Feasibility Study Of Green-manure-rape And Winter-wheat Rotation In The Weibei Dryland Based On Crop Models

Excessive use of chemical fertilizer in agricultural production has caused irreparable serious consequences,such as soil fertility attenuation,groundwater pollution,and so on.It is an economic and effective method to use green manure instead of chemical fertilizer to reduce fertilizer pollution in agricultural production.Crop growth simulation model is a technology based on computer language to represent the physiological and ecological processes of crop growth,which has incomparable advantages in agricultural production management and research.In this study,the growth and development of rapeseed?Brassica napus L.?were primarily evaluated through the structural equation model based on yield and relevant economic traits of rapeseed planted in the regional trial experiments conducted in the Hybrid Rapeseed Research Center of Shaanxi Province at the Dali County in Shaanxi Province in 2007-2016.Then based on the experimental data of yield and phenology of rapeseed in 2009-2015,we chose three kinds of crop growth simulation models?i.e.STICS,DSSAT and APSIM?,which were mainly used in the world.The experimental data from the years with abundant precipitation were selected for model calibration,the calibration precision of three models,represented by the statistic of relative absolute error(R_ARE),was all within 5%,respectively.And the experimental data obtained from the rest years were used for model validation.Then the optimal crop model was determined to simulate the rape growth in the study area.In order to further verify the simulation accuracy of the selected optimal model,further model verification was carried out based on the yields and phenology dates obtained from the regional trial experiments of rapeseed in eleven different sites in five different provinces?Gansu,Shaanxi,Shanxi,Henan,Anhui,and Jiangsu?in 2004-2016.Finally,based on the experimental data of winter wheat in multiple years?2005-2015?in the Changwu County in Shaanxi province,the selected optimal model was used to simulate two different cropping modes of summer fallow&winter wheat and green manure rape&winter wheat rotation.The two cropping modes were compared for winter wheat yield,change of soil moisture and nutrients in the hope of clarifying the feasibility of planting green manure rape in this area.Some main conclusions have been drawn based on the results as follows.?1?There was a strong positive correlation between the yield per plant and the number of effective pods per plant and the number of branches.With the increase of planting density,the yield per plant had a obvious trend of decrease,which was mainly achieved by the number of effective pods per plant,but the overall yield showed a trend of increase.Therefore,the main direction to increase rapeseed yield was to increase the planting density properly and to cultivate varieties that were density-tolerant and with more kernels and branches.?2?Compared with the DSSAT and APSIM models,the STICS model had the highest simulation accuracy of rapeseed yield and phenology dates in the Dali County,while the three models had relatively poor simulation accuracy in the years with severe water stress,especially the DSSAT and APSIM model.The results showed that the models need to be further improved for their simulation of water stress.According to a comprehensive analysis,the STICS model was the most suitable crop model for simulating winter rapeseed growth in this region.?3?The STISC model was good at phenology simulation in all of the eleven sites in five provinces.However,the simulation precision of rapeseed yield was obviously low.Thus,it was proved that there was a big advantage in the STICS model to simulate phenology of rapeseed,but some disadvantage for the yield simulation.The STICS model needs to be improved in the aspect of grain formation.?4?Based on the STICS simulation results,the cropping mode of green manure rape&winter wheat rotation did not show a positive impact on the growth and development of winter wheat,but caused yield reductions to different degrees.However,as one of the main reasons of soil nitrogen leaching,returning rapeseed biomass as green manure to the field could effectively control the content of soil nitrate nitrogen,and thus greatly reduce the amount of soil nitrogen leaching,which has certain positive significance for the groundwater environment.