Effects of Irrigation Scheduling on Spring Wheat Cultivars

Wheat is grown on more hectares in South Dakota than any other crop. Cold temperatures leave winter wheat susceptible to freeze injury in much of the state's wheat belt so over half of the wheat hectares are planted to spring wheat. As irrigated hectares have increased in the state, interest has risen in the production of spring wheat under irrigation as an alternative to or in rotation with corn and other crops. Little information is available on irrigation practices in spring wheat production in South Dakota. Irrigation studies have been done in the state as early as 1949 but results have been inconsistent. Recent irrigated yield trials at Redfield and Gettysberg, South Dakota indicate that improved grain yields can be achieved with irrigation, but improvement depends on many factors. In 1984, 25 cultivars were grown in these irrigated trials. At Redfield, little yield improvement was seen over dryland yields. Improvement at Gettysberg was greater. Grain yields obtained under irrigation are disappointingly low when compared to the apparent yield potential of these cultivars. The average yield of the top nine cultivars grown under irrigation at Gettysberg was 4.37 Mg/ha while the same nine cultivars averaged 6.34 Mg/ha at Fargo, North Dakota under dryland conditions during the same 2 year. Of course, many factors contribute to these yield differences including effects of the preceding crop, diseases, temperature and photoperiod, even if we assume that irrigation eliminates the effects of water stress. If proper irrigation scheduling is not utilized however, avoidable yield losses due to water stress could be a factor. Therefore, this study was initiated at Redfield, South Dakota with the objective of determining an irrigation schedule that would optimize the grain yield of adapted cultivars and aid in determining genetic yield potential when water is not a limiting factor.