CEREAL CULTIVATION WESTERN AREA 377 



except as it may be considered necessary for keeping up 

 the future supply. Phosphorus is the most likely of all 

 mineral foods to be insufficient. It is lacking in Colorado 

 soils, and in soils of a large part of the Great Basin. This 

 food may be supplied in barnyard manure, but only to 

 the extent, it is .said, of about two pounds to a ton of the 

 manure. It may also be added in the form of the com- 

 mercial product, as superphosphate or raw rock phosphate. 



The chief soil amendments in this area will be accom- 

 plished by (1) applications of barnyard manure, by 

 (2) green-manuring, and (3) in crop rotations. Humus 

 probably always contains phosphorus in combination. 

 In California soils it comprises. 01 to .08 per cent of the 

 humus, throughout the entire depth to which humus 

 reaches, though the quantity is always greatest in the 

 upper few feet. 



406. Commercial fertilizers. In view of the condi- 

 tions just described, it is an open question whether 

 commercial fertilizers may be profitably employed in this 

 area, considering their cost. As in the Great Plains, there 

 is little or no reliable information on the matter resulting 

 from experiments. Such experiments have been con- 

 ducted in Australia where conditions of climate and crop 

 adaptation, at least, are similar to those of portions 

 of this area, particularly California and Arizona. At 

 Wagga, New South Wales, 2-years trials of many fertilizers 

 for wheat were made in which superphosphates gave 

 results uniformly good, and better than any other fer- 

 tilizer. The addition of only 100 pounds of superphos- 

 phates to the acre resulted in a gain of 13^ shillings an 

 acre above the cost of manure, and an increase in acre- 

 yield of 4 bushels above that of the unmanured plat. 

 The rainfall was 8 to 12 inches during the time the wheat 



