Influence of different application rates of nitrogen to soil on rhizosphere bacteria.

Abstract

The bacterial populations in the rhizosphere of wheat were investigated under different soil nitrogen regimes. Two different levels of nitrogen (250 and 50 mg N per plant) were added as a single application or split in time during growth, and consequently smaller amounts were given each time. The different application methods enabled the study of the bacterial populations in relation to nitrogen concentrations in the roots and in the soil with comparable rates of plant biomass production. When the nitrogen was applied as a single dose at the start of the experiment significantly larger numbers of bacteria (colony forming units) were found in the rhizosphere than in the other treatments. This was correlated with higher nitrogen concentrations in the roots and with higher levels of extractable mineral nitrogen in the soil. In contrast, the numbers of fluorescent pseudomonads were smaller when a high nitrogen rate was applied once. Possible mechanisms for the observed changes in the microbial populations are discussed. (Abstract retrieved from CAB Abstracts by CABI’s permission)