LAND AS A BASIS OF AGRICULTURAL PRODUCTION 83 



are more or less readily exhausted and require considerable 

 effort to increase or replenish their supply. In the humid 

 regions where the water needed by plants is abundantly sup- 

 plied by nature this element of fertility requires little or no 

 attention, but in the arid regions water ranks first in economic 

 importance. The carbon dioxide gas of the air is as important 

 to plant growth as is water, but it is present in such great 

 abundance that it has no value placed upon it and hence does 

 not enter into the list of economic conditions which require 

 our attention. 



In comparing the value of two pieces of land physical pro- 

 ductivity is not a safe basis for the reason that the physical 

 product of two pieces of land may be the same but the values 

 of the products may be very different, due to differences in the 

 cost of marketing the products. 



When a man contemplates the purchase of a farm, he wants 

 extent of land with even topography and he wants this land 

 to be fertile, but what is sometimes even more significant than 

 these qualities is the location of the farm which he is to cultivate. 

 In fact the physical and chemical characteristics of the land are 

 greatly influenced by its location. Heat and moisture, and the 

 character of the rocks from which the soil is formed vary greatly 

 from place to place. But besides these variations in the natural 

 conditions, there are variations in the social conditions which 

 influence the production and sale of products. Large popula- 

 tions are in some places concentrated on small areas, leaving 

 vast territories sparsely settled. This variation in the density 

 of population may be explained, in part at least, in terms of 

 variation in the physical environment, but our especial interest 

 is in the effect and not the cause of this variation in the density 

 of population. The farmer who is near a great center of 

 population, such as London or New York, can sell his products 

 for the same price which is paid for like products which have 

 been shipped great distances. Thus it is that of two pieces 

 of land possessing the same physical productivity, or fertility, 

 the farmer prefers the one located nearer a great center of popu- 

 lation, because of the greater " farm value " of the products. 



