The water requirements for 10 main crops in recent 46-year according to 20 meteorological stations in Beijing region were calculated by FAO-56 approach. The variable trends in crop requirement and deficit for 10 crops were analyzed. Based on the cropping pattern in 2006, the regional field water balance was evaluated too. Results show that:the long-term average water requirement for 10 crops range from 308.6 to 729.2 mm; the water requirement for most crops except winter wheat show significant increase trend by 0.49 to 1.17 mm per decade; the water deficit for summer maize, spring maize, soybean, rice and peanut show the significant increase trend by 1.I0 to 1.45 mm per decade; the total water demand for 10 crops in the field is 1293.8×106m3 and the water demand for vegetable, spring maize and summer maize are 379.1×106m3(530.6mm), 291.7×106m3(400.Smm), 285.1×106m3 (452.2mm)and 194.6×106m3 (308.6mm)respectively, which account for 88.9% in total water demand; the precipitation can not meet water demand of 10 crops in different year types.%本文利用FA056灌溉分册推荐的作物系数法计算了京郊地区20个站点近46年10种主要农作物的需水量.并计算了需水量与亏水量的变化趋势,并以2006年北京种植结构为基础,对自然状态下的农田水量平衡状况进行了分析.结果表明:10种主要农作物的多年平均需水量在308.6-729.2mm之间;除冬小麦外,其他作物的需水量变化均呈显著上升趋势,每10年增加量在0.49-1.17mm之间,而亏水量变化则表现为夏玉米、春玉米、大豆、水稻和花生等作物显著上升,每lO年上升1.10-1.45mm;10种主要农作物在自然状态下的多年平均总需水量为1293.8×106m3,蔬菜、春玉米、冬小麦和夏玉米的需水量分别为379.1×106m3(单位面积折合530.6mm)、291.7×106m3(400.8mm)、285.1×106m3(452.2mm)和194.6×106m3(308.6mm),占总需水量的88.9%;不同水文年型下,降水均不能满足作物生长需要,农田水分以亏缺为主.
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