The influence of the wheat rhizosphere on phosphorus desorption kinetics in calcareous soils amended with municipal sewage sludge

Abstract

Plant growth in arid environments is limited by phosphorus (P) availability because of the low concentration of P in the soil solution. In addition, soil processes in the rhizosphere affect the mineral nutrition of plants. Thus, greenhouse and laboratory experiments were conducted to evaluate the effects of the wheat rhizosphere on P desorption kinetics in 10 calcareous soils amended with municipal sewage sludge (MSS) investigated in a rhizobox. The kinetics of P desorption in the bulk and the rhizosphere soils were determined by successive extraction with 0.5 M NaHCO3 in a period of 2 to 840 h at 25 ± 1 °C. In addition, available P, P in the soil particulate fraction (PF; >53 μm), microbial biomass carbon (MBC), alkaline phosphatase (ALP) and dissolved organic carbon (DOC) were determined. Available P and PF-P decreased whereas DOC, ALP and MBC increased in the rhizosphere soil compared with those of the bulk soil. The results of the kinetics study showed that the mean of desorbed P in the rhizosphere soil was higher than that of the bulk soil. Desorption kinetics of P from the rhizosphere and the bulk soils conformed reasonably well to simplified Elovich and power function models. The results of this research indicated that the wheat rhizosphere modified the P desorption characteristics and the cumulative P desorbed after 840 h from the rhizosphere and bulk soils could be a suitable method for practical use to express the available P in calcareous soils amended with MSS.