FACTORS UNDERLYING GRAIN YIELD SPATIAL VARIABILITY IN THREE IRRIGATED WHEAT FIELDS

Abstract

Three irrigated wheat fields in western Yolo County, California, were studied to determine the magnitude andcauses of spatial variability in grain yield. Point samples of soil properties were taken on a regular 61 m grid in eachfield. False color infrared aerial photographs were taken of each field under bare soil conditions and twice during thecropping season. Yield monitor data were collected at harvest. Two of the three fields showed substantial spatialvariability in grain yield. Correlation analysis and CART (classification and regression trees) were used to identifyfactors underlying grain yield spatial variability. Primary causes of variability were soil texture, weed level, and soilphosphate level. Results of the CART analysis were used to subdivide the two fields with high spatial variability intomanagement zones.