Response of cotton during flowering and boll-forming period to groundwater table and heat stress as well as determination of drainage index

Abstract: Cotton production is frequently limited by periods of subsurface waterlogging and heat stress in Hubei plain area of China in summer, but the combined effects of surface waterlogging and heat stress on cotton have been rarely studied. In order to investigate the effects of groundwater table (WT) on main morph-physiological traits and yield of cotton under high temperature (HT) condition as well as determination of drainage index, the combination of WT and HT stresses was carried out by test-pit in Irrigation and Drainage Experimental Station of the Four Lake Engineering Management Bureau, Jingzhou, China in 2012 and 2013. WT were set as 0, 30 and 50 cm with waterlogging for 10 days and HT duration for 6 days (from 10:00 to 16:00 per day) during flowering and boll-forming period of cotton. The morphological indexes as plant height (PH) and complex ratio of red stem to green stem (R/G), and physiological traits as photosynthetic efficiency, leaf pigments and antioxidant enzymes along with yield components were measured and analyzed. The results were as follows: the PH and R/G of cotton were decreased in WT treatments of 0 and 30 cm, whereas they were not significantly different in HT situation. Chlorophyll (Chl) content and photosystem II potential photochemical conversion efficiency of leaf (4 th from top) decreased with increasing WT under HT condition. The relationship of either Chl or photochemical conversion efficiency with WT and HT could be described by linear models (R2=0.961-0986, P<0.01). Superoxide dismutase (SOD) and peroxidase (POD) activities of leaves (4th from top) increased firstly and then declined and catalase (CAT) activity declined with the increment in WT, but malondialdehyde (MDA) content increased. SOD and POD activities decreased remarkably while MDA content increased rapidly at WT of 0-30 cm with HT stress, indicating that HT exacerbated the degree of membrane lid peroxidation. However, HT contributed to subsurface waterlogging tolerance by maintaining a higher SOD and POD activities at WT of 50 cm. The yield losses of the combination of WT and HT attributed principally to a reduction of boll numbers and boll quality. The reduction of seed yield was highest in the treatment of WT+HT (33.7%), followed by WT (26.2%) and HT (7.5%). Assuming the reduction of 15%-20% of seed yield was accepted, the sum of excess soil water of 80 cm (SEW80) during flowering and boll-forming period was 216.0-321.2 cm·d with 6 days of HT for WT 0-50 cm. The study may provide valuble information for cotton stress-resistance cultivation and drainage management in Hubei plain lake region of China.