ABSTRACT
The studies reviewed in the previous chapter define productivity in physical terms as crop output per acre per year. This definition is adequate when considering erosion effects on particular soils at particular times and places when all other factors affecting production are held constant. But to judge the significance of erosion-induced productivity loss from a national perspective, an economic dimension must be given to the estimates of loss. Knowledge that erosion is reducing yields of corn or soybeans or wheat by so many bushels per acre per year does not provide enough information for this judgment. We need to know the value society places on corn, soybeans, and wheat to decide the importance of the losses and to determine how much can justifiably be spent on erosion control to reduce them or on other measures to offset them. That is to say, we need to know the economic cost of the losses. Moreover, when the losses extend over a period of time, their cost must be calculated in present value terms, so a rate of discount must be brought into play.
