Simulation For The Growth And Yield Of Cotton In Response To Soil Aeration Stress

Appropriate water condition in the fields is the basic guarantee for normal growth of field crops.Heavy rains and poor field drainage usually bring perched groundwater(waterlogging)and ponded water(submergence)problems to the fields.When waterlogging and submergence hinder the growth and yield of field crops,then soil aeration stress occurs.Aeration stress seriously restrict the agricultural production in the districts liable to flooding.China is one of the countries in which flooding disasters frequently occur.As a result of global climate change,flooding disasters occur more frequently in China and bring greater damage to local agricultural production.The middle-lower reach of the Yangtze river plain is one of the three main regions for producting cotton in China,and its cultivating areas for cotton is about one third of the total cultivating areas for cotton in China.Due to the effect of subtropical monsoon climate,the middle-lower reach of the Yangtze river plain receives concentrated and heavy rains from June to August when local cotton plants are through critical growth stages.When drainage systems are defective and field water table managements are improper,aeration stress is likely to occur in the cotton fields.Considering that cotton is sensitive to aeration stress,the aeration stress frequently occurring from June to August in the middle-lower reach of the Yangtze river plain poses a great threat to local cotton production.Therefore,it is crucial to(?)study the responses of cotton to aeration stress,(?)explore the rational field drainage index,and(?)propose new yield-simulation methods under aeration stress.This study is financially supported by two State Natural Science Funds named"Study on dry crop water production function under water logging stress" and "Study on a unified model for crop water production function under water logging and drought stress".Hubei province,which is located in the middle-lower reach of the Yangtze river plain,was the study area;and cotton was the experimental crop.Lysimeter experiments under aeration stress were continuously performed from 2003 to 2011.Based on the data from these experiments,many statistical and simulation methods including variance analysis,regression analysis,correlation analysis,structural equation modeling and dynamic yield modeling were performed.Consequently,the response of cotton growth and yield under aeration stress with respect to different stress occurring time(at seedling stage,budding stage,flowering stage and boll-opening stage)and different stress forms(waterlogging,submergence,and submergence followed by waterlogging)was analyzed.Anew drainage index applicable to submergence followed by waterlogging during multi-growth stages was proposed.Finally,an empirical and dynamic yield model(improved Morgan model)as well as a mechanism and dynamic yield model(improved CROPR model)under aeration stress were established.The main results are as follows:(1)Waterlogging inhibited the growth of cotton morphology less than submergence even with a longer duration,while submergence followed by waterlogging stress inhibited the most.The aeration stress occurring in the budding stage and flowering stage inhibited the growth of morphology characteristics significantly(p<0.05),while the inhibition in the boll-opening stage was not significant.Leaf area index was the most sensitive morphology index describing the response of cotton to waterlogging stress,followed by stem diameter and plant height.The average yield reduction rate of waterlogging was smaller than that of submergence and submergence followed by waterlogging stress.Aeration stresses occurring in the flowering stage reduced cotton yield significantly,but little yield-reducing effect was found in the boll-opening stage.And the yield-reducing effect of aeration stress at the budding stage was between other two growth stages.The adverse effect of aeration stress on seed cotton yield was greater than that on dry matter yield.(2)Structural equation modeling(SEM)was performed to reveal the relationships among aeration stress,hot weather,cotton growth and yield at various cotton growth stages.The model results showed that including high temperatures would affect the identification of the growth stage most sensitive to aeration stress.When high temperatures were included,cotton sensitivity to aeration stress at the flowering stage was three-fold higher than those at other stages.Both aeration stress and high temperaures had significant effects on cotton yield while the interaction between them was only significant in one experiment,which may be related to the magnitude of aeration stress effect.Cotton reproductive growth was significantly impeded by aeration stress while vegetative growth was not.This result was probably caused by the recovery of vegetative growth,which was also demonstrated in this study.(3)Under submergence followed by waterlogging,the drainage indices based on division of submergence duration and waterlogging duration,compared with the indices based on division of surface and subsurface,can describe the relationship between the aeration-stress degrees and yield reduction more stably over different years.In the process of submergence followed by waterlogging,submergence would reduce the yield-reducing effect of waterlogging on cotton yield.And when this effect of submergence on waterlogging was included,the yield reduction of waterlogging was 0.293 times as much as that of submergence.Based on the above analysis,a new index named CSFEW30 used under submergence followed by waterlogging during multiple growth stages has been proposed.And this drainage index was proved to be significantly(R2=0.629,n=15,p<0.001)related to cotton yield reduction rate.(4)Two dynamic models(Morgan model and CROPR model),which are commonly used for simulating crop yield response under water deficit were improved to apply under aeration stress.The improved Morgan model is an empirical model while the improved CROPR model is a mechanism model.Both of these two improved models have adopted crop response functions that are well connected with field water tables;thus,they are practical in field drainage.Each of the two models has its own advantages,so one should adopt the proper model according to actual conditions.To be specific,the improved Morgan is an empirical model which only requires a small amount of data and its simulation accuracy is acceptable.The improved CROPR is a mechanism model which emphasize the crop response mechanism under aeration stress;thus,it performs better than the improved Morgan.Both of the two improved models performed well in simulating cotton dry matter growth and seed cotton yield under aeration stress.In summary,the results of this study have revealed the response of cotton growth and yield under various existing aeration-stress situations.And also,a drainage index applied under submergence followed by waterlogging during various cotton growth stages has been proposed.Moreover,the dynamic yield models that are closely related to field water table management have been established.The results of this study could offer valuable references for the planning,design and management of field drainage under flooding disasters.