Nonuniform sprinkler irrigation and crop yield

Abstract

The influence of nonuniform water application by sprinkler on the variability of soil water content and corn yield was studied on two experimental plots differing in their texture and hydraulic characteristics (Table 2). Variograms, autocorrelations and cross-correlations of soil water contents (θ), crop yield of sweet corn (Y), and net water application (Q) were calculated (Fig. 2). The correlograms show trends which are similar for all these three variables, θ , Y and Q. The trend of soil water content and crop yield appears to be casued by the trend in water application. Filtering out the trends by scaled variograms shows that soil properties of both experimental plots may be considered as homogeneous so that the responses of soil water content and in turn of crop yield resulted mainly from the nonuniformity of water application (Fig. 3). Redistribution of soil water after irrigation caused crop yield to be more uniform in plot B, in which the soil hydraulic properties led to more significant water flow, than in plot A. The coefficient of variation of dry matter yields in the two plots were 24 and 34%, respectively (Table 5). Dry matter yield response to net water application, as measured in collection cans, was fitted to the Mitscherlich's model — the “law of diminishing returns” (Fig. 4). Using normal distribution to characterize the probability density function of water application (Fig. 5) and the Christiansen coefficient to characterize the uniformity criteria in the fitted Mitscherlich's model enabled relative crop yield to be expressed as a function of Christiansen coefficient and the total amount of irrigation water (Fig. 6).