INFLUENCE OF THE NITROGEN-CONTENT OF STRAW AMENDMENTS ON NITROGENASE ACTIVITY IN WATERLOGGED SOIL

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 C2H2 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 N2(C2H2) fixation and the increase was highly significantly correlated (r = 0.80) with the water-soluble N content of the straw. Incorporation of NH4 + and NO3 - in amounts equivalent to those present in the original straw delayed the onset of nitrogenase activity but did not significantly affect the amount of N2(C2H2) fixation in soil amended with the water-insoluble fraction of straw. However, when the water-soluble fraction was added with the water-insoluble fraction, N2(C2H2) fixation was suppressed. © 1979.