WASHINGTON IRRIGATION SCHEDULING EXPERT (WISE) SOFTWARE. B. G. Leib and T. V. Elliott 1 ABSTRACT

WASHINGTON IRRIGATION SCHEDULING EXPERT (WISE) SOFTWARE B. G. Leib and T. V. Elliott 1 ABSTRACT A large portion of Washington s agricultural economy is derived from the irrigation of highvalue fruit and vegetable crops. Washington irrigators are recognizing that irrigation management makes a significant contribution to the yield and quality of these high-value crops. At the same time, salmon recovery efforts (water quantity) and high nitrates in groundwater (water quality) are threatening irrigators access to their water supply. Scientific irrigation scheduling is a water management method that will help maintain in-stream flows, reduce leaching of agricultural chemicals, and insure crop quality and yield. The Washington Irrigation Scheduling Expert (WISE) Software is being developed to meet the needs of Washington irrigators. WISE is written in JAVA with NetBeans DeveloperX2 components to allow cross platform operation and easy access to reference evapotranspiration (ET) from Washington s 59 Public Agriculture Weather Stations (PAWS). The graphical user interface is intuitive and will help the user input their field-specific parameters such as crop type/timing, soil moisture and irrigation system specifications. WISE employs a short-term water balance that can be adjusted for soil-moisture conditions. WISE is not a black box calculation of when and how much to irrigate since important steps are displayed and made apparent to the user. This feature also makes WISE an educational tool that teaches the principles of irrigation scheduling. INTRODUCTION Since the early 1980 s many irrigation scheduling programs have been developed for microcomputers (Harrington & Heerman, 1981). However, the two most influential in the developmental process of the Washington Irrigation Scheduling Expert (WISE) software were SCHED developed by Buchleiter et al. (1988) and Washington Irrigation Forecaster (WIF) developed by Best et al. (1986). SCHED calculates a daily water balance to estimate the present soil moisture depletion and this depletion in conjunction with a future estimate of`crop evapotransporation is used to predict the earliest and latest dates to irrigate a particular field. WIF uses a soil-moisture measurement to determine the present soil moisture depletion and this sensor-derived depletion is used with a future estimate of crop-water use to predict the earliest irrigation that will refill the soil profile to a predetermined level. Both SCHED and WIF irrigation scheduling methods have been used successfully by agricultural consultants (Salazar et al., 1996; Dockter, 1996). One of the design principles used to develop WISE was to create a tool that producers could use without the aid of professional consultants. As such, it was assumed that producers would not be willing to enter all the book-keeping required by SCHED or perform the soil-moisture sensor calibration required for WIF. Therefore, WISE employs a short-term water balance that can be adjusted according to measured soil-moisture trends. Also, the graphical user interface is intuitive and will help the user input their field specific parameters such as crop type/timing, soilmoisture and irrigation system specifications. 1 B. G. Leib, Extension Irrigation Specialist, and T. V. Elliott, Public Agricultural Weather System (PAWS) Technician, Irrigated Agriculture Research and Extension Center, Washington State University, 24106 N. Bunn Rd, Prosser, WA 99350

Another design principal for WISE was to allow the operator to easily apply their own expertise to irrigation scheduling. WISE is not a black box calculation of when and how much to irrigate since important steps are displayed and made apparent to the user. This feature also makes WISE an educational tool that teaches the principles of irrigation scheduling. WISE is a deterministic program and not a true expert system. However, the flexibility of WISE should allow irrigators to be the expert in WISE. Finally, the present version of WISE and any future upgrades should be easily accessible to irrigators. WISE and the JAVA virtual machine are downloadable from the website http://wise.prosser.wsu.edu. As a JAVA program created with NetBeans DeveloperX2, WISE crosses platforms of differing computers and operating systems. Reference ET is accessible from Washington s Public Agricultural Weather System (PAWS) via the web link http:\\index.prosser.wsu.edu. In 1998 survey of Washington irrigators indicated that 75% owned computers and 50% had access to the internet (Leib, 1999). DATA ENTRY As an example of how WISE can be used, a field named Center-Pivot, Sweet Corn was created and then selected on the Farm Organization page (serves as a file manager) causing the Field Scheduling page to appear with default values as shown in Figure 1. The Field Scheduling page is the main route to selecting and entering reference ET, crop, soil water, and irrigation system parameters for a field. Once these parameters are entered, most will not need to be reentered during normal operation. Figure 1. Default Field Scheduling Page

