IRRIGATION GUIDELINES FOR OILSEED CROPS IN THE U.S. CENTRAL GREAT PLAINS

Development, water use and yield formation of oilseed crops are inter-related. Greatest yields are expected with a well-established canopy, a plant population sufficient to support a large number of seeds set per acre and favorable weather conditions for an extended seed fill period. Oilseed water requirements closely follow canopy formation and evaporative conditions. Irrigation scheduled by the water balance method results in higher yields than with irrigation scheduled by growth stage. A straight-line relationship between yield and water use indicates the yield threshold (maximum water use with no expected yield) and yield response to increased water use. When precipitation, available soil water and limited irrigation fail to meet crop water requirements, yield reductions depend on the degree of plant water stress at critical stages of growth. Full-season soybean with full irrigation offers greatest productivity potential. A smaller yield threshold and extensive rooting system for sunflower provides advantages for limited irrigation or double-crop conditions. Winter canola can provide good productivity during fall and spring growing seasons when heat stress can be minimized