Effects of summer fallow in Guanzhong irrigation area

Field trials were carried out to study the effects of summer fallow on water storage and NO^-₃-N accumulation in soil profile and the following crops.The results showed that the storage effect of water in the period of summer fallow was related to the precipitation.The NO^-₃-N accumulated in the soil profile increased significantly during the period of summer fallow,and the distribution of accumulative NO^-₃-N changed with the amount of precipitation during fallow period: 96.8% of NO^-₃-N was accumulated in the 0～80cm soil layer and 8.2 percentage in the 80～120cm slil layer in 1993 with lower precipitation,but 57.1 in the 0～80cm soil layer and 42.9 in the 80～120cm soil layer in 1992 with higher precipitation.After fallow,the crop yield and N uptake were significantly higher than that of the crop in succession.In the total cycle of crop rotation,the total grain and above-ground yields of three crops without fallow were almost the same as that of two crops after fallow.