THE FIELD EXPERIMENTS ON THE FIELD-RESPONCE OF CROPS TO WATER AND FERTILITY IN THE SOUTH OF THE LOESS PLATEAU
Li Yushan, Zhang Xiaozhong and Guo Minhang (Northwestern Institute of Soil and Water Conservation, Academia Sinica)
The field experiments were conducted on dryland of Changwu high-land in 1985 and 1986.Grain yield, water requirements and consumptions for wheat and corn, the changes in moisture storage down to a depth of 2—3m. were measured. Data of field experiments showed that there was insignificant difference at 5 per cent level for grain yield among different treatments of water supply and there was extreme significance at 1 per cent level among different tretments of fertilization under any level of water supply. It can be concluded that the balance between requirement and supply of water has been approxmately reached in the experimental region and the primary constraint for crop yield at present is poor fertility, not water deficit.Analysis of water balance on cropland showed that satisfection ratio of water supply was 90.4—100% for wheat and 83.7—100% for corn in experimental years. Water supply of 200 mm to wheat was from soil water storage over whole growing period and more than 200 mm to corn in the period of summer drought or autumn drought. The change of soil moisture in soil profile down to a depth of 3 m. at harvesting period were studied. lt seems that soil moisture higher than permanent wilting percentage is readily available.