Abstract:
A method for the automatic irrigation of plants, wherein the temporal progression of soil moisture is determined from measured soil moisture values, and said progression is used for the calculation of an optimized irrigation time duration, such that both water excess in the soil and soil drying are avoided as much as possible. Preferably, the time duration of irrigation is constantly evaluated and optimized using comparisons of measured values with prespecified moisture- and dryness threshold values (GWmoist, GWdry), and automatically adjusted to changing environmental conditions and/or plant requirements.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an apparatus and a method for the automatic regulation and control of an irrigation of plants in accordance with the preamble of the independent patent claims. It relates, in particular, to an apparatus and a method for an optimized irrigation time without water excess and without the soil drying out. 
         [0003]    2. Description of Related Art 
         [0004]    When plants are irrigated, in particular lawns or agricultural land, use is made of irrigation systems that are controlled by a timer. The user can set, on the latter, both the instant and the duration of the irrigation, there being on the market various timers for the control of a variety of irrigation zones and with different levels of complexity. 
         [0005]    This type of irrigation control is low in flexibility, that is to say irrigation is performed over the preset time duration and at the preset instants, irrespective of the effective need of the plants that are to be irrigated. 
         [0006]    So-called rain sensors are also known that, when rain is falling, measure the amount of rain and block the timer when a defined amount is exceeded so that no irrigation is performed while it is raining. 
         [0007]    It is true that this method avoids an irrigation during or after a rain event. For example, in cool or rainless weather irrigation is performed, however, though sufficient moisture is present in the soil and there is thus no need to irrigate. 
         [0008]    In recent years, soil moisture sensors have been connected to timers. These sensors measure the current moisture in the soil and enable the timer, and thus initiate watering, only upon falling below a critical soil moisture that can be set. Most of these soil moisture sensors are expensive to procure and maintenance-intensive, and the measurement result depends strongly on other parameters, such as the fertilizer content. They have therefore not been able to establish themselves on the market. However, a novel soil moisture sensor that does not have these disadvantages has also been developed in accordance with WO 2006/081693. 
         [0009]    Such an improved soil moisture sensor can now be used to prevent irrigation from being performed unnecessarily. However, the amount of water administered per watering cycle is still set by the user on the timer, and is therefore fixedly prescribed. The amount of water effectively required can, however, deviate strongly from the set amount, and it also varies with short term and long term climatic fluctuations. Experience shows that in the case of crops, in particular, once a watering time has been set, users tend to adapt to the current climatic conditions only in exceptional cases and mostly not change it throughout the entire year. 
         [0010]    When consideration is given to the ever more topical problems associated with rising water consumption, particularly in countries with scarce water reserves, the aspect of carefully managing water as a resource becomes very important. The avoidance of unnecessary water consumption belongs here, as well. Immense quantities of water (80% of the entire water consumption) are used globally in the irrigation of crops and green areas. It is estimated that half thereof could be saved by intelligent irrigation. 
         [0011]    It is therefore an object of the invention to provide an intelligent method for the control and regulation of an irrigation time with the aid of which, with an automatically set watering time, no excess water is poured and, on the other hand, the soil is prevented from drying out. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The object is achieved by the method according to the invention as it is described in the patent claims. The invention also includes an apparatus with the aid of which the method can be carried out, and an electronic regulation that can be installed in an appropriate apparatus. 
         [0013]    The method relates to an intelligent method for the control of irrigation that, on the one hand, is capable of automatically fixing an irrigation time such that no excess of water is poured. On the other hand, the soil is also prevented from drying out. The method is also capable of automatically compensating short term, medium term and long term temperature changes such as occur in the course of a year, preferably in such a way that an optimum amount of water is always poured even without manual intervention. When crops are irrigated they also require more and more water with increasing size and/or leaf area. The inventive method takes account of application specific conditions such as system parameters and environmental parameters, and is also capable of automatically compensating an increase in demand as described. 
         [0014]    The method is based on a novel evaluation of the soil moisture time profile measured by a soil moisture sensor. In particular, the soil moisture sensor described in WO 2006/081693 can be used to this end. However, it is also possible to use any arbitrary soil moisture sensor that permits electronic measurement of moisture values. A sensor is then combined with the inventive electronic regulation and/or appropriate evaluation electronics, for example in the form of a chip. 
         [0015]    The soil moisture is repeatedly measured with the aid of a soil moisture sensor and appropriate evaluation electronics in the method for the regulation and control of an automatic irrigation device. The time profile of the soil moisture is analyzed in this case before and after an irrigation operation, and an irrigation time is calculated from a moisture value before irrigation and a moisture value after an irrigation. A system specific characteristic K is considered in the calculation of the irrigation time, said characteristic preferably being determined in an initial calibration measurement and checked and adapted in subsequent measuring steps. 
         [0016]    The regulation of the inventive apparatus is preferably designed such that even when environmental conditions and plant size change, on the one hand the plant is always supplied sufficiently with moisture, but on the other hand not too much water seeps unused into the soil. 
         [0017]    A moisture scale used in this case has two limit values that can be set: in the direction “dry”, the limit value that fixes a minimum moisture, and the limit value that fixes a maximum moisture are defined by an input from the user. In the direction of higher moisture, a further limit value “wet” is reached when the soil is saturated with water. This limit value is defined in advance, that is to say is system-induced, for a sensor in use, because a sensor cannot become wetter than wet. An aim of the control is now, on the one hand, not to fall below the limit value for “dry” excessively, including over a lengthy time, so that the plants do not suffer drought damage and are not exposed to drought stress. On the other hand, however, it is also important that the limit value for “moist”, which corresponds at most to that of “wet”, be reached only for a short time, because additional water would seep away and could not be used by a plant. 
