152 POMOLOGY 



ter of the soil, and, as has ah-eady been pointed out, where 

 there is a lack of organic matter there is also likely to be a 

 lack of nitrogen. Under those conditions, legumes proved 

 to be far superior for green-manures as evidenced by their 

 effect on the succeeding crops. The yield of a number 

 of crops following legume green-manures when compared 

 with those following non-legumes showed the following in- 

 creases: An average increase with potatoes of 39 per cent; 

 with com, 45; with cabbage, 44; with sugar-beets, 43 per 

 cent, respectively. Legumes alone gave as good or better 

 results than non-leguminous green-manure crops plus an 

 annual application of 540 pounds of nitrate of soda to 

 the acre. 



Of more direct interest in this connection is the measur- 

 able effect of green-manuring on citrus fruit-trees. The 

 trees on plots where legumes have been turned in annually 

 were superior in every way to those similarly fertilized but 

 where no leguminous green-manure crops had been used. 

 Green-manuring resulted in a 30 per cent increase in size 

 of tree and a 68 per cent increase in yield at the age of ten 

 years. ^ 



134. Effects of the cultural methods on the soil. — Before 

 examining the effect of these cultural systems on the trees, 

 it would be well to follow the investigations as they affect 

 the soil itself. While the student must consult works on 

 soil science for a fuller treatment of this subject, yet some 

 reference to it is necessary in order to secure a basis for 

 the cultural methods used in orchards. 



It is axiomatic that an abundance of available inorganic 

 plant-food materials and moisture will give a better devel- 

 opment of the trees and production of fruit than when these 

 are deficient at the critical period of development. It is, 

 of course, equally detrimental to have excesses of moisture 

 1 Mertz, W. M. Calif. Agr. Exp. Sta. Bull. 292. 1918. 



