842 ANNUAL REPORT OiT THIS] Off. Dog. 



How much phosphate to apply, as with other plain rooas, wni 

 depend upon the requirements of the crops grown with reference to 

 the soil in question. 



Luxuriant plant growth or large crops and intensive soil culture 

 are s^-nonvmous with the rapid conversion of plant food into crops. 

 The demand for plant food must, therefore, be greatest where the 

 consumption is greatest as will be indicated by the yield of the 

 crop. This demand must be supplied, either from rendering the 

 natural plant foods of the soil available or else they must be supplied 

 through artificial applications. Hence, the quantity of phosphoric 

 acid to apply must be regulated with reference to the natural soil 

 supply and the requirements of the crops being growr. 



From what has been said it must not be inferred that phosphoric 

 acid can only be applied advantageously on the better grades of 

 soils. This would be absolutely incorrect, for under favorable cir- 

 cumstances relatively larger results are secured from the appli- 

 cation of phosphates on poor and even neglected and exhausted soils, 

 but in such cases the applications should be made with greater pre- 

 caution and intelligence as the conditions are more special and entail 

 greater risks than on soils in better condition. 



The points as to what kinds of phosphates to use in particular 

 cases and how to use it, will develop in connection with the discus- 

 sion of different phases of the subject as presented in the subse- 

 quent pages, and each person will need to study this portion of the 

 subject and make such application as may seem best under the par- 

 ticular circumstances with which it is being dealt. 



POINTS AFFECTING THE AVAILABILITY OF PHOSPHATES. 



The form in which phosphoric acid offers the best all-round ad- 

 vantage to the practical farmer is a very delicate and difficult one 

 to determine. Keasoning on the basis of the generally admitted 

 theory that all elements must be in solution before they can enter 

 into the interior of plants, it would then naturally follow that prefer- 

 ence will be given to those phosphates which are most readily soluble 

 or subject to dissociation. This will depend principally upon two 

 conditions 



1. The form and general characteristics of the phosphate. 



2. The nature and composition of the soil to which the particular 

 phosphate is applied. 



In general, phosphates with the same chemical and physical char- 

 acteristics are equally valuable when used under like conditions, 

 no matter from what source they have been obtained. The many 

 factors which enter into the availability of phosphates can be con- 



