Effects Of Climate Change On Cotton Growth And Yield

Cotton is the most widely planted fiber crop in the world and plays an important role in the national economy.Climate change changes the environmental factors of crop growth such as sunshine,moisture and soil through the changes of temperature and precipitation,and then affects the phenological,growth potential,planting system,pest control and farmland management of cotton,and finally affects the yield.Therefore,studying the feedback mechanism of cotton growth on climate change is of great practical significance for regional planning of cotton planting and increasing and stabilizing yield.Based on the data of cotton growth,management measures,meteorology and soil,this study first analyzed the temporal and spatial variation characteristics of the main meteorological factors during cotton growth period by using the linear slope and MMK trend test method.Secondly,based on the first-order difference method,Pearson correlation coefficient,path analysis and multiple linear regression method,the change trend of cotton each phenological was analyzed,the effects of crop management and climate change on cotton phenological were separated,and the relationship between cotton phenological and yield change were explored.Then,the qualitative and quantitative relationships between climate change and cotton growth and yield were explored based on statistical analysis method and AquaCrop crop model.Finally,the published research results were compiled by using Meta-analysis method to explore the response of cotton yield to temperature,precipitation,CO₂ concentration changes,and adaptation measures.The main conclusions are as follows:(1)Effects of climate change on cotton phenology at 79 sites in main cotton producing areas of China were analyzed by first order difference method,Pearson correlation coefficient,path analysis and multiple linear regression.It was found that emergence,squaring,flowering,and boll opening dates of cotton advanced by 0.026-0.351 days year^-1,respectively,sowing and maturity dates were delayed by 0.170 and 0.337 days year^-1.The average phenological from sowing-emergence,squaring-flowering,and flowering-boll opening were shortened about 0.19-0.30 days year^-1,emergence-squaring,boll opening-maturity and the sowing-maturity were delayed by 0.11,0.77,and 0.082 days year^-1,respectively.Precipitation shortens the length of most phenological periods except during boll opening-maturity.The effect of sunshine hours on the various cotton phenological was the opposite of that of precipitation.In general,the increase of average temperature,minimum temperature and maximum temperature shortened the length of cotton phenology.The impact of climate change on cotton phenological was weaker than the individual impact of crop management and the combined impact of climate change and crop management.Under the combined impacts and isolated impact of crop management,the phenological from sowing-emergence and squaring-flowering were shortened while other phenological stages were extended.The isolated impact of climate change shortened the phenological from sowing-emergence,emergence-squaring,and flowering-boll opening,extended squaring-flowering,boll opening-maturity,and sowing-maturity,implying that the longer-duration cotton varieties in a changing climate might be a better choice for planting,this could be a viable strategy for adapting to climate change.In addition,the study found that the delay of sowing,emergence,squaring,flowering,and boll opening dates reduced seed cotton yield,but with the increase of cotton sowing-emergence,flowering-boll opening,boll opening-maturity and sowing-maturity,seed cotton yield increased.(2)Based on the long-term series data of actual observations,the effects of climate change on cotton growth and yield at 19 stations in Xinjiang were explored.The results showed that plant height at the cotton flowering stage,seed cotton yield,cotton stalk weight,and lint percentage generally increased significantly at most sites.The temperature(maximum temperature,minimum temperature,and average temperature)during the cotton growing period had a positive impact on seed cotton yield and cotton stalk weight,but a negative impact on plant height at the flowering stage and lint percentage at most sites.In addition,plant height at the flowering stage,seed cotton yield,and lint percentage responded positively to changes in precipitation but showed uncertainties in response to the changes in sunshine hours and average air relative humidity at different sites.The relationship between climatic variables and cotton growth and yield indices was site-and region-specific.Pearson's correlation was used to analyze the correlation between each cotton growth and yield index and the climatic factors.The correlations were positive or negative and were mostly insignificant.Additionally,In addition,the model established by stepwise regression method was better than Pearson's univariate correlation,and the accuracy of the model was improved in each site.The optimal regression model selected after the introduction of nonlinear variables can explain 8.1-69.9%,8.5-75.3%,7.1-56.1%and 10.4-85.7%changes of plant height at flowering stage,seed cotton yield,cotton stalk weight and lint percentage,respectively.