220 The Principles of Fruit-growing. 
the direct addition of nitrogenous materials, like 
nitrate of soda, sulfate of ammonia, or some of the 
animal compounds. 
The grower should also remember that the plants 
need all the elements of plant growth, and not one 
of them alone. For example, a heavy application of 
nitrogen upon soil which is deficient in potash and 
phosphoric acid cannot be expected to give useful 
results. In the same way, the application of pot- 
ash to soil which is very poor in nitrogen or phos- 
phorie acid would be comparatively useless. The 
heavy loamy or clay lands nearly always contain 
an abundance of potash and phosphoric acid in 
a more or less unavailable condition, and much of 
these materials can be liberated to the plant by care- 
ful tillage and the incorporation of humus. MHow- 
ever, it is nearly always advisable, in orchards 
which are bearing, to add these materials in the 
shape of manures or concentrated fertilizers. The 
quickest results following the use of fertilizers will 
be seen upon the sandier lands. Two or three 
years often elapse after the application of chemical 
fertilizers to heavy lands before any decided results 
are observed. In other words, clay lands ordinarily 
show quicker results from tillage than they do from 
the application of fertilizers. The farmer should 
bear in mind that he should never rely exclusively 
upon chemical plant-foods, because they contain no 
humus, and the soil is apt to become hard and _ life- 
less. They should be used in judicious rotation, or 
in connection with cover crops, or stable manures, 
