| The problem of non-point pollution is getting worse and biodiversity has declined in farmland in Erhai watershed. These caused by unreasonable cropping patterns and excessive fertilizer input. The research studied configuration of root system, distribution of plant type, demand regulations of nitrogen and phosphorus, economic benefits and environmental risks, A cropping pattern of minimizing low pollution was constructed based on economic feasibility, mutual promoting interspecific relationship, environmental friendly by survey and field experiments, and further research patterns of mutual competition among crops mechanism. Through improving useful efficiencies of nitrogen and phosphorus, reducing loss risk of nitrogen and phosphorus from farmland, non-point pollution of farmland could be controlled. It is important to improve water quality and control further development of eutrophication in Erhai Lake. The major results are as follows:(1) Balance and accumulative characteristics of nutrients in farmland. There are nutrients surplus in all cropping systems and have big differences in northern Erhai Lake. Input amount of fertilizers in rice-garlic rotation system is highest in northern Erhai Lake. The corresponding nutrients surplus, residual amount of nitrate and ammonium nitrogen in soil are notable higher than in rice-legume, rice-cereal. rice-oil crops and rice-pasture rotation systems. Thus, Optimization of cropping systems and nutrient balance regulation should be kept in order to gain high nutrients use efficiencies and low pollution risk. (2) The risk of nitrogen and phosphorus loss from farmland. Water from farmland could increase water volume in ditch and both clearly vary. Nitrogen content in farmland water and nitrogen loss in rice-garlic rotation system was highest in northern Erhai Lake. Furthermore, relationship between loss and rate of nitrogen is markedly positive. Fertilization is one of major factors accelerating the risk of nitrogen loss with form of soluble nitrogen and phosphorus with form of sand-bound state.(3) Screening environment-friendly cropping system. Using Fuzzy Comprehensive Assessment, Photosynthesis, heat, water, nutrients use efficiencies and properties, yield and quality of crops are emphasized through whole screening process. The results showed that total scores for vicia fava and garlic intercropping systems is highest (0.70) in 14 cropping patterns, the cropping system is a environment-friendly cropping pattern based on evaluation of economic and environment. The band area of garlic was three times more than vicia faba.(4) Ecological and economic benefits in environmental-friendly cropping pattern. There are increases of dry matter accumulation and radiation use efficiency at later stage and chlorophyll content in garlic of vicia fava and garlic intercropping system. Root of garlic and vicia fava grow more deeply than monoculture. Quantity and weight of rhizobium are increased leading to fixing nitrogen. There has an intercropping advantage in yield than monoculture. Land equivalent ratio is 1.15. Nitrogen absorption and utilization of garlic and vicia fava were promoted contributing to decrease of residual nitrate in soil. Comparing to monoculture of garlic, decrease of residual nitrogen is more 10% than optional fertilization, while decrease of residual nitrogen is more 50% than conventional fertilization. Therefore, the garlic and vicia fava intercropping can reduce the loss of nitrogen and phosphorus from farmland.(5) Content of microbial biomass C and N were influenced by environment-friendly cropping pattern, Compared with monoculture, intercropping could increase microbial carbon and nitrogen. Content of microbial carbon of soil gradually decreasing with soil depth increased;content of microbial nitrogen of soil gradually decreasing with soil depth increased in intercropping patterns. But Content of microbial nitrogen of monoculture patterns (GM and FM) had no significant difference among different layers of soil. The microbial biomass nitrogen of converge bands and vicia fava bands had no significant difference in 0-20cm soil layer in intercropping patterns, but they both were significantly higher than garlic bands. The microbial biomass nitrogen in converge bands was the highest and in vicia fava was the lowest. Microbial biomass nitrogen in three bands had significant differences in 20-40cm soil layer. The microbial carbon in 20-40cm soil layer in converge bands was significantly higher than in garlic and vicia fava bands. The ratios of SMB-C/SMB-N were no significant different among the different cropping patterns, but the ratios of SMB-C/SMB-N were significant different in different soil layer. The ratios were gradual reduced with soil depth. In addition, the present study showed that a positive relationship between content of total nitrogen and Olsen-P and microbial carbon and nitrogen exited.(6) Utility and transition of nitrogen in environment-friendly cropping pattern. Residual nitrogen in soil accounts for a major part of nitrogen applied. In some extent, intercropping could promote nitrogen use efficiency by more than 6.54%. decease residue of nitrogen by 6.74%, and decease loss of nitrogen by more than 3.06%. The amount of residue nitrogen decreases with depth of soil. Content of residual nitrogen in soil are deferent among various cropping patterns. Monoculture garlic has a highest content of residual nitrogen in soil in all cropping patterns and intercropping of garlic and vicia fava lowest. Nitrogen use efficiency in garlic and vicia fava intercropping is notable higher than in monoculture garlic. Nitrogen could be transferred from vicia fava to garlic. Furthermore, the amount of nitrogen relocation has a marked difference in cropping systems, with the amount between 10.18% and 15.76% of nitrogen applied.
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