Activities of rhizosphere microorganisms as affected by application of organic amendments in a calcareous loamy soil I. Carbon assimilation

Abstract

The activities of soil microorganisms in the rhizosphere (R) and nonrhizosphere (S) regions of alfalfa and wheat plants, growing in calcareous loamy soil of Saudi Arabia, as influenced by application of organic amendments such as sludge and wheat straw, were studied in pot experiments for 7 weeks. The study showed that counts of aerobic heterotrophic bacteria in the rhizosphere soil of both alfalfa and wheat plants significantly increased due to application of organic amendments accompanied by a high decomposition rate for the carbonaceous materials. Application of sludge to the soil enhanced the rhizosphere microorganisms during all experimental periods as compared with those treated with straw. Straw manure clearly enhanced the aerobic cellulose decomposing bacteria, especially in the rhizosphere region. The total mi‐crobial counts in the rhizosphere of alfalfa were generally higher than those of the wheat plants in the first and second weeks and at the end of the period, especially when sludge was appl...