CONCURRENT OBSERVATION OF SEVERAL PROCESSES OF NITROGEN-METABOLISM IN SOIL AMENDED WITH ORGANIC MATERIALS .2. EFFECT OF FARMYARD MANURE ON AMMONIFICATION, NITRIFICATION, DENITRIFICATION, AND N-2 FIXATION AT DIFFERENT LEVELS OF SOIL-MOISTURE

Under different moisture conditions, the concurrent processes of ammonification, nitrification, denitrification, and N2 fixation in soils treated with different levels of farmyard manure (FYM; 0, 1, 2, and 3% of soil dry weight) were analyzed. All the four processes occurred readily only under moisture conditions corresponding to 60% of maximum water-holding capacity (MWHC), and were stimulated by FYM application, whereby anaerobicity was induced by the marked increase of the respiration activity. At moisture levels higher or lower than 60% MWHC, some of the processes were suppressed. Denitrification was prevented when the MWHC was less than 60%, while the nitrification was suppressed at 100% MWHC and under flooded conditions. The application of 1% FYM resulted in a substantial decrease of the ratios of denitrification to N2 fixation, irrespective of the moisture levels, and the ratios increased with the increase of the levels of FYM. In each FYM application, the value of the ratio of denitrification to N2 fixation was the highest at moisture levels of 60% or 100% MWHC.