34 



THE ELEMENTS AND THE SOIL 



Water needed under arid conditions. 

 Under dry-farming conditions, Widtsoe calculates that 



1 acre-inch of water will produce 2> bu. wheat 

 10 acre-inches of water will produce 25 bu. wheat 

 15 acre-inches of water will produce 373^ bu. wheat 

 20 acre-inches of water will produce 50 bu. wheat 



if all the water could be saved and be fully utilized in plant growth. 

 Under average cultural conditions in arid regions, he concludes that 

 approximately 750 pounds of water are required for the production of one 

 pound of dry matter. 



Plant-Food in the Soil 



In estimating plant-food, chemists usually catalogue only the three 

 elements (or combinations of them) that are likely to be much depleted 

 by the growing of crops, nitrogen, phosphorus, potassium. (These 

 determinations were made by the solution-in-hydrochloric-acid 

 method, sp. gr. 1 . 115. Other analytical methods in use would give 

 higher readings, particularly in phosphorus and potash, as stronger 

 acids are used to make the soil solutions.) 



Plant-food in surface soils, with calculations to pounds in an acre (Roberts) 



