SOIL VARIABLES AND INTERACTIONS AFFECTING PREDICTION OF CROP YIELD PATTERN

Variables accounting for the majority of soybean Glycine max yield variation, measured on 40 farm fields on either Cecil or Pacolet soil (clayey, kaolinitic, thermic Typic Hapludults) landscapes were previously identified. As clay content at 0-0.1 m increased from 3 to 18%, crop yield was greatly decreased, modulus of rupture was increased, and the yield response to pH, rainfall, and soil water tension was reduced. Soybean yield on soils with clay contents >20% at 0-0.1 m was significantly modified by soil C content. At 39.2% clay, crop yield was affected very little by soil water tension at 0.1 m, by rainfall, or by pH at 0 to 0.1 m. Over 255 mm of rainfall between Day 214 and 280 increased yield only on sites with high C levels. -from Authors