Simulation Of Crop Yield And Nitrogen Leaching Response To Irrigation And Fertilization In The North China Plain

Based on the background of typical intensive plant area in the North China Plain, Daxing district of Beijing, the parameters of Root Zone Water quality Model Version2.0(RZWQM2) was estimated by the collected data of field experiment irrigated with sprinkler. The uncertainty of these model input parameters and model outputs were also analyzed. The calibrated RZWQM2model was used to quantify the relevance of the transport of water and nitrogen in agricultural field and the pollution load of nitrate leaching in groundwater. The pedo-transfer function for Daxing district was established based on the soil saturated conductivity and soil physical characteristics. The influence factor of nitrogen content and nitrogen accumulation of soil profile in Daxing district, and the response of spatial distribution of nitrogen leaching to varying agricultural management practices and meteorological conditions were analyzed on a spatial scale. The main objectives and conclusions are as follows:(1) Choosing the Daxing district in Beijing as the study area, the spatial variation of particle composition and soil nitrate content were studied based on the measurement and analysis of regional sampling points. Pedo-transfer function of Daxing district was established and applied to predict the saturated hydraulic conductivity other sampling points. The effects of different soil plant types, soil textures and crop plant on the spatial distribution characteristics of soil nitrogen content and accumulation within different soil depth in Daxing district. The results showed that, soil nitrate content of most sampling points was decreased with increasing depth of soil profile. The effect of different plant types on nitrate content was obvious. Outdoor and protected vegetable field contained more nitrate nitrogen in soil profile. The towns of Panggezhuang and Beizangcun where soil contained more sand, and the towns of Zhangziying and Caiyu where planted intensively fruits and vegetables were the main district susceptible to nitrate pollution.(2) Based on the data of field experiment, PEST was used to calibrated and validated RZWQM2model. The simulations using PEST optimation showed a good fit with observations, and was obtained in a more efficient and precise way. The results indicated that the RZWQM2model could be used in simulating the crop growth and transport process of water and nitrogen in the double-rotation crop system of waxy maize and winter maize.(3) The sensitivity and uncertainty of model parameters, the uncertainty of model outputs were analyzed using General Likelihood Uncertainty Estimation (GLUE) method which based on Latin Hypercube Sampling (LHS) method. The weighted combined likelihood function aggregated different observation variables was proposed to determine the uncertainty range of RZWQM2model outputs. The results showed that the nitrogen accumulation with1m depth of soil profile was sensitive to the parameters of nitrification rate coefficient, thermal time of emergence stage for maize, and vernalization and photoperiod coefficients for wheat. The parameters of soil saturated hydraulic conductivity, nitrification and denitrification and hydrolysis of rate coefficient played a key role to crop yield. The uncertainty ranges for different model outputs calculated by combined likelihood function included generally better the observations.(4) The research on the effect of different application rate of irrigation and nitrogen fertilizer on crop yield and nitrogen leaching of root zone showed that, the crop yield and nitrate leaching was not sensitive to the fertilizer amount when the irrigation was very less. Nitrate leaching was mainly occurred in the growth period of waxy maize due to more precipitation during this time. When the irrigation and fertilizer for waxy maize and winter wheat were both40cm and400kg ha-1, respectively, the nitrate leaching into groundwater equaled to47.9%of application amount of nitrogen fertilizer. In the condition of normal irrigation and fertilization, NUPE, NUE, NPFP, and Wpi was relatively higher. In the long-term time, the time of nitrate leaching from upper soil (lm) to lower soil (2m) or groundwater (15m) was basically the same under same irrigation condition, but nitrate leaching had a increasing time-lag with soil depth. Under different irrigation conditions, nitrate leaching time was shorter when irrigation amount was larger.(5) The responses of nitrogen leaching in different depth and crop yield to varying agricultural management practices and meteorological conditions were simulated by combing the RZWQM2model and ArcGIS software. As the results showed, all the increasing of irrigation and fertilizer, temperature, and precipitation could enhance crop yield and nitrogen leaching. On spatial scale, the effects of different influence factors to nitrate leaching at depth of groundwater lever were not same due to the various soil texture. The groundwater of sandy soil area in the western Daxing district are vulnerable to nitrage pollution.