210 MASSACHUSETTS HORTICULTURAL SOCIETY. 



acid, all its potash, and a part at least of its nitrogen, from diffi- 

 cultl}' soluble compounds in the soil ; and I think it is now easy to 

 understand why, as so often observed, commercial fertilizers do 

 their best work when used with stable manure : the abundance of 

 carbonic acid generated by the fresh application of such manure 

 assists in the re-solution of the insolubilized phosphoric acid and 

 potash of the commercial manure, as well as of the difficult!}' sol- 

 uble native food of the soil. Some writers consider this to be 

 such an important function of stable manure that they condemn 

 the practice of allowing it to rot in the 3'ard at all ; they would 

 have all the decay go on in the field, just where the products of this 

 decay are needed for their action on the soil. It was somewhat 

 interesting as well as amusing, while I was writing this, to meet 

 with the statement in an English paper, that a patent had been 

 taken out in England for charging a soil with carbonic acid through 

 pipes laid near the surface. A few good results of such a s^'stem 

 would be worth more in illustration of the principle that I have 

 been explaining than the patent will ever be worth to the inventor. 

 No results are given, but you see that it is exactly what Stoeckhardt 

 did, and I have no doubt that it would increase the yield of crops ; 

 but, as long as we can still get hold of any humus-forming material 

 at reasonable rates, we have a far cheaper method of attaining the 

 same end. 



There are other ways in which humus may, and doubtless does, 

 favor the production of crops ; but, to m}' thinking, all of them taken 

 together do not sum up for so much as does this one way that I 

 have been speaking of. 



We can compare stable or other animal manures in another yvay 

 that may explain the reason why less satisfactory^ results are some- 

 times obtained with the latter ; I refer to the comparative cost of 

 plant food in the two kinds of manure. You are aware that the 

 Directors of the Experiment Stations of Massachusetts, Connecti- 

 cut, and New Jersey have, in the past few years, conferred to- 

 gether in the spring to determine what ma}'^ be considered as a fair 

 valuation per pound, of nitrogen, phosphoric acid, and potash, in 

 their various degrees of solubility as found in these manures. The 

 figures thus given represent the retail cost of these substances, in 

 the markets of the State where they are sold as raw materials to 

 be worked up into the various brands of fertilizers offered for sale 

 during the year. 



On the basis of this scale of values adopted for 1884 I think it 



