Influence of salinity, rice straw and water regime on nitrogen fixation in paddy soils

Abstract

SummaryIn a laboratory incubation study, the effect of natural and artificial soil salinity on the soil N2fixation, nitrogenase (C2H2reduction) and N2-fixing populations was evaluated in rice soils under two water regimes. N2fixation was less pronounced in two saline soils and in a normal non-saline soil amended with salt mixture (salinity level of 4 and 30 dS/m) than in a non-saline soil under flooded and nonflooded conditions. Flooded soils amended with rice straw showed higher N2-fixing activity than the non-flooded soils at all salinity levels used in the study. Leaching the saline soil improved N2fixation. An increase in the soil salinity led to a decrease in the populations of at least three groups of N2-fixing micro-organisms. The population density of anaerobic N2fixers and Azospirillum in a saline soil increased considerably after leaching or after addition of rice straw. Azotobacter populations were little affected by the salinity levels used in this study. Results indicate that soil amelioration for salinity with leaching and organic matter addition would improve the implicated microbial populations and N2fixation in salt-affected rice soils.