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灌溉水的产出弹性对每一作物来说极无伸缩性，表明减少灌溉水的供应可能对作物产量只有相对较小的影响。本文报告了对美国17个西部州13种灌溉作物的柯布—道格拉斯和二次方程生产函数的预测。预测了每一作物的规模利益，灌溉水的产出弹性，水和土地之间的边际替代率。用统计测验的J—测验判断两种函数形式是否是正确的描述。结果表明：4种作物（大麦、高粱、甘薯和水稻）接受柯布—道格拉斯函数的描述，3种作物（棉花、蚕豆和甘薯）接受二次方程函数的描述。
The output elasticity of irrigation water is extremely non-stretchy for each crop, suggesting that reducing the supply of irrigation water may have only a relatively small effect on crop yields. This paper reports the prediction of the Cobb-Douglas and quadratic production functions of 13 irrigated crops in 17 western states of the United States. The scale benefits of each crop are predicted, the output elasticity of irrigation water, and the marginal rate of substitution between water and land. J-tests using statistical tests to determine whether the two forms of function is correct description. The results showed that the four crops (barley, sorghum, sweet potato and rice) accepted the Cobb-Douglas function description and the three crops (cotton, broad bean and sweet potato) accepted the description of the quadratic equation function.