关键词: 森林生态效益, 联立方程组, 过度可识别, 三步最小二乘估计

Abstract: By using the last 46--54 years precipitation data from 80 meteorological stations and the 0-100 cm soil water content data at 10 stations in the Huanghuai Plain, the relationships between the irrigation water requirement and water requirement by winter wheat, and between the precipitation in winter wheat growth 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 ifferent climatic years were studied. 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 located 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 irrigation was required. However, in the north of this line, irrigation should be made, with the irrigation amount increased northward, being about 60-100 mm and 100-190 mm and irrigating 1-2 times or 2 times. In the south of this line, no irrigation was required. In the years of plentiful precipitation, the zero isoline moved northward by 0.5-1.0 latitude, and the irrigation
 area and irrigation amount decreased obviously; while in the years of short precipitation, the zero isoline moved southward by 1.0-1.5 latitude, and the irrigation area and irrigation amount increased obviously.

Key words: Forest ecological benefits, Consociation equation set, Excessiveness identification, Three steps least square estimatation