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Fluid Journal : Fluid Journal 1993-1995
FFFReview Effective Nitrogen Management Effective Nitrogen Management Effective Nitrogen Management Effective Nitrogen Management Effective Nitrogen Management N-use efficiency/environmental satety hinge on how wellthis mobile nutrientis managed. How essential is nitrogen to plant growth? Acorncropwilltakeupto215lbsofNina growing season. Soybeans 315 lbs. Alfalfa as high as 450 lbs. Clearly, it is a critical com- ponent. N is a part of every living cell. Plants require large amounts of it for normal growth. How well it is managed in a farm operation will determine whether or not a crop is successful. In this article, we will look at the nature of nitrogen and how it behaves. Understanding nitrogen and how it works goes hand in hand with good N manage- ment. Versatile Nitrogen plays many roles in promot- ing plant growth. Yield booster. Plants take up most of their N as the ammonium (NH4+) or nitrate (NO3-) ion. Some direct absorption of urea can occur through the leaves, and small amounts of N are obtained from materials such as water soluble amino acids. Except for rice, most agronomic crops take up most of their N as nitrate, which is the most common source found in soils. However, research has shown that crops use substan- tial amounts of NH4 if it is present in soil. Certain corn hybrids have a high require- ment for NH4+-N that helps boost yields. Wheat has also shown the benefits of NH4+ nutrition. One reason for the higher yields is that NO3- reduction in the plant requires energy (NO3- is reduced to NH4+ , then converted to amino acids inside the plant). This energy is supplied by carbohydrates, which otherwise could be used in grain formation. Enhances photosynthesis. Nitrogen is necessary for chlorophyll synthesis and, as a part of the chlorophyll molecule, is involved in photosynthesis. Green pigment in chlorophyll absorbs light energy needed to initiate photosynthesis. Chlorophyll helps convert carbon, hydrogen, and oxygen to simple sugars. These sugars and their conversion products stimulate most plant growth increase. Lack of N and chloro- phyll means the crop will not use sunlight as an energy source to carry on essential functions. Increases protein. Nitrogen is also a component of vitamins and energy systems in the plant. It is an essential component of amino acids, which form proteins. Thus, N is directly responsible for increasing protein content. Deficiency signs We've just seen what nitrogen can do. Now we'll look at what happens when it is lacking in plants. Yellowing. Adequate N produces a dark green color in the leaves by a high concen- tration of chlorophyll. Nitrogen deficiency results in chlorosis (yellowing) of the leaves because of declining chlorophyll. This yellowing starts first on oldest leaves, then develops on younger ones as the deficiency becomes more severe. Stunting. Slow growth and stunted plants are indications of N deficiency. Less tillering. Small grains and other grass-type plants tiller less when N is in short supply. Fewer leaves. Inadequate N leads to low protein in seed and plant vegetative parts. Deficient plants usually have fewer leaves. Higher moisture. Corn supplied with insufficient N will have a higher moisture content than corn adequately fertilized with N. Early maturity. Certain crops such as cotton may reach maturity earlier than plants with adequate N. Water use efficiency Anytime a missing nutrient increases plant yield when it is applied, water use efficiency is also increased. In a Minnesota study, for example, corn plants taking up the same amount of water showed yield increases of 66 bu/A after N rates applied at planting were doubled from 100 to 200 lbs/ A. Applying the 200-lb/A rate through irrigation in eight 25-lb/A increments, added another 34 bu/A. In a Colorado study, 150 lbs/A of N on corn gave a little over 2 bu/A more per inch of water under wet conditions and almost 2.75 bu/A more per inch of water under dry conditions. Thus, applying optimum rates of N--- not too much nor too little---has resulted in improved water use efficiency while minimizing potentially negative effects on the environment. Nitrogen cycle The amount of soil N in an available form is small. Most soil is tied up in organic form. Very little is found in the rocks and minerals from which soils were formed. Most all soil N originated in the earth's atmosphere Figure 1. Diagram of nitrogen cycle Spring 1994 The Nitrogen Cycle Atmospheric Nitrogen Ammonium Fertilizer Conversion Legume Conversion Atmospheric Conversion Denitrification Nitrate Protein Plant Absorption Plant & Animal Wastes
Fluid Journal 1996-1998