62 VEGETABLE GARDENING 



tonseed meal decays rapidly and ranks with blood in the 

 availability of its nitrogen, but its high value as a cattle 

 food is rapidly reducing its use as a fertilizer ; natural or 

 Peruvian guanos were formerly used very extensively, 

 but the supplies are practically exhausted, so the material 

 is now of little commercial importance. Nitrogen for all 

 classes of vegetables should be derived from at least two 

 different sources, usually including nitrate of soda. 



106. The use of phosphoric acid. — Phosphoric acid is 

 most essential in growing cereal crops, but it is scarcely 

 less important in vegetable gardening. Soils deficient in 

 phosphorus fail to give large yields and the crops are 

 also slow in maturing. In vegetable gardening, more 

 importance is attached now to the use of phosphoric acid 

 than ever before, and the gardener should not lose sight 

 of the fact that most soils are lacking in this plant food. 



Rock phosphates are the chief sources of. supply. They 

 vary from 12 to 18 per cent in available phosphoric acid, 

 Raw and steamed animal bone are also in common use, 

 and bone tankage is employed by some vegetable grow- 

 ers. Thomas slag, also known as iron phosphate and 

 Thomas phosphate, which contains 15 to 20 per cent of 

 phosphoric acid, is another desirable form. 



107. The use of potash. — Potash is especially important 

 for the root crops, as beets, carrots, turnips, radishes and 

 parsnips. It also enters largely into the composition of 

 many other vegetables. Applications are particularly im- 

 portant for sandy soils and for muck lands. 



Muriate of potash is the most common form used by 

 vegetable growers; but sulphate of potash is preferred 

 for potatoes, and kainit is used sometimes by asparagus 

 growers. 



108. Rate of application. — The rate of application of 

 chemical fertilizers depends upon such factors as (i) the 

 character of the soil, (2) the previous crop grown and 

 the manner in which it was fertilized, (3) the moisture 



