Concurrent Observation of Several Processes of Nitrogen Metabolism in Soil Amended with Organic Materials : V. Effects of Long-Term Application of Farmyard Manure and Nitrogen Fertilizer on N Cycling Processes in Upland Field Soil

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In upland field experiments, concurrent ammonification of organic N and resultant nitrification processes were observed in farmyard manure (FYM)-treated plots. The applied N-fertilizer (urea) was hydrolyzed to NH_4-N and subsequently nitrified resulting in pulsed inputs of NH_4-N and NO_3-N in soil, which affected the denitrification and N_2 fixation processes. The actual denitrification process was not substantial except for the short period following the simultaneous application of FYM and urea. At this time, the level of NO_3-N in soils was high together with the large number of denitrifiers. The denitrification rates increased ranging from 1.00 to 3.56 kg N_2O-N/ha/d by the application of FYM. The positive effect of the long-term application of FYM on N_2 fixation was observed within the application rate of 20 t FYM/ha, although a larger number of N_2 fixers was observed with higher application rates. The maximum rates of N_2 fixation ranged from 13.0 to 21.0 g N_2-N/ha/d. In the control plot the fixation was less than 9.0 g N_2-N/ha/d. N_2 fixation was inhibited by the pulsed input of NH_4-N in soil originating from urea, as anticipated, but the inhibitory effect lasted for an unexpectedly long period of time, even when the NH_4-N level in soil decreased to the original low level. The number of N_2 fixers also decreased by the application of urea.
社団法人日本土壌肥料学会の論文