Yield reduction analysis and determination of drainage index in cotton under waterlogging followed by submergence

Abstract: In order to study the effects of submergence and waterlogging on cotton yield, submergence and waterlogging experiments in lysimeters of three stress forms with different degrees and different growth stages were conducted in the Irrigation and Drainage Experiments Station of Wuhan University from 2008 to 2011. Three stress forms with different degrees included submergence for 1-3 days, waterlogging for 3-8 days, and submergence for 1-5 days followed by waterlogging for 3-8 days. The experiment was performed in 3 cotton growth stages: budding, flowering and boll opening stage. In this study, 2 types of drainage indexes including sum of flood depth and excess soil water under submergence (SWFDH), sum of excess soil water under waterlogging ( SEW' 30), sum of flood depth under submergence (SFW) and sum of excess soil water under submergence and waterlogging (SEW30), were used to quantify stress degrees of submergence and waterlogging. The effects of submergence and waterlogging on cotton yield were quantified by yield reduction rate factors (YR) of each stress forms, and thus weight factor of waterlogging was determined. The responses of three growth stages to submergence followed by waterlogging were quantified by YR of each growth stages, and thus generalizing yield reduction rate factors (NYR) of three growth stages were estimated. Based on NYR and weight factor of waterlogging, a new drainage index cumulative sum of flood depth and excess soil water (CSFEW30) was put forward. The results showed that the drainage indexes, SWFDH and SEW' 30, could well describe the relationship between the degree of submergence and waterlogging with yield reduction more stably than SFW and SEW30 in different years. The yield reduction rate factors of submergence and waterlogging were 0.266%/(cm·d) and 0.202%/(cm·d), respectively. Yield reduction under waterlogging was 0.759 times that under submergence. Without considering the effect of submergence on yield reduction of following waterlogging, the calculated yield reduction would be 43.1% higher than the actual yield reduction. And when the effect was taken into account, the yield reduction of waterlogging was 0.293 times as much as that of submergence. Flowering stage was the most insensitive growth stage for cotton under submergence and waterlogging, followed by budding stage and boll opening stage. Yield reduction rate factors of three growth stages are 0.114%/(cm·d), 0.150%/(cm·d) and 0.033%/(cm·d), respectively, and thus the proportion of yield reduction in the three stages was 0.760:1:0.220. Without considering the effects of submergence and waterlogging in former growth stages on yield reduction in latter stages, the calculated yield reduction would be 8.8% higher than the actual yield reduction. The effects of submergence and waterlogging on yield in former stages would extend to latter stages slightly. Drainage index CSFEW30 was of highly significant (R2=0.629, n=15, P＜0.001) linear relationship with yield reduction, which provides evidence for the determination of drainage standard of cotton under the submergence and waterlogging control.