THIRTY-FOURTH FRUIT-GROWERS^ CONVENTION. 165 



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Avill be promoted at the expense of the fruit buds, which then develop ' 



imperfectly, resulting in a decreased, instead of an increased, fruitage ] 



of the tree. ■ 



■ PHOSPHORIC ACID. ; 



There are two other of the fertilizing elements which we must return ,: 



to our soils in order to maintain their fertilit3\ namely, phosphoric \ 



acid and potash. Nitrogen, as we have seen, promotes the growth and ; 



sustains the vigor of the tree ; phosphoric acid, it is believed, promotes i 

 a large yield of fruit. M^'- idea is that in growing fruits we should 

 supply phosphoric acid quite generously. But the form in which we 



will get, the most benefit from it is a question more difficult to decide ; , 



and even scientific men, after years of field experiments, are not well ' 

 agreed on the subject. 



If we buy superphosphates, for example, we will get a large per- i 



centage of the phosphoric acid in a water soluble form; if w^e buy I 



Thomas phosphate powder, we will get a high percentage of phosphoric j 



acid with but very little of it in soluble form; and if Ave buy untreated j 



bone meal we will have a material in which a medium percentage of j 



the phosphoric acid is water soluble, but w^hich is all ultimately avail- \ 



able to the tree. These three materials, together with guano phosphate, ; 



are the phosphate materials we see the most of in California. j 



The advantages and the disadvantages of a soluble phosphate may be j 

 stated in this way: When soluble phosphoric acid becomes distributed I 

 in the soil, a process of fixation rapidly takes place, the phosphoric 

 acid uniting with the lime and other alkaline bases present in the , 

 soil. This process is what is commonly' spoken of as ''reversion." If 

 there is plenty of lime in the soil, the lime will be the first of these ^ 

 alkaline bases to get the acid, and the reverted phosphoric acid is then 

 just as valuable as it was before, because, in this form, it is still avail- 

 able to the roots of the trees. If, however, there is not much lime j 

 in the soil, but a good deal of iron and alumina, these bases will get i 

 the acid; which, particularly in the case of iron, would pretty effectu- j 

 ally lock it up, and it is in this respect that possible loss of phosphoric \ 

 acid takes place. You will notice, then, that there is little danger of ^ 

 loss by leaching, because the phosphoric acid, by the process of com- j 

 bination, becomes fixed in the soil, and the only loss is in cases where ^ 

 the soil may be very deficient in lime and very rich in iron. Soils of ; 

 this character are, I think, quite uncommon in Southern California. \ 

 I\Iy understanding is that our soils are, as a rule, rich in lime, and 

 therefore we may use phosphates freely in any form without having \ 

 the phosphoric acid either washed out of the soil or locked up by j 

 combination with an iron base. "But if the soluble phosphate is ; 

 ([uickly converted into an insoluble form, it may well be asked what \ 

 has been gained by all the trouble and expense of converting the i 

 insoluble phosphate into a soluble form?" This question is raised j 

 in a bulletin of the West Virginia Experiment Station, and the answer | 

 is so admirably stated that, although I have quoted it more than once, 

 I think it will bear repetition. The author says the chief advantage 

 is a matter of "distribution." ^ 



When the soluble phosphate is applied to the soil it quickly passes into solution, 

 and, as the soil water is never at rest, the phosphate solution soaks through the 



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