         [0018]    In order that the local conditions relating to soil composition as well as to water ingress per unit area are taken into account from the start in a regulation, at the beginning of the method, this is, as a rule, at the start of an irrigation period, preferably a calibration measurement is carried out. In this case, a soil moisture sensor is introduced into a soil to be irrigated. It is preferably inserted to a specific depth. This depth is dependent on the position of the roots and lies in a preferred range of 5-30 cm. Irrigation is then performed briefly, preferably by an existing sprinkler or a drip fed irrigation. Depending on the soil permeability, this irrigation will be detected earlier or later by an increase in the moisture content at the sensor. The time covered up to this detection is, on the one hand, a measure of the permeability of the soil but also, on the other hand, of the water ingress at the location of the sensor. 
         [0019]    The ratio of the difference in moisture value before the irrigation and moisture value after the irrigation to the time of the irrigation can be regarded as a user specific characteristic K. K takes account both of the local soil composition and of the installed irrigation performance. The characteristic K tells us by how much a moisture value changes when pouring is performed over a specific time, for example one minute, and with a specific amount of water. This factor K is determined automatically during the calibration step initially carried out, this corresponding in essence to a first measurement, and is used for the further measurements. It would also be possible to input an initial value of K, for example in accordance with empirical values, in advance. A subsequent regulation adapts the characteristic as appropriate to the prescribed moisture limit values. 
         [0020]    In a preferred embodiment of the method, the characteristic K is repeatedly checked, preferably cyclically, it also being possible for an irrigation to be performed cyclically. In this case, K is compared, preferably after a measurement that is performed after an irrigation, with an upper limit value that corresponds to a moist soil. Depending on the desired/actual value deviation, K is enlarged or reduced by a factor. Since K is inversely proportional to the irrigation time in the present calculations, a reduction of K is apposite when the irrigation time is to be lengthened, that is to say when, for example, a measured moisture value has not reached an upper moisture limit value after an irrigation. An enlargement of the characteristic K that therefore leads to a reduced calculated irrigation time is apposite when an upper limit value “moist” is reached after the irrigation, but the aim is to prevent this limit value from being exceeded too far. It is preferred to choose a moisture value below a moisture limit value for a completely wet soil as an upper limit value. It is also possible thereby to determine an exceeding of the limit value. 
         [0021]    In practice, an upper limit value that defines a water saturated state corresponds to that soil moisture for which the soil is saturated with water so far that no more water seeps into the subsoil because of gravity. This property of the soil is denoted as field capacity (GW FK ). Sandy soils have a low field capacity, while soils with a high proportion of organic materials such as peat or humus have a high field capacity. Such a moisture limit value based on the field capacity can therefore lie below a limit value for a “wet” soil. 
         [0022]    The calibration operation described above can also be used to determine such a field capacity automatically. To this end, irrigation is continued after the characteristic K has been determined over a lengthy time, for example 1-2 hours. It is to be ensured that the soil is supersaturated. After a lengthy waiting time, for example of 2-12 hours, it can be assumed that the excess water has run off into the subsoil. The moisture value is then determined again and this corresponds to the field capacity GW FK , and can be stored in the system. When there is a manual input of an upper limit value “moist” that overshoots the GW FK , the user can now be alerted to this circumstance, for example by an alarm report. It would also be possible for the upper limit value “moist” to be set automatically to the moisture value corresponding to the field capacity. 
         [0023]    In a further embodiment of the method, an irrigation time calculated automatically with a characteristic K is increased or decreased directly by a factor D, that is to say by an amount of water given in a prescribed irrigation device. Such a fixed supply or removal of water determined by concrete measurements can be advantageous when, for example, agricultural land is to be kept wet or moist or less moist over a somewhat longer time. In the case of a calculated irrigation time, an amount of water is optimized to an optimum relationship between saving water and drying out. However, a customary moisture sensor cannot be used to distinguish between wet, somewhat too wet or much too wet. A higher supply of water through a change in the characteristic K can elude accurate monitoring. If the aim is now to keep an area moist or wet or less moist over a somewhat lengthy time, this can be achieved by the supply of, or reduction by a defined amount of water. With certain limitations, this can also be achieved by reducing or decreasing the moisture limit values. 
         [0024]    An exceeding of a maximum amount of water on purpose, that is to say an exceeding of the amount of water that is sensible in accordance with a field capacity GW FK , can, for example, be apposite when, by way of example, the aim is to prevent the soil from being salted. An excess of water ensures that the salt cannot accumulate in the critical root area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Different stages and aspects of the method, as well as preferred embodiments of the method, are explained in more detail below with the aid of exemplary figures. In the drawing: 
           [0026]      FIG. 1  shows the calibration measurement and the determination of the field capacity; and 
           [0027]      FIG. 2  shows a soil moisture profile. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The graph in  FIG. 1  shows the profile of the moisture level F against time Z. The soil moisture content is measured at regular intervals Mn, Mn+1, Mn+2 . . . . At the instant Mn, the soil moisture content is still above a set limit value GWdry that corresponds to a minimum soil moisture that is to be reached. At the instant of the following measurement Mn+1 at the instant t 0 , the soil moisture content, the first moisture value FW 1 , is below the set limit value GWdry. An irrigation operation is correspondingly initiated and terminated at the instant t 1 . The instant t 1  or the irrigation time t 1 -t 0  is preferably selected to be very short, for example 5 min., for a calibration measurement, in order to reliably prevent over-irrigation. At a second instant t 2 , a control measurement, for example approximately ½ hour after the irrigation, is carried out, and a further moisture value FW 2  is measured. Thereafter, the system determines a characteristic K from the measured values in accordance with the specified formula: 
         [0000]    
       
