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recommended that this should be replaced ly the use of basic slag as 

 the cheapest material. It is importanl however for the agriculturist 

 to examine into the following facts — 1st how much need to be 

 supplied, 2nd how much is naturally supplied, and 3rdly how much 

 might be applied with advantage to produce a maximum yield. 



.'!. In some places we hear of yields of five or six or even more 

 pounds per tree, but taking the production at 35,000,000 lbs. that 

 amount has probably come from as many as 35, 000, 000 trees in 

 Trinidad or a yield of 1 lb. per tree for large and small trees alike. 

 A tree on lands of the Botanical Department has yielded 7 lbs. of 

 dried cacao at one picking. If it were shown that extra yield was 

 due to the presence of extra phosphoric, acid it. would be strong 

 evidence in favour of its application, but as yet, we await experi- 

 mental results and the recommendation rests principally upon the 

 inferences drawn from reasoning, " that what is taken away, must be 

 replaced." That the amount of 230 tons is taken out of the soil 

 there is no reason to doubt, but that it must need be all replaced 

 artificially, is open to question. 



4. How much need be supplied artificially can only be ascertained 

 by experiment, as it is fairly clear that a certain amount must of 

 necessity be supplied naturally, and again an uncertain amount, by 

 what I have in previous writings termed the " incidental increment." 

 How much this amounts to. we cannot say, but that such an incre- 

 ment occurs there appears to be little doubt, as how else could we 

 explain the production of crops for years where no artificial stimulant 

 or plant food has ever been applied ? 



5. If such an amount as 230 tons is carried away annually at the 

 rate of *23 ounces per tree, taking the yield for convenience at 1 lb. 

 per tree, it is seen that in 50 years some 11 lbs. 8 oz. of phosphoric 

 acid per tree has been carried away during that period. There are 

 not a few estates in Trinidad where the average per tree is much 

 higher than 1 lb. and for every pound or portion thereof a propor- 

 tionate amount of phosphoric acid must be taken away per tree. 

 Too much of one constituent is known to be prejudicial to growth, 

 and if the total amount of 11 lbs. 8 ozs. or a 50 years supply was 

 stored originally in the soil (a not very likely contingency) the plants 

 would not yield to the same extent as if less were present. Now if 

 230 tons is taken away yearly there must either be a store upon 

 which the plants can draw already in the soil, or it must be supplied 

 from other sources not as yet too well known, or studied. If no 

 material is added, and only a certain amount available, where does 

 the plant obtain its supply, unless from some incidental source ? 

 Unless a supply is available the plants would be in danger of becoming 

 barren, yet we know for a fact that many estates, where no artificial 

 supply has been given have produced regular crops year after year 

 for 50 years and over, which is strong evidence that undetermined 

 sources of supply exist which annually provide a certain amount, if 

 not the necessary quantity. 



If crops can be increased by the application of phosphoric acid, 

 it would tend to show that an insufficient quantity exists in soil, or 

 is unavailable, but if the crop is not increased by artificial applications, 

 it would be direct evidence that the natural supply is sufficient. 



