SOIL MANAGEMENT OR CONTROL 5 



of fertilizers is on the plant rather than on the soil, and is 

 independent of other factors. That is, while it is admitted that 

 other factors influence plant growth, it has been held that the 

 effect of the fertilizer is not to modify the influence of the other 

 factors but to directly influence the plant by increasing its food 

 supply. As a consequence, it has also been generally assumed 

 that the influence of fertilizers is additive, that is, the increase 

 in yield of crop is proportional to the increase in fertilizer added, 

 and the increase in yield produced by adding two fertilizers is 

 the sum of the increases which would have been produced by 

 each alone. In this form the theory is essentially a quantitative 

 one, and fertilizer practice should be easily susceptible of con- 

 trol by chemical analyses. But the large mass of data obtained 

 from plot experiments shows that fertilizer effects are not 

 additive. Indeed, the addition of some one or more fertilizer 

 constituent is sometimes followed by a decreased yield. For 

 example, about 20 per cent, of the trials of fertilizers on soils 

 growing corn and reported by the American State Experiment 

 Stations show a decreased yield. And furthermore, in spite of 

 the quantitative character of the theory, and the numerous 

 analyses of soils and of plants which have been made, there is yet 

 lacking any authoritative method for determining in quantitative 

 terms the fertilizer needs of a soil. That analytical methods 

 have a very restricted value in indicating even qualitatively the 

 fertilizer needs of the soil is evidenced by the fact that within 

 the past few years a number of the State Experiment Stations 

 have publicly announced their unwillingness to undertake them. 1 



*In this connection see: The texture of the soil, by L. H. Bailey, 

 Cornell University Agr. Expt. Sta., Bull. No. 119 (1896); Suggestions 

 regarding the examination of lands, by E. W. Hilgard, University of 

 California, College of Agriculture, Circ. No. 25 (1906) ; Chemical analy- 

 sis of soils, by William P. Brooks, Massachusetts Agr. Expt. Sta. Circ. 

 No. 11 (1907) ; Testing soils for fertilizer needs, by F. W. Taylor, New 

 Hampshire Agr. Expt. Sta., Circ. No. 2 (1908) ; The uses and limitations 

 of soil analysis, by J. T. Willard, The Industrialist, Kansas State Agri- 

 cultural College, 34, 291 (1908) ; Soil analysis, by Wm. Frear, Pennsyl- 

 vania Agr. Expt. Sta., Chem. Circ. No. 1 ; How to determine the fer- 

 tilizer requirements of Ohio soils, by Chas. E. Thorne, Ohio Agr. Expt. 

 Sta., Circ. No. 79 (1908) ; Concerning work which the station can and 

 cannot undertake for residents of the state, by Joseph L. Hills, Vermont 

 Agr. Expt. Sta., Circ. No. 3 (1909). 



