Irrigation water requirement by winter wheat in Huanghuai Plain: Affecting facto rs and characteristics in different climatic years.

By using the last 46-54 years precipitation data from 80 meteo rological stations and the 0-100 cm soil water content data at 10 stations in the Huanghuai Plain, the relationships between the irrigation wa ter requirement and water requirement by winter wheat, and between the precipita tion in winter wheat gro wth season and the soil water content at planting time were analyzed, based on t he principles of farmland water balance. In the meantime, the characteristics of irrigation water requirement by winter wheat in different climatic years were s tudied. In the study area, the isoline of irrigation water requirement by winter wheat was basically in latitudinal distribution, with the requirement increased gradually from south to north. In normal years, the zero isoline was locate d in Xuchang-Fugou-Zhecheng-Luyi-Bozhou-Xiaoxian-Xuzhou. Along this line, the water requirement by winter wheat was in balance with water supply, and no or less i rrigation was required. However, in the north of this line, irrigation should be made, with the irrigation amount increased northward, being about 60- 100 mm an d 100-190 mm and irrigating 1-2 times or 2 t imes. In the south of this line, n o irrigation was required. In the years of plentiful precipitation, the zero iso line moved northward by 0.5-1.0 latitude, and the irrigation area and irrigatio n amount decreased obviously; while in the years of short precipitation, the zer o isoline moved southward by 1.0-1.5 latitude, and the irrig ation area and irrigation amount increased obviously.