THE WATER-COST OF DRY MATTER 139 



sand or poor in clay. However, the fertility of the soil, 

 as expressed in plant-food content, or in good structure, 

 seems to be of more importance than the texture of the 

 soil. Any fertile soil, of whatever texture, will produce 

 dry matter at about the same cost of water, providing all 

 other factors are approximately the same. 



99. Mineral food or soil fertility. The fertility of a 

 soil, especially as measured in mineral food, is a large 

 determining factor in the water-cost of dry matter. It 

 has been shown in Chapter VI that transpiration is 

 affected by the dissolved mineral constituents of the soil. 

 The actual quantity of water required to produce one 

 pound of dry matter is, likewise, materially influenced by 

 the mineral plant-food in the soil. In practically every 

 investigation, from the first to the latest, soils rated as 

 fertile, because of their large annual yields, invariably 

 yielded dry matter at a lower water-cost than less fertile 

 soils. This law, that crops grown on fertile soils are pro- 

 duced at a lower cost than those grown on an infertile 

 soil, has been especially brought out by the diminished 

 water-cost of crops grown on soils to which commercial 

 fertilizers have been applied. The Utah experiments 

 showed that, on moderately fertile soils, the transpiration 

 ratio could be varied from 247 to 639 by applying very 

 small quantities of commercial fertilizers. On two very 

 infertile soils, the transpiration ratio due to fertilizers was 

 reduced, in the case of the sand from 1,012 to 459, and in 

 the case of the clay from 1,331 to 445. Soils of high fer- 

 tility, however, did not respond to the application of 

 fertilizers so far as the water-cost of dry matter was 

 concerned. Leather, working under Indian conditions, 

 came to the conclusion that suitable manures enable plants 

 to economize water in the production of dry matter As 



