| The intensive production characterized by excessive water and nitrogen input leads to serious non-point source pollution problem such as groundwater nitrite pollution in the winter wheat-summer maize rotation cropping system of high-yielding area in northern China. These problems are urgently to be solved. In this study, we chose the first built "Tons of Grain County" in the north area to the Yangtze River since1990-Huantai County as the study area. Based on the previous work in our research group, the database of basic physiochemical properties of Huantai County was perfected and created through collecting historical information, soil sampling and determination with GIS software. From the parts of soil chemical properties of the database and with the aid of GIS software and geostatistical method, the spatio-temporal organic matter in topsoil distribution characteristics and its causes were analyzed since the second soil survey of Huantai County (1982-2011). On the basis of this database, the digital distribution maps of soil physical and hydraulic parameters were established, and spatial distribution characteristics of the parameters were analyzed. Though reorganizing and analyzing the data about fertilizer inputs and grain yield record in Huantai yearbook of1980-2010, the county’s actual fertilizer inputs and its utilization efficiency were studied from a practical view point to preliminarily define the reasonable range fertilizer input in Huantai County. After verifying the parameters of water and nitrogen transformation within the crop root zone and crop growth in WHCNS model as well as inputting soil physiochemical parameters layers, the model was applied to simulate water and nitrogen transformation and crop growth at county scale to valuate the effects of nitrogen loss control and grain yield maintenance under different water and nitrogen management modes. The main results and conclusions are as follows:The SOM contents around the high-yielding area of Huantai County were13.2,15.1and18.7g kg-1in1982,1996and2011, respectively. The SOM increase rate from1996to2011was as much as twice that during1982-1996. These results indicated that the effects of human activities on SOM content strengthened during the period from1982to2011. During1982-1996, increases of SOM were due to increasing manure and chemical fertilizer application caused by adjustments of land use types and changes in farmers’practices of agricultural production. The SOM in different types of soil were significantly different. While during1996-2011, the main reason for the SOM increase was the large quantity of straw incorporation. And the differences of SOM in different types of soil shortened.After Analyzing relevant data in Huantai Yearbook from1980to2010, we found that during nearly30years, large amounts of fertilizer per unit planting area were generally applied in this region, exceeding the average value of the high level fertilization region in China. In recent years, the traditional NPK fertilizer has gradually been replaced by compound fertilizer, and the NPK fertilizer application ratios tend to be balanced. Reduction of the fertilizer efficiency with fertilizer application increase showed that the agricultural production mode of which expected high yield relying on increasing chemical fertilizer application was unscientific in local. The appropriate N fertilizer application rate ranged from210-247kg hm-2that can maintain the crop yield in Huantai region. However, on the present condition of NO3-N accumulation in soil profile caused by previous excessive N fertilizer application, this suggested application rate might be further optimized.The verification results for soil water, heat, carbon and nitrogen simulation (WHCNS) model showed that soil water content and crop aboveground biomass accumulation, simulated and measured values were all in good agreement within the crop root zone, and nitrogen transport simulated and measured results had the same trend in general. The model verification results were within the acceptable range. Additionally, in order to solve the problem that the hydrodynamic parameters for the numerical simulation of soil water and nitrogen movement at regional scale are difficult to obtain, the method of pedo-transfer functions (PTFs) was adopted. Inputting the soil clay content in Huantai County to the Rosetta and SPAW Hydrology model, important soil physical and hydraulic parameters as bulk density, saturated hydraulic conductivity, saturated water content, residual moisture, field capacity, wilting point were output. It showed that the distribution of soil clay content was greatly impacted by soil parent materials. The predicted spatial distribution of different parameters were generally variable. But the degree of variability is reasonable for parameters and they can be used as the basic input parameters for model running at the county scale.The simulation results at county scale showed that compared with conventional water and nitrogen management scheme, optimized water and nitrogen management scheme only made winter wheat and summer maize yields reduced by4.8%and0.7%, respectively. But40%nitrogen and33%irrigation water were saved during the winter wheat season, while33%water and33%nitrogen during the summer maize season. Correspondingly, the nitrogen utilization efficiency of winter wheat and summer maize increased by28.6%and17.3%, respectively. Though optimizing water and nitrogen management, the reduction of water leakage was accomplished and thus, the water utilization efficiency, especially the irrigation water use efficiency increased by60.9%and45.1%during the the winter wheat and the summer maize season, respectively. The nitrogen leaching and residual nitrogen accumulated in2m soil profile reduced. Meanwhile, the production cost decreased by436yuan mer hactre and10.358million yuan during the rotation cropping year around the county by cutting off the nitrogen fertilizer consumption. So it could be concluded that the dual goals of economic and environmental benefits were achieved by optimizing water and nitrogen management in this region. |
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