Influences of Spatial Variations of Soil and Nonuniform Sprinkler Irrigation on Spring Wheat Yield in Arid Regions

Field experiments were conducted on a sandy soil to study the effects of spatial variations of soil and nonuniform sprinkler irrigation on spring wheat yield in arid regions. The spatial variations of field capacity and soil texture were investigated. It was found that field capacity can be represented by both normal and lognormal distribution functions and a lognormal distribution function fits best to the observed silt and clay contents. As expected, field capacity greatly depends on the contents of silt and clay, increasing with the contents. Usually, a larger variation of silt and clay contents results in a larger variation of field capacity. Field experiments also demonstrated that both sprinkler nonuniformity and spatial variation of soil had effects on crop yield, but soil variation seemed to be more important for the studied soil. The spatial variation of soil should therefore be considered in selecting the target sprinkler uniformity. As the considerably less precipitation in arid regions cannot compensate for the negative effects of nonuniformly applied water on crop yield, a greater target sprinkler uniformity should be used in arid regions than in humid and semi-humid regions.