480 INVESTIGATION BY CULTURE EXPERIMENTS 



but in part at least, and probably in large part, to the stimulating 

 action of the soluble salt. 



The soluble salts were applied in addition to phosphorus and the 

 yields compared with the results obtained where the same amounts 

 of phosphorus were applied without the soluble salts mentioned. 

 Limestone was also provided in all cases. The soil is not well 

 supplied with decaying organic matter, the action of which will 

 largely, or, if provided in abundance, entirely take the place of the 

 action of the soluble salts as such. Additional experiments on the 

 Fairfield field include an equally complete test with kainit and 

 potassium sulfate on land to which 8 tons per acre of farm manure 

 had been applied. As an average of 56 tests with each material, 

 200 pounds of potassium sulfate increased the yield of corn by 1.6 

 bushels, while the 600 pounds of kainit gave 1.4 bushels' increase, 

 as compared with 5.4bushels' and 9.9 bushels' increase, respectively, 

 where these soluble salts were applied in the absence of manure, 

 all other conditions being the same. 



Thus, where farm manure is supplied, the soluble salts produced 

 but little effect and are not used with profit. On the other hand, 

 phosphorus usually produces its greatest effect when used in con- 

 nection with organic matter. 



In Table 95 are given the results obtained during seven years on 

 the Du Bois experiment field, in Washington County, Illinois, 

 on the same soil type (gray silt loam on tight clay). In this field 

 there are two independent series of ten plots each, and the crop 

 yields reported in the table are in all cases the average from two 

 plots with like treatment. 



For convenient comparison it may be stated that at conservative 

 prices the value of the seven crops on the untreated land is $34.30, 

 while $99. 1 1 represents the corresponding value from an acre treated 

 with lime, bone meal, and potassium sulphate, costing $46.25. 



The yellow silt loam is found in all glaciations, and much more 

 abundantly (relatively) in the unglaciated areas in the South 

 Central states. Like most of the soils of the Central states, it 

 consists of a loessial deposit. It occupies much of the sloping lands 

 or hillsides, not only in the original hilly sections (as in the un- 

 glaciated, or driftless, areas from southern Illinois to northern 

 Mississippi) , but also in the broken land regions along most of the 



