212 The Principles of Fruit-growing. 
barn manures with safety; yet, even here it is a 
question if economy would not. dictate tillage and 
late green manures to supply the nitrogen, except, 
perhaps, for a season or two when an attempt is 
making to rejuvenate an orchard. Mulching a sod 
orchard with manure often gives fairly good results 
in cases in which the land cannot be cultivated; but 
better results in the way of fertilizing and in freedom 
from weeds and insects can be obtained by pastur- 
ing closely with sheep or swine. 
Chemical fertilizers. — Nitrogen, potassium and 
phosphorus are the elements which need to be ap- 
plied to orchard lands; and to these should some- 
times be added lime, mostly for its secondary effects 
upon the soil. 
Nitrogen is particularly efficacious in promoting 
growth. “The general tendency of nitrogenous ma- 
nures is toward the excessive production of wood 
and foliage,” writes E. F. Smith, after having made 
many explicit experiments upon peach trees.* In 
fact, the amount of growth and the color of foliage 
are reliable guides for the application of nitrogen. 
When mature or bearing trees make a foot or 
more of growth upon all shoots, and when the 
leaves are of good size and dark color, the orchard 
probably has enough nitrogen. A free application 
of nitrogen to such orchards might do more harm 
than good, in promoting growth at the expense of 
fruit, or, in the case of some stone fruits, in pro- 
* Bull. 9, Section of Veg. Path., Botanical Div. U.S. Dept. Agr., 142. 
