizer-application parameters. Applying a TWI threshold is discussed in connection to steps  915  and  918 . At step  915 , the TWI threshold is applied to each zone or portion of a zone within an application cell. In one embodiment, the threshold is applied to an attribute value or index value representative of the zone. In another embodiment, the TWI threshold is applied to the attribute value or index value associated with each discrete land unit or location point within the zone or zone-portion falling within the application cell. Based on the result of the threshold application, the zone or portion of zone falling within the application cell is designated to receive a fertilizer type. In one embodiment, the zone or zone-portion falling within the application cell are designated as receiving either a conventional-type fertilizer or an enhanced-type fertilizer, based on whether attribute values or index values associated with each zone are below or above the TWI threshold. In another embodiment, the zone or zone-portion falling within the application cell are designated as receiving either a conventional-type fertilizer or an enhanced-type fertilizer, based on whether a majority of attribute values or index values associated with discrete land units or location points within the zone or zone-portion falling within the application cell are below or above the TWI threshold. In one embodiment, the set of determined fertilizer-application parameters also includes a risk-avoidance level. A risk-avoidance level, which is described above in connection to  FIG. 8 , may be used to scale the TWI threshold (or other attribute threshold) prior to applying the threshold to each zone, based on the user&#39;s tolerance for risk, such as the risk of loss of conventional fertilizer due to environmental loss mechanisms, which is expressed by the risk avoidance level parameter. 
     At step  918 , each application cell is associated with information indicating the fertilizer type designated for each zone or zone-portion falling within the application cell, based on the operation performed in step  915 . 
     Continuing with  FIG. 9 , at a step  920  a decision is made regarding whether to apply other fertilizer-application parameters. The decision to apply other fertilizer applications is determined based on parameters present in the set of determined fertilizer-application parameters. If another application parameter is to be applied, then at a step  925 , application cells are coded for or associated with information based on an application of the parameter. For example, a set of fertilizer-application parameters may include a mixed-types parameter for indicating whether an application cell may receive a single type of fertilizer or a mixture of fertilizer types. If a mixed-types parameter is present and indicates that a cell is permitted to receive only a single fertilizer type, then at step  925 , that cell is coded for or associated with information indicating that only a single fertilizer type may be applied to the cell. 
     At a step  950 , a fertilizer product is determined for each application cell. In one embodiment, the product is determined based on fertilizer-application parameters specifying the fertilizer type or types, quantities, or mixture ratios to be applied for a given attribute value or range of attribute values, based on attribute values or index values associated with zones or zone portions within the application cell. In one embodiment, these application parameters include user preferences of fertilizer application or recommended application products, which may be received from a fertilizer retailer. In one embodiment, the attribute values of location points or discrete land units enclosed by an application cell are used to determine a fertilizer product. In this embodiment, a product may be determined based on fertilizer parameters and an average, median, or representative value of the attribute values associated with discrete land units or location points within an application cell. 
     One embodiment of step  950  is provided on the right-hand side of  FIG. 9 . In this embodiment, a fertilizer type may associated with each zone within the application cell, based on fertilizer-application parameters. The fertilizer type may be determined based on a representative attribute value or index value associated with the zone or based on attribute values or index values of discrete land units or location points within the zone. 
     At a step  960 , a decision is made regarding whether an application cell is permitted to receive a mixture of fertilizer types. The decision is determined based on whether the cell was coded or associated with information provided by a mixed-types parameter, at step  925 . As previously explained, a mixed-types parameter may indicate whether the cell is permitted to receive a single fertilizer type or mixture of types. 
     If the application cell is not permitted to receive a mixture of fertilizer types, then at a step  962 , it is determined which fertilizer type is associated with the zone or portion of a zone occupying the greatest area of the application cell. By way of example, if a cell includes two zones, a first zone occupying 60% of the application cell and a second zone occupying 40 percent of the application cell, then the fertilizer type associated with the first zone is determined. At a step  964 , the application cell is coded for receiving, or associated with, the fertilizer type determined in step  962 . 
     On the other hand, if a cell may receive a mixture of fertilizer types, then at a step  963  a proportion of area within the application cell occupied by each zone or portion of a zone is determined. In one embodiment, step  963  first determines how many zones or zone portions fall within an application cell. In one embodiment, a mixture of fertilizer types is applied only to application cells enclosing more than one zone or zone-portion. Thus, where only one zone is within an application cell, the application cell will receive only fertilizer associated with that zone, regardless of whether the cell is permitted to receive a mixture. Accordingly, if only one zone or portion of a zone is present in the application cell, then that zone is determined to occupy 100% of the application cell, in this embodiment. 
     If more than one zone or zone-portions is within the application cell, then the area of the application cell occupied by each zone is determined. At a step  965 , a mixture ratio of fertilizer types is determined based on the proportion of areas determined in step  963 . As described above, in this embodiment, each zone has a fertilizer type associated with it. Accordingly, in one embodiment, the fertilizer types used for the mixture ratio determined in step  965  are the fertilizer types associated with each zone falling within the application cell, or with a zone portion falling within the application cell. The ratio may correspond to the proportion determined in step  963 , in one embodiment. By way of example, assume that a cell includes two zones: one zone that has a low TWI value and occupies 60% of the application-cell area, and another zone that has a high TWI value and occupies the remaining 40% of the application-cell area. Assume also that a mixed-types parameter indicates that a mixture of fertilizer types is permissible. Then according to one embodiment the mixture ratio of fertilizer types to apply may be determined based on the proportional areas occupied by each zone. Here, the ratio might be 60% conventional fertilizer to 40% enhanced fertilizer. At a step  967 , the application cell is coded for receiving, or associated with, the fertilizer type or types and mixture ratio, where applicable, determined in step  965 . 
