ILLINOIS FIELD EXPERIMENTS 



473 



of total potassium, more commonly in the subsurface or subsoil, 

 but sometimes in the surface soil, also; and yet the untreated soil 

 is unproductive, while the addition of potassium salts produces 

 large and very profitable increases in the yield of corn, oats, etc. 



In pot-culture experiments the author has even been able by the 

 addition of potassium sulfate to correct to a considerable extent 

 the injurious property of magnesium carbonate that has been 

 purposely applied to ordinary brown silt loam prairie soil which is 

 known to contain abundance of available potassium. These facts 

 are mentioned here because he recommends, in humid sections, 

 trial applications of potassium salt to all classes of peaty and alkali 

 soils that are unproductive after being well drained, whenever 

 the supply of farm manure is insufficient. It should be understood 

 that plenty of farm manure, preferably quick-acting, or readily 

 decomposable, manure, such as horse manure, will supply potas- 

 sium and thus accomplish everything that potassium salts can 

 accomplish, and on some swamp soils manure produces good re- 

 sults where potassium is without effect. 



In pot-culture experiments soils containing injurious amounts 

 of magnesium carbonate have been treated with calcium sulfate 

 (land-plaster) which brings about a double decomposition, or inter- 

 change, forming the harmless insoluble calcium carbonate (lime- 

 stone) and the very soluble magnesium sulfate, which is subse- 

 quently leached out, leaving the soil productive. (Seepage 171.) 



The new Manito experiment field is on alkali soil consisting of 

 peaty, clayey sand with some gravel, and containing sufficient 

 total potassium for normal crop yields. In Table 92 are recorded 

 the treatment applied and results obtained in 1907. 



TABLE 92. CORN YIELDS IN ILLINOIS SOIL EXPERIMENTS: NEW MANITO 

 FIELD: PEATY ALKALI SOIL 



