"New/February 1991/10M.""Water Quality.""Focus area : nutrients and bacterial wastes.""Nitrogen in the environment.""Published by University Extension. University of Missouri-Columbia.

Buchholz, Daryl

Killpack, Scott

University of Missouri: MOspace

Focus Area NutrientsWater and Bacterial Wastesn Quality PUBLISHED BY UNIVERSITY EXTENSION, UNIVERSITY OF MISSOURI-COLUMBIA - Nitrogen in the Environment ­How Nitrogen Enters Groundwater N Scott Killpack and Daryl Buchholz, Extension Agronomy itrogen can be found in many different organic and inorganic forms in our environ­ment. The air we breathe is composed of 78% nitrogen. Nitrogen can also be found in many varied forms in the soil. Plants need nitrogen from the soil for proper growth and develop­ment, but are only able to use very specific forms of nitrogen. Plants can not use the form of nitrogen found in the atmosphere. Natural biological process carried out by microorganisms in the soil, convert organic nitro­gen to inorganic forms, which plants are able to use. Organic nitrogen is a common .compo­nent in plant residues and organic matter. Ultimately org~nic nitrogen is converted to inoJ;­ganic ammon~um (NH4+). Plants can use this form of nitrogen, but ammonium is quickly converted to nitrate (N03-) in warm moist soils. Nitrate is the form of nitrogen that is most used by plants for growth and development. Where crops are grown, nitrates can also ema­nate from nitrogen fertilizers and manures. Nitrate, regardless of its source, is the form of nitrogen that can get into groundwater. Nitrate Movement in the Soil Unlike ammonium, nitrate does not attach to soil particles and as a result, is easily moved by water. How nitrates move with water in the soil can be best illustrated by what takes place when soils become wet from rainfall. When rainfall takes place, the soil becomes wet and the air spaces between soil particles begin to fill with water. If rainfall is heavy enough, the air spaces become filled to a point that forces of gravity will cause water to move downward in the soil. As water moves downward, nitrates Nitrate will also be carried, downward with Movement water. The downward movement of nitrates in the soil is referred to as leaching. $0.25 WQ256 Printed with Soy Ink on Recycled Paper Achivver ion -- See xtsio.mi souri.duWhat Affects the Degree of Nitrate Leaching How much leaching will take place is strongly influenced by how much water a soil can hold. For example, by their nature sandy type soils can not hold as much water as clay type soils. This means that leaching of nitrates will take place much more easily in a sandy soil compared to·a clay soil. Often times, leaching is not a significant factor in heavy clay soils. Other factors which can affect nitrate leaching in­clude amount of rainfall, amount of water use by plants and how much nitrate (N03-) is present in the soil system. Conditions When Nitrates May Enter Groundwater Whether nitrates continue to leach downward, and into groundwater, depends on underlying soil and/Nitrate is more likely to move downward In sandy soli than In clay soil. Graphic by or bedrock conditions, as well as depth to groundwa-Scott Killpack. ter. If depth to groundwater is shallow, and the underlying soil is sandy, the potential for nitrates to enter groundwater is relatively high. However, if depth to groundwater is deep and the underlying soil is heavy clay, nitrates will not likely enter groundwater. In some cases where dense hardpans are present, nitrate leaching will not progress beyond the depth of the hardpan. Minimizing Groundwater Contamination from Nitrates The potential of nitrates from animal manures and nitrogen fertilizers getting into ground­water can be reduced through good management practices. Applying manures and nitro­.gen fertilizers when crops are actively growing, and using nitrates for growth and develop­ment, will reduce the amount of nitrate in the soil system, and thus the amount that could potentially be leached. However, little can be done to minimize the leaching of nitrates into groundwater that result from the ongoing decay of organic matter in the soil. In this situa­tion, nitrates are simply a natural biological result, of an ongoing cycle of nitrogen transfor­mation processes in the soil. For information on health concerns of high nitrates in water, seeWQ258. This material is based upon work supported by the United States Department of Agriculture, Exten­sion Service, under special project number 89-EWQI-1-9203. • Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 191':..~)}University in cooperation with the United States Department of Agriculture. Gail L. Imig, Director, ~Extension Cooperative Extension Service, University of Missouri and Lincoln University, Columbia, UNIVERSITY OF MISSOURI Missouri 65211.• An equal opportunity institution. COLUMBIA WQ256 New/February 1991/10M 

How nitrogen enters groundwater (1991)

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