560 VARIOUS FERTILITY FACTORS 



wick soils. The New Brunswick soils are said to be representative 

 of the district. In commenting upon the analytical data, Professor 

 Shutt says : 



"Since we must suppose, from the information furnished, that the culti- 

 vated soil was originally identical, or practically so, with the virgin soil t it is 

 evident that great exhaustion of fertility has taken place, due, no doubt, to suc- 

 cessive cropping without any adequate return of plant food." (Report for 

 1899, page 133.) 



It is certain that on sloping lands a very considerable part of the 

 total loss of humus, nitrogen, and phosphorus is due to soil erosion, 

 although this is the minor factor on nearly level lands. It should be 

 kept in mind that in respect to loss of humus, and of the plant food 

 contained in humus, sheet washing on uniform slopes may be even 

 more effective than gullying, and that it is extremely important and 

 necessary to prevent or at least to reduce to the minimum both 

 forms of erosion, the sheet washing by means of cover crops, deep 

 contour plowing, contour ridging, or terracing, if necessary, and 

 the gullying by frequent dams and by keeping the draws in per- 

 manent meadow. 



President Van Hise makes the following statements regarding 

 the loss of phosphorus from Wisconsin soils, as determined by 

 " quantitative studies ": 



"Whitson finds as the result of an average of nine typical tests that 'the sur- 

 face 8 inches of virgin soil contains 1256 pounds of phosphorus per acre, while 

 that of the cropped fields contains but 792 pounds, an average loss per acre on 

 these cropped fields of 464 pounds, or 36 per cent of its original content. The 

 average of cropping for these fields has been 54. 7 years.' In other words, during 

 the past half century in Wisconsin one third of the original phosphorus of the 

 soil has been lost in the cropped fields. What has been proved for Ohio, 

 Illinois, and Wisconsin and other states where tests have been made is unques- 

 tionably true for the other states in the country which have been settled for 

 some time. 



"In what conditions will the soil of the United States be as to phosphorus 

 content fifty years hence if this process of depletion be allowed to continue un- 

 checked?" (See page 221 of "Conservation of Natural Resources," published 

 by the American Academy of Political and Social Science, Philadelphia, 1909.) 



It may be noted that a loss of 464 pounds of phosphorus in 55 

 years is only 8^ pounds per annum; and, if we deduct i\ pounds 

 for loss in drainage (see Table 74), the loss by cropping does not 



