Evaluation Of Cotton Yield Gaps And Potential For Production Increase In China Based On GYGA Protocol

As an important economic crop in China,cotton was mainly planted in the Yangtze River Valley and the Yellow River Valley in history,and has rapidly transferred to Xinjiang since 1980.At present,the cotton area in Xinjiang accounts for 79%of the country.Past studies have shown that the rapid expansion of Xinjiang’s cotton area has caused a series of environmental problems,increased the burden of arable land,and is not conducive to the cotton sustainable development in China.In addition,the cotton yield in Xinjiang and other provinces has gained slowly in the past 10 years,and has stagnated at different levels.Therefore,what needs to be urgently resolved is to clarify the current production status,yield gap and potential of different cotton planting areas in China.The Global Yield Gap Atlas（GYGA）protocol was used in the study to"bottom-up"assess yield gap in different climatic zones,provinces and national levels.Based on the yield gap assessment and cotton area,the exploitable production gap was clarified.Finally,China’s cotton self-sufficiency in the future were discussed under different scenario according to the historical trends of cotton yield and producing area.The main results are as follows:（1）The calibration and validation results show that CROPGRO-Cotton model can be used to simulate potential yields in different regions because of the accurately simulation in growth period,dry matter production distribution,and mature yield of different varieties.The coefficient of determination between the calibrated and measured value is greater than0.94 in cotton growth period,aboveground biomass and yield,and the normalized root mean square error is small,3%,18%,and 3%,respectively.The coefficient of determination between the validated and measured value is greater than 0.93,and the normalized root mean square error is 4%,19%,and 6%,respectively.（2）The results of yield gap evaluation based on GYGA protocol show that there is potential for cotton yield increase in China.First,36 reference weather stations were selected from 863 weather stations,distributed in 8 climatic zones.The cotton area in the selected climate zones accounts for 90%of cotton area in China,indicating that the scope of this study is representative.Then,the potential yield,actual farmer yield,and yield gap in buffer zones of 36 reference weather stations were evaluated,and the evaluation results were upscaled to climate zone,province,and national level.The potential yield and actual farmer yield of cotton lint in China are 2722 and 1624 kg ha^-1,respectively,and the relative yield gap（as a percentage of the yield gap in potential yield）is 40%.The ranking of relative yield gaps of China’s major cotton planting provinces is Hubei（45%）,Hebei（44%）,Anhui（41%）,Xinjiang（40%）,and Shandong（37%）.（3）By yield gap closure,the cotton production in China could increase by 1.4×10⁶ t.The potential for production increase in Xinjiang is 9.9×10⁵ t,accounted for 71%of China.The top 10 counties including Awat,Shache,Kuqa,Jiashi,Xayar,Bachu,Shule,Usu,Korla and Shawan account for more than 50%of potential for production increase in Xinjiang.Outside of Xinjiang,Hubei（1.1×10⁵t）and Hebei（1.0×10⁵t）have greater potential for production increase,accounting for 8%and 7%of the country.（4）The current cotton self-sufficiency rate in China is 68%.The results of scenario analysis show that self-sufficiency rate can also be increased to 90%in 2030 by yield increase to 75%of potential yield in Xingjiang.At the same time,the yield gap closure in other provinces could increase the self-sufficiency rate of cotton to 94%in 2030.Therefore,it is conducive to China’s cotton production to achieve self-sufficiency in the future by stabilizing cotton production in the Yangtze River Valley and Yellow River Valley,and closing the yield gap in Xinjiang and other regions with great potential for production increase.