Abstract:
A method for forming a binder-free granular or semi-granular fertilizer is disclosed, which comprises mixing a seed material and primary and secondary nutrient sources in a blender under heat until a slurry is formed, transferring the slurry to a long dryer, and drying the product under vacuum and thereafter gradually cooling the product to produce a granular or semi-granular fertilizer with a core of a seed material and a coating of secondary nutrient salts crystallized thereabout, with nutrients and biologically active agents entrained therein. The fertilizer formed has excellent stability and may be urea-free.

Description:
This is a continuation of copending application Ser. No. 07/236,320 filed on Aug. 25, 1988, now abandoned, which was a continuation of Ser. No. 07/124,361 filed Nov. 23, 1987, now abandoned, which was a continuation of Ser. No. 06/867,594 filed on May 27, 1986 now abandoned, which was a continuation of Ser. No. 06/506,860 filed on June 22, 1983 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a process for the production of fertilizers provided with biologically active agents and the fertilizers produced thereby. More specifically, a process is provided by which a granular or semi-granular fertilizer can be formed which may further incorporate various organic agents, particularly in a folial fertilizer form. 
     2. Description of the Prior Art 
     It has long been the practice to artificially enrich the nutrients available to crops to enhance and accelerate their yield by application of fertilizer to the crops, particularly to the ground or water supply for the crops. Similarly, fertilizers are commonly used to improve the growth of plants desired for their aesthetic characteristics. Recently, industry attempts have focused on the provision of a fertilizer which is applied to and absorbed through the leaves of the plants, or a folial fertilizer, as a more efficient, and in the long run, less expensive method of fertilizing. Such folial fertilizing methods also lend themselves to the introduction or incorporation of biologically active agents, particularly growth regulators to further stimulate growth. As a result, those of skill in the industry have also focused on developing means to provide a fertilizer including such agents in a granular or semi-granular form. Unfortunetly, such attempts have met with numerous problems. 
     Among the most important of the problems encountered is the difficulty in providing a fertilizer with all the necessary nutrients in a form useful, particularly as a folial fertilizer. The formation of granular, or semi-granular fertilizers, which can be discretely dispensed with the aid of water, has long been sought, but rarely achieved. Frequently, attempts to provide such fertilizers have resulted in products which quickly separate and lose their integrity or are non-uniform to begin with. 
     Further problems encountered in the effort to provide granular, folial fertilizers is the difficulty in binding the nutrient to the core of the granule. Although traditionally a binder in the nature of a wax or oil is employed, as described in U.S. Pat. Nos. 3,295,950 and 3,580,715, these are unsuitable for folial fertilizers, as leaf absorption requires the fertilizer components to be water soluble. 
     One alternative is described in U.S. Pat. No. 3,867,124, which employs a urea-ferrous sulphate complex as a binder for the nutrients about core prill. However, urea is a highly concentrated nitrogen source, and application of urea in a folial fertilizer may cause nitrogen burning, or phytotoxicity. 
     Another problem encountered in the provision of biologically active agents is that many of these agents are denatured or &#34;killed&#34; at relatively low temperatures, particularly those agents which are, or based on, complicated protein structures. As many of the prior art attempts to form granular fertilizers, with or without biologically active agents, have employed relatively high heats, above 200° F., these processes cannot be used to form a fertilizer incorporating a biologically active agent of this type. 
     Accordingly, there persists an industry-wide need to provide a granular or semi-granular fertilizer, particularly a folial fertilizer prepared without a binder, which may further incorporate one or more biologically active agents. 
     SUMMARY OF THE INVENTION 
     It is accordingly one object of this invention to provide a process whereby granular or a semi-granular fertilizer may be made, which fertilizer retains its integrity over an extended shelf life. 
     It is another object of this invention to provide a binder-free folial fertilizer which is absorbed by the plant relatively quickly. 
     It is yet another object of this invention to provide a granular or semi-granular fertilizer which incorporates biologically active agents. 
     These and other objects of the invention can be achieved through use of the process and fertilizer disclosed hereinbelow. 
