Activities of rhizosphere microorganisms as affected by application of organic amendments in a calcareous loamy soil. 2. Nitrogen transformations

Abstract

The activities of some nitrogen transforming microorganisms in the rhizosphere of both alfalfa and wheat growing in a calcareous loamy soil of Saudi Arabia as affected by organic amendments have been studied in a greenhouse experiment. The organic amendments were sludge (narrow C/N ratio) and wheat straw (wide C/N ratio), applied at 2% w/w to the soil. The asymbiotic nitrogen fixers, either aerobic or anaerobic, as well as the nitrifying bacteria, were determined in the rhizosphere and nonrhizosphere soils periodically for 7 weeks. Total nitrogen, organic carbon, ammonium, and nitrate nitrogen were determined in the same samples. Results showed that treatment of the calcareous loamy soil with organic amendments significantly enhanced the microbial population transforming nitrogen (asymbiotic N2 fixers and nitrifying bacteria) in the rhizosphere and nonrhizosphere soils of both plants with high values for the former during most of the experimental periods. However, the rhizosphere effect was not obvious in...