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 sometimes applied by aspara- 
gus growers. Wood ashes are also used extensively. 
108. Rate of application. — The rate of application of 
chemical fertilizers depends upon such factors as (1) the 
character of the soil, (2) the previous crop grown and 
the manner in which it was fertilized, (3) the moisture 
