THE MONTHLY BULLETIN. 



CALIFORNIA STATE COMMISSION OF HORTICULTURE 

 Vol. V. May, 1916. No. 5 



OUR PRESENT KNOWLEDGE OF CITRUS 

 FERTILIZATION.* 



By H. J. WebbeRj Director of the Citrus Experiment Station, University of 



California, Riverside, Cal. 



In continuing this discussion I can not clo better probably than to 

 summarize shortly our present knowledge of the methods of fertilization 

 in order to get the ciuestion before you in its entirety. 



The citrus grower in determining the best method of fertilization to 

 use in his grove is confronted by a maze of contradicting so-called facts 

 and theories. It is at present impossible to decide on any particular 

 system of fertilization that can be said to be the best or that can even 

 be recommended unhesitatingly as good. The whole subject is being 

 investigated through the combined efforts of growers and the scientists 

 of the College of Agriculture and of the United States Department of 

 Agriculture. Information is accumulating, from which in a few years 

 a more rational method of fertilization of citrus orchards can undoubt- 

 edly be formulated. In the mean time orchards must continue to be 

 fertilized. Can any suggestions of value be derived from the various 

 experiments at the present time? The following disconnected com- 

 ments on the results of various experiments may be of some value as 

 throwing light on certain problems: 



The factor that seems to stand out most prominently in various 

 experiments and in the experience of good growers is the great import- 

 ance of adding organic matter to the soil. The great majority of our 

 desert soils are apparently lacking in humus. The most satisfactory 

 methods of increasing the organic matter in the soil is apparentlj^ 

 through the growth of leguminous cover crops, such as bitter clover 

 {Melilotits indica) and purple vetch {Vicia atropurpurea) , and by the 

 use of such materials for fertilizers as stable manure, alfalfa hay, bean 

 straw, and the like. Our understanding of the reasons for this beneficial 

 action of organic matter is as yet very imperfect. Organic matter is 

 known to open up the soil, render it lighter, and better the tilth. Such 

 soils are more porous and take the irrigation water better, and do not 

 seem so prone to form a plow sole. An abundance of organic matter 

 in the soil also favors the development of the bacterial flora of the soil 

 that are known to be of such importance in breaking down and trans- 

 forming the various manurial elements into forms soluble and available 

 to the plant. 



The evidence available regarding the use of cover crops points strongly 

 to the greater value of using leguminous plants instead of cereals or 

 other nonlegumes, primarily because the legume not only adds organic 



I> *Address before the Special Citrus Convention, San Bernardino, Cal., Febru- 



ary 19. 1916. 

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