Effect Of Limited Irrigation On Yield And Yield Response Under Climate Change Of Winter Wheat In The Guanzhong Plain

Limited precipitation and water shortages are the main concern for winter wheat(Triticum aestivum L.)production in the arid and semi-arid areas of northwest China.However,an unreasonable irrigation system will not only affect the growth of winter wheat,but also cause a waste of water resources.The water resources conditions will be changed as with climate change,which will have a certain impact on the growth of winter wheat.This study has analyzed the water requirement of winter wheat under different irrigation levels and different planting densities based on two irrigation experiments which were conducted under a rainout shelter and under field conditions during the 2011—2012 and 2012—2013 growing seasons in the Guanzhong Plain.The shelter experiment included three irrigation levels(full irrigation,100%ET;medium water deficit,80%ET;and severe water deficit,60%ET)and the filed experiment had three irrigation levels(the same with shelter experiment)and three planting densities(340 kg hm-2,240 kg hm-2 and 140 kg hm-2).At the mean time,the CSMCERES-Wheat model was calibrated and evaluated based on the two years' experiments data,and was used to optimize the planting date for the winter wheat in Guanzhong Plain.At last,5 global climate models(GCMS)and different representative concentration pathways(RCPs)were used to predict the climate change in 2020-2100 projections under different scenarios,and simulated the yield response of winter wheat under different climate change scenarios.The main results are included as follow:(1)Determined the effect of different irrigation regimes on winter wheat growth and development,the result indicated that the jointing stage was the most sensitive stage for water deficit,and followed by anthesis day due to a reduction in biomass,yield,and WUE.And the water stress applied during the tillering stage will not result in severe yield decrease for winter wheat.For the field condition experiment,high planting density and medium irrigation amount was the optimum irrigation management which will obtain the highest grain yield and water use efficiency.(2)Evaluated the performance of Cropping System Model(CSM)-CERES-Wheat for simulating the impact of different irrigation regimes on winter wheat growth,development,and grain yield.The simulation results showed that the model performed well as indicated by a close correspondence of simulated crop phenology,final above-ground biomass,leaf area index(LAI)and grain yield with observed data.The model was inaccurate in simulating winter wheat biomass under stressed conditions.The normalized root mean square error was less than 2% for phenology,15.4% for final above-ground biomass and 14.8% for grain yield.The model could fairly simulate the LAI,andwas inaccurate in simulating winter wheat leaf biomass under stressed conditions,the difference between simulated and observed values reached 70%.The sowing date analysis showed that a delayed sowing date from 7 September to 27 October caused a decrease in average yield of 36.7% for all the rainfed and irrigated scenarios.Optimum sowing date was determined to be 7 October for the local farming system.(3)Evaluated the capability of the CSM-CERES-Wheat model to simulate the cumulative evapotranspiration,daily evapotranspiration and soil water content of winter wheat(Triticum aestivum L.)in 2011—2012 and 2012—2013 growing seasons under semiarid conditions.The daily ET was measured using weighting lysimeter that installed in the experimental plot.The ability of the CSM-CERES-Wheat model using two different ET approaches,i.e.,Priestley-Taylor(PT)and Penman-Monteith(PM),and the simulation results were evaluated and compared.The results showed that the CSM-CERES-Wheat model with both the PT and PM approach simulated cumulative ET,daily ET and soil water content has great agreement with measured data,the difference of cumulative ET and daily ET was less than 5.4% and 3.4% respectively compared with observed values.The CSM-CERES-Wheat model simulated cumulative ET for the winter wheat in two growing seasons through PT approach was less than PM approach,the relative difference between two approaches was ranged from-3.11%~-0.05%.The model could simulate soil water content correctly as well,in the depth of 0~20 cm,the RMSEn between simulated result based on two ET approaches and the observed values was 39.38%,the result was relative high and not good,but from 20 cm depth,the RMSEn between simulation results that based on two ET approaches and observed values was less than 23.1%,and the simulation in the depth of 40~60 cm got the best agreement.The model with both the PT and PM approach simulated the above-ground biomass and grain yield accurately as well.The RMSEn for the two growing seasons was 13.57% for the PT approach and 22.76% for the PM approach for final above-ground biomass,and 11.80% for the PT approach and 15.42% for the PM approach for grain yield,both the simulated results had a good agreement with the observed values.The model using the PT approach provided less ET and higher soil water content than those derived from the PM approach as compared with the measured data.Additionally,the model using the PT approach provided higher final above-ground biomass and grain yield than those derived from the PM approach as compared with the measured data.However,the model with both two approaches could simulate the total above-ground biomass and grain yield that had the RMSEn within 25% of measured data.(4)It is obvious that the warming trend in Guanzhong Plain,both the highest temperature and the lowest temperature for the different GCMs and RCPs are showed an upward trend.The growth range for January in 2100 projection is close to 16 0C in Weinan,which was simulated with HADCM3 model under RCP8.5.Rainfall varies in different months,in general,the rainfall showed an increasing trend in February,June and December,and a reduction trend in April,September and October.The solar radiation in Baoji and Weinan area showed an upward trend,while the solar radiation is greatly reduced in Wugong.The maturity date of winter wheat in Baoji and Wugong area shortened 3~35 days compared with the baseline under different climate change scenarios,while the maturity date in Weinan area increased 17~52 days compared with the baseline.The winter wheat yield in Baoji,Wugong and Weinan is mainly increased in different GCMs and RCPs scenarios during the 21 st century.