14肥料经济学--项目分析与贴现率.docVIP

项目分析与贴现率 Murray Fulton教授 加拿大萨斯卡彻温大学农经系、合作研究中心 　　引言 Introduction　　前两讲关于肥料经济学的讨论论述了为获得最大利润，用于不同作物的各种肥料施用量的决策原则，其共同的主题是，肥料的最佳分配发生在肥料单位用量的增加所带来的边际收益等于由此而产生的边际成本的时候。这一原则的得出是基于一个假设条件，即成本和收益发生在同一个时期。　　In the two lectures on the economics of fertilization, I presented a framework for making decisions about the amounts of various fertilizers to use on different crops in order to maximize profits. A common theme in both lectures was that an optimal allocation of fertilizer would take place when the marginal benefit of applying another unit of fertilizer equaled the marginal cost of this additional unit. Implicit in the development of this rule was the assumption that the costs and benefits occurred at the same time.　　然而，众所周知，项目的成本和收益很少同时发生。在许多情况下，费用得现在支付，而收益则要一段时间后才能获得。此外，一旦开始有了收益，往往会持续一段时间。　　It is well known, however, that the costs and benefits associated with projects rarely occur at the same point in time. For example, in many cases, the cost is incurred now, while the benefits may take some time to occur. In addition, when the benefits do occur, they may last for a period of time.　　例如，新建一个化肥厂需要现在投资，而收益却要等到正式投产后才能获得，且投产后头几年的收益会比以后少，因为新增的产量需要一定的时间才能充分进入分销系统。同样地，一个对农民进行平衡施肥培训的推广项目，涉及到大量的创办费，而一旦进行了投资，相当长的一段时间内都能从中获益。而且与建肥料厂一样，项目实施头几年的收益可能会比较小。这是因为，新技术和措施刚出现时通常不容易被采用，虽说少部分农民也许会先采用，大多数却愿意等等，看这种新方法是否真有好处。最后一个例子与肥料施用有关，施用磷肥和钾肥的经济效益在施肥当季并不能全部发挥出来，而是在以后的各季中能继续发挥作用。　　For example, the construction of a new fertilizer plant means incurring a cost now. The benefits, however, do not occur until the plant is operating. Even then, the benefits in the early years are likely to be less than in later years, when the additional production can be fully integrated into the distribution system. In a similar fashion, the development of an extension program to educate farmers about the benefits of balanced fertilizer involves a major initial cost. Once this cost is incurred, the benefits are likely to last for a substantial period of time. In addition, as with the fertilizer plant,