(3)This study analyzed the impact of climate change on cotton growth at 40 sites in China's main cotton planting areas based on the AquaCrop model.The results showed that the AquaCrop model has good applicability in China's cotton planting area and can better simulate the growth process of cotton.Precipitation of most sites in the study area showed an insignificant increasing trend from 1978 to 2018,average temperature,minimum temperature,maximum temperature,and?10 ^oC accumulated temperature showed a significant increasing trend,while the average air relative humidity,wind speed and diurnal temperature difference mainly showed a decreasing trend.Sunshine hours and solar radiation showed an increasing trend in the northwest inland area,and a decreasing trend in the Yellow River and Yangtze River cotton areas.The simulated above-ground biomass,potential yield and water use efficiency showed an increasing trend in 98%,98%,and 93%of the sites,and showed a significant increase in most sites,while the actual evapotranspiration during cotton growth period mainly showed a decreasing trend.The increase in CO₂ concentration is the main reason for the increase in cotton production.By calculating the Pearson's correlation coefficients and stepwise regression equations between cotton growth indices and climatic factors,it was found that the main climatic factors affecting above-ground biomass were wind speed,solar radiation and maximum temperature.The main climatic factors affecting actual evapotranspiration were wind speed,solar radiation,sunshine hours and average relative humidity.The main climatic factors affecting potential yield were wind speed,solar radiation,sunshine hours and minimum temperature.Climate factors explained the changes in actual evapotranspiration during cotton growth period,above-ground biomass,potential yield,and water use efficiency of65.1-95.5%,9.7-74.5%,14.8-68.3%,and 15.2-90.4%.Overall,cotton growth was closely related to changes in wind speed,solar radiation,minimum and maximum temperature.(4)Based on the AquaCrop model,the impact of future climate change on cotton yield in China and its adaptation measures were simulated.The study found that the climate prediction data under SSP2-4.5 and SSP5-8.5 emission scenarios showed that temperature at 40 sites in the main cotton producing areas of China showed a significant increasing trend,especially under high emission scenarios(SSP5-8.5).The precipitation during the cotton growth period also showed an increasing trend,but the temporal and spatial variability was large,and the precipitation in 2080s of SSP5-8.5 scenario changed the most.Reference crop evapotranspiration mainly showed a decreasing trend in 2040s under SSP2-4.5 scenario,while it mainly showed an increasing trend in 2080s and SSP5-8.5scenario.Future climate change have a positive effect on irrigated cotton yield.Compared with the baseline period,under the SSP2-4.5 scenario,the cotton yield increased by 10.51%and 13.67%on average in 2040s and 2080s,respectively;under the SSP5-8.5 scenario,cotton yield increased by 14.76%and 28.04%in 2040s and 2080s,respectively.The increase of cotton yield in SSP5-8.5 scenario was more significant than that in SSP2-4.5scenario,because the future CO₂ concentration in SSP5-8.5 scenario was much higher than that in SSP2-4.5 scenario,and the fertilizer effect of CO₂ was more significant.In addition,early sowing was conducive to the increase of cotton yield.Compared with the conventional sowing date(April 20),early sowing(March 31)could increase the cotton yield of most sites in 2040 s and 2080 s by 1.99%and 2.41%on average under SSP2-4.5scenario,1.88%and 2.63%on average under SSP5-8.5 scenario.This finding supports early sowing strategy for cotton production in China to optimize yield under future climate conditions.(5)By compiling all published research results,the possible impact and uncertainty of climate change on cotton yield were qualitatively and quantitatively explored by Meta-analysis.The study found that temperature,precipitation,CO₂ concentration,and adaptation measures had significant effects on cotton yields.When air temperature increased by 1^oC,cotton yield decreased by 7.79%.When precipitation and CO2concentration increased by 1 mm and 1 ppm,cotton yield increased by 0.102%and 0.05%,respectively.The cotton yield under certain adaptation measures(changing the sowing date,cultivar,irrigation amount,etc.)was 32.65%higher than that without adaptive measures.The role of CO₂ fertilization on cotton yield was also key for denoting the signal and magnitude of the impact of climate change.Without considering the CO₂ fertilization effect,the impact of climate change on cotton yield was negative.Considering this effect,the future yield situation will be more optimistic.Adaptation measures(changing sowing dates and cultivars)could also alleviate the negative effects of climate change to a certain extent.Increasing the number of climate models reduced the median range and outliers of the percentage change in cotton yield(PCY)by comparing the PCY simulated by single or multi-GCM(?2)models.Therefore,increasing the number of GCMs reduced the uncertainty of crop simulations in studies of the impact of climate change.In addition,the differences,crop model,and climate scenarios had a significant impact on the PCY,which depends on local climate and soil properties,cultivation methods,and management practices.