Reference ET By clicking the mouse on the automated weather station shown in Figure 1, the Reference ET page is accessed for a field, in this case the center-pivot irrigated sweet corn field shown in Figure 2. The main function of this page is to connect a field to one of PAWS s fifty-nine weather stations. The closest or most representative PAWS station is selected by clicking the mouse on the automated weather station of Figure 2 and selecting the desired station off a map of Washington. In this example, the Matthews Corner station was chosen. Figure 2. Reference ET Page. PAWS weather data is updated to WISE by clicking on the calendar symbol of Figure 2 and choosing a forecast date which during normal operation of the program is the actual date. Since PAWS collects real-time weather data, the needed data is available by 2:00 am of the forecast date. After clicking the done button for the forecast date, a pause connection menu appears and your PAWS userid and password need to be entered. Once the userid and password are entered they are saved and do not need to be reentered thereafter. By clicking on the connect button of this menu, WISE will download the relevant PAWS data for all fifty-nine weather stations via the internet. Once the data is downloaded for a forecast date, the internet connection is no longer needed. Therefore, WISE does not require a continuous internet connection and thus frees telephone lines for other purposes such as business calls or allows mobile scheduling from a laptop. PAWS data can also be downloaded from the Field Scheduling page or the Farm Organization page. Once the PAWS data is downloaded, the ET source to be used in the forecast is determined by selecting one of the four buttons on the right as seen in Figure 2: 1) Past 3 Days, 2) Historical ET, 3) Calculator, or 4) Own Estimate. If the Past 3 Days is selected, the average reference ET rate of the three previous days is used in the forecast. Also the weather data and the reference ET are displayed for each of the last three days. If Historic ET is selected, the average reference ET for the upcoming week is used in the forecast based on all the previous years of data at the selected weather station. This historic average is automatically updated each year data is added to the PAWS database. Again, the historic weather data is displayed along with the reference ET. The Calculator button calculates a reference ET rate based on weather data entered by the

operator. Weather forecasts in combination with the weather data displayed on this page will help guide the entry of weather data into the ET calculator. The Recalc button must be selected every time a weather data entry is changed in the ET calculator. Finally, the Own Estimate button allows reference ET to be entered from a source external to WISE such as media reports from radio or newspapers. If PAWS is not used with WISE, Offline can be entered as the userid in the connection menu providing a historical data set from the Headquarters Station at WSU- Prosser. In WISE, alfalfa reference ET is calculated with a modified Penman Equation using variable wind functions developed in Kimberly, ID (Wright, 1982; Jensen, Burman & Allen, 1990). More information on the PAWS network and calculation of reference ET can be found at http://index.prosser.wsu.edu. Crop Parameters By clicking the mouse on the crop picture shown in Figure 1, the Crop Parameter page is accessed and shown in Figure 3. The main function of this page is to properly approximate the actual cropping conditions to produce a valid irrigation schedule. From the crop parameter page, the desired crop is selected by again clicking the mouse on the crop picture and selecting the crop from 42 of the main crops grown in Washington. In this example, sweet corn was chosen and the default values for the emergence/harvest dates, crop coefficient, root depth, management allowable deficit (MAD) and refill point (desired soil moisture after irrigation) are loaded into the crop parameter page for this field. Figure 3. Crop Parameter Page. In WISE, the crop coefficients are based on FAO values from Dorenbroos and Pruitt (1977) that in turn were compared to Washington conditions in a WSU bulletin EB1513 authored by James et al. (1989). Root depths and MAD values were taken from WSU-Bulletin by Ley et al. (1994).

