| Studies on chemical transformation and translocation of phosphorous in soil and its availability to crops have been permanent research topics in soil and plant nutrition science since phosphorous is distinguished to be one of the essential macro nutrients for plant growth. With an increasing concern on environmental issues in recent years, phosphorous as a key chemical element for eutrophication control has been focused by more and more environmentalists. From viewpoint of both high efficient use of resources and environment protection, it is of great significance to increase utilization of phosphorous by plants, decrease phosphorous accumulation in soil and reduce phosphorous loss from soil.Based on a review of research development on chemical behaviors of phosphorous in soil and its cycling in agroecosystem, this dissertation dealt with chemical fractions, transformation and cycling of phosphorous in red soil and paddy soil of subtropics in central China, using techniques of laboratory incubation, field investigation and field experiments. Research aspects contained effects of organic material and phosphate addition on transformation of microbial biomass P and inorganic P fractions in red soil and paddy soil, effects of different fertilizer treatments, paddy-upland rotation and changes of groundwater level on microbial biomass P, inorganic P fractions and its availability to crops, as well as distribution, inorganic fractions and cycling of phosphorous in an alluvial plain etc. Emphasis was focused on the relation of changes of microbial biomass P to inorganic P transformation in soil. The main results were showed as follows:(1) Incubation experiment by using the paddy soil developed from Quaternary red soil showed that total inorganic P in paddy soil with organic materials addition(glocuse and rice straw) significantly decreased compared to the control without organic materials addition, where the decrease of total inorganic P was dominantly caused by release of iron phosphate (Fe-P) . On the other hand, soil microbial biomass P was significantly raised by organic materials addition. So it was suggested that possibly phosphorous immobilization mediated by soil microorganisms resulted in the release of phosphorous fixed by soil inorganic particles.(2) Incubation experiment by using the upland red soil derived from Quaternary red clay indicated that total inorganic P in red soil was also significantly reduced and microbial biomass P was markedly raised by glucose addition. What was different from the case in paddy soil was that total inorganic P decrease was dominated by Al-Pdecrease, accounting for more than 60% of total inorganic P decrease. Following 60 days incubation, almost all the phosphate added into the soil in the treatment cf single phosphate addition was transformed into inorganic P forms fixed by the soil minerals. However, in the treatment of phosphate combined with glocuse addition, only 46.5% of applied phosphate was transformed into inorganic P forms fixed by soil inorganic minerals and 53.5% of that was transformed into other forms of phosphorous non-fixed by soil inorganic minerals such as microbial biomass P. It was assumed that addition of organic carbon into upland red soil stimulated the transformation of applied phosphate into microbial biomass P and other forms of phosphorous non-fixed by inorganic minerals, and possibly reduced the fixation of applied phosphaU by soil inorganic minerals.(3) Long-term field experiments proved that microbial biomass P in pacdy soils were greatly raised by long-term application of organic manure combinsd with chemical fertilizer, otherwise, there were minor or no increase of microbial bi Dmass P in paddy soils under the condition of long-term application of single chemical fertilizer. Both Al-P and Fe-P as a percentage of the total inorganic P presented an increase tendency and O-P as a percentage of the total inorganic P showed a decrease tendency in all the treatments with organic manure application. Thus, it was concluded that organic m...
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