Exploitation and utilization of summer fallow farmland on main river valley areas in Tibet

According to the present situation of agricultural resources and summer fallow land on mainriver valley areas in Tibet,it is climatically possible for summer fallow land to implement perennial cropping system in thermal and moisture conditions,using perennial accumulated temperature and rainfall in ten days.Lhasa and Lhoka regions locate in main field in middle river valley areas of Tibet.The analytical results show: As for the 86 types of perennial cropping patterns in winter wheat areas,the range of accumulated temperature is from 2 000℃ to 4 750℃,mean accumulated temperature is 3 475.1℃.The change of rainfall in this region is from 456 to 744 mm,average rainfall is 636 mm While there are 23 patterns in winter and spring wheat mixed planting areas,their range of accumulated temperature is from 2 050℃ to 3 850℃,mean accumulated temperature is 2 778.7℃.The change of rainfall is from 446 to 580 mm,the average rainfall is 528 mm.Results in the field experiments of this areas for summer fallow farmland in 2006 showed that the optimum cropping ratio of winter wheat intercropping common vetch in Lhasa was 66% to 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 region.Forage yield of sole cropping is higher than intercropping with grain.