56 DRY FARMING 



able to plants. Thus the loss of 2,200 pounds of nitrogen, 

 the average of the six comparisons, represents the dis- 

 sipation of a great amount of organic matter. The 

 practice of summerfallowing especially hastens the de- 

 composition and dissipation of organic matter, and if 

 the practice is a necessary evil, provision must at least 

 be made in the future for supplying the humus-forming 

 materials. The actual amount of nitrogen removed 

 by crops is probably less than one-third of the figure 

 given, the other two-thirds, 1,467 lbs, being lost mainly 

 through surface washing, soil blowing or drifting, and 

 perhaps leaching. 



The phosphorus loss, 567 pounds, is far greater than 

 could be explained by removal in crops. Phosphorus 

 being contained principally in insoluble form in the 

 soil, is not lost by leaching. Surface-washing and per- 

 haps soil-blowing or "drifting" are largely responsible 

 for the losses not accounted for in the crops. 



The figures in table XII. are not to be taken at their 

 absolute value, however. We cannot be certain that a 

 sample of soil from cropped land had at one time the 

 same composition as a sample of virgin land adjoining. 

 However, when repeated comparisons show the same re- 

 sult, we have a good "indication" of the results of our 

 farm practices. That a tremendous loss in organic 

 matter does occur is a matter of common observation, 

 and the bad effects are plainly evident in working the 

 land, 



40. The Rothamsted Experiments on Soil-Fertility. — 

 The best information on the value of soil treatment as 

 opposed to no treatment in good systems of crop rotation 

 is from the Rothamsted Experiment Station near Lon- 

 don, England. Two rotations are compared as follows: 



