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United States Department of Agriculture

Agricultural Research Service

Title: Nitrate Leaching in Irrigated Corn and Soybean in a Semi-Arid Climate

Authors
item Klocke, N - NLK ENGINEERING
item Watts, D - UNIV. OF NEBRASKA-LINCOLN
item Schneekloth, J - UNIV. OF NEBRASKA
item Davison, D - UNIV. OF NEBRASKA
item Todd, Richard
item Parkhurst, A - UNIV. OF NEBRASKA-LINCOLN

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 1999
Publication Date: December 31, 1999

Interpretive Summary: The nitrate form of nitrogen (N) is an essential crop nutrient. It exceeds the EPA maximum contaminant level for drinking water in some areas of intensive crop production. Corn production in the western Corn Belt depends on N fertilizer and irrigation to achieve high yields. Nitrate is removed from the crop root zone by water that moves through the soil and may reach ground water if N fertilizer and irrigation are improperly managed. Remova of nitrate from the crop root zone by water is called leaching. This 8-year study compared water loss and nitrate leaching of two irrigated farming practices in the western Corn Belt of Nebraska; corn grown year after year (continuous corn), and corn that alternated with soybean (corn-soybean rotation). Current best farming practices of the region for N and irrigation were used. Nitrate leached from the crop root zone even when irrigation and N were carefully managed. The amount and timing of rain contributed to nitrate leaching. The amount of leached nitrate and nitrate concentration were significantly greater in the corn-soybean rotation compared with continuous corn. Average nitrate concentration in continuous corn and the corn-soybean rotation exceeded the maximum contaminant level for drinking water. Nitrogen was probably over-applied in the corn-soybean rotation, and N recommendations for rotations that include soybean should be reevaluated. Best farming practices must be modified in order to reduce potential nitrate contamination of ground water. Modifications may include lower crop yield goals and reduced N fertilizer and irrigation.

Technical Abstract: The nitrate form of nitrogen (N) is an essential crop nutrient. It exceeds the EPA maximum contaminant level of 10 mg/L in drinking water in some regions of intensive crop production. Corn production in the western Corn Belt depends on irrigation and N fertilizer to achieve high yields. Nitrate is leached from the crop root zone and transported to ground water when N fertilizer and irrigation are improperly managed. This research compared water loss and nitrate leaching from continuous corn and corn-soybean cropping systems in the western Corn Belt of Nebraska. Corn and soybean were grown in fourteen undisturbed isolated soil columns (0.9-m diameter and 2.4 m deep) called percolation lysimeters, installed in sprinkler irrigated field plots. Best management practices of the region for N and irrigation were used. Water and nitrate that leached through the crop root zone was extracted weekly from the bottom of lysimeters from 1991 through 1998. Nitrate leached from the crop root zone even when irrigation and N were carefully managed. The amount and timing of rain contributed to nitrate loss. Average annual loss of nitrate-N and nitrate concentration in leached water were 75% greater in the corn-soybean rotation than in continuous corn. Annual nitrate-N losses averaged 52 kg/ha from continuous corn and 91 kg/ha from the corn-soybean rotation. Average nitrate concentration was 24 mg/L for continuous corn and 42 mg/L for the corn-soybean rotation. Not enough N credit was given to the soybean crop, so that N fertilizer was over-applied to the following corn crop. The N credit of soybean in rotations needs to be reevaluated. Current best management practices must be modified to reduce nitrate losses and may include lower crop yield goals and reduced N fertilizer and irrigation.

Last Modified: 9/23/2014
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