142 



Under "Soil Productivity" (Science, February lo) T. C. Cham- 

 berlin discusses (i) the early origin of soils and of soil vegetation; 

 (2) the sources, wasting, and mixing of soils, the direct relation 

 between film-water and productivity; (3) the great relative con- 

 tact of soil air and the special advantage of its action; (4) the 

 minute forms of plant and animal life which themselves more or 

 less parasitic or predatory on each other modify the inorganic 

 activities, and the fact that the "productivity of soils is measured 

 more by the efficiency of its complex of activities than by any 

 mere measure of its inorganic constituents"; (5) the importance 

 of the capillary cycle in maintaining the supply of potash and 

 phosphorus in the soils, and the selective action of certain soils 

 in concentrating potash and phosphorus surfaceward; (6) that 

 the capillary cycle and the plant cycle contribute to a potash 

 and phosphorus cycle, and that "it is not, in the main, the 

 material substance of the soil that is needed for food, but the 

 energy locked up in grains, fruits, etc.," and therefore that the 

 return of plants or their products to the soil is a most effective 

 mode of maintaining soil productivity; (7) and that, despite 

 alarming reports to the contrary, the lands most densely in- 

 habited and intensely cultivated — at home and abroad — do, unit 

 for unit, show an increase in productivity. 



In answer to this Professor Cyril G. Hopkins has written a 

 lengthy answer (Science, March 17) quoting the experiments 

 at the Illinois State College and Rothamsted. At the latter 

 place in a four-year rotation, including always a legume crop, 

 "the yield of turnips decreased from 10 tons in 1848 to less than 

 I ton per acre as an average for the last 20 years ; that the barley 

 decreased from 46 bushels in 1849 to 14 bushels as an average 

 for the last 20 years; that the clover has decreased from 2,8 

 tons per acre in 1850 to less than one half -ton average since 1890; 

 and that the wheat produced 30 bushels in 1851, and 33 bushels 

 average during the next 12 years, but only 24 bushels since 1890, 

 and 20 bushels per acre since 1900. 



"As an average of the last twenty years the value of the four 

 crops on the unfertilized land at Rothamsted is $33.83 (from four 

 acres), but where the same crops were grown on adjoining land 



