The Long-term Monitoring Research Of Soil Nutrient And Crop Yields In The Gully Area Of The Loess Plateau

Loess Plateau is the major grain production in the Northwest of China. Poor nutrient and lack of water are the main factor that limiting the agricultural development. Chinese Academy of Sciences Changwu Agroecosystem National Field Research Station is one of the Chinese Ecosystem Research Network(CERN) that including 36 scientific research field station. Up to now, Changwu station has been monitoring nearly 30 years for long-term dynamic monitoring of meteorology, hydrology, soils, biological and agricultural economy of local. In this study, explore the response of soil nutrients and biology to the different fertilization and different terrain conditions by field sampling, investigations and research analysis; and explore the water use efficiency and soil moisture changes in the different type of rainfall to investigate the relationship among nutrients, moisture and crop yield; in the last, evaluating the applicability of the DSSAT model to study area and predicting the wheat production of different nitrogen fertilize. The main conclusions of this study were as follows:(1) The soil organic matter, total nitrogen, phosphorus and potassium content in each fertilizer treatment have been increased in different degree under long-term fertilization. They were increased 1.97 g/kg、0.13 g/kg、8.42 mg/kg and 8.4 mg/kg in HF, increased 2.2 g/kg、0.06 g/kg、11.86 mg/kg and 0.9 mg/kg in HM, increased 1.44 g/kg、0.05 g/kg、3.06 mg/kg and 27 mg/kg in NM. For CK treatment, soil nutrients must be decreased under no fertilizer for long time and its soil fertility would be degenerate. Organic fertilizer increased the soil nitrification, denitrification and soil microbial activity, so that the soil nitrogen only increased in the chemical fertilizer treatments while others werereduced. The fertilization levels, thermal condition and the precipitation can influence the crop yields significantly.(2) Long-term fertilization can improve the soil nutrients of the plateau and terraces effectively. Contents of soil organic matter, total nitrogen, available N and potassium in the plateau increased 0.72g/kg、0.02g/kg、1.23mg/kg and 34.06mg/kg, phosphorus content decreased; Contents of soil organic matter, total nitrogen, available N and phosphorus in the terrace increased 2.42g/kg、0.1g/kg、15.0mg/kg and 2.49mg/kg, potassium content decreased. In general, the effect of improving in terrace is more significant, because that its initial levels of soil physical and chemical properties were lower. The crop yields in plateau were higher than in terrace, it should take appropriate measures to improve the soil fertility and quality of terraces, and to improve the crop yields.(3) The crop water consumption and the precipitation showed a positive correlation, but the WUE and the precipitation showed a negatively correlation, the ET and WUE in the plateau were higher than terrace. Precipitation of summer fallow period to the soil water supply was closed to the type of annual rainfall, and the effect to the plateau was significant. In the Loess Plateau Gully farmland ecosystem, soil water of 0-300 cm depth was influenced significantly by rainfall. In different type of annual rainfall, the depth of soil water active, sub-active and stable layer were different. Soil water active layer was 0-100 cm depth in the plateau under the normal year, the sub-active layer was 100-180 cm depth and the stable layer was under 180 cm. Compared to the normal year, the depth of water active layer was increased significantly in the wet year, it can reach to 300 cm depth, and there is no stable layer among 0-300 cm, the sub-active layer was not obvious. In terraces, the boundaries of soil water moisture fluctuation was 160 cm in the normal year, soil water stable layer moved up in the dry year, the soil water active layer depth was increased in the wet year and no stable layer in 0-300 cm soil depth.(4) The DSSAT crop growth simulation model is applicable for the winter wheat growth and development in the farmland ecosystem of Loess Plateau gully area. Through the simulation and prediction of nitrogen fertilization trial, we found that N4M2(N135kg/hm2、M30000kg/hm2)is the best ratio of nitrogen fertilization in the farmland of local resarch. It could reduce the amount of nitrogen fertilizer but maintain the high crop yields, improve resource efficiency and reduce environmental pollution.