Nitrogen in soil

Forms of nitrogen in the soil

    Nitrogen is another important property in the soil. It is one of the primary nutrients that is essential to living, grow and reproduce for plants. Nitrogen in soil has two forms as organic nitrogen and inorganic nitrogen.

                      Most of the nitrogen in the soil is found in organic material in the soil. The organism in the soil like plants, animals, and microorganism has lots of compounds that are rich in organic matter. Their wastes and dead bodies are accumulated in the soil. Organic nitrogen can be found in amino acid (20-50%), hexamine (5-10%) and amino sugar (1%) in their cells. This nitrogen is available for plants only after decomposition by soil microorganisms.

                    Inorganic nitrogen is accumulated in soil by fixation of atmospheric nitrogen by soil microorganisms in the soil. The small amount of inorganic nitrogen is produced during thunderstorms by lighting as NO-3.These NO-3 are reached to the soil by dissolving in precipitation as nitric acid.

The soil nitrogen cycle

Degradation of the organic matter will result in the release of ammonium and nitrate nitrogen, a process called mineralization. Inorganic nitrogen is added to soil after fixation of atmospheric nitrogen and organic nitrogen by soil microorganisms.

                                   Mineralization of nitrogen can be divided into two chemical reactions. They are ammonification and ammonium hydrolysis.        Ammonification is a transformation of organic nitrogen to ammonia.

R−NH2+H2O→NH3+R−OH+energy

Ammonium hydrolysis is a transformation of ammonia to ammonium by reacting with water molecules.

NH3+H2O→NH4++OH−

                                Ammonium is rapidly converted into nitrate at a high concentration of oxygen called nitrification. Ammonium is unstable under aerobic conditions. Nitrification is also divided into two chemical reactions. Ammonium is transformed into nitrite in the first step. Nitrosomonas are one of the transforming bacteria of ammonium to nitrate under aerobic conditions.

                2NH4++3O2 →2NO-2 +2H2O+4H+

Oxidation of nitrite is transformed into nitrate by Nitrobacter under the aerobic condition at the second step.

2NO2− +O2 →2NO3

NO-3 is relatively highly soluble in water that can be absorbed by roots of plants more easily.NO-3 can be easily leached through the soil due to the solubility.