Date of Award:

1984

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Agricultural Systems Technology and Education

Advisor/Chair:

Donald L. Snyder

Abstract

This study analyzed the economics of irrigation scheduling for alfalfa hay in the Cache Valley, Utah area. Yield, evapotranspiration (ET) and irrigation drainage loss, along with the costs and returns per acre attributable to irrigation scheduling, were simulated through the use of a computerized plant growth model. The model created yearly "irrigation schedules" for alfalfa hay based on actual climatic, soil and plant characteristic data from the Utah State University Greenville Experiment Station. The model calculated the irrigation schedules based on a soil-water balance equation which never allowed the available soil water to go below the crop stress point.

The production variables (yield, ET, drainage, water application efficiency) achieved with the model-calculated schedules were contrasted against the same variables under conventional practices of zero, five and eight irrigations per season. Under five and eight irrigations, the amount of water applied at each irrigation was varied from one to eight inches, which simulated irrigations ranging from 3.4 to 26.6 hours per set.

The yearly irrigation schedules created by the soil-water balance equation maximized crop evapotranspiration and yield. Irrigation drainage was negated while water application efficiencies of 100% were achieved by applying only enough water at each irrigation to refill the soil profile.

Using model-estimated yield, net profit for each irrigation option (scheduling, zero, five and eight irrigations) was calculated using nine different irrigation cost scenarios. Based on the 16 years of simulation, irrigation scheduling averaged a lower net profit when compared against five irrigations at three and four inches per irrigation. Compared against eight irrigations at two and three inches per irrigation, net profit for the model-calculated schedules averaged higher or equal.

Irrigation scheduling is an excellent method of determining optimal irrigation frequency and amount, and may have a significant impact on net income if an irrigator is substantially over or under irrigating. However, once an optimal pattern of irrigations is established using a scheduling technique it may be more profitable for an irrigator to discontinue incurring the cost of irrigation scheduling and simply use the pattern each successive season, modifying it slightly for an annual variations in climate.

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