YIELD AND NITROGEN USE EFFICIENCY OF IRRIGATED CORN IN THE NORTHERN GREAT-PLAINS

Nitrogen and water are the two most common limitations to crop production in the semiarid northern Great Plains. Little is known about N use efficiency by irrigated corn (Zea mays L.) in this region. A study was conducted to determine how irrigation and N fertility levels affect growth and N use efficiency by corn. Corn was grown under three irrigation levels: precipitation plus irrigation equal to one, two, and three times the calculated evapotranspiration (ET) rate. Fertilizer use efficiency was determined using N-15-enriched fertilizer applied at rates equivalent to 100 and 200 kg N ha(-1). Grain and dry matter yields, N content, and utilization of fertilizer N all exhibited yearly variations, probably the result of annual weather patterns, especially temperature. For years when temperatures during the growing season were below the 30-yr average and affected corn growth, there were no differences in yields and N content between the two fertility levels. For years when temperatures during the growing season were warm enough for favorable growth, corn responded to increasing N fertility with 60% greater yields, 75% greater N content, and 60% greater percentage N derived from fertilizer with the higher N fertility treatment. Averaged across rates, grain utilized 35% and stover an additional 15% of the applied fertilizer, while 30% remained in the upper 0.6 m of the soil profile at the end of the growing season. Twenty percent of the applied fertilizer could not be accounted for, lost to leaching or denitrification. Supplemental irrigation and N fertilization are viable management practices available to producers in the semiarid northern Great Plains.