Spatial and temporal variations of water supply and demand during the growth stage of summer maize above the Bengbu Sluice in the Huaihe River Basin, China
Crop water supply and demand is an important reference for rational and scientific irrigation. The imbalance of water supply and demand is also the root cause of agricultural drought and flood. Based on meteorological data from 91 stations from 1961-2015 above the Bengbu Sluice in the Huaihe River Basin, we calculated effective precipitation of summer maize byeffective utilization coefficient method. The water demand was calculated by the Penman-Monteith (P-M) formula andcrop coefficient methodrecommended by the FAO. The spatial and temporal characteristics of water supply and demand of summer maize were analyzed, and the change of water budget index during summer maize growth periods was discussed. The water deficit status (including effective precipitation, water demand, water shortage and water deficit index) during the growth period of summer maize at typical stations were also discussed. The results showed that the effective precipitation in the summer maize was higher in the southern region and lower in the northern region in the past 55 years, and the change trend of each site was not obvious. The spatial distribution of water requirement presented a pattern oflower in the southern region and higher in the northern region, and the whole growth period and the growth stage in summer maize at most sites showed a significant decreasing trend. The spatial distribution of water deficit presented a pattern of waslower in the southern region and higher in the northern region, and most sites showed a significant decreasing trend in the whole growth period and sowing-seeding period. The trend of the other growth stages was not obvious. Comparison of the five typical stations showed the following findings. The water deficit degree of summer maize in northern Zhengzhou station was the most serious. The water deficit amount was about 369 mm in the whole growth period, and the water deficit index was about-0.61. The water deficit degree of Jinzhai station in the south was the lightest. The water deficit amount was about 159 mm in the whole growth period, and the water profit and loss index is about-0.29. Comparison of the water deficit status of summer maize at different growth stages can draw the following conclusions. The water deficit was more serious in the middle and late growth stages than in the early stage. During the tasselingmaturity period, the water shortages at the five stations were 120 mm, 63 mm, 116 mm, 81 mm and 123 mm, respectively, and the water profit and loss indices were-0.60,-0.33,-0.58,-0.42 and-0.59, respectively.