     At a step  970 , a rate of fertilizer is determined for each application cell. A rate is an amount per unit area of land; thus in determining the rate, the quantity or amount of fertilizer to be applied to an application cell can be determined. A rate of fertilizer to apply to the cell is based on a set of fertilizer-application parameters. Where a mixture of fertilizer types is to be applied, a rate may be determined for each component fertilizer type, in one embodiment. In another embodiment, a rate for a mixture of fertilizer types may be determined from the application parameters. At a step  980 , each application cell is coded for receiving, or associated with, the rate determined in step  970 . 
     Having thusly described illustrative embodiments for facilitating methods for applying agrochemicals to an application area and managing agrochemical application, it will be apparent to one of skill in the art that such embodiments can be used for in many possible applications including, for example: applying anhydrous ammonia with and without nitrification inhibitor, depending on attribute values; applying other fertilizer sources such as P fertilizer, with and without Avail; applying liquid forms of conventional versus enhanced efficiency fertilizers; applying N fertilizer sources based on soil textural differences detected by measuring soil ECa; using other soil or landscape characteristics to improve estimates of TWI (e.g., depth to impermeable layer, residue cover, soil texture, vegetation, soil structure); or incorporating other factors that may affect location and type of fertilizer applied such as environmental regulations, health and safety, and other economic considerations. 
     Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention. By way of example, another land or soil attribute that can be used for delineating zones of land for receiving different fertilizer- or agrochemical-product applications is soil texture and differences in soil texture that may exist across a field. An attribute value representing soil texture can be a quantitative variable (i.e., % sand, % silt, and % clay) or can be a categorical metric based on soil textural classes (e.g., silt loam). The soil-texture attribute can be measured by several methods including (a) taking grid soil samples and analyzing each sample for soil texture, and (b) using an on-the-go field-based sensor such as apparent electrical conductivity (ECa) or a near-infrared (NIR) sensors. Such field sensors provide indirect measures of soil texture, but using calibration information, their measurements are interpretable into quantifiable soil texture information. From the obtained attribute values, fertilizer or agrochemical product application decisions can be based, for example, on a percentage of a sand (e.g., for N applications) or % clay (for P applications), in one embodiment. Here, a higher percentage of sand might result in a higher quantity of enhanced efficiency N fertilizer to be applied; or a higher percentage of clay might result in a higher quantity of enhanced efficiency P fertilizer to be applied, depending on other application-area information and application parameters. Like wetness, application parameters including attribute-threshold values and risk avoidance levels may be used to alter the determined agrochemical product to be applied to the application cells. 
     Still other land or soil attributes that may be used in our technologies include the location of drainage tiles in an application area, which in one embodiment may be based on or determined from a geographically-referenced map of the location of the drainage areas. In this embodiment, enhanced efficiency fertilizer is be placed over the top of a drainage tile to reduce immediate loss into drainage tile, and conventional fertilizer is placed between drainage tile. Furthermore, buffer areas can be established, for example if an application area is near a surface water resource, so that the enhanced efficiency fertilizer is placed in a buffer area nearer the water source and conventional fertilizer is placed away from the water resource. 
     In other embodiments, this variable-product application technology may be utilized to apply phosphorus in the presence or absence of a phosphorus stabilizer such as Avail in areas with clay mineralogy that fixates phosphorus, low vs. high soil wetness index to avoid loss and enhance efficiency, and based on soil-pH levels; to apply fertilizer catalysts, also called soil amendments (such as NutriLife MAX); and micro-nutrient applications, which can be impregnated, in one embodiment, can use soil pH and soil organic matter to delineate zones for application or zones for avoiding application. 
     Still another embodiment relates to fungicides: the wetness index may be utilized to indicate areas likely to have a higher incidence or severity of disease when applying preventative or curative fungicides. For example, a preventative fungicide can be applied to the entire field, while a curative fungicide is injected into the spray solution at certain locations in the field. This may be used as a foliar application, but also used as a possible seed treatment. Still another embodiment relates to herbicides. For example, in one embodiment herbicides such as the chloroacetamide, HPPD, and triazine families that are soil applied and/or have residual soil activity are used. These are generally sold as premixes; additional product(s) may be injected in areas where loss of residual activity is expected. Our technology may be used to delineate areas of the field, based soil or land characteristics, and to determine and/or apply automatically different herbicide rates or herbicide sources. For example, Guardsman Max herbicide application rate for coarse soil is 2.5-3 pts/acre when there is less than 3% organic matter and 3-4 pts/acre when there is more than 3% organic matter, but in a medium or fine soil rates are 3-4 pts/acre when organic matter is &lt;3% and 4-4.6 pts/acre when organic matter is &gt;3%, which may increase efficacy, reduce runoff potential, differences in chemical and physical breakdown, leaching loss, and other environmental losses. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described.