Irrigation scheduling tools provided by Purdue and MSU Extension

Questions such as “When to start irrigating?” or “How much water to add?" can be answered by checkbook irrigation scheduling.

For over 25 years, Michigan State University and Purdue University have been developing and improving tools to assist in irrigation management. “Checkbook” irrigation scheduling is still a key factor in irrigation management.

MSU and Purdue have developed irrigation scheduling tools that range from a paper system to sophisticated computer spreadsheets that load data daily for producers. “Used correctly, all of these tools help producers estimate how much water the plant has used and how much water the soil has left to provide for the crop,” says Lyndon Kelley, Michigan State University/Purdue Extension Irrigation Educator.

Irrigation scheduling by accounting for changes in available soil moisture provides information on the timing and amount of water to apply to meet crop needs. Checkbook irrigation scheduling, confirmed with soil moisture monitoring, can improve irrigation scheduling decisions. Checkbook scheduling is discussed below.

Checkbook method of irrigation scheduling follows the concept that the soil in your field is like a bank checking account. Rainfall and irrigation applications are deposits into the checking account. Rainfall and irrigation may need to be reduced to reflect the effective amount added to soil moisture. Daily water removal from evaporation and transpiration (evapotranspiration or ET) from the field and crop would be considered withdrawals from the account. Soil has a maximum amount of water that can be held (called field capacity), so water added beyond the soil’s water holding capacity is lost to the account. Irrigation applied at a rate exceeding the infiltration capacity will cause surface runoff and be lost to the soil water balance account. 

Four different checkbook irrigation scheduling tools are available through Purdue or MSU Extension:

Enviroweather computes daily estimate of potential ET and project’s ET demands for seven days at each of the 58 strategically-located weather stations in Michigan calculating rET using wind, relative humidity and net solar radiation, in addition to temperature to estimate crop ET demands. For available estimate, pick the station nearest to you, and then click on one of the categories listed near the top of the screen (e.g. Field crops). Then click on “Potential Evapotranspiration”. For corn and soybeans, clicking the “Crop ET Estimate button”, then entering the emergency’s date will track crop ET as the crop develops. A free service of Enviroweather Network sends daily reports of ET from the previous four days and projected values for the next week by text or email to producers that sign up.

MSU Soil Water Balance Sheet is a paper version of a checkbook scheduler that producers can use reference evapotranspiration (rET) data from their own ET gauge station or rET data from Purdue’s PAC center weather stations. For Michigan, producers can use the Enviroweather data listed above. The Soil Water Balance Sheet helps producers convert the rET.into a estimate water removal for either corn or soybeans in their field.

MSU Excel Version of Scheduler allows greater flexibility and adaptability to irrigators who are comfortable using Excel. This method will provide results for all of Michigan and the upper tier counties in Indiana. Reference crop ET can be taken from each of the Enviro-weather stations where the program will use crop specific coefficient to adjust for your crop stage of growth.

Irrigation Scheduler is a simple, computerized irrigation scheduling checkbook model from the Agronomy Department of Purdue University. This method can be used throughout Michigan and Indiana. Crop specific rET values are estimated using the daily high and low temperatures, and rainfall provided by the producer or weather data can be imported from the internet.

In Michigan, irrigation scheduling is required to be in compliance with Generally Accepted Agricultural Management Practices.

All of the above mentioned irrigation scheduling tools, plus other irrigation management information, is available at the Irrigation program page on the Michigan State University Extension website.

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