y8 SOILS AND FERTILIZERS 



acid-soluble potash, the purchasing of potash fer- 

 tilizers is more necessary, but with 0.40 per cent. 

 of acid-soluble potash the way is open to render this 

 potash available for crops. The various ways of ren- 

 dering acid-insoluble potash and other compounds 

 available for crop production, as by rotation of crops, 

 use of farm manures, use of lime and green manures, 

 or by different methods of cultivation have not been 

 sufficiently studied as yet to offer a solution to all of 

 the problems of how to render inert plant food avail- 

 able. 



95. Distribution of Plant Food. In studying the 

 chemical composition of a soil, the surface soil and 

 the subsoil both require consideration. It frequently 

 happens that the surface soil and subsoil have entirely 

 different chemical, as well as physical, properties, and 

 that a soil fault, as lack of potash in the surface soil, is 

 corrected by a high per cent, of that element in the 

 subsoil. This is particularly true of the western prairie 

 soils, where the surface soils generally contain less 

 potash and lime, but more nitrogen and phosphoric 

 acid than the subsoils. When jointly considered the 

 surface and subsoil have strong crop-producing powers, 

 but if considered separately each would have weak 

 points. 



Since crops take their food mainly from the silt and 

 clay, the amount of plant food present in these grades 

 of particles determines largely the reserve fertility of 

 the soil. A soil in which 70 per cent, of the total 

 potash is present in the silt and clay, is in better con- 

 dition for crop production than a similar soil with a 



