256 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
should not be greater than that which can be immediately 
disposed of. It is better, therefore, to apply it in small doses 
at a time. 
The ammonia salts are not so rapid in their action. The 
nitrogen they contain must first undergo reconstruction into 
nitrate before it is available for absorption. Some time must, 
therefore, be allowed for these changes to take place. As the 
danger of the salt being washed out of the soil is not great, it 
may with advantage be applied in autumn. One must be 
careful, however, not to mix sulphate of ammonia with say basic 
slag, as the free lime contained in basic slag would act upon it, 
setting free the ammonia. They should be applied separately. 
Organic nitrogenous manures must also undergo changes 
into ammonia and then into nitrate before absorption takes 
place. They are, however, retained by the soil, which reduces 
the danger of their being washed out and lost, so that they may 
with safety be applied in autumn. 
As we have already seen, nitrogen may be supplied in the 
form of green manure, especially by the cultivation of lupine, 
which has previously been well supplied with basic slag and 
kainit. Another great advantage derived from the cultivation 
of these plants is the beneficial action of their deep-sinking roots 
on the subsoil, which they perforate, and give the roots of the 
young trees a better chance of penetrating later into the lower 
layers of soil, thus firmly fixing the tree and also tapping the 
water in these lower layers. 
Phosphoric Acid.—The application of basic slag is the best 
means of supplying this important and beneficial ingredient to the 
soil. The phosphoric acid it contains is not soluble in water, but 
is brought into solution by the action of the root-hairs. The 
presence of humus further renders the phosphorus more available 
for absorption by the trees. The action of the basic slag is 
gradual, and hence more permanent. Of course, the finer it is 
ground the quicker is its action, and, further, the addition of 
potash salts and nitrogenous manures hastens the process. 
Super-phosphate, as a source of phosphoric acid, is, owing 
to its acid nature, less suitable than basic slag on soils poor 
in lime. 
Potash.—This substance can be supplied in various combina- 
tions, but some of the salts contain chlorides which are distinctly 
injurious to tree-growth. As a crude salt kainit is the best, 
