"New/February/1991/10M.""Water Quality.""Focus area : nutrients and bacterial wastes."" Nitrogen in the environment -- Focus type.""Published by University Extension. University of Missouri-Columbia.""This material is based upon work supported by the United States Department of Agriculture, Extension Service, under special project number 89-EWQI-1-9203.

Buchholz, Daryl

Killpack, Scott

University of Missouri: MOspace

Focus Area NutrientsWater Bacterial Wastesn Quality and PUBLISHED BY UNIVERSITY EXTENSION, UNIVERSITY OF MISSOURI-COLUMBIA - Nitrogen in the Environment -- Focus Type ­Nitrogen Fixation N Scott Killpack and Daryl Buchholz, Extension Agronomy itrogen can be found in many forms in our environment. Nitrogen is also very important for plants to live. The earth's atmosphere is made up of 78% percent nitrogen in the form of a colorless, odorless, non-toxic gas. The same nitrogen gas in the atmosphere can be found in spaces between soil particles. However, plants are unabl.e to use this form of nitrogen. Certain microorganisms found in the soil are able to convert atmospheric nitrogen into forms plants can use. This is ca.lJ.ed biological nitrogen fixation. Types of Nitrogen Fixation , In addition to biological fixation that takes place by microorganisms in the soil, fixation can also take place chemically. An example of this is in the fertilizer industry where atmospheric nitrogen (N2) can be combined with hydrogen (H+) to make anhydrous ammonia (NH3), and other nitrogen fertilizer products. Chemical Nitrogen Fixation Combine Atmospheric Nitrogen (N2) plus Hydrogen (H+) Production of Nitrogen Fertilizer Products Symbiotic Nitrogen Fixation One of the most interesting forms of biological nitrogen fixation, is that which takes place by micro­organisms living in very small nodules on the roots of certain plants, such as legumes. This is called symbiotic nitrogen fixation. A symbiotic relationship, is an association or relationship where both organisms mutually benefit. In this case, microorganisms obtain food and energy from the root of the plant while producing nitrogen the plant can use for growth and development. The form of nitrogen so produced, is the same form of nitrogen that is found in several types of commercial nitrogen fe~iliz~rs. ~ Biological Nitrogen Fixation ~ AmmoniumAtmospheric Atmospheric nitrogen in the~NitogenNitrogen - spaces between soil particles(NH +)(N ) 4 can be converted by microbes in the soil or on nodules on the roots of certain plants to forms of nitrogen the plant can use. 2$0.25 WQ261 Printed with Soy Ink on Recycled Paper Archive version -- See extesion.missouri.eduand is not further converted to nitrate (N03-).Importance of Nitrogen Although nitrogen exists in many forms in the Fixation to Crops soil, it is the nitrate form that primarily affects water quality.The microorganisms ability to fix atmospheric nitrogen is often discussed in terms of the plants Upon the eventual death of the legume plantability to fix nitrogen. The amount of fixation nitrates will be produced. This happens .because that takes place is strongly influenced by soil the legume plant residues are easily broken conditions. Factors such as moisture, tempera­I down by microorganisms in the soil resulting in ture, oxygen supply and fertility in the soil can the production of nitrates. However, This influence fixation. Disease and insects can also usually takes p~ace at a time when a subsequent affect the degree of nitrogen fixation. crop is growing taking advantage of the nitrates so produced. One of the most common groups of plants that fix nitrogen are legumes. Of the total nitrogen The presence of nitrate in the soil is desirable required by legumes, generally about half is because it is required by plants for growth and nitrogen fixed from the atmosphere, with the development. However nitrate is highly mobile remainder being taken up from residual nitrate and easily moves with water. The results of a in the soil. This means that where legumes are heavy rain can move nitrates downward in the grown, outside applications of manure or fertil­ soil, below the root zone of plants. Whether izer nitrogen are not needed. nitrates continue to move downward, and into Different legumes also vary in the amount of groundwater, depends on underlying soil and/ total nitrogen they can fix. Listed below in the or bedrock conditions, as well as depth to table are common legumes used in agriculture groundwater. If depth to groundwater is shal­and the total amounts of nitrogen they fix during low and the underlying soil is sandy, the poten­a growing season. tial for nitrates to enter groundwater is relatively high. However if depth to groundwater is deep Common Legume Total Nitrogen and the underlying soil is heavy clay, groundwa­Crops Fixed ter contamination from nitrates is not likely. (pounds/acre/year) Once nitrates get into groundwater, the greatest Alfalfa	 70 - 200 concerns are for infants, less than one year old, Field Peas	 155 -175 and for young and pregnant animals. HighRed Clover	 60 -100 levels of nitrates can be toxic to newborns caus­Soybeans	 20 - 275 ing anoxia, or internal suffocation. Seek alterna­tive water sources if nitrate levels exceed the hnplications to ·Water health standard of 10 ppm nitrate-nitrogen. Do not boil water to eliminate nitrates, It increases Quality nitrate levels, rather than decreases them. The The process of nitrogen fixation by legumes, by most common symptom of nitrate poisoning in itself, probably does not significantly impact babies is a bluish color to the skin, particularly water quality. This is because the ammonium around the baby's eyes and mouth. These (NH4+) produced from fixation is readily used by symptoms of nitrate toxicity are cOmD;lonly the legume plant for growth and development, referred to as the 'blue-baby" syndrome. This material is based upon work supported by the United States Department of Agriculture, Extension Service, under sp~cial project number 89-EWQI-1-9203. University	 • Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914 ~ in cooperation with the United States Department of Agriculture. Gail L. Imig, Director, ~Extension Cooperative Extension Service, University of Missouri apd Lincoln University, Columbia, UNIVERSITY OF MISSOURI Missouri 65211.• An equal opportunity institution. COLUMBIA WQ261	 New/February/1991/10M 

Nitrogen fixation (1991)

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