Research On Microbial Transformation Of Phosphorus And Its Effectiveness In Upland And Paddy Red Soils

Most of the phosphorus (P) in the red soils were usually associated with kaolinite, the oxides and hydrous oxides of iron (Fe) and aluminum (Al), so that the validity of soil phosphorus and the utilizing efficiency of phosphate fertilizer are very low. Soil microorganisms play an important role in the transformation of soil organic matter and soil nutrients (such as C, N, P, S, ect.). Researches on the mechanisms of soil phosphorus transformation and the functional microorganisms which involving in the soil phosphorus transformation can provide a theory reference for the effective usage and management of phosphorus in red soils. To know better the mechanisms in which organic amendment induced the microbial transformation of P in upland and paddy red soils, responses of culturable microbial diversity and changes in the microbial biomass C (MB-C) and P (MB-P), Olsen-P, adsorbed inorganic and organic P fractions were investigated using a series of long-term field trials in Hunan, China. The main results were summarized as follows:i)The data obtained from a 45-day incubation experiment showed that, compared with the treatment of control, the amount of culturable bacteria and fungi in the soil amended with rice straw were increased by 271.4%～518.8% and 2900%～3608% respectively, during the incubation period of upland soil, the treatment of both rice straw and fungal inhibitor (actidione) increased the amount of culturable bacteria by 34.1%～81.4% compared to the rice straw. In the treatments of rice straw and bacterial inhibitors (tetracycline and streptomycin sulphate), the amount of culturable bacteria decreased by 14.3%～43.48% compared to the rice straw, however, the amount of culturable fungi increased by17.1%～37.6%. During the incubation period of the flooded paddy soil, the amount of culturable bacteria increased by 115.3%～362.2% in the treatment of rice straw application, whereas the amount of culturable fungi decreased by 5.8%～27.8%, compared to the control (without rice straw amendment). The amount of culturable bacteria decreased by 39.0%～76.2% in the treatment of rice straw and bacterial inhibitors compared to the treatment with rice straw only.ii) Throughout the 45-day incubation period, the addition of rice straw significantly increased the amounts of MB-C and MB-P by 187.5%～193.1% and 135.8%～148.7%, respectively, in the upland soil, and increased the amounts of Olsen-P by 27.5%～32.9%. Whereas in paddy soil, the addition of rice straw increased the amounts of MB-C, and MB-P often changed in the incubation period, but also increased the amounts of Olsen-P by 16.0%～21.2%.iii) At the end of 45-day incubation period, the treatment of rice straw increased the amounts of Fe- and Al-bound P and total inorganophosphorus significantly in upland soil, and increased the amounts of LOP, MLOP, MSOP and total organophosphorus. The treatment of rice straw increased the amounts of Fe-bound P, LOP and total organo- phosphorus in paddy soil, and decreased the mount of Ca-bound P.iv) Moreover, both of the fungal and bacterial groups taken part in the microbial transformation of P in upland and paddy red soils, but the fungal group made a relatively larger contribution in upland soil, and in paddy soil the role may be played by the bacteria..