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Title: SPATIAL VARIABILITY OF WATER APPLICATION AND PERCOLATION UNDER CENTER PIVOTIRRIGATION

Author
item JORDAN, ROBERT - IRRIG CONSULT &ENGR. INC.
item DUKE, HAROLD
item HEERMANN, DALE
item BUCHLEITER, GERALD

Submitted to: European Conference on Precision Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/15/1999
Publication Date: N/A
Citation: Jordan, R.W., Duke, H.R., Heermann, D.F., Buchleiter, G.W. 1999. Spatial variability of water application and percolation under center pivotirrigation. European Conference on Precision Agriculture Proceedings.

Interpretive Summary: We studied two fields of corn in eastern Colorado which are irrigated by center pivot sprinkler systems to determine how uniformly the water is applied over course of the growing season and to estimate the amount of water that returns to the groundwater. Rain gauges were set out in several locations to check the accuracy of a computer program that had been developed to calculate the depth of irrigation at any position in the fiel based on how many irrigations were applied and how fast the machine ran during each irrigation. These calculated depths, along with soil properties, were used in a second computer program to estimate how much water is used by the crop, and by difference from application at any point, how much returns to the groundwater. We concluded that there is significant variability in irrigation water application, and that this variability coupled with variability in soil properties results in significant variability of groundwater recharge across a field. These results lend credibility to recommendations that irrigation systems be improved to make irrigations more uniform and demonstrate the value of applying fertilizers on a precision basis to provide for crop needs when, where, and in the amounts needed.

Technical Abstract: The water distribution in two center pivot irrigated fields in eastern Colorado, USA was simulated for the 1998 growing season based on actual irrigation applications. The simulated application depths show significant differences in both water application depth and uniformity due to changes i topography and periodic operation of an end gun on the systems. The season nirrigation application information and soils information taken from the US ural Resources Conservation Service soil surveys and from laboratory analyses were divided into discrete zones, the data were input to an irrigation scheduling program, and the calculated daily water balance was used to estimate variability in deep percolation over the fields. The variability in water application and in available water holding capacity create significant spatial variability in deep percolation across the field