222 BACTERIA AND SOIL FERTILITY 



It is estimated that the rivers of North America carry to the 

 ocean each year 474,000,000 tons of soluble constituents, a 

 quantity sufficient to cover one hundred acres to a depth of nearly 

 three thousand feet. Although the greater part of this is common 

 salt and other non-valuable compounds, yet there are appreciable 

 quantities of plant-food in such waters, as is witnessed by the 

 33.4 pounds of potassium, the 22.8 pounds of nitrogen, and the 

 3.5 pounds of phosphorus which work at the Utah Experiment 

 Station has found to be the average quantity contained in one 

 acre-foot of the streams of the intermountain region. Drain 

 waters are even richer than this, and as much as 133.0 pounds per 

 acre- foot of water have been found in some cases. 



Loss of Nitrogen. — Carefully controlled experiments extend- 

 ing over half a century have been conducted at the Rothamsted 

 Experimental Station where the yearly rainfall is about thirty 

 inches, and the annual loss of nitrogen was found to be 35.5 

 pounds per acre. This is about the loss which experiments cover- 

 ing a period of ten years indicate occur at the Greenville (Logan, 

 Utah) Experimental Farm, where twenty-£ve inches and over of 

 irrigation water is applied to a soil during a season. The quan- 

 tity actually leached from the soil is greater with large than with 

 small but oftener applications of irrigation water. Moreover, 

 the plants growing on the soil modify materially the loss of ni- 

 trates in the drain water. 



The economic value of this is seen from the fact that this 

 quantity of nitrogen in the form of commercial fertilizers, at 

 Lnty-five cents a pound for the nitrogen, would cost $8.88. 

 Moreover, grain grown on soil from which the available nitrogen 

 is being continually leached is low in protein. Undoubtedly, the 

 great merits of our dry-farm wheats as bread-makers in a large 

 measure is due to the fact that the scanty rainfall during the 

 growing season is not sufficient to remove the soluble nitrogen 

 from the roots of the growing plants. Hence, it is taken up by 

 the growing plants with the result that the gluten content of 

 the wheat is high. In irrigated districts there is a great tendency 

 to over-irrigate, hence low-protein gram is produced. 



