Influence of the nitrogen content of straw amendments on nitrogenase activity in waterlogged soil

Abstract

The effect of the nitrogen content of barley ( Hordeum vulgare) and rape ( Brassica campestris) straw on the nitrogenase activity in waterlogged straw-amended soil was investigated in laboratory incubation experiments. Nitrogenase activity was measured with the C 2H 2 reduction assay periodically throughout the incubation of soil-straw mixtures for 34 days at 25°C and 87 days at 16°C. Suppressed nitrogenase activity in soil amended with rape straw in preliminary experiments was attributed to the high N content of the straw. Removal of the water-soluble fraction of both barley and rape straw generally increased N 2(C 2H 2) fixation and the increase was highly significantly correlated (r = 0.80) with the water-soluble N content of the straw. Incorporation of NH 4 + and NO 3 − in amounts equivalent to those present in the original straw delayed the onset of nitrogenase activity but did not significantly affect the amount of N 2(C 2H 2) fixation in soil amended with the water-insoluble fraction of straw. However, when the water-soluble fraction was added with the water-insoluble fraction, N 2(C 2H 2) fixation was suppressed.