POTASH 71 



usually are kept on the farm, and returned in the manure; and not because 

 it leaches away from the soil less rapidly than phosphoric acid. The great 

 office of potash in the plant seems to be the structure of starch, since it is 

 found that while all the conditions needed for the assimilation of carbon from 

 the air (the process through which starch is formed), may be present, the 

 starch is not formed without the presence of potash in sufficient quantity. 

 Now, as all woody structure is formed from the starch, it is evident that 

 potash is an important matter in the building up of the plant. Plants like 

 potatoes and corn, which make large surplus quantities of starch to store 

 away in tubers and grain, require large percentages of potash in their food. 



SOILS WHICH NEED POTASH MOST. 



Light, sandy soils near the coast are more apt to be deficient in potash 

 than the heavy clays, especially the clays that are the result of the decomposi- 

 tion of granitic rocks, which naturally contain a larger percentage of potash. 

 But even in some of these soils the application of potash may be found profit- 

 able, because the potash may be, and commonly is, in the form of an insoluble 

 silicate, and this becomes very slowly available to plants through the action 

 of the carbonic acid in the rain water. Black, peaty soils, resulting from the 

 decomposition of vegetable matter, are very commonly deficient in potash, 

 and it is a common remark on the South Atlantic coast that a certain soil will 

 grow upland rice, but will not make a crop of Indian corn. This is mainly 

 because of the deficiency of mineral matters, chiefly of potash. It is a com- 

 mon and almost universal practice among the manufacturers of fertilizers 

 to make the phosphoric acid much larger in proportion than the potash, and 

 it has been shown by experiment that the average commercial fertilizer has, 

 as a rule, too small a percentage of potash in proportion to the nitrogen and 

 phosphoric acid. The plants, like peas and clover, which give us nitrogen 

 free of cost, are great consumers of phosphates and potash, and they can do 

 far more of their important work if well supplied with the mineral elements 

 of plant food. The average complete fertilizer mixture contains not more 

 than 1 to 2 per cent, of potash, while for tobacco, potatoes, and corn and some 

 other crops the potash on light soils should be as high as 10 per cent, for the 

 best results. Therefore, it is important for the progressive farmer to make 

 his own fertilizing mixtures, so that he can vary the proportions to suit the 

 different crops grown ; and if he practices the best rotation, he will find little 

 use for the complete fertilizers, will finally buy nothing but phosphoric acid 

 and potash, and will use these freely for the purpose of getting more of the 

 nitrogen fixed in his soil. 



