Influence of bean rhizosphere on the biological properties and phosphorus fractionation in the calcareous soils amended with municipal sewage sludge

Abstract

The biological and chemical conditions of the rhizosphere are known to considerably differ from those of the bulk soil, as a consequence of a range of processes that are induced either directly by the activity of plant roots or indirectly by the stimulation of microbial population and activity in the rhizosphere. Information about phosphorus (P) fractionation in the rhizosphere soils amended with municipal sewage sludge (MSS) is limited. were We carried out greenhouse experiments using a rhizobox in order to evaluate the effects of bean rhizosphere on the various inorganic P (Pi) fractions, organic P (Po), P in particulate fraction (PF-P), Olsen-P, dissolved organic C (DOC), microbial biomass P (MBP) and alkaline phosphatase (ALP) enzyme in 10 calcareous soils amended with MSS (10 g MSS was added to 1 kg soil). Non-occluded P, occluded P, calcium phosphate and residual P were also quantitated. The results showed that DOC, MBP and ALP activity strongly increased and PF-P and Olsen-P decreased in the rhizosphere soils compared with in the bulk soils (P<0.05). The contents of non-occluded P, occluded P and residual-P fractions in the rhizosphere soils were lower than in the bulk soils, while the contents of calcium phosphate and organic P in the rhizosphere soils were higher than in the bulk soils. Simple correlation coefficients showed that P uptake had positive relationship with non-occluded P, occluded P, calcium phosphate fractions and PF-P in the rhizosphere soils. The results suggest that the short-term application of MSS to the calcareous soils may increase Po and calcium phosphate fractions in the rhizosphere soils, and calcium phosphate fraction is potentially available to crops.