         
           
             K 
             = 
             
               
                 
                   
                     FW 
                     2 
                   
                   - 
                   
                     FW 
                     1 
                   
                 
                 
                   
                     t 
                     1 
                   
                   - 
                   
                     t 
                     0 
                   
                 
               
               . 
             
           
         
       
     
         [0000]    The characteristic K is stored in the system. 
         [0029]    The measurement operation can also be carried out in two or more stages, t 1 -t 0  then corresponding to the total time over which irrigation has been performed. The result of the calibration measurement is used to determine the irrigation time for the following measurements. 
         [0030]    After the measurement at the instant t 2 , the irrigation is continued, preferably over a longer time, for example 1-2 hours, up to the instant t 3 . A waiting time, preferably of several hours, is inserted thereafter. A measurement is carried out anew at the instant t 4 . The measured value GW FK  corresponds to the field capacity. In the case of a humus rich soil, this can be equal to GWwet. The determination of GW FK  can also be undertaken or omitted independently of the calibration measurement. 
         [0031]      FIG. 2  shows a typical profile of the soil moisture, and the principle of a continuous correction of the irrigation time in combination with a preceding calibration measurement. 
         [0032]    After the calibration measurement, preferably in accordance with  FIG. 1 , the first regular measurement is carried out at the instant Mn+2. Since the current moisture value FWn+2 lies under GWdry in the example shown, an irrigation is initiated. The irrigation time BDn+2 is now calculated as follows using the measured moisture value FWn+2 and the characteristic K determined in accordance with the calibration measurement: 
         [0000]        BDn+ 2=( GW moist− FWn+ 2): K  
 
         [0033]    After the irrigation, the moisture value is determined in turn by a control measurement. In the example shown, the intended target value GWmoist has not yet been reached (Delta&gt;0), that is to say the irrigation time was still too short, the factor K determined in the calibration measurement too large. 
         [0034]    The system now calculates the irrigation time BD for the following irrigation Mn+3 as follows: the difference between the target value GW and the current moisture (GWmoist FWn+2) before the measurement Mn+2 is divided by a characteristic K reduced by x. As a result, a longer duration is obtained for the subsequent irrigation at the instant Mn+3. The corresponding formula reads as follows: 
         [0000]        BDn+ 3=( GW moist− FWn+ 3):( K−x )
 
         [0035]    It is now assumed, in the example shown, that the target value GWmoist has been reached owing to the correction performed, and this is confirmed by a subsequent control measurement. 
         [0036]    This would mean the target has been reached, and it is possible as shown previously to regulate further or, given conditions which are not changing, to irrigate straight away. 
         [0037]    If GWwet has been selected as an upper moisture limit value, the problem resides in the fact that it is not known whether too much water has not been given, since the sensor cannot display a “too much”. It can therefore be assumed as a precaution that too much has been poured without, however, being able to know this. 
         [0038]    The way in which this problem is solved is preferably that whenever GWwet is reached a small negative deviation of specific magnitude is automatically adopted, and this is included in the calculation of the duration for the following irrigation. The characteristic K is enlarged in this case by a factor y. 
         [0039]    The appropriate formula then reads as follows: 
         [0000]        BDn+ 5=( GW wet− FWn+ 3):( K+y )
 
