(a) State three ways by which nitrogen is added to soil in the Nitrogen cycle.
(b) List five ways by which nitrogen is lost from the soil.
(c) State the importance of the Nitrogen cycle.
(d) Explain three processes leading to the formation of nitrate from organic matter in the Nitrogen cycle.
Explanation
(a) Ways by which Nitrogen is added to the soil in the Nitrogen cycle: (i) Direct fixation by lightening during rainfall. (ii) Incorporation into the soil by free living bacteria/non-symbiotic bacteria. (iii) Nitrogen fixing bacteria in root nodules/biotic nitrogen fixation by rhizobium spp. (iv) Decomposing organic matter. (v) Application of nitrogenous fertilizer. (vi) Ammonification. (vii) Nitrification.
(b) Ways by which soil Nitrogen is lost from the soil: (i) Bush burning. (ii) Leaching. (iii) Crop removal. (iv) Erosion of top soil. (v) Denitrification. (vi) Volatilisation. (vii) Oxidation reaction. (viii) Reduction reaction.
(c) The importance of the nitrogen cycle: It is the nature's way of regulating the amount of nitrogen in the soil and air.
(d) Explanation of the processes involved in the formation of nitrate from organic matter in the nitrogen cycle: (i) Putrefaction. (ii) Amminization. (iii) Ammonification/mineralisation. (iv) Nitrification. Putrefaction: Decay of plant and animal remains into simpler nitrogenous compounds by micro-organisms. Amminization: Products from putrefactions reaction converted to simple amino compounds and amines. Ammonification: Conversion of amino compounds and amines into ammonium (NH4+) compounds. Nitrification: Oxidation of ammonium compounds into nitrites and nitrates.