Effects of irrigation rate and plant density on maize water use efficiency and grain yield

Irrigation induced water quality and quantity problems on soils underlain by coarse-grained, glacial aquifers in Central Minnesota has been and continues to be a major environmental concern. Best irrigation management strategies can help protect water resources and reduce the negative impact of irrigation on the environment. With that goal, this study was conducted in Westport, MN, from 2016 to 2018 to quantify the effect of reduced irrigation levels and plant density on maize yield and water use efficiency. Three irrigation rates (100%I: 1.0, 75%I: 0.75 and 50%I: 0.50 of estimated evapotranspiration (ETc)) and three plant densities (49,000, 74,000 and 99,000 plants ha^-1) were investigated under linear-move sprinkler irrigation. The results showed non-significant interaction between irrigation rates and plant density. There was non-significant grain yield difference between 75%I and 100%I, indicating that 75%I can produce optimum maize yield. Grain yield was significantly higher in 99,000 plants ha^-1than other plant density. Maize yield increased with increase in plant density from 49,000 to 99,000 plants ha^-1in 2016, whereas in 2017 and 2018 grain yield increased with increasing plant density from 49,000 to 74,000 plants ha^-1but further increase in plant density did not significantly enhance the grain yield. In 2016 and 2017 maize growing seasons, weekly average soil water storage (SWS) in 100%I treatment was significantly greater than for the 50%I and 75%I treatments in top 0.46m of soil profile. The irrigation water use efficiency (IWUE = Y/I) increased with a decrease in irrigation rate from 100%I to 50%I whereas crop water use efficiency (CWUE = Y/ETc) increased with an increase in irrigation rate from 50%I to 100%I. The results of this study indicate that optimum yield and water use efficiency could be obtained by using reduced irrigation rates (75%) and medium plant density(74,000 plants ha^-1). In regions like Central Minnesota where irrigation induced water quality issues are of major concern, decisions to increase either CWUE or IWUE should be based primarily on environmental factors and not just on the increase in yield.