| Phosphorus?P?is an essential element for plant growth,but the available P is widely deficient in the global arable land,and the supply of soil available P has become a major limiting factor on global agricultural production.Increasing the content of available P by applying chemical fertilizer is the most common and effective method today,but the available P is easily fixed by the soil.The utilization rate of phosphate fertilizer is only 10%to 25%in the current season,and low utilization rate of phosphate fertilizer has increased the agricultural expenditures,accelerated the depletion of phosphate rock resources in China.At the same time,soil P accumulation caused by over-application of phosphate fertilizers will lead to huge risks for the safety of ecological environment.Therefore,improving the availability and activity of soil P is the key to solving the problem.Vermicompost is a kind of green ecological organic fertilizer and soil amendment which produced by organic waste fermentation and the enzymatic action of earthworm's digestive system,it is clearly distinguished from ordinary composts in physical,chemical and biological properties,and has been widely studied in various fields in recent years.In this study,the representative vegetable cabbage?Brassica chinensis L.?in Guangdong Province was used as the experimental plant,a pot experiment and a field experiment were carried out to analyze the changes of plant biomass,water soluble Fe???,hydrochloric acid extractable Fe???,soil microorganisms and P forms etc under the application of vermicompost,and study the effects and mechanism of vermicompost application on P mobilization in paddy soils.The study are expected to provide a scientific theoretical basis for improving the utilization rate of phosphate fertilizer in cultivated land and protect cultivated land resources.The results indicated that:?1?The application of vermicompost significantly increased the microbial biomass content and the storage of phosphorus by microorganisms in both the bulk and rhizosphere soil,and the microbial biomass C/P ratio in rhizosphere soil was 1.9to 2.0 times higher than that in bulk soil in all the treatments.Compared with CK,vermicompost application significantly increased acid phosphatase activity and the contents of Olsen-P and various P species in soil.Moderately stable organic P?NaOH-Po?had a significantly negative correlation with both microbial biomass P and acid phosphatase activity in all vermicompost treatments.These results indicated that:vermicompost application significantly increased acid phosphatase activity and NaOH-Po content,and drove forward the P fixation by soil microorganisms while effectively promoted the activation of NaOH-Po,and microbial biomass P or P fixation by microorganisms was higher in bulk soil than in rhizosphere soil.?2?In A2(80 g·kg-1)and A3(120 g·kg-1),microbial biomass P had a significantly negative correlation with labile organic P?NaHCO3-Po?.NaHCO3-Po had a significantly positive correlation with NaOH-Po,and stable organic P?C.HCl-Po?had a significantly negative correlation with both NaOH-Po and NaHCO3-Po.These results indicated that:While promoting the mineralization of NaOH-Po and NaHCO3-Po,vermicompost promoted the formation of C.HCl-Po as well.At the same time,C.HCl-Po had a significantly positive correlation with microbial biomass P in all vermicompost treatments.Besides,C.HCl-Po had a significantly negative correlation with both NaHCO3-Po and NaOH-Po in A2 and A3.These results indicated that Microbial biomass P promoted the formation of C.HCl-Po.?3?The application of vermicompost led the soil pH tend to be neutral or be weakly acidic,and increased the soil Eh.Vermicompost application could effectively promote the dissolution and reduction of Fe???,the results showed that hydrochloric acid extractable Fe???had a significantly negative correlation with NaHCO3-Pi and NaOH-Pi.These results indicated that vermicompost application could promote the release of NaOH-Pi by promoting iron reduction.With the exception of C.HCl-Pi,vermicompost application greatly increased the contents of various P species in soil.Particularly,the labile P?including Resin-P,NaHCO3-Pi and NaHCO3-Po?was significantly increased.Besides,Correlation analyses indicated that:NaHCO3-Pi had a significantly positive correlation with NaOH-Pi,Resin-P had a significantly positive correlation with both NaHCO3-Po and NaOH-Po.?4?On the one hand,The combination of vermicompost and fertilizer could help to produce microbial anaerobic environment through the capillary pores,and on the other hand,improve microbial aerobic environment through the non-capillary pores.The combination of vermicompost and chemical fertilizers or single application of chemical fertilizers could promote the activity of acid phosphatase and the storage of P by soil microorganisms.But,under the combined application of vermicompost and chemical fertilizers,the storage of P by soil microorganisms was much higher than that of single application of fertilizers.In addition,the lifting effect of combined application of vermicompost and chemical fertilizer on the content of labile P?including Resin-P and NaHCO3-Po?was more obvious than that of single application of fertilizer,and The combination of vermicompost and fertilizer was beneficial to reduce the production of HCl-Po relative to single application of vermicompost. |
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