中文摘要：

流转农地是否可持续利用不仅直接影响着农户的经济收益，还对农地利用过程中所伴随的一系列外部性收益有影响。本文将流转农地进行改良性投资的收益分为经济收益和外部性收益，运用投入产出理论分析经济收益，运用结构分解法分别估算增加有机质价值、增加肥力价值、减少化肥造成水污染价值和减少农药造成环境污染价值，最终确定外部性收益；结合改良性投资成本，通过实物期权模型确定流转农地进行改良性投资的最优时机，并提出鼓励流入方进行改良性投资的相关政策建议。

英文摘要：

The sustainable use of agricultural land of circulation not only directly affects the economic profits of the farm ers, but also affects externality income in the process of agricultural land use. The profits of the improvement of invest ment on agricultural land of circulation were divided into two parts： one is economic profits, the other is externality in come. The economic profits were analyzed by using the theory of input and output; the externality income was determined by using the structural decomposition methods to estimate the increasing value of the organic matter, the soil fertility and the reducing value of water pollution caused by fertilizer and environmental pollution caused by pesticide respectively; the optimal timing of the ameliorable investment on the agricultural land of circulation was determined by using the real op tions model combined with the cost of ameliorable investment, and the relative policy recommendations such as encoura ging the inflow side to conduct the ameliorable investment were put forward.