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 orchari' 

 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. Ap-.. 142. 



