SPATIAL AND TEMPORAL VARIABILITY OF CORN GRAIN-YIELD ON A HILLSLOPE

The purpose of this study was to relate the temporal and spatial varia bility of corn (Zea mays L.) grain yield on a Typic Fragiochrept soil on a hillslope to soil properties and topographic features. Corn grain yields were sampled from a field that measured 280 by 150 m using a g rid and five transects. One-hundred forty yield measurements were take n on the grid (1983-1985) and 190 measurements on the transects (1984 and 1985) from plots 5.3 m long and two corn rows wide. Measurements o f soil surface elevation, soil organic matter (OM), P, and K contents were also taken at the grid plot locations. These data were analyzed u sing the methods of spectral analysis. Yield spatial and temporal vari ability was strongly related to surface undulations and the value of s urface curvature was found to be a useful parameter to quantify variat ions in topography. The intra annual differences in weather had the la rgest effect on grain yield at locations where the magnitude of curvat ure was large. Where the magnitude of curvature was small, the correla tions of yield for the wet (1984) and dry (1985) years were highly sig nificant. Yields correlated with soil P, K, and OM only in the dry yea r, 1985. Yields in the relatively dry years (1983 and 1985) correlated with depth to fragipan. Elevation data helped us interpret the spatia l and temporal variability of grain yield by separation of areas with convex curvature from areas with concave curvature.