KWRRI Research Reports


Agricultural practices can have a significant impact on water quality. The effects of leguminous winter cover crops on leaching of NO-3; from soil have been investigated in this project. Legume cover crops, by fixation of atmospheric N, can reduce the amount of fertilizer N required to produce summer grain crops. The methods initially used to evaluate cover crop effects on No; transport included suction probe lysimeters and measurement of NO-3; in soil samples collected to a depth of 90 cm. These measurements demonstrated extreme spatial variability in NO-3; distribution and water movement. This made it impractical to compare effects of different treatments. Soil transformations of legume and fertilizer N sources were compared using 15N labelled amendments. Less of the vetch N was found in leachable forms and, after 2 to 3 months in soil, losses of vetch N were smaller than losses of fertilizer N. To resolve the problem of spatial variability and to make direct measurements of leaching, 16 lysimeters were constructed from 55 gallon drums. These were treated with either fertilizer or legume N. Early measurements show greater NO-3; leaching with legume N, due to the mulch effect reducing evaporative water removal. However, there has been insufficient time to fully evaluate the treatments. This experiment will be continued.

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Funding Information

The work upon which this report is based was supported in part by funds provided by the U.S. Department of the Interior, Washington, D.C., as authorized by the Water Resources Research Act of 1984. Public Law 98-242.