138 i he Use of Manures in Forestry. [may, 
in the better types of soils the necessary food salts are present 
in sufficient quantity, and that artificial manuring is only 
of importance where the soil has deteriorated, or in cases 
where it is desired to carry a crop quickly over some critical 
period, such as danger from frost or game. Owing to the 
relatively deep position of the roots, manuring with ordinary 
manures is practically without result on middle-aged woods. 
The only possibility of encouraging the development of such 
woods seems to lie in bringing about the quicker decomposi- 
tion of the fallen leaves and twigs, either by working the 
soil, or, better still, by the application of lime. The irriga- 
tion of a sixty-year-old pine wood at the Berlin Irrigation 
Works with sewage water was tried, but was a distinct failure, 
as a monthly application during the chief vegetation period 
of the year caused, in two years, the death of many stems. 
Considerably better results were obtained by irrigation experi- 
ments at Gorlitz, where irrigated plantations of spruce, 
Weymouth pine, and Scotch pine showed a better growth 
than those not irrigated. In this case, however, the woods 
treated were, at the most, thirty years old, and the importance 
of age seems to be shown by the fact that at the Berlin Irriga- 
tion Works new plantations on irrigated areas have shown 
good growth. A form of manuring in pine woods which 
offers prospects of success is the covering of the soil with a 
layer up to 8 inches deep of city refuse. The City of Berlin 
has experimented in this direction, with the result that after 
two years the pine woods treated showed excellent develop- 
ment. 
It is, however, in the planting and early growth of trees 
on poor soils that artificial manuring assumes importance. 
Soil analyses show that in poor, sandy soils the nitrogen 
contents have been reduced to a minimum, and consequently 
this element is the chief consideration ; phosphoric acid also 
plays an important part, but potash is only of subordinate 
importance. As nitrate of soda and sulphate of ammonia 
are too rapid in their action for a slow-growing crop, the 
chief difficulty in manuring on sandy soils is to supply 
nitrogen in a slowly available form at the least cost. Up 
to the present, experiments indicate that this can best be 
done by utilising the nitrogen contained in plant residues in 