         [0040]    A reduction in the irrigation time via an enlargement of K can also be desired given a selected moisture limit value GWmoist, for example when the aim is to keep a watering deep on purpose, by way of example in order to save as much water as possible or to keep plants not too moist as far as possible. A multiplication factor can also be selected instead of the factors x, y that are to be subtracted and added. This factor would then be correspondingly smaller or larger than 1. 
         [0041]    Since the moisture is still high at the instant Mn+4 in the example of  FIG. 2 , that is to say lies above GWdry, no irrigation is initiated. However, at the instant Mn+5, the lower limit value GWdry is undershot, and an irrigation with the calculated period BDn+5 is started. 
         [0042]    Should there be rain between the measuring points Mn and Mn+i, this is of no consequence, since the next irrigation is only initiated once GWdry is undershot. If it begins to rain just before a measurement, the measurement is interpreted in a more or less incorrect fashion depending on the amount of rain and duration, but this is automatically corrected again in the subsequent measurement. 
         [0043]    In conventional measurement cycles, measurements are carried out, as a rule, every few hours, for example every 3-6 hours. If a measurement cycle Mn, Mn+1, . . . is selected to be very short, however, for example every half hour, it is possible to dispense with control measurements after an irrigation since said measurements fall into the regular measurement cycle. In the case of short measurement cycles, it should be ensured that use is made of moisture sensors with a low energy consumption. 
         [0044]    With the aid of said regular algorithm, one is now able to set up an irrigation control which does not demand of the user any sort of knowledge relating to the nature of the soil, water input per m 2  and irrigation time. After the sensor has been placed in the soil, the system is started, calibrates itself and automatically regulates the irrigation time so as to attain an optimum soil moisture cycle. 
         [0045]    All that the user needs to set as a function of the plants to be irrigated are the two limit values GWdry and GWmoist. The system can be fashioned such that a table presented by the system can be used to select sensible values that are then taken over as constants. 
         [0046]    The determination of the measurement cycles can be performed in a way similar to the timers currently available. The latter mostly permit the setting of the start time and the duration of an irrigation, it also being possible by installing a photodiode to record the day/night cycle and, correspondingly, to determine the beginning of an irrigation by day or at night. Moreover, the minimum duration between two irrigations can be defined. 
         [0047]    In the limit case, problems can arise owing to the inflexible stipulation of the minimum duration between, for example three irrigations, for example three day cycles, that is to say irrigation every third night, by way of example. Specifically, this means when supply of water stored in the ground is insufficient in a phase of high temperature or given crops with a very high water requirement in order to meet the requirement of this time, the result being that drought stress occurs for the plants. 
         [0048]    The regulation described here can, however, recognize such a case very easily and preferably shorten the duration between two cycles automatically. For example, if the moisture value at the time of measurement undershoots a specific critical dry limit value several times in succession, although the regulation has respectively adapted the irrigation time upwards, this is a clear indication that the irrigation cycle has been selected to be excessively long. In such a case, the system can, for example, make a report, or automatically reduce the cycle duration. It is appropriate to display or report, in particular, if an irrigation cycle is permanently prescribed in a system, for example, because of weather conditions (sun), because of use (meadow or swimming pool) or because of regulations (irrigation only at specific times). If, for example, a moisture limit value “dry” is then undershot several times, it is not permissible to increase the irrigation time on the basis of the external conditions. 
       LIST OF REFERENCE SYMBOLS AND FORMULAE 
       [0000]    
       
         Mn, Mn+1 . . . Moisture measurement n, n+1, . . . at predetermined, regular time intervals 
         t 0 , t 1 , t 2  . . . Instants at which an action is initiated and stopped (for example measurement, start/stop of an irrigation, etc. . . . ) 
         F Moisture value (of a substrate, for example, earth, lawn etc.) 
         FW 1 , FW 2  First, second measured moisture value 
         GWdry; GWmoist Limit values “dry”, “moist” that can be set 
         GW FK  Moisture limit value corresponding to the field capacity 
         GWwet Fixed limit value “wet” 
         characteristic K=FW 2 −FW 1 /t 1 −t 0 
       System characteristic that is determined by calibration measurement and takes account of user specific details   Irrigation time BD=GWmoist−FW/K   Irrigation time calculated with the aid of measured and determined values   
     
         x,y Correction factors for K for the optimized calculation of the irrigation time after an excessively short or excessively long irrigation time.