THE VEGETABLE GARDEN 



versa. At present there are five different grades 

 on the market containing anywhere from seven 

 to nineteen or twenty per cent of phosphoric acid. 

 Its price also varies according to its contents. 



When soluble phosphoric acid is added to the 

 soil it becomes " fixed " or insoluble by combining 

 with lime, making lime phosphate, or by uniting 

 with iron or alumina. The former is the most desir- 

 able form, as the phosphoric acid in lime phos- 

 phate is more readily reconverted into available 

 forms for plant use by the fermentation of organic 

 material in the soil than are the phosphates of iron 

 and alumina. Therefore, to insure the formation of 

 lime phosphate, it is necessary that the soil should 

 be well supplied with lime and humus. 



The other element, potash, which it is necessary 

 to add to the soil is derived mainly from muriate 

 or chloride of potash, sulphate of potash, and 

 unleached hardwood ashes. Most of the potash, 

 other than the ashes, comes from mines in Ger- 

 many. Sulphate of potash is a much better form 

 to use because the chlorides in muriate of potash 

 seem to have an unfavourable effect on crops. 

 This is particularly true of tobacco and potatoes. 



Kainit is frequently offered and sold by dealers. 



[40] 



