Concurrent observation of several processes of nitrogen metabolism in soil amended with organic materials

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Abstract
The effects of the amendment of organic materials (OM) such as rice straw (RS, C/N = 52) and farmyard manure (FYM, C/N = 14), and application of N fertilizer (NH4-N) to soil on the numbers of total bacteria, denitrifiers, and N2 fixers were investigated under upland conditions (60% maximum water-holding capacity and looded conditions). At the same time the rates of the concurrent processes of ammonification, nitrification, denitrification., and asymbiotic N2 fixation were determined. The number of total bacteria was not significantly different between upland and flooded conditions. It was interesting to note that the number of denitrifiers under upland conditions was equivalent to or sometimes larger than that under flooded conditions and the number of anaerobic N2 fixers was equivalent to or sometimes larger than that of the aerobic ones. All the microbial populations increased by the OM amendment, while the application of N fertilizer did not consistently result in their increase. The number of denitrifiers did not necessarily determine the actual level of denitrification and the number of N2 fixers was not consistently correlated with the N2 fixing activity. The simultaneous application of OM (RS, FYM) and N fertilizer (NH4-N) to soil under upland conditions increased the number of denitrifiers and induced the denitrification process, while it significantly depressed the N2 fixation activity, though this practice also increased the number of N2 fixers.