April 21, 1911] 



SCIENCE 



615 



before the Geological Club of the University 

 of Chicago aimed at so fundamental and com- 

 prehensive a presentation of the subject and 

 the report of it by himself in Science, Feb- 

 ruary 10, p. 225, is cast with such pedagogic 

 effect that it is much to be regretted that a 

 goodly part of the discussion was not incor- 

 porated with the report, as without this some 

 statements are likely to be interpreted in a 

 way widely at variance with authentic data 

 and hence in a way to be misleading. 



Although most that is said is undisputed, 

 this presentation in fifty-three terse state- 

 ments of somewhat unusual form is certain 

 to convey to younger students of the subject 

 the impression that each and all of these 

 phases of the great problem of soil produc- 

 tivity have been brought into the clear light 

 . of science and are here set out in proper order. 

 This is, of course, not true and not intended 

 to be so understood but the great confidence 

 accorded to the author's utterances is in 

 danger of leading to the acceptance of his 

 suggestions and beliefs as established knowl- 

 edge, and to assigning to minor factors an 

 importance far too great. 



The importance of capillarity in supplying 

 potassium and phosphorus to crops, empha- 

 sized by the figures which are cited, will be 

 understood as being much greater than can 

 be the case. Indeed, instead of the " capillary 

 cycle " and the " plant cycle " tending on the 

 whole to the concentration of potassium and 

 phosphorus toward the surface of the soil 

 contributing to " secular maintenance," as is 

 implied, quite the reverse tendency is the case, 

 as may be seen from a comparison of the com- 

 position of soils and of rocks. We cite the 

 complete analyses of 27 soils given by Hop- 

 kins' in the form of mean values for three 

 depths. 



In this series Y4 per cent, of the cases in 

 the second depth have the potassium higher 

 than in the surface soil, and 59 per cent, of 

 the cases in the third depth have the content 

 higher than in the surface sample. The 

 larger amount of phosphorus compounds in 



' ' ' Soil Fertility and Permanent Agriculture, ' ' 

 pp. 82-87. 



the surface soil is not a case of concentration 

 due to the action of either or both cycles 

 named, but has occurred in spite of them and 

 is less than it would have been because of 

 their action. The most pronounced effect of 

 both " cycles " is to leave soluble ingredients 

 upon or above the surface of the soil whence 

 they are transported to the sea by both 

 surface drainage and wind action, the loss in 

 this way being materially greater than the 

 supply by capillarity to the root zone. 



to 6| inches 581 16,376 



6| to 20 inches 485 16,649 



20 to 40 inches 488 16,936 



Sedimentary rock 

 Igneous Sand- Lime- 



Rock Shale stone stone 



Pounds per million 



Potassium 24,400 26,981 10,959 2,740 



Phosphorus . . . 1,100 7,426 3,494 1,747 



The phosphorus content" of all rocks is seen 

 to be higher than that of soils, and the higher 

 content of sediminetary rocks will not be as- 

 cribed to either capillary or plant action, but 

 to other processes named in the article. It 

 must of course require a positive addition of 

 plant food elements to cultivated soils, in 

 amounts equal to or greater than all removals, 

 to perpetuate indefinitely uniform or in- 

 creasing productivity. 



Studies like those of Professor Whitson' of 

 phosphorus in cultivated and virgin soils indi- 

 cate, in the case cited, an average loss of 

 P,Ob during about sixty years, of 1,255 pounds 

 per acre, from the cultivated soil, and in but 

 three of the nine comparisons was the loss 

 less than that which would be assigned to 

 removal by crops. It may fairly be ques- 

 tioned whether this difference is due entirely 

 to greater loss from the cropped soils, but it 



^ ' ' Data of Geochemistry, ' ' Bull. No. 330, U. S. 

 Geol. Survey, pp. 26-27. 



= Research Bulletin No. 2, University of Wiscon- 

 sin Agr. Expt. Station. 



