Irrigation Externalities and Agricultural Sustainability in South‐eastern Nigeria
研究了尼日利亚东南部灌溉集约化对农业可持续性的影响，发现灌溉初期提高了生产率和利润，但随后土地边际生产率转为负值，且灌溉农场产量稳定性低于雨养农场，表明灌溉外部性对可持续农业政策构成两难。
Agricultural intensification by irrigation is increasingly regarded as the key to solving food supply problems in Sub‐Saharan Africa. Conversely, mounting empirical evidence suggests that irrigation externalities might preclude long‐term sustainability of arable agriculture. Choosing between intensive irrigation schemes and less intensive farming systems is therefore, problematic. The paper examines the implications of irrigation intensification in south‐eastern Nigeria using adjacent rain‐fed farms as the counterfactual. The analyses found mixed results. When first introduced, the irrigation scheme increased marginal factor productivity and gross margins but this has subsequently declined to the extent that the marginal factor product of land has become negative. The annual yields of the irrigated farms were also less stable than those of the less intensive rain‐fed farms. These results indicate the dilemma that irrigation externalities present to sustainable agricultural policy and suggest a need to look again at the potential for developments in rain‐fed systems.