PROPOSITIONS CONCERNING INDUSTRY The productivity of land depends on the variety of human wants. We have seen that the in crease of land demands increased knowledge concerning its productive possibilities, rather than increased area. Every new item of know ledge brought to light by practical cultivators or by experiment stations is the equivalent of added acres. A change in the methods of cul tivation, which permits two crops in the year where there had been but one, is equivalent to the doubling of the land area. It does not follow that the total product will be doubled. This depends upon the remaining limitation, as of capital or labor. But the contribution to the product from land will be doubled.
Another condition of the productivity of land lies in the variety of wants. Just as the divi sion of labor is limited by the extent of the market, so the productivity of land is limited by 300 the variety of products desired. The positive statement of this truth is that every increase in the variety of wants puts some land to a better use and so adds to its productivity. Oftentimes the increased variety in consumption, which thus favorably influences industry, springs not from the discovery of some commodity hereto fore unknown, but from the removal of some prejudice which has prevented the general use of a familiar commodity. Fantastic or fashion able whims have often foolishly retarded the full development of agriculture by demanding products which can be produced at home only with great difficulty ; or by demanding foreign products which can be procured only by ruinous exploitation of home resources in the produc tion of one or two commodities for which an export market has been found. The proposi tion, however, does not refer to a diversity of wants within the country merely. The diversi fication may come equally from new foreign demands: Whatever enables a community to put its land to better use by cultivating crops for which its peculiar properties are more exactly suited, is of eco.omic advantage.
The soil is a result of gradual accumulation, and must be renewed either by natural or by arti ficial means. The soil is to be looked upon as a fund of productive qualities capable of exhaus tion. In some favored localities nature contin
ually renews the fertility of the soil by carrying new elements to replace those withdrawn as plant food. Fine silt and organic matter are brought on the wind, or by inundating rivers in even greater quantities than are used up, so that soil increases each year in depth and fertility. Fields which can be plentifully supplied with manures may be similarly enriched by the agency of man while yielding annual crops. In general, after lands have been cultivated for a longer or shorter period, depending upon the degree of their original fertility, it will be neces sary to supply those elements which either were originally scarce or have become so by cultiva tion. Western prairie lands have in some in stances yielded a single annual crop for thirty years or more in succession, but this soon be comes a wasteful exploiting of nature's accumu lations, and a limit is finally reached when the land must be put to other uses or allowed to lie fallow. An intelligently selected rotation of crops, with a timely supply of the particular elements of soil that are found to be lacking,' will keep the land in good working order indefi nitely. It thus tends to become more like a factory in which materials are supplied and handled in strict accordance with the results expected, and less a mere game of hazard played out by the chances of the distribution of plant food.
Cultivation, the shifting of population, the cheapening of transportation, and other social changes tend to equalize the productivity of differ ent areas. Primitive society finds greater differ ences in the productivity of the different parts of the land at its disposal than a society in which there is a well-developed consumption and diversified industry of the kind that we have come to regard as normal. The decrease of rent gradually effected in the course of ordi nary cultivation through the improvement of poorer soils is first noticeable. The cheapening of transportation and the spread of population to new areas has a profound effect in the same 1 See p. 39.