Induction of aerobic nitrogen fixation and enhancement of wheat straw decomposition by inoculation with a crude culture from sugarcane litter

Abstract

Addition of an aerobic N 2-fixing crude culture from sugarcane litter to wheat straw with or without the indigenous wheat microflora resulted in gains of up to 6.6 mg N g −1 original straw (equivalent to 33 kg N fixed ha −1 for 5 t ha −1 straw crop). Peak N 2 fixation (C 2H 2 reduction assay) preceded peak CO 2 evolution. Microbial biomass N increased concurrently with N gain. In contrast, when straw was inoculated with the indigenous wheat microflora alone, there was no N gain and there was little change in microbial biomass N. Weight loss of straw 60 days after it had been inoculated with the crude cane culture plus the indigenous wheat microflora was 2.6–3.2 times the weight loss of straw inoculated with the indigenous wheat microflora alone. Addition of small amounts of N (0.51 mg N g −1 straw, as ammonium sulphate or as fungal N) to straw inoculated with the crude cane culture increased N 2 fixation and straw weight loss. Addition of large amounts of N (4.5 and 8.5 mg N g −1 straw) to the crude cane culture in straw suppressed N 2 fixation and weight loss of straw was less than when no N was added.