The Crop Water Allocator (CWA) is a tool to evaluate strategies to allocate limited irrigation on selected crops based on economic returns. It was developed by Kansas State University’s Southwest Research-Extension Center, Department of Agronomy, Department of Biological and Agricultural Engineering, and Department of Agricultural Economics with programming support from Sprout Software.  The project was funded in part by the Ogallala Aquifer Program, a consortium of the USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.

Neither the programmers nor Kansas State University are to be held responsible for the information generated from this program.

BACKGROUND

Water supplies for irrigation are declining in many irrigated regions due to lower pumping capacities, smaller surface water supplies, or regulated restrictions of water applications. To reduce irrigation, irrigators can consider choosing crops with smaller irrigation requirements, growing crops in rotation within the same fields, or irrigating fewer acres. Irrigators with shrinking water supplies who are evaluating these choices need to know the potential net economic returns from each combination of crops and water applications to each crop that suit their management systems.

The Crop Water Allocator (CWA) has been developed for irrigators to allocate limited water among selected crops. CWA calculates net economic returns from all possible combinations of crops, irrigation allocations among crops and ranks the net returns from maximum to minimum values. By changing rainfall, production costs, commodity prices, irrigation costs, irrigation efficiency, and maximum yields, CWA users can find changes in net returns in response to these input variables.

Net economic returns do not include fixed costs associated with land and equipment investments. Net return is calculated with this formula:

(Crop Yield X Crop Price) – (Production Costs) – (Irrigation Costs).

Crop yields are determined from applied irrigation. Yield-irrigation relationships have been developed from field research to quantify crop yields from irrigation over a range of water application from dryland to full irrigation. These data along with weather parameters from 30 years were used as inputs to a crop simulation model. The model was executed for applied irrigation and annual precipitation (0 to 24 inches). The following graphs are yield-irrigation results for each crop grown in silt loam soils.

Crop production costs can come from the CWA user’s own information or from default production costs that were developed by in the Kansas State University Farm Management Guide crop budgets available on www.agmanager.info . Irrigation costs are calculated from pump discharge rate (gpm) pumping lift (ft), operating pressure (psi), fuel cost, labor for irrigation, and repairs and maintenance.

The user of CWA can choose one of five possible ways to divide the field which are called “land splits” (100%; 50%-50%; 75%- 25%; 33%-33%-33%; 50%-25%-25%; or 25%-25%-25%-25%). The user can choose one land split for each execution of CWA or hold “land split” constant as other inputs are changed. The program will assign every combination of every selected crop to each part of the land split. More crops than land splits can be selected for CWA analysis. One crop may be in more than one part of the rotation. Irrigation is then allocated to each crop in each combination of selected crops for the rotation.

Net return results from all combinations of crops in each part of the rotation and irrigation level are “stacked” from maximum to minimum. The user can scroll through the largest net return results that are displayed on the output screen. Some of the crop combinations in the rotation may not be feasible for the user even though they have more net return than others. For example, soybeans in all parts of the rotation would not be feasible because continuous soybeans are not recommended or it may not be feasible to plant wheat in the crop season following a summer grown crop.

CWA assumes that farming practices are carried out with good crop management in dryland, limited irrigation, and full irrigation situations. The yield relationships with irrigation that are the foundation for the model are based on research and management practices in “best management” crop production. Crop management that does not meet “best management practices” will not achieve the predicted results of CWA.

FIELD AND IRRRIGATION INPUT TAB--- Field and Location Information

Acres: Land area may be a field, a farm, a watershed, or a river basin. The program calculates results on a per acre basis so the program is not dependent on land size. The total amount of water supplied to the designated area would need to be included for the irrigation cost calculations.

Soil Type: One of three soil types can be selected: (1) silt loam with the capacity to store 2.4 inches of available water per foot of soil; (2) loamy sand with the capacity to store 1.3 inches of available water per foot of soil; or (3) fine sand with the capacity to store 0.9 inches of available water per foot of soil. Available water is the soil’s ability to hold water between “field capacity” and “wilting point”. At field capacity the water that drains easily through the soil (in 1-2 days) cannot be retained. The remaining water is held and available for crop uptake. At wilting point the soil is so dry that the plant can no longer extract water and it dies. The water held in the soil between field capacity and wilting point is its available soil water storage capacity.

