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Irrigation at K-State Research and Extension

Using KISCORN for Irrigation Scheduling of Corn

Freddie R. Lamm
Research Agricultural Engineer
KSU Northwest Research-Extension Center
Colby, Kansas
Phone: 785-462-6281 Fax: 785-462-2315
Email: flamm@ksu.edu


Do not use KISCORN for shallow on sandy soils as some assumptions will not hold true.

KISCORN is a spreadsheet template to be used for irrigation scheduling of corn. It is available in Microsoft Excel for Windows. KISCORN is a simple and easy-to-use template which keeps track of the crop water budget. KIS stands for Keeping it Simple and indeed it does. There are more sophisticated irrigation scheduling programs available, but KISCORN will meet the needs of many irrigators. The same procedure can be easily done on pencil and paper without a computer. However, KISCORN performs the simple calculations, and gives a tidy and neat permanent record. KISCORN allows for three fields to be scheduled with one template. Additional fields can be handled with additional templates using a different filename.


The crop coefficients (Kc) used in this template have been found to be acceptable for the semi-arid region of western Kansas. The crop coefficients could be easily changed by unprotecting or unlocking the crop coefficient column and then entering your own values. The crop coefficients (Kc) are multiplied with the reference evapotranspiration (ETr) to get the actual evapotranspiration (AET) of the corn.

KISCORN assumes an emergence date between April 1 and May 31 will be entered into the template. The month and day columns of the spreadsheet will not perform acceptably if this condition is violated. The crop coefficients are probably most valid for emergence dates ranging from April 25 to May 20 in the Central Great Plains.

KISCORN also assumes the soil profile is at field capacity at crop emergence. This is generally an acceptable, if not always accurate, assumption early in the growing season for irrigated corn on silt loam soils in western Kansas. Depletion (DEP column) of the soil water in the profile increases as evapotranspiration (AET) occurs. Depletion is reduced by irrigation (IRR) and rainfall (RAIN). If depletion becomes negative, it is set to zero, which is analogous to saying no additional water can be added to a full pitcher. Rainfall is considered to be 100% effective in the template. If one wishes to reduce the rainfall to reflect inefficient events or excessive runoff, one must alter the entered value for the RAIN column.

In using KISCORN, the irrigator tries to maintain the depletion (DEP column) below an acceptable preset amount. This might be 1-2 inches for a center pivot sprinkler irrigation system or maybe 2-5 inches for a surface-irrigated field. With a little experience, the irrigator can anticipate irrigation events in the near future, based on the climatic conditions from the near past. As the anticipated date approaches, the calculated depletion shows the irrigator what adjustments are needed in the schedule.


Loading KISCORN is similar to loading other templates used by Microsoft Excel.

At the beginning of the season, the emergence month and date must be entered in the cells at the top of the spreadsheet. These only need to be entered once.

Values for reference evapotranspiration (ETr) and rainfall (RAIN) are entered daily into the appropriate columns. ETr can usually be obtained for various locations in the state from the local media, crop consultants, groundwater management districts, or Kansas State University.

Irrigation (IRR) is needed when the depletion (DEP) reaches the preset amount. After irrigation, the irrigation amount is entered. The irrigation schedule is a guide throughout the season. The irrigator should also use the progress of the corn as an additional guide. Other non-irrigation factors can affect crop growth and development. Short-term water stress can occur even under well-watered conditions. KISCORN can save water and can help manage a restricted water supply.