Emergence/harvest dates are derived from local experience and the refill point is set to 100% or field capacity. These default values are intended as guidelines and should be adjusted by the user to better reflect actual cropping conditions. The emergence and harvest dates are changed by entering the appropriate dates in the two calendar menus at the bottom of the page. Also, the crop parameters can be scaled by a factor that is set by the slider between the calendars. These adjustments affect the magnitude and time span of the whole growing period. If finer adjustments are required, Advanced User mode allows changes to the crop parameters for up to five crop-growth stages. A graph of each crop parameter will be displayed in the upper left window when it is selected for viewing or adjustment. In advanced user mode, the selected crop stage will also be high-lighted in this graph. Soil Moisture Trends By clicking the mouse on the sensor graph shown in Figure 1, the Soil Moisture page is accessed (Figure 4). The main function of this page is that of entering and graphing soil water content. However, soil-moisture measurements are not needed to run WISE. WISE can be completely ET driven and the resulting soil-moisture trends are only intended as a check/correction on the ET schedule s validity. In fact, soil-moisture data that is hand recorded or graphed on another software package can be used to adjust WISE by adding or subtracting water from the schedule in the correction box of the Field Scheduling page, Figure 1. This correction box is only self updating if the Sensor Depletion button is selected on the Field Scheduling page of Figure 1. The WISE developers do not recommend selecting the Sensor Depletion button unless the user is confident of their sensor calibration and that appropriate values for both available water holding capacity and field capacity have been determined. In this example, WISE will simply graph the soil-moisture trends for a silt loam soil with available water holding capacity of two inches per foot and a field capacity of three inches per foot. The Soil Moisture page of Figure 4 allows input units to be in/ft, in/in, % volume, % available, and other (for units like centibars and there is no conversion to volume of water) so that readings from most soil moisture sensors including feel/appearance can be entered without the need to convert units. It is more important that the field capacity value match the sensor s reading at field capacity instead of a text book or lab value for field capacity. A text book or lab value for available water will be sufficient if the sensor can accurately measure the relative changes in soil moisture. If Other is chosen for units, field capacity and available water are simply the upper and lower limits for soil moisture, respectively. It is also important to enter the soil s available water holding capacity for the field even if a soil moisture sensor is not used because available water will be used to generate warnings if irrigation decisions are not appropriate for the situation. The sensor data is entered into the soil-moisture page of Figure 4 by clicking on the Measurement Date button, selecting the appropriate date and recording the soil moisture into the matrix of sensor locations versus measurement depths. The Measurement Date button can also be used to edit previously entered data. The soil moisture trends are graphed in the desired output units with the exception of Other which must always be graphed as Other. The refill and MAD lines are automatically generated from the crop parameter page of Figure 3 and the soil water holding characteristics entered in this page. Individual data lines are graphed as selected in the check boxes on the right-hand side of the page. A mouse window can be used to zoom into a smaller part of the soil moisture graph and the Plot Fill button will zoom out showing the entire data set for the year.

Figure 4. Soil Moisture Page. Irrigation System Parameters By clicking the mouse on the irrigation picture shown in Figure 1, the Irrigation System page is accessed and shown in Figure 5. The main function of this page is to select the type of irrigation system and enter the hydraulic parameters that correspond to the field in order to calculate an application rate. From the Irrigation System page, click the mouse on the irrigation picture and select the type of irrigation from the 10 systems available. In this example, a center pivot nozzled at 8 gpm per acre is used to irrigate the sweet corn. The gross application rate is calculated by dividing the flow rate of the irrigation system by the area into which the flow is applied and converting the units to inches per hour. Since some of the water applied can be lost to evaporation, runoff, and deep percolation, an efficiency factor is applied to calculate a net application rate. The range of efficiencies for different irrigation systems is: 80 to 95% for drip, 60 to 85% for center-pivot sprinklers, 60 to 80% for solid set sprinkler, 60 to 70% for set-move sprinklers, and 35 to 60% for surface irrigation (Ley, 1997). Since the goal of WISE is to achieve the highest efficiency possible, it is appropriate to choose a high efficiency from the actual range of measured efficiencies. If the chosen efficiency is lower than the potential efficiency, using WISE correctly will force the actual efficiency to be lower than possible. In addition to the irrigation system parameters, the expected irrigation interval and duration must be entered so that the WISE forecast will match the user s management preferences. An irrigation log and rain log can be maintained for an operator s own book-keeping, although this is not a necessary task for the operation of WISE. If the Crop ET button is checked on the Field Scheduling page of Figure 1, the start date of the last irrigation must be entered into the irrigation log. This option assumes that the last irrigation returned soil moisture to the desired level and then tracks the accumulated ET since the last irrigation as an estimate of soil-moisture

depletion for the present WISE schedule. This option is helpful when the irrigation interval is increased beyond a week. Figure 5. Irrigation System Page. EXAMPLE IRRIGATION SCHEDULE After the necessary parameters are entered, WISE calculates an irrigation schedule on the Field Scheduling page (Figure 6) for the center-pivot irrigated sweet corn example. For the forecast date of June 27, 1999, WISE shows the reference ET of 0.26 in/day (based on the past three days) multiplied by the crop coefficient of 1.0 to calculate actual ET rate of 0.26 in/day. The actual ET rate is multiplied by seven days and the soil-moisture correction of 0.0 is added to this product to calculate a required application of 1.83 in/wk. The required application is divided by the net application rate of 0.014 in/hr to calculate an operation time of 129.6 hours per week. If the irrigation frequency is fixed at five revolutions per week, pivot speed should be set at twenty-six hours per revolution. If the irrigation duration is fixed at thirty hours per revolution, 4.3 irrigations should be initiated during the week. Either Fixed Frequency or Fixed Duration needs to be selected so that the appropriate schedule will be summarized on the Farm Organization Page. In most cases, WISE schedules are predictions of irrigation frequency and duration without reference to specific dates. This frees operators with many high-frequency irrigation systems from becoming bookkeepers to schedule irrigation. This approach works well if irrigation frequencies are around one week or less. However, some irrigation types like side-roll, handmove, and solid-set sprinklers along with surface irrigation are operated on longer frequencies. WISE will produce a date forecast for these systems if the either the Crop ET Since Last Irrigation or Sensor Depletion options are checked. WISE forecast also project four weeks in

