Effects Of Climate Change On Yield,Water Use And Soil Nutrients Of The Crop Production Systems On The Loess Plateau

Global climate change will inevetabally affect the unstable grain production system on the Loess Plateau in China.The practices of including forages crops into grain based systems,implementing stubble cover and applying no-tillage are able to enhance the stability of agricultural systems with buffering the negative impacts caused by climate change.How the productivity and water use processes of the local agricultural systems are affected by the crop production system diversification and conservation tillage under climate change conditions are not fully understood.This study evaluated the adaptability of APSIM?Agricultural Production Systems sIMulator?in simulating the various crop productions in the rainfed area of the Loess Plateau,and then simulated traditional and improved crop systems under climate change scenarios with analyses of crop yield,evapotranspiration distribution,water use,soil nutrients and economic returns.The results are as follows:1.APSIM was validated with good accuraciy in simulating production and resources use of winter wheat?Triticum aestivum?,maize?Zea mays?,soyben?Gyleine max?and lucerne?Medicago sativa?at the Qingyang Loess Plateau Research Station of Lanzhou University based on field experiments.Soil and wether parameters were measured onsite and crop parameters were measured from field experiments.Validation results showed that APSIM could accurately simulated the yield and biomass of maize,winter wheat and soybean in a maize-winter wheat-soybean rotation?MWS?,with the determination coefficients?R²;Determination Coefficient?are 0.81-0.87,0.82-0.95 and0.72-0.92 for maize,winter wheat and soybean,respectively?P<0.01?,while the maximan root mean squared error?RMSE;Root Mean Squared Error?accounted for 30%of mean observed values.For the soil water storage,APSIM gave R² of 0.43-0.65 and0.43-0.47 for the maize-winter wheat-soybean rotation and lucerne grassland,respectively?P<0.01?,and the RMSE accounted for 11.7-17.8%and 12.0-20.2%of mean observed values.Moreover,APSIM showed R² of 0.70-0.99 and 0.68-0.97 for the soil NO₃-N?0-200 cm?and soil organic carbon?SOC;0-30 cm?,respectively?P<0.05?,and the RMSE accounted for 13.1%and 17.2%of mean observed values.Therefore,in general,the results verified that APSIM has been successfully calibrated,and it could be used for simulating crop yield,hydrological dynamics and soil nutrients dynamics in the scenario analysis to assess the changes of various compositions in crop production systems under different climatic conditions.2.The effects of precipitation and air temperature changes on the productions of continuous winter wheat,continuous maize and lucerne grassland were evaluated.New climate scenarios were established by changing annual precipitation?-20%,-10%,historical,+10%and+20%?and temperature?-1.5°C,-1°C,historical,+1°C and+1.5°C?based on the historical weather data during 1961-2010.Results showed that the yields of three crops tend to decrease when temperature increased and precipitation decreased,with the maximal reductions of 38.7%,40.3%and 41.8%for wheat,maize and lucerne,respectively.Wheat and lucerne maintained the greatest yield when the air temperature decreased and the precipitation increased,with the maximal improvements of 29.8%and51.7%,respectively.Maize reached its greatest yield when the precipitation increased and the air temperature remained unchanged?increased 22%compared with baseline?.In general,the effect of climate change on variation range of lucerne yield was the minimal across three crops,thus lucerne could adapt to the climate change better than winter wheat and maize.3.The impacts of long-term conventional tillage?CT?and conservation tillage?no-tillage with stubble retention;NTR?on crop yield and water use pattern of a maize-winter wheat-soybean rotation during 1961-2010 were quantified.The results showed that NTR significantly improved soil water storage before each rotation phase0-159 mm?72 mm on average;P<0.01?compared with treatment CT.For winter wheat,the grain yield and biomass were significantly improved by NTR?1805 and 4309 kg/hm²on average,P<0.01?,but NTR had no obvious effect on the grain yield and biomass of maize and soybean?P>0.05?.NTR also significantly improved plant transpiration?T_c?,but decreased soil evaporation?E_s?and evapotranspiration?ET;P<0.05?.In addition,plant transpiration and soil evaporation for maize growing seasons were insignificantly different between CT and NTR?P>0.05?.Moreover,grain yield water use efficiency?WUE_Y?and biomass water use efficiency?WUE_B?of wheat and soybean were significantly improved by NTR?1.9-8.0 kg/hm²·mm;P<0.05?.Consequently,the no-tillage with stubble retention has great potential on enhancing soil water retaining,crop yield and water use in the maize-winter wheat-soybean rotation.4.Based on the historical weather data of Qingyang,Gansu,this study generated the RCP?Representative Concentration Pathways?4.5 and RCP8.5 projections from Global Climate Model?GCM?from the Coupled Model Inter-comparison Project Phase 5?CMIP5?using the protocols specified by ACSGTR?AgMIP Climate Scenario Generation Tools with R;www.agmip.org?.Then this study conducted long-term scenario analyses for five crop production systems under generated scenarios:continuous maize?M?,continuous winter wheat?W?,lucerne grassland?L?,maize-winter wheat-soybean rotation?MWS?and lucerne-winter wheat?LW?;meanwhile treatment CT and NTR were implemented for continuous maize,continuous winter wheat,maize-winter wheat-soybean rotation and lucerne-winter wheat rotation.The results showed that the grain yields of cereals reduced by 1.2-39.4%in the future scenarios compared with baseline,however,RCP4.5 scenarios improved the lucerne yield by 4.0-12.3%.The values of Plant transpiration decreased when the pathway value enhanced and the time-scale advanced,while the RCPs reduced and improved soil evaporation for CT and NTR,respectively.Soil NO₃-N?0-200 cm?in maize-winter wheat-soybean rotation and SOC?0-30 cm?in lucerne-winter wheat rotation were the highest among the crop production systems,followed by lucenre-winter wheat rotation.Lucerne grassland presented highest gross profit?GP;38.4-46.1×10⁴ RMB/hm²?and water profit?WP;24.32-28.71 RMB/hm²·mm·phase?among the systems,followed by lucerne-winter wheat roation.Climate change showed relatively large negative on the economic return of continuous maize,continuous winter wheat and maize-winter wheat-soybean rotation?from-39.2%to+3.7?.However,the gross profit and water profit of lucerne grassland and lucerne were 0.8-12.8%hinger by RCP4.5 scenarios compared with baseline data.Overall,the lucerne-winter wheat rotation has great potential on yield and economic profit under limited water supply/availability under the projected future climate changes in the local environment.Through the further calibration and evaluation in simulating crop yield,soil water dynamic and soil nutrients,the capabilites of APSIM in describing complicated crop production systems were confirmed.This study also clarified how production and resources use of different crop production systems changed under future climate scenarios,and illuminated the advantages of enhanced systems wit diversified cropping and conservation tillage.The results could provide guidance for understanding response of grassland agricultural systems to climate change,and could present practical significances for improving ecological environment and enhancing agricultural production on the Loess Plateau.