| Huang-huai-hai Plain of China is featured of heavy rainfall in June-September, which accounts for60%-70%of total annual precipitation. The heavy rainfall-induced soil waterlogging stress during the summer rainy season (June-September) is one of the major constraints for summer maize (Zea mays L.) production in the region. In this study, the Xundan No.20, corn varieties was used as tested maize, field experiments and pot experiments were conducted during the summer maize growing season from2011to2013at Hefei Agrometeorological Experimental Station in Anhui province and Zhengzhou Agrometeorological Experimental Station in Henan province. Surface and subsurface waterlogging duration the seedling, jointing and tasseling stages were designed, in order to investigate the effect of waterlogging stress on the growth,photosynthesisi, dry matter accumulation and distribution, grain yield of summer maize and determine the critical days of waterlogging stress. The waterlogging grade indexes of summer maize based on morphological characteristics, physiological characteristics and crop water surplus indexes were built. According to the daily meteorological observation data of46stations from1971to2010, the crop water surplus indexes of each ten days in summer maize growthing period were cacultated, the waterlogging spatial distribution and changing tendency of summer maize were analized. This research can provide information and technical service on disaster prevention in Huanghuai plains, and reduce the yield loss caused by waterlogging.The achievements obtained as fllows:(1) The surface waterlogging was assumed to be5cm depth of water on soil surface and the subsurface waterlogging was considered to be90%of field capacity. Compared with CK, the surface waterlogging for3-7days at the seedling stages resulted in an average decrease in yield with58.8%-69.8%, the grains per spike decreased significant, while the100-grain weight was not changed so much. The surface waterlogging for3days at the jointing and for5days at tasseling stages resulted in an average decrease in yield with28.4%and42.8%, the grains per spike decreased not significant, and then the100-grain weight decreasing was the main reason of yield loss. Waterlogging stress not only reduced the height of maize plant, but also affected the characters of the accumulation aboveground dry matter weight and leaf area per plant. The proportion of aboveground dry matter in leaves stems and corncob was changed, the proportion of corncob was reduced. The grain filling rate at25-35days after silking in the surface waterlogging for5days at the jointing or tasseling stages was decreased. Therefore, effective measures should be taken to avoid waterlogging for3days at jointing stages or5days at tasseling stages, when heavy rainfall occurred in the growing season of summer maize.(2) Waterlogging stress not only reduced the leaves chlorophyll contents of summer maize significantly,but also affected the net photosynthetic rate of leaves. The reasons for net photosynthetic rate reducing as waterlogging1-3days at seedling stage was non-stomatal factors, however, stomatal factors were predominating factors when waterlogging were above5days. Waterlogging stress reduced the maximum net photosynthetic rate and light saturation points by15%-61%and8.0%-43.9%, respectively. Energy and water use efficiency, dark respiration and light compensation points were also reduced. Leaves of summer maize can be increasing the adaptability of waterlogging by increasing the net photosynthetic rate under low-light conditions and reducing their own energy consumption.(3) According to the different degrees of waterlogging on growth and development, physiological process and yield loss of summer maize, the waterlogging grade indexes of morphological indexes, physiological indexes and crop water surplus indexes were built, respectively. The morphological indexes including plant height, leaf area per plant, Effective stems per m2, and aboveground dry matter weight. The physiological indexes including leaf chlorophyll content, net photosynthesis rate, transpiration rate, stomatal conductance and intercellular CO2concentration. On the principle of field soil water balance, the crop water surplus index (Q) on a decade basis was constructed with the chief budget terms such as the precipitation, crop water requirement, the original soil water content and seepage. Soil relative moisture and and soil texture were selected to establish the waterlogging grade indexes according to the growth process of summer maize. The whole growth duration of summer maize was divided into four stages, namely sowing to emergence, emergence to jointing, jointing to tasselling, and tasselling to maturity. Waterlogging was classified into three grades, including light waterlogging, moderate waterlogging, and severe waterlogging. The waterlogging grade indexes were determined for each stage and grade.(4) Waterlogging frequency in the whole growth period of summer maize in Huanghuaihai region was0%-30%. High value area were mainly distributed in Huoshan in the southern, Qinhuangdao in northern, Weihai and Qingdao in Eastern of the region. The waterlogging frequency was about30%. Low value area were mainly in the northern and southeastern of Hebei, western of Henan and northern of Shandong province, its waterlogging frequency were around10%. Light and severe waterlogging frequency were both between5%-10%in the whole growing period, while the moderate frequency of waterlogging were within5%. Emergence to jointing and jointing to tasseling were two main stages of waterlogging in growth period of summer maize. The climate trends of crop water surplus indexes in whole growth period were as follows: decreased in northern area, increased in central and south central area, while unchanged in central and eastern. |
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