Annual Rainfall: The total amount of precipitation that can be expected during the calendar year. Annual rainfall can be from 11 to 24 inches. Changing the value for precipitation from one execution of the program to the next, leaving all other inputs the same, will give the influence of precipitation on net economic return.

Applied Irrigation: The amount of groundwater applied on the field or surface water diverted to the field is units of inches (the depth of water over the area irrigated). “Applied irrigation” is the same as “gross irrigation”. The annual applied irrigation is in units of inches.

Land Split: Irrigated or non-irrigated acreage can be divided five ways: 100%; 50%-50%; 75%-25%; 33%-33%-33%; 50%-25%-25%; and 25%-25%-25%-25%. The user can choose one land split for each execution of CWA or hold “land split” constant as other inputs are changed. The program will assign every combination of every selected crop to each part of the land split.

FIELD AND IRRIGATION TAB – Irrigation Information

Discharge Rate: The flow of water from the pump (gallons per minute) to the irrigated area. The discharge rates of all pumps that supply water to the field or fields need to be summed for the analysis.

Season Pumping: The hours that the pump operates during the year. The program calculates the applied irrigation that the pump could deliver from the discharge rate, hours of pumping, and acreage. If more than one pump delivers water to the irrigated area, enter the average hours pumped by the wells. This is the upper limit of water applied by that system.

Pumping Lift: Static water level in the well plus draw down of the aquifer during pumping in feet. This is the distance the pump needs to lift water to the surface.

Well-head Pressure: The water pressure (in psi) at the top of the well is part of the calculation of irrigation costs.

Irrigation System Efficiency: Net irrigation (water delivered to the ground surface and available for evapotranspiration) divided by applied water. Suggested efficiencies:

Fuel types: Possible fuel types and units of costs are:

Fuel Cost: The user enters the cost based on the units of measurement.

Operation Costs: Total tillage, planting, herbicide, and insecticide application costs can be entered in this section. For each item, the number of operations should be multiplied by the cost per acre and entered into the appropriate box. Default operation costs are based on custom rates from www.agmanager.com .

Harvest Costs: Harvest costs can be determined from a flat rate or itemized costs.

Additional Returns and Costs: Users can enter income from non-cash crop enterprises such as grazing wheat pasture, utilizing crop residues, or government payments into “Misc. Returns”. Crop insurance premiums can be included in “Misc Costs”. Note: because government payments (direct and counter-cyclical) will be the same regardless of the crop planted, this information is irrelevant in terms of determining the optimal crop mix, but this information can be entered for cash flow purposes.

CALCULATING RESULTS

Clicking the “Calculate” button after all inputs are entered produces the results in the output table.

Rank: The results are in rows delineated by the highest to lowest net return.

Acres: The land area devoted to each crop.

Crop: The crop combination for in each section of the field. The same crop may be in more than one section of the field.

Yield: The crop yield derived from the applied irrigation for that crop.

Applied Irrigation: The depth of water applied on that crop-section of the field. The total volume of applied irrigation (irrigation depth X acres) is distributed among the crops for the best net return. Lower ranking options may have different allocations of water among the same crop combination, but the same volume of water designated in the inputs will be distributed in every option.

Operating Costs and Returns: The total of crop production costs and irrigation costs for each crop in the ranked option. Returns are the net returns (yield X price – operating costs) for each crop in the ranked option.

Total Net Return: The total net return is the whole field net return resulting from averaging the returns for each crop.

PINNING OPTIONS FOR NEXT EXECUTION

The “pins” to the right of the “Total Net Return” column can be activated by clicking the pin icon for the option that will be retained for the next execution of CWA. The pinned options will appear at the top of the ranking and the new execution’s ranked options will follow. The pinned options will not be “re-ranked” with the options from the next execution. The pins can be removed by clicking on the pin icon.

ADJUSTING SIZE OF INPUT AND OUTPUT TABLES

Clicking on the small bar between the input and output tables and dragging it sideways allows the user to shrink or expand one or the other of the tables.