Bromide and Nitrogen‐15 Tracers of Nitrate Leaching under Irrigated Corn in Central Nebraska

Abstract

Abstract Nitrate leaching from agricultural fields into groundwater has caused environmental and health concerns. A study was conducted during 1992–1993 in the Central Platte Valley of Nebraska to assess the nitrate leaching potential under recommended center‐pivot irrigation and fertilizer best management practices for continuous corn ( Zea mays L.). At time of planting corn, potassium bromide (KBr) and double‐labeled 15 N ammonium nitrate (10 atom% 15 NH 4 15 NO 3 ) tracers were applied at rates of 200 kg Br ha −1 and 30 kg N ha −1 to four 6.1 by 3.7 m plots that were representative of major soil types on the 32.1‐ha field. Soil and plants sampled 7 wk after planting and at harvest in 1992, and in the spring of 1993, were analyzed for Br and N content and a mass balance was determined. At corn harvest, 41% (81.9 kg ha −1 ) of the applied Br loss from the top 1.2 m of soil was attributed to leaching. Also, 54% (16.2 kg ha −1 ) of the tracer applied was lost from the system; 41% (12.3 kg ha −1 ) through leaching; and 13% (3.9 kg ha −1 ) through denitrification and volatilization. By time of planting in the spring of 1993, 70% (139.3 kg ha −1 ) of the applied Br and 46% (13.8 kg ha −1 ) of the fertilizer N leached below 1.2 m. High negative correlations were found between soil clay and silt contents, and Br or NO 3 leaching. Despite use of best management practices for irrigation water and N applications, large amounts of nitrate can be lost through leaching under irrigated corn in this subhumid climate on fine‐ to medium‐textured soils.