     A granular or semi-granular fertilizer (granular, as used, is intended to refer to a particulate substance, substantially all of the particles passing through a mesh of size 8-20, while semi-granular is intended to mean a particulate substance wherein substantially all of the particles pass through a mesh size 20 or greater) may be made by mixing a seed material and conventional nutrients in a blender, preferably a jacketed ribbon blender. Secondary or micronutrients, such as iron, magnesium, manganese, copper, boron, zinc and molybdenum are also added. Either the hydrates of these micronutrients are selected so as to provide sufficient waters of hydration to form a slurry in the blender, or an additional water source is added to achieve the same effect. A biologically active agent is added at this initial step. Blending is continued, with heating, until a slurry is formed, whereupon the mixture is transferred to a holding tank, or in a continuous process, a dryer. 
     The mixture is transferred to a dryer provided with mechanical agitators which act to move the mixture through the dryer. Heat is applied in the dryer, preferably under a vacuum, but the dryer is of sufficient dimension to provide a pathway long enough to allow the mixture to cool and recrystallize in an unheated portion of the dryer. The product that exits from the dryer is a granular or semi-granular fertilizer, comprised of a seed material, provided with a nutrient and micronutrient-containing coating, the coating further containing one or more biologically active agents. 
     This invention may be further understood by reference to the detailed description provided below. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The granular or semi-granular fertilizer of this invention may be prepared by mixing a seed material, generally in the form of prills, together with conventional nutrients and, if desired, one or more biologically active agents, with the micronutrient waters of hydration or alternative water source sufficient to form a slurry, in a first blender, maintaining the blender at a temperature of about 115° F.-140° F., and mixing until a slurry is formed. A particularly preferred temperature is 128° F. To ensure good maintenance of an even temperature, a jacketed ribbon blender is preferred as the blending device. Although the time required to form a slurry will vary with the load, on a commercial scale, this mixing will take approximately 15-20 minutes. 
     After slurry formation, the mixture is transferred to a holding tank, if a batch process is being employed. Thereafter, or, in a continuous process, directly, the load is transferred to a dryer provided with mechanical agitators, and is preferably maintained under a vacuum. 
     The dryer employed in this process must be relatively long as compared with its diameter (a minimum ratio is approximately 5:1) and is preferably provided with a tube surrounded by a cylindrical shell, the shell being suitable for receiving steam or other heated substance in the space between the shell and the tube of the dryer, into which tube the slurry mixture is introduced. A vacuum, or near vacuum, approximately 15 inches to 20 inches of mercury, is preferably applied to the dryer interior. The mechanical agitators of the dryer are preferably a plurality of small, vari-pitched paddles, or similar device suitable for moving the mixture along the dryer length. A particularly suitable jacketed vacuum dryer is marketed by Strong-Scott Company of Minneapolis, Minn., under the name Solidaire Dryer. 
     As the load is introduced to the dryer indirect heat is applied through the jacket by conduction of a heated gas or liquid into the aforementioned cylindrical shell, such that the temperature of the inner wall of the shell is maintained at approximately 140°-150° F. No heat is applied to the last half of the dryer, and the product is allowed to cool as it travels the length of the dryer, solidifying and exiting as a granular or semi-granular product, at about 90° F. To assist in directing the flow of vapors and fertilizers in the dryer, as well as enhance heat transfer, a small amount of sweep gas, e.g., nitrogen, may be introduced to the dryer. 
     The fertilizer produced by this process is comprised of a seed material coated with nutrients and micronutrients and optionally one or more biologically active agents. Exemplary seed materials include potassium nitrate, ammonium nitrate, urea, calcium nitrate, sodium nitrate potassium sulfate and ammonium sulfate, generally in the form of prills. The seed material should be selected so as to meet the desired size restrictions (i.e., granular or semi-granular). 
     The seed material is coated with a coating containing nutrients and secondary micronutrients. As exemplary nutrients, one or more of phorphous, potassium and urea may be included in the mixture. It is important to note that, in contrast to prior art systems, urea need not be present for the formation of a coating about the prill, and is included optionally, only as a nutrient. If urea is either not desired or is supplied by an alternative source, the fertilizer may omit urea. The fertilizer may also include a buffer, which may be urea or carbamate. 
