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Nitrate Leaching as Influenced by Water Application Level and Nitrification Inhibitors¹

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.

Key Words: urea • groundwater • nonpoint-source pollution • supplemental irrigation • nitrapyrin • Terrazole

¹ Contribution from Soil & Water Conserv. Res. Unit, USDA-ARS, NCR, Ames, IA 50011.

² Soil Scientist, USDA-ARS, Ames, Iowa.

Received for publication April 22, 1983.