Integrated Crop Management

N management influences on N losses through tile lines

Subsurface tile drainage from row-crop agricultural production systems has been identified as a major source of nitrate entering surface waters in the Mississippi River Basin. Tile drainage studies have been conducted on three drainage research facilities at two locations in Minnesota since 1973. Nutrient and crop management systems, including rate and time of nitrogen (N) application, N sources (fertilizer, dairy manure, and hog manure), nitrification inhibitors, cropping systems, and tillage systems have been evaluated to determine their agronomic and environmental characteristics. Results from these studies have been instrumental in the development of best management practices for nutrient management in Minnesota. This information is applicable to much of north central Iowa because the soils, cropping systems, and climate are similar.

The primary factors that influence the nitrate content of surface and subsurface waters draining agricultural landscapes can be divided into two categories: uncontrollable and controllable. Uncontrollable factors include precipitation, other climatic factors, and soil mineralization. Controllable factors include agricultural management practices that can be used by crop producers to best fit the needs of their enterprise and include 1) cropping system used, 2) rate of N applied, 3) time of N application, 4) placement method, 5) use of a nitrification inhibitor, and 6) tillage systems.

Loading of nitrate-N into surface water is a function of amount of drainage water and nitrate-N concentration in the transported water. The amount of drainage water leaving the landscape is largely a function of climate and soil properties, e.g., precipitation, texture, and infiltration rate. Drainage is further influenced by the temporal distribution of precipitation within a year and the amount of annual or growing season precipitation.

Numerous studies conducted on subsurface, tile drainage plots at Waseca and Lamberton, Minnesota, show the following:

Use of best management practices by farmers reduces nitrate losses to subsurface drainage. But, will these practices be sufficient to reduce nitrate losses to meet the environmental goals of society? If not, will policies be developed to effect changes in land use, cropping systems, N application practices, subsurface drainage systems, or will other mitigating practices be required?

This article originally appeared on pages 164-165 of the IC-486(21) -- August 20, 2001 issue.

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