Optimal Scheduling and Minimizing Deep Seepage in Microirrigation

Abstract

The emitter flows of a microirrigation system as well as the irrigation water applied in the field can be expressed as a normal distribution when the uniformity coefficient is larger than 70% or the coefficient of variation is less than 30%. This normal distribution can be further simplified to a straight line distribution. The linearization approach can provide simple solutions to evaluate quantitatively the volumes of deficit and deep seepage based on the uniformity of the irrigation application, the evapotranspiration requirement of the crop and the total amount of water applied. An optimal solution was developed considering the cost of water, the value of the crop, the loss of fertilizer, and other chemicals through deep seepage, and the cost of treating the groundwater when it is contaminated. All the parameters required in the optimal solution can be evaluated by irrigation experiments except for the cost of treating contaminated groundwater, which is not readily available at the present time. An alternate solution was developed to prevent groundwater contamination by minimizing deep seepage in irrigation practices. This was done using the concept of deficit irrigation. A computer program was used to simulate different microirrigation uniformity coefficients and irrigation applications. When a microirrigation system is designed for more than 90% uniformity and scheduled for 10% deficit irrigation, deep seepage can be minimized to less than 1% of the total amount of water applied.