One of the key points that came out of the study is the average difference in yield between irrigated and dryland wheat across the time period – an 18 bushel-per-acre advantage for irrigation, Holman said.

“Irrigated wheat in western Kansas has increased about 0.5 bushel per acre per year,” the researcher said. Specifically, the yield increase in southwest Kansas dryland wheat was 0.3 bushel per acre per year and in northwest Kansas dryland, 0.8 bushel per acre per year.

“Another interesting thing that came out of this study is how dryland wheat in southwest Kansas differed from dryland wheat in the northwest part of the state, in terms of factors influencing yield and yield improvement over time,” Holman said.

The difference was largely caused by more freeze damage and worse stand establishment in the southwest, compared to the northwest. Dryland wheat in the southwest was affected more by October precipitation (stand establishment) and April temperature (spring freeze injury) than by crop yield improvements made over the past 55 years. Crop yield improvements included things such as new variety releases and improved agronomic practices, such as with fertilizers and pesticides.

Dryland wheat yields in northwest Kansas, however, were affected most by crop yield improvements (breeding and agronomic practices). Fall stand establishment was a secondary factor behind breeding and agronomics. Spring freeze did not affect dryland wheat yields in northwest Kansas. Behind fall precipitation, early spring precipitation was important for increasing yield. Precipitation that fell later in the growing season did not improve yield but could help improve test weight.

Irrigated wheat yields were only affected by temperature. For both dryland and irrigated wheat, warm fall and June temperatures reduced yield, while warm late-spring (May) temperatures increased yield. Irrigated wheat in southwest Kansas was not significantly affected by spring freeze damage, which implies that drought-stressed wheat may be more susceptible to spring freeze injury than wheat that is not stressed. 

Together, these results suggest northwest Kansas is a more favorable environment than southwest Kansas to grow dryland winter wheat, Holman said. There was no difference in irrigated wheat yields between the southwest and northwest.

Future dryland crop breeding and agronomic research needs to improve winter wheat establishment and improve the tolerance of wheat grown in southwest Kansas to spring freeze damage, he said. Both dryland and irrigated wheat will benefit from increased tolerance to warm fall and June temperatures.