Assessment Of The Impact Of Future Climate Change On Maize Production And Adaptation Strategies In The Agro-pastoral Ecotone Of Northwestern China

Mitigation of the impacts of climate change on agriculture is one of the most important challenges that threatens the sustainability of global food production systems.The agro-pastoral ecotone of northwestern China(APENC)serves as a key ecological shelter in preventing desertification and ensuring ecosystem services and food production in China.Maize is a staple crop in the APENC,accounting for more than50%of the total sown crop area in the region.Therefore,maize production in the APENC plays an important role in maintaining local food security.However,little is currently known about the effects of climate change on the main staple maize production and adaptation strategies in the APENC.The study used the DSSAT model,driven by future daily climate data from 20 GCMs calculated for the Coupled Model Intercomparison Project Phase 5(CMIP5)under two Representative Concentration Pathway scenarios(RCP4.5 and RCP8.5),to evaluate the impacts of future climate change on two typical maize crops(rainfed maize and irrigated maize)in the APENC and to assess three potential adaptation strategies.The objectives of this study were to(1)evaluate the performance of the DSSAT using in sit observation data in the APENC,(2)investigate the effects of future climate scenarios change on maize yield,growth period and water use efficiency,and(3)identify specific adaptation strategies and assess the impacts of different combinations of adaptation strategies on maize and water use efficiency.The main findings are as follows:(1)The study used the generalized likelihood uncertainty estimation(GLUE)method to estimate the genotype parameters based on field trial data.The n RMSE values of simulated and observed maize yield were 2.37%and 2.84%for the calibration and validation periods,respectively,which falls within a satisfactory range.The results showed that the R²,RMSE,and n RMSE values of the whole dataset between the simulated and measured soil water content ranged from 0.57 to 0.91,from 0.016 to0.038,and from 16.5%to 41.7%,respectively,for each of the soil layers.Overall,CERES-Maize model after calibration can accurately simulate soil water content and maize yield in the study area.(2)The results showed that rainfed maize yield during the 2030s,2060s,and 2090s would change by+21.7%,+16.4%,and+12.6%under the RCP4.5 scenario and+25.1%,+4.8%,and-12.3%under the RCP8.5 scenario,respectively.Irrigated maize yield would change by+3.9%,-16.3%,and-20.4%under the RCP4.5 scenario and+0.1%,-31.2%,and-53.1%under the RCP8.5 scenario in the 2030s,2060s,and 2090s,respectively.The future increase of CO₂ concentration would lead to increased maize yield,which would increase the rainfed and irrigated maize yield by 1.3%?4.8%and0.6%?5.7,respectively.Although an elevated CO₂ concentration would lead to increased maize yield,the impact of air warming on the maize yield would be far greater than it.It would lead to earlier maturation and a shorter period for the formation and accumulation of dry matter,causing less accumulation and thus reduced grain yield.The statistical analysis showed that there is a significant negative correlation between maize yield and temperature.The annual average temperature rises by 1?,the maize yield would decrease by 11.3%.Future climate change will have a positive effect on rainfed maize yield,which can be attributed to rising precipitation.Future climate change would have a negative effect on maize water use efficiency.The water use efficiency of rainfed and irrigated maize varies from-31.1%to 1.7%and from-36.7%to 0.6%,respectively.Elevated CO₂ concentration would lead to increased water use efficiency of rainfed and irrigated maize from 1.6%to 18.7%and from 0.1%to 5%,respectively.(3)The study used the CERES-Maize model to simulate the impact of planting dates on the maize yield.The simulated results showed that delaying planting date would increase the maize yield.The optimal planting dates of rainfed and irrigated maize were between April 25 and May 25 and between May 5 and May 25,respectively.Compared with the local normal planting date,by using optimal planting dates,the rainfed maize yield could be enhanced by 3.5%?22.5%and irrigated maize yield could be enhanced by 14.4%?51.1%.The distribution of precipitation during the maize growth period in the APENC did not match well the water demand for maize.Thus,in the CERES-Maize model,the study set 32 irrigation combinations in five key growth stages(planting,emergence,jointing,tasseling,and grain filling)with 0 irrigation,1 irrigation,2 irrigations,3irrigations,4 irrigations and 5 irrigations.The simulation results showed that applying supplemental irrigation at the tasseling and grain filling stages could significantly increase the rainfed maize yield.Implementing this adaptation strategy,the rainfed maize yield could be enhanced by 15.3%?28.2%.The development of climate resilient crop cultivars with adapted genotypes is one of the most effective approaches to mitigate the negative impact of climate change on maize.The study selected six key cultivar parameters to explore cultivar adaptive traits under future climatic condition.In total,4096 potential combinations of cultivar parameters were generated.The simulated results indicate maize ideotype has a larger thermal time from seeding emergence to the end of juvenile and higher potential kernel number.(4)The CERES-Maize model was used to simulate the effect of the coupling of different adaptation strategies on the rainfed and irrigated maize yield and water use efficiency.The simulated results showed that it was difficult for a single adaptation strategy to completely offset the negative impact of future climate change on the irrigated maize.The maximum increase in the maize yield and water use efficiency is achieved under the coupling scenario of the best sowing date and the best variety.Coupling the optimal planting date and maize ideotype would increase the irrigated maize yield and water use efficiency most,which could be enhanced by 29.4%?73.2%and 16.3%?48.7%.For rainfed maize,if only considering the coupled two adaptation strategies,the coupling of the best supplemental irrigation scheme and the maize ideotype will result in the highest maize yield,which can increase the yield of the rainfed maize by60.9%?95.5%.Since supplementary irrigation strategy will reduce the maize water use efficiency,the coupling of the optimal planting date and the maize ideotype can increase the maize water use efficiency most,which can increase the rainfed maize water use efficiency by 15.4%?28.8%.The coupling of three adaptation strategies has the largest increase in the irrigated maize yield.Under this coupling scenario,irrigated maize yield and water use efficiency can be increased by 87.5%?101.1%and 18.9%?28.9%,respectively.The results of this study will provide theoretical basis for the adaptation of maize to climate change and the sustainable development of agriculture in the APENC.