     Also included in the coating are secondary or micronutrients, which are familiar to those of ordinary skill in the art. Among these micronutrients are iron, magnesium, manganese, copper, boron (generally added as boric acid), zinc and molybdenum. The micronutrients are generally added to the fertilizer mixture as hydrated salts of the micronutrient, e.g., hydrated sulfates. One or more of the micronutrients must be included in order to form the coating. Thus, the fertilizer of this invention is essentially &#34;binder free, in that no binder need be employed to form the nutrient coating. Although Applicant does not wish to be bound by this explanation, it appears that the micronutrient salt is dissolved in the slurry. As the mixture is dried, the salt(s) recrystallize about the seed material, and, assuming sufficient mixing or mechanical agitation, in uniform amounts. Other nutrients present are entrained in this recrystallization coating. Thus, the fertilizer of this invention may be characterized as &#34;binder-free&#34; in that no binder need be employed to form the nutrient coating. For this reason, if the micronutrient is not introduced as a hydrated salt sufficient to provide enough waters of crystallization to form a slurry, an alternate source of water, such as addition of H 2  O directly to the mixture, must be provided. 
     As noted, because of the low temperatures employed in the process for manufacturing this fertilizer, the fertilizer may optionally include biologically active agents incorporated in the coating. Although a wide number of agents, particularly growth regulators, are known to those of skill in the art, and generally any agent which is not denatured at temperatures below about 150° and is otherwise uneffected by the mixture can be employed, particularly preferred growth regulators include GA 3  (gibberellic acid), NAA (1-naphthalene acetic acid), CCC (chloroethyl choline chloride), kinetin, ABA (abscisic acid), DMSO (dimethylsulfoxide) and BAP (benzylaminopurine). 
     Although the composition of the fertilizer, and the raw mixture prior to drying, will vary depending on the nature of the seed material used, nutrients and micronutrients selected, and biologically active agent employed, if any, general ranges can be identified for the important nutrients, particularly on an elemental basis. Nitrogen should be present in amounts of 0-36% on an elemental basis. Potassium should be present in amounts of 2-4%, particularly for folial fertilizers, as potassium appears to be critical in the process by which the fertilizer is absorbed by the plant. In folial fertilizers, phosphorus should be present in trace amounts, whereas, in ground fertilizers, phosphorous should be present in amounts of from 0-15%. Generally, in ground fertilizers, nitrogen will be present, at a maximum, of about 30%. 
     If urea is to be used, it should be present in amounts of 1-4%. 
     The micronutrients employed will be present in varying amounts, as determined by the needs of the plant to be fertilized, the ground condition, etc. One of ordinary skill in the art will recognize and be aware of the varying needs, and adjust the formulations accordingly. Generally, micronutrients, as the elemental metal, are present in amounts varying from about 0.01%-3%. In particular, iron, on an elemental basis, should be present in amounts of from 0.75-1.5%; manganese from 1.5-3%; and copper, boron, zinc and magnesium from 0.011-1.0%, molybdenum 0.002 max. all on an elemental basis. 
     The biologically active agents are generally present in extremely small quantities, as is well known in the art. See, e.g., Economic Botany, Vol. 12, No. 3, July-September 1958, pages 213-255, as to the extremely small quantities of gibberellic acid having substantial growth effects. Generally, the biologically active agents of this invention should be present in the fertilizer mix at between 10 -4  -10 -6  M SOL. 
     As an illustrative example not intended to limit the invention, the following composition has been prepared according to the above-disclosed process and used with good results. 
     
         ______________________________________                 Amount                 Present OnFertilizer Component  Elemental Basis______________________________________Nitrogen (As Potassium                 1%Nitrate Prills)Iron (As Ferrous Sulphate)                 1%Manganese (As Manganese Sulphate)                 2%Copper (As Cupric Sulphate)                 0.08%Boron (As Boric Acid) 0.02%Zinc (As Zinc Sulphate)                 0.05%GA.sub.3               0.003%______________________________________ 
    
     A fertilizer prepared according to the above-described process may be conveniently applied to the ground or the leaves of the plant to be fertilized by spraying, using water as a carrier. Of course, the amount of water required per acre will vary with the equipment used per application, including the type of nozzle employed, the discharge rate of the nozzle and the speed of the vehicle or person carrying the nozzle. Spray patterns should be uniform and penetrate the upper leave canopy of the plants being fertilized, if a folial fertilizer is employed, to cover the leaves as thoroughly as possible. This may be achieved by using above ground irrigation systems, ground application equipment, backpack sprayers and/or aerial applicators. Although one of ordinary skill in the art may determine, without the exercise of inventive faculty, the amount and frequency of fertilizing necessary, the amount of fertilizer, and frequency of application, for a large number of commercially important crops is provided in Table 1. 
