Makch 17, 1911] 



SCIENCE 



423 



recently accepted the post of Government 

 Botanist in charge of the botanical section of 

 the Biological Commission of the Department 

 of Agriculture and of the Bureau of Forestry 

 in Mexico. 



DISCUSSION AND CORRESPONDENCE 



y SOILS AND CROPS 



If we accept Professor Chamberlin's view, 

 " that the total eon of productive soils may be 

 assigned a period of at least tens of millions 

 of years " (as expressed in his article on 

 " Soil Productivity " in Science, February 

 10, 1911, and if we accept his endorsement of 

 Cameron's estimate for the United States that 

 the capillary waters are carrying potassium 

 toward the surface at the rate of from 40 to 

 83 pounds per acre per annum, while the total 

 average removal amounts to only 23 pounds 

 (20 pounds in crops and 3 pounds in drain- 

 age), then we might expect the potassium to 

 accumulate in the surface soil at the rate of 

 1,700 to 6,000 pounds per acre per century, or 

 at the rate of 17,000 to 60,000 pounds per 

 thousand years, on normal level lands not 

 subject to surface erosion; we might expect 

 the surface soils to be many times richer in 

 potassium than the corresponding subsoils, 

 and the older soils to be much richer than 

 those of more recent but similar origin. 



In contrast with these theoretical deduc- 

 tions the science of chemistry reveals the facts," 

 for example, that the common prairie lands of 

 the oldest Ulinoisan Glaeiation contains as an 

 average 12,470 pounds of potassium per mil- 

 lion of dry surface soil and 14,050 pounds per 

 million of the subsoil; that the more recent 

 Early Wisconsin Glaeiation contains 18,120 

 pounds in the surface and 19,650 pounds in 

 the subsoil; and that the Late Wisconsin 

 Glaeiation contains 22,510 pounds in the sur- 

 face and 26,690 in the subsoil. 



The corresponding timbered soil types con- 

 tain, in the oldest Ulinoisan Glaeiation, 15,- 

 100 pounds of potassium (per million of dry 

 soil) in the surface and 16,050 pounds in the 



'Illinois Experiment Station Bulletin 123 and 

 unpublished data. 



subsoil; while in the Early Wisconsin Glaeia- 

 tion the respective amounts are 18,080 and 

 21,100 ; and in the Late Wisconsin Glaeiation 

 there are 23,800 pounds in the surface and 

 26,100 in the subsoil, per million of dry soil. 

 If two inches of water soak into a soil and 

 if one inch escapes by evaporation and the 

 other by subdrainage, the net result is not 

 gain but loss of soluble minerals, under nor- 

 mal conditions. In level or slightly undula- 

 ting upland areas, such as the loess-covered 

 prairies of the Central-West, which neither 

 receive deposits from overflow nor lose par- 

 tially depleted soil by erosion (especially 

 while protected by prairie grasses), the opera- 

 tion of the natural law tends steadily toward 

 soil depletion, with respect to the mineral ele- 

 ments; and this law has been in operation 

 since the glacial or loessial age, wherever the 

 climatic conditions have been similar to those 

 now prevailing in our humid sections. The 

 accumulation of organic matter (including 

 some phosphorus) in such glacial or loessial 

 soil begins some time after its deposition and 

 continues until a maximum is reached, after 

 which the organic matter, as well as the val- 

 uable mineral elements, tends to decrease, the 

 latter because of leaching, as from the begin- 

 ning, and the former because the rate of decay 

 finally exceeds the rate of growth or accumu- 

 lation. 



That phosphorus is an essential constituent 

 of the living tissues of plants and that it ac- 

 cumulates in plant residues in prairie soils 

 are well-established facts, but a theory that the 

 phosphorus brought to the surface in capillary 

 moisture exceeds that removed by crops and 

 drainage is not supported by the composition 

 of soils of similar origin and different age. 

 Thus ultimate analysis shows per million of 

 dry surface soil 420 pounds of phosphorus in 

 the oldest Blinoisan Glaeiation, 595 in the 

 more recent Early Wisconsin, and 705 pounds 

 in the Late Wisconsin. 



Even the theories of the federal Bureau of 

 Soils and the estimates of the United States 

 Department of Agriculture must be heavily 

 discounted if they stand opposed to estab- 

 lished facts; for one fact outweighs a thou- 



