124 The Potato 



form in which to buy potash. The chlorine in the com- 

 bination with the potash has some tendency to make soils 

 sour, and in some experiments ^ has produced smaller yields 

 and poorer quality than when sulphate of potash was used. 

 The latter, 47 to 49 per cent potash, is more expensive and 

 is but little used except for tobacco fertilizers. Kainit is a 

 raw material of low grade (12 per cent potash), and is rela- 

 tively higher in price a pound of potash contained in most 

 places on account of the freight on material of less value. 

 Potash fertilizers are mixed in the soil after applications 

 and are not likely to be lost by leaching. The solutions in 

 soil water are rather caustic, and heavy applications are 

 likely to burn the roots of plants if applied close to the 

 seed. The old idea of mixing fertilizers according to the 

 chemical composition of the crop has led to the use of 

 fertilizers containing much more potash than practical 

 experience of farmers and scientific experiments warrants. 

 Mixed fertilizers often contain 7 to 12 per cent of potash. 

 A number of experiments by the Geneva and other agri- 

 cultural experiment stations have shown that this is too 

 high for profit. Five per cent is usually all that will pay. 

 Potash is so abundant in most American soils that nitro- 

 gen and phosphorus are likely to be much more needed. 



CALCIUM 



Calcium, in the form of lime, is seldom so deficient in 

 American soils as to render its use directly necessary as a 

 fertilizer for potatoes. In fact, very heavy yields of pota- 

 toes are often grown on soils too acid to grow clover. The 

 potato seems to be very tolerant of acid conditions. Heavy 

 applications of lime produce conditions under which the 



• Brooks, Mass. Expt. Sta. 



