POTASH AND SULFUR FERTILIZERS 181 



purpose the lime in the ashes is even more effective than the 

 potash because there is more of it. 



233. Insoluble potash fertilizers. — Many rocks contain 

 potash ; for this reason there is a large quantity in soils. It 

 has been proposed to grind the rocks that are richest in pot- 

 ash and to use them for fertilizer. Experiments with finely 

 ground feldspar have been conducted by a number of investi- 

 gators, but have given little encouragement for the successful 

 use of this material. An insoluble form of potash is not 

 given any value in the rating of a fertilizer. 



234. Effects of potash on plant growth. — Plants require 

 potash in order to make a normal growth. If no available 

 potash is present, the elaboration of sugar and starch in 

 plants is curtailed"^ Crops like potatoes and sugar beets, that 

 produce much starch and sugar, are greatly benefited by an 

 abundant supply of potash. It also has other functions in 

 plants that make it indispensable. The grain of cereals fills 

 out better and weighs more to the bushel and the straw is 

 stronger, when a good supply of potash is available. Leg- 

 umes are usually greatly benefited by potash. The large 

 formation of sugar and starch affords the nitrogen-fixing 

 bacteria the kind of food which they need, and to obtain 

 which they live in symbiosis with the legume. If part of 

 a clover and timothy field be well fertilized with potash, 

 and another part receive none, it is likely to be the case that 

 the proportion of clover to timothy will be much greater on 

 the fertilized part of the field than on the unfertilized part, 

 unless the natural supply of available potash is unusually 

 large. 



Potash tends to delay ripening of plants, but not to the 

 same extent as does nitrogen. It also has an influence 

 similar to that of phosphoric acid, in that it helps to overcome 

 the tendency of nitrogen to make plants less resistant to dis- 

 ease. 



