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土壤保护措施效益的评估通常用成本——效益分析法。类似的方法有逼近分析法,主要用于对一定时期内土壤退化造成产量下降的恒定推算上。实践证明,用逼近分析法所得结果在定量及定性两方面误差很大。静态产量降低模型往往过高反映出土壤侵蚀流失量,并加大了分析中流失量的权重,因而,很可能过高地估算了保护措施的效益或得出相反的结果。如果实际产量在前期不再下降,所得的分析结果就是相反的,因为在产量是恒定降低的假设前提下,产量的降低很可能会持续下去。本文用肯尼亚的资料来说明产量模型在评估中的误差结果。
The effectiveness of soil conservation measures are usually assessed by cost-benefit analysis. A similar approach is the approach of approximation, which is mainly used for constant projections of the decline in production due to soil degradation over a period of time. Practice has proved that the results obtained with the approach approach in quantitative and qualitative error is very large. The static yield reduction model tends to overestimate the amount of soil erosion loss and increase the weight of the loss in the analysis, so it is likely to overestimate the benefits of protective measures or to the contrary. If the actual output is no longer declining in the earlier period, the result of the analysis is the opposite, since the reduction in output is likely to continue on the assumption that production will be constant. In this paper, we use the data from Kenya to illustrate the error results of the production model in the assessment.