Nitrogen fixation and denitrifying activity of a grey forest soil and transformation of nitrogen with application of nitrogenous fertilizers
Umarov, M.M.; Shabaev, V.P.; Stepanov, A.L.; Solov' ev, G.A.; Bolysheva, T.N.
Agrokhimiya (2): 3-10
ISSN/ISBN: 0002-1881 Accession: 002905903
In 2-year experiments in Russia using lysimetric containers a study was made of the effect of different forms and doses of 15N nitrogen fertilizers applied to soil under barley and timothy grass [Phleum pratense]. Nitrogen-fixing activity in the rhizosphere began with germination and reached a maximum in the heading and milky-ripeness phases, subsequently declining little if at all before the end of the vegetative period. Mineral nitrogen fertilizers inhibited the nitrogen-fixing activity of the soil only in the initial phases of plant development (germination to heading); the inhibitory effect was particularly marked at high doses. In the following phases and up to the harvest, even with application of high doses the associative nitrogen-fixing activity in the fertilized variants was equal to or even exceeded that in the non-nitrogen variant owing to better development of the plants. The denitrifying activity of the soil increased from germination and was maximal in the period from stem elongation to heading and had appreciably decreased by the harvest. Application of nitrogen fertilizers led to an increase in the denitrifying activity of the soil at all development phases. The magnitude of nitrogen volatilization from the soil, and the volatilization of fertilizer 15N, increased with increasing fertilizer dose. Volatilization of fertilizer nitrogen accounted for 70-100% of total losses from the soil. The effectiveness of nitrogen fertilizers and their influence on the amounts of nitrogen additionally taken up by the plants depend to a considerable extent on the ability of the soil to provide the plants with nitrogen and on the level of nitrogen fixation and denitrification processes in the soil.