advance, but the last three weeks are always based on historic ET and not current actual conditions. Figure 6. Example Field Scheduling Page. As noted earlier, WISE shows the steps needed to calculate an irrigation schedule on the Field Scheduling page of Figure 6. By displaying the simple irrigation scheduling logic, operators are more likely to understand irrigation scheduling and have confidence in the forecasts or adjust the schedules according to their own expertise (the real expert in WISE). The WISE schedule seen in Figure 6 including the soil moisture graph can be printed by clicking on the Print Detailed button. A one line summary schedule of all selected fields can be printed from the Farm Organization page. ADOPTION BY IRRIGATORS The development of WISE was initiated in October of 1998 and an alpha version was released in May of 1999 for testing during the growing season. A Beta release occurred in December of 1999 as a dependable version for the 2000 growing season. During this time frame, WISE and Computer Aided Irrigation Scheduling were promoted by 29 workshops (1,278 attending), 12 field (401 attending) and 207 individual contacts. So far, this effort has resulted in two existing and three new irrigation scheduling providers preparing to use WISE in the 2000. There have been over thirty individual downloads of WISE and hopefully by the time this paper is presented there will be many more.

REFERENCES 1. Best, K.R., L.G. James, and T.W. Ley 1986. An interactive computer model for forecasting irrigations: A project completion report submitted to state of Washington Water Research Center and U.S. Department of the Interior. 2. Buchleiter, G. W., H.R. Duke, and D. F. Heermann. 1988. User s guide for USDA-ARS irrigation scheduling program SCHED. USDA-Agricultural Research Service Agricultural Engineering Research Center, Colorado State University, Fort Collins, CO. 3. Dockter, D. T. 1996. AgriMet The Pacific Northwest Cooperative Agricultural Weather Station Network. In C.R. Camp, E.J. Sadler and R.E. Yoder (Eds.) Evapotranspiration and Irrigation Scheduling. Proceedings of the International Conference. pp. 75-80. San Antonio: ASAE. 4. Doorenbos, J. and W. O. Pruitt. 1977. Guidelines for predicting crop water requirements. Irrigation and Drainage Paper 24, Food and Agriculture Organization of the United Nations. 5. James, L. G., J. M. Erpenbeck, D. L. Bassett, and J. E. Middleton. 1989. Irrigation requirements for Washington estimates and methodology. Cooperative Extension Bulletin No. EB 1513. Pullman: Washington State University. 6. Jensen, M. E., R. D. Burman, and R. G. Allen. 1990. Evapotranspiration and irrigation water requirements. NewYork: American Society of Civil Engineers. 7. Harrington, G. J. and D. F. Heermann, 1981. State of the art irrigation scheduling computer program. In Irrigation Scheduling for Water and Energy Conservation in the 80 s. Proceedings of the American Society of Agricultural Engineers Irrigation Scheduling Conference. pp.171-178. St. Joseph, MI: ASAE. 8. Leib, B.G. 1999. 1998 survey of Washington s irragition scheduling providers. Washington Irrigator Newsletter, February Issue, Washington State University Cooperative Extension, Prosser, WA. 9. Ley, T. W., R. G. Stevens, R. R. Topielec, W. H. Neibling 1994. Soil water monitoring and measurement. Paper PNW 475. A Pacific Northwest Publication. 10. Ley, T. W. 1977. Design considerations for tree fruit irrigation systems. In W. J. Bramlage (Ed.) New England Fruit Meetings. Proceedings of the One Hundred and Third Annual Meeting Massachusetts Fruit Growers Assoc, Inc. North Amherst, MASS: Massachusetts Fruit Growers Association. 11. Salazar, L,J., K.R. Thompson, and K. Crane 1996. Computerized irrigation scheduling in the San Luis Valley of Colorado. In C.R. Camp, E.J. Sadler, and R.E. Yoder (Eds.) Evapotranspiration and Irrigation Scheduling. Proceedings of the International Conference. pp. 75-80. San Antonio: ASAE.