Soil Nitrogen Research Paper

2.3.5 Soil Nitrogen

Soil nitrogen is a vital nutrient compound for plant growth. The primary source of soil nitrogen is gaseous N2 in atmosphere; however a few bacteria can use this directly. The other plants and organisms can use nitrogen unless it is chemically bound to oxygen, hydrogen or carbon. About 99% of combined nitrogen is present in the organic matter fraction of soil, and can be converted to plant available nitrogen due to various biochemical reactions, that naturally take place in soil. The amount of nitrogen utilized by crops is large; however, the available amount to crops is small. Consequently, the crop uptake of nitrogen exceeds the rate at which organic nitrogen becomes available. Thus, soil nitrogen gains much attention

Nitrogen in organic material is present in the form of amine groups (NH2) as constituents of amino acids and amino sugars. This nitrogen in the amine group is covalently bound to a carbon and two hydrogen atoms in ring and chain structures and thus becomes unionizable. The remaining two electrons of nitrogen atom can bond to the negatively charged clay surfaces. In this way, both the soil structure and the organic compounds are stabilized and the organic matter becomes resistant to decomposition. About 2-3% of organic nitrogen is being mineralized in a year and becomes available to

This form of ammonium is called as the non-exchangeable ammonium and is released to soil solution very slowly. Fixation by clay minerals: Several clay minerals such as vermiculite, illite, montmorillonite, and kaolinite attract the ammonium ions in soil solution. The ammonium ions, which are held on the surfaces, are the exchangeable ones; however, sometimes the interlayer areas of these minerals trap these ions. In other words, they are fixed to the mineral like a rigid part of it and can’t