144 THE BOOK OF WHEAT 



Whitney takes the position that if the soils of eastern and 

 southern United States have any less plant food than when 

 first cultivated, they at least have all the ingredients essential 

 for crop production. This position is certainly supported by 

 statistics that have been given on the amount of. plant food 

 contained by soils. An acre of very fertile soil contains about 

 70,000 pounds, or 2 per cent, of potash in the first foot of 

 ground. A crop of wheat removes about 15 pounds of potash 

 from each acre. It has been estimated that the first eight 

 inches of soil contain on an average enough nitrogen to last 90 

 years, enough phosphoric acid to last 500 years, and enough 

 potash to last 1,000 years. 1 This supply is materially increased 

 when we consider the great depth penetrated by the roots of 

 wheat. It must also be borne in mind that the loss of plant 

 food is often much greater than that removed by crops; for 

 example, it has been given as three to five times as much in the 

 case of nitrogen. 



Extensive farming, nevertheless, soon reduced the produc- 

 tivity of our first cultivated soils, and with the opening of the 

 large and level western wheat fields of fully as great fertility 

 as was ever possessed by any soils of the United States, many 

 of the older lands were abandoned. Now, however, most of 

 the farm lands of the west have ""-een occupied, the standard or; 

 farming is being raised, and conditions have so changed as to 

 make it seem profitable again to resume the cultivation of these 

 abandoned lands. But they must be farmed by intensive meth- 

 ods, of which fertilizing is a valuable part. Some lands have 

 already been restored to fertility and are being cultivated with 

 profit. 



Missouri soils are still rich in plant food, yet their produc- 

 tivity is much less than it was 50 years ago. Commercial fer- 

 tilizers had been profitably used in wheat raising in Ohio over a 

 decade ago. Growing a leguminous crop on light sandy soil 

 deficient in humus increased the yield of the following crop of 

 wheat over 50 per cent in Arkansas. When 400 pounds of a 

 complete fertilizer were used in addition, the following 2 

 years the wheat crop averaged over 70 per cent more than on 

 soil not thus treated. Manure treatment and the application 

 of phosphorus is found very profitable in Illinois. 

 1 Kept. Mich. Board Agr., 1905, p. 147. 



