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

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 de- creased in the rhizosphere soils compared with in the bulk soils （P〈0.05）. The contents of non-occluded P, oc- cluded P and residuaI-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 cal- careous soils may increase Po and calcium phosphate fractions in the rhizosphere soils, and calcium phosphate fraction is potentially available to crops.

Effects of sugarcane residue biochar and P fertilizer on P availability and its fractions in a calcareous clay loam soil

Biochar has the potential to affect the cycle of phosphorus(P),but the underlying mechanisms of its effects remain poorly understood in calcareous soils.Our understanding of the effects of biochar is limited in calcareous soils during incubation.Therefore,this study was conducted to investigate how the availability and mineral fractions of P change after the addition of combined biochar and P fertilizer during incubation in calcareous soil.Sugarcane residue(raw SR)and biochar(400℃for 2 h)were added to soils treated with 50 mg kg−1 of P,in the form of Ca(H_(2)PO_(4))_(2)·H_(2)O,at 0.5 and 1%(w/w).The soils were incubated at 25±1℃for 120 days.Available P(Olsen P)contents and mineral P fractions were measured after various incubation times(7,30,90,and 120 days).Biochar addition remarkably increased the amount of available P when compared with the raw SR treatment and the control condition(P<0.05).After 30 days of incubation,the amount of available P in the soils decreased and remained unchanged thereafter.The results indicated that the addition of 50 mg kg−1 of P as fertilizer significantly augmented the labile P and P associated with Fe and Al in all the treatments at all incubation times(P<0.05).In comparison with P treated with raw SR,P associated with Fe and Al was significantly enhanced after biochar addition(P<0.05).Significant correlations were found for available P with labile P and P associated with Fe and Al.We found that biochar addition could increase available pools,thus improving available P concentrations at various incubation times.Therefore,we conclude that sugarcane residue biochar can enhance the available P in calcareous soils.