A landscape-scale study conducted in a center pivot irrigated field in Lamesa on the southern High Plains of Texas showed that site elevation affected the spatial pattern of soil water content (SWC), soil NO_3-N, total N uptake, and lint yield of cotton (Gossypium hirsutum L.), irrigated with 50 percent and 75 percent cotton potential evapotranspiration (ET). In this study, soil and cotton crop variables were measured on a 15-m interval along a 710 m (50 percent ET) and 820 m (75 percent ET) transect across the field. Geostatistical methods (autocorrelation and crosscorrelation analysis), and multivariate autoregressive state-space analysis were used to quantify and describe the spatial association of soil water, sand, N uptake, and lint yield with site elevation. Here we use a topographic factor, determined from neighboring site slopes, to explain variability of SWC, cotton N uptake, and lint yield measured in this landscape-scale study. The coefficient of determination (R~2) increased when thetopographic factor was included in the regression of lint yield vs. N uptake. This simple method gives insights on the association of soil water and N use with site elevation and slope in a large field.
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