     
                       TABLE 1______________________________________APPLICATION SCHEDULE                  APPLICATION          RATE    TIME______________________________________VEGETABLES COMMER-CIALLY PRODUCEDBeans (Snap, Pole, Lima)            1.8-2.5 lbs.                      3 Weeks after plant-            per acre  ing 1 Week before                      Blossoms appearBeets and Carrots            1.8-2.5 lbs                      20th-40th-60th Day            per acreBroccoli, Cabbage, Cauli-            1.8-2.5 lbs                      20th-40th-60th Dayflower, Collards, Kale,            per acreLettuce, Mustard, Spinach,TurnipsSweet Corn       1.2-2 lbs 1-2 applications at            per acre  12-18-36 inches highCucumbers, Cantaloupes,            1.2-2 lbs Apply when vinesSquash, Pumpkin and            per acre  begin to run -Watermelon                 1 Week before                      Blossoms appearEgg Plant        1.2-2 lbs 1 Week before            per acre  Blossoms appearHerbs, Parsley, Radishes,            .5-1 lb   20th-40th-60th DayRhubarb          per acreOkra             1.8-2.5 lbs                      1 Week before            per acre  Blossoms appearOnions           .5-1 lb   Apply when Onions            per acre  are about 4 inches                      highPeas (English, Southern)            1.2-2 lbs 1 Week prior to set            per acre  of BloomIrish Potatoes   1.2-2 lbs 1 Week before            per acre  Blossom appearSweet potatoes   1.2-2 lbs Apply when Vines            per acre  begin to run - 1                      Week before                      Blossoms appearField Potatoes   1.8-2 lbs 1 Week before            per acre  Blossoms appear -                      When first fruits are                      the size of a quar-                      ter - 2-3 Weeks later                      if desiredTrellished Tomatoes            1.2-2 lbs 1 Week before(Staked)         per acre  Blossoms appear -                      When first fruits are                      the size of a quar-                      ter - 2-3 applications                      When production is                      extended over a                      long period of timePepper           1.8-2.5 lbs                      1 Week before            per acre  Blossoms appear -                      When first fruits are                      the size of a quar-                      ter - 3 Weeks later                      if desiredFIELD &amp; FORAGE CROPSCorn (for, grain Corn and            2.3-5 lbs 10 Days prior toSorghum Silage   per acre  tassleCotton           2-3.5 lbs 6th Leaf stage - 1st            per acre  Bloom at Boll set                      prior to full Boot                      Stage and Full                      Head EmergenceGrain Sorghum, Sweet            2-3.5 lbs 6th Leaf stage -Sorghum, Sugar Cane and            per acre  prior to Bloom &amp;Sunflower                  when every new set                      of Blossoms appearSmall Grains (Wheat, Oats,            2-3.5 lbs 1 Application inBarley, and Rye) per acre  Fall - 1 in Mid-                      Winter and 1 in                      SpringSoybeans         1.8-2.5 lbs                      6 Days prior to set            per acre  of BloomTobacco          1.8-2.5 lbs                      1 Application 4            per acre  weeks after                      transplantingAll Forage Crops 2-3.5 lbs 3-4 times per year            per acrePeanuts          1.8-2.5 lbs                      6 days before 1st set            per acre  of Blossoms and                      when every new set                      of Blossoms                      appears.______________________________________ 
    
     Although this invention has been disclosed above with regard to particular and preferred embodiments, and with specific reference to precise compositions, application times, etc., these are advanced for illustrative purposes only. Variations will occur to those of ordinary skill in the art without the exercise of inventive faculty, which remain within the scope of the invention as claimed hereinbelow.