| Excess application of chemical fertilizers has resulted in widespread environmental problems, such as degeneration of soil fertility and pollution of soils and waters, which restrict seriously the sustainable development of agricuture and society. In this study, field experiments were carried out to investigate the effects of different fertilizer application modes on crop yield, nutrient uptake, soil enzyme activity, number of microbes (bacteria, actinomycetes and fungi), and diversity of microbes in rice(Oryza sativa L.)-wheat (Triticum aestivum L.) rotation system. Furthermore, soil pot experiments were employed to investigate the effects of different P fertilizer resources on soil P forms and phytase activity. In addition, the phytase activity and its distribution in the sediments of Liangzhi Lake and Yue Lake and in the soils around were investigated. The main results were summaried as follows:(1) The effects of N fertilization modes on crop yield, nutrient uptake, soil enzyme activity, and number of microbes as well as diversity of microbes were studied under a2-year field experiment of rice-wheat rotation. The result showed that20%reduction of local farmer's traditional N fertilizer did not change significantly crop yield, N uptake, soil enzyme activity and number of microbes (bacteria, actinomycetes and fungi). On the basis of20%reducing N fertilizer,50%replacement of N fertilizer by organic manure increased the activity of sucrose, protease, urease and phosphatase by46%-62%,27%-89%,33%-46%, and35%-74%respectively, and the number of microbes, i.e. bacteria, actinomycetes and fungi by36%-150%,11%-153%and43%-56%respectively. Additionally, organic fertilizer replacement had a Shannon's diversity index (H) of2.18, which was higher than that of other modes of single N fertilizer application. The result suggested that reducing N fertilizer by20%and applying organic manure in the experimental areas could effectively lower the production costs and improve significantly soil fertility and biological properties.(2) The effects of different Slow-Released (SR) fertilizer application modes on soil enzyme activity and soil microbes as well as the microbial diversity were investigated in rice-wheat cropping system. The results showed that, in comparison with no N control group, four SR N fertilizer application modes increased the soil enzyme activity and the number of soil microbes significantly in both wheat and rice soils. Compared to pure Urea application mode, the soil enzyme activity was higher and the number of soil microbes was greater in other three SRF modes (SR-Urea, SR-Urea/Urea, SR-Urea/Urea/Org.N). Particularly in SR-Urea/Urea/Org.N mode, the activity of sucrase, protease, and urease were increased by5%-38%,4%-15%, and2%-5%respectively, and the number of soil bacteria, actinomycetes, fungi were increased by9%-27%,3%-14%,13%-28%respectively. In addition, compared with Urea control group, nutrient uptake of wheat and rice, microbial diversity index (Shannon's diversity index) of SR-Urea/Urea/Org.N mode was increased by13%-26%,10%-16%,15%-103%respectively. The results indicated that combined application of SRF and organic manures was a good precaution to improve the soil biological properties and soil fertility in rice-wheat cropping system.(3) Different P fertilizer application modes were studied for the effects on crop yield, nutrient uptake, soil enzyme activity, number of microbes, and diversity of microbes under the rice-wheat rotation system. The result showed that20%reduction of traditional application amount of P fertilizer did not decrease crop yield, amount of nutrient uptake, soil enzyme activity, and the number of soil microbes. However,20%reduction the P applied and mixed application of organic manure and chemical P fertilizer increased not only the activity of phosphatase, sucrase, protease and urease, but also the number of soil microbes, as well as the Shannon's microbial diversity index (H), although it had no impacts on crop yield and nutrient uptake. The results indicated that A20%reduction of P fertilizer could be a possible agricultural measure for reducing farmland pollution, and the combined application of organic manure and chemical P fertilizer could be recommended for improving soil fertility in the study areas.(4) Soil pot experiments were carried out to investigate the effects of different P fertilizer resources on soil P forms and phytase activity. The result showed that, compared with superphosphate, the application of organic manure and calcium phytate increased rice yield by9%-18%and15%-32%respectively. Application of calcium phytate increased the phytase activity by16%-20%, the ratio of labile organic phosphorus by73%-117%, and the ratio of Al-P, and Fe-P by15%-46%.(5) The ecological effects of soil phytase activity and the input history of phosphorus in soil sediment were investigated around the areas of Liangzhihu Lake. The results indicated that phytase activity in the lake sediments decreased with the sampling depth, with the reduced percentages at2m of the sediment profile being74%for Liangzi Lake, and66%for Yue Lake respectively. However, opposite situation was found in water inlet of lake, ie, phytase activity in the lower sediment was73%-108%higher than the surface sediment. In farmland of Hubei Academy of Agricultural Sciences(NKY), phytase activity of soil reached the crest value at0.5m depth(271.4U/g), and then decreased with the sampling depth, phytase activity was lowest in the soil with2.0m depth(127.6U/g). The same result was found in farmland of Heshengqiao district in Hubei Province(HSQ), phytase activity of soil reached the highest bracket at0.2m depth(373.6U/g), was lowest in the soil with2.0m depth(127.6U/g). Phytase activity of soil in East-West-Lake district in Wuhan City(DXH) was decreased with the sampling depth in (0-1.0m,1.0-1.9m,2-2.5m), respectively. The results indicated that, compared with submerged soil, phytase activity in the rhizosphere soil was higher.
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