Nitrate Leaching as Influenced by Water Application Level and Nitrification Inhibitors

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Abstract
The effects of water application level and nitrification inhibitors on NO3−‐N leaching from a sandy loam soil were evaluated using soil columns and nonweighing field lysimeters. In soil columns (297 mm diam by 1.2 m deep) fertilized with 224 kg N ha−1, addition of the nitrification inhibitor nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] reduced NO3−‐N leaching losses by 51 and 30 kg ha−1, respectively, for the 12.7‐ and 38.1‐mm weekly water application levels. Both nitrapyrin and Terrazole (5‐Ethoxy‐3‐trichloromethyl‐1,2,4‐thiadiazole) (Olin Corp., Little Rock, Ark.) inhibitors were equally effective in reducing total NO3−‐N leaching losses from soil columns after 100 d for the 38.1‐mm water application level. The change in flow‐weighted NO3−‐N concentration due to use of nitrification inhibitors was about −0.4 to −1.0 mmol L−1.Annual NO3−‐N leaching losses measured at the 1.2‐m depth in field lysimeters cropped with corn (Zea mays L.) over a 3‐yr period averaged about 12 kg ha−1 less (7%) for nitrapyrin‐coated urea. The results were not consistent since nitrapyrin reduced NO3−‐N leaching during the growing season by 12 and 17% for 2 of the 3 yr and post season leaching by 35% for 1 yr. The change in flow‐weighted NO3−‐N concentration (3‐yr avg) due to nitrapyrin was −0.4, −1.5, and +0.9 mmol L−1, respectively, for the growing season, post season, and preemergence periods. Nitrification inhibitors may help to minimize nonpoint‐source pollution on sandy soil where supplemental irrigation is used by reducing and/or delaying NO3−‐N leaching particularly during the growing season when N is utilized by plants.