LAND AS A BASIS OF AGRICULTURAL PRODUCTION 8l 



on " A " land yields $1.60, whereas each dollar expended upon 

 " B " yields only $1.50. The productivity of " A " is, there- 

 fore, $1.60 X 10, or 16, while the productivity of " B " is $1.50 X8, 

 or 12. Thus while the capacity ratio of " A " and " B " is 

 5 to 4, the efficiency ratio is 16 to 15 and the productivity ratio 

 is 4 to 3. How much more can a given farmer afford to pay 

 per acre for " A " land than for " B " land? 



Productivity of land may be thought of in terms of pounds 

 or bushels of product per acre, physical productivity ; or pro- 

 ductivity may be thought of in terms of the value of the prod- 

 uct per acre, economic productivity. Land varies greatly in 

 physical productivity due to differences in its physical and 

 chemical properties, and it varies greatly in its economic pro- 

 ductivity because of differences in the value of the product per 

 unit in different localities as well as in the kinds and quantities 

 of products on different pieces of land. 



Under the physical conditions which are conducive to plant 

 growth are included : (1) the moisture and (2) the tempera- 

 ture of the soil and the air, (3) topography, and (4) the mechan- 

 ical structure of the soil. The amount of rainfall and sunshine 

 remaining the same, the moisture and the temperature of the 

 soil, and its capacity for retaining the chemical elements of 

 fertility vary greatly from place to place because of differences 

 in the size of the particles of the soil. By cultivation the soil 

 may be improved to some extent, in this respect. By drainage 

 and by irrigation the moisture of the soil can be modified, and 

 by the use of glass and artificial heat the temperature of both 

 the soil and the atmosphere can be regulated. But in most 

 places and for most purposes Nature has done infinitely more 

 for man than he can do for himself in providing the land with 

 these desirable physical qualities. 



From the standpoint of the economist the most important 

 chemical conditions of plant growth are : (1) nitrogen, (2) phos- 

 phoric acid, (3) potash, and (4) water. Other chemical com- 

 pounds contribute to plant growth, but these four are the 

 ones which require special attention because they are present 

 in the soil in limited and varying quantities, and because they 



