Exploitation And Utilization Of Summer Fallow Farmland On Main River Valley Areas In Tibet

Tibet is a rigorous region of limited natural resources and poor agricultural productive conditions in China, with severe problems of lower productive level and fragile ecosystem on farmland, as well as forage grass shortage for animal husbandry in agricultural area. Through development of multiple cropping to exploit the sunlight resources, thermal resources, water resources and soil resources of farmland in summer fallow period is very helpful for improvement of soil fertility and to prevent field ecosystem degradation, and can increase forage for animal raising of the region to realize combination of farming and grazing, and also can increase economic incomes of farmers. The 14 counties of Lhasa and Shannan district in middle river valley areas of Tibet was taken as research region, the natural resources, economic conditions and agricultural productive level of the region were analyzed. Based on summary of development history and research progresses, the situations of thermal resources and precipitation during summer fallow period of the region were analyzed and evaluated, and the weather possibility for multiple cropping on the region was also analyzed. The crop yield and economic benefits were investigated by field experiment of several multiple cropping patterns. The main progresses and achievements of this study are as following:(1) Sunlight and water resources on river valley agricultural region of Tibet are abundance, and socioeconomic base and agricultural conditions in the region is relatively good. The thermal and rainfall resources during summer fallow period are relatively rich. It is good for exploitation of summer fallow farmland of the region. Summer fallow period (from July to September) of the region is 85-110 days, accumulated temperature in Lhasa and Shannan is 1287.9 C and 1322.5 C, rainfall is 308.2mm and 279.4mm respectively.(2) On river valley region of Tibet, average accumulated temperature of 88 multiple cropping patterns in winter wheat areas and 22 multiple cropping patterns in winter wheat and spring wheat mixed planting areas is 3475.1 C and 2778.7 C separately. Average accumulated temperature over zero degree in Lhasa and Shannan district is 2914.8 C and 3117.1 C respectively. The thermal resources of 14 counties in the region could basically meet demand of multiple cropping to exploit summer fallow farmland, accordingly. The counties with high temperature in Shannan district could use sequential cropping and warm demand crops, and counties with low temperature in Lhasa district could use relay-inter cropping and transplanting, and choose cool demand crops, and use double cropping with green manure, forage crops and vegetables.(3) On river valley region of Tibet, average water requirement of multiple cropping patterns based on winter crops and spring crops are 636 mm and 528 mm respectively. Average annual rainfall in Lhasa and Shannan districts is 425mm and 537mm separately. Rainfall shortage in both districts can not meet water requirement of multiple cropping. But predominant irrigation conditions on the river valley areas in Tibet can provide good guarantee for water requirement of multiple cropping.(4) Results of field experiments for summer fallow farmland exploitation in the river valley areas in 2006 showed that, the optimum cropping ratio of winter wheat intercropping common vetch in Lhasa wais 66%:33%; spring barley intercropping maize was an optimum cropping patterns in spring barley intercropping maize, potato and common vetch in Lhasa and Shannan. But spring barley intercropping common vetch had higher economic value in three cropping patterns in Shannan district. Forage yield of sole cropping is higher than intercropping with grain crops.