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在人工控制试验条件下，采取二次通用旋转组合设计，系统研究了冬小麦一夏玉米一年二作制中上、下两茬作物的水肥耦合效应。结果表明，水肥耦合存在一个阈值。低于阈值下限水平，氮（N）、磷（P）无明显增产效应，水分利用效率低；高于阈值上限，水肥互作效应呈减小趋势；在阈值范围内，水肥互作增产效应明显。增加N、P投入和适宜限量供水是提高水利用效率的重要途径。通过对所建数学模型的计算机模拟，提出了不同决策目标下的水肥优化方案。
Under the artificial control test conditions, the second general rotation combination design was adopted to systematically study the coupling effect of water and fertilizer on the crops of the upper and lower in the second crop of winter wheat and summer maize. The results show that there is a threshold for water-fertilizer coupling. Below the lower threshold level, nitrogen (N) and phosphorus (P) had no significant increase effect and low water use efficiency. Above the upper threshold, the interaction effect between water and fertilizer showed a decreasing trend. Within the threshold range, . Increasing N, P input and suitable limited water supply are important ways to improve water use efficiency. Through the computer simulation of the mathematical model built, the optimal scheme of water and fertilizer under different decision-making targets is proposed.