The Checkbook Irrigation Scheduling Method

The ability to irrigate alleviates the problem that plagues all dryland farmers - lack of rain at a crucial stage of crop development. However, all irrigators have to contend with rain and therefore need a decision aid which allows them to determine when to irrigate and how much water to apply. Crop stress results from too little water and too much water can reduce yields and leach nutrients from the root zone. Either way a crop suffers. A method of scheduling irrigation events will help balance the amount of water received from rain and the amount applied by irrigation.

The "checkbook" method of irrigation scheduling is a soil water accounting method. It gets its name from the familiar checkbook bank account. The amount of water stored in the soil in the root zone is the account balance. Water that infiltrates into the soil in the form of rain or irrigation is considered a deposit. Water removed from the soil by the crop or evaporation from the soil surface is considered a withdrawal. The object of irrigation scheduling is to maintain a balanced soil water account.

The checkbook method used for this research is outlined in NDSU Extension bulletin AE-792, Irrigation Scheduling by the Checkbook Method. An electronic copy of publication AE-792.pdf (1.2 mb) is available. The checkbook method of irrigation scheduling requires you to measure or obtain from local sources the maximum daily air temperatures. Crop water use can be estimated from tables shown in the publication. This data is entered, by hand, into a tabular daily account and the soil moisture deficit is calculated on a daily basis. At a predetermined soil moisture deficit, irrigation must be started.

Instead of manually entering all the data for all of our plots, we developed a computerized version of the checkbook. We collaborated with Minnesota Extension to develop a computer program that incorporates both the North Dakota and Minnesota checkbook methods of irrigation scheduling. The program will run on any machine with Windows 3.1, 95 or 98 operating system. It requires about 5 megabytes of hard disk space and about 5 megabytes of RAM. We sell the program for $30 (US), which includes the disks and a manual. If you would like a copy or have questions, contact Tom Scherer at NDSU (tscherer@ndsuext.nodak.edu) or Jerry Wright at the University of Minnesota Extension Service (jwright@tc.umn.edu).