PHOSPHATES IN MASSACHUSETTS AGRICULTURE. 147 



Massachusetts farmers, then, should apply phosphoric acid for most 

 crops, but certainly not to the exclusion of potash. However abundant 

 the phosphoric acid it will not take the place of potash. However largely 

 applied it will not reduce the necessity for the apphcation of potash for 

 most crops. It has no direct influence, so far as known, on the extent 

 to wliich inert soil potash is rendered available. Since, however, without 

 doubt some phosphoric acid should be applied in our ordinary farm and 

 garden practice, the question whether, as Hopkins and his disciples be- 

 lieve, fine-ground rock phosphate is the best form is important. Two 

 series of experiments in this station throw light upon the question. Both 

 have been carried out on medium silt loams containing an average per 

 cent, of humus and possessing excellent physical characteristics. 



EXPERIMENTS FOR COMPARISON OF DIFFERENT 

 PHOSPHATES. 



The two sets of experiments designed to show the comparative effective- 

 ness and value in agriculture of different phosphates which have been 

 conducted here have both extended over a considerable number of years, 

 and the conditions have been, so far as can be judged, as favorable to the 

 activity of the more insoluble materials as will usually be found in our 

 upland soils. The soil structure and texture are such as to favor opti- 

 mum moisture conditions, and at the same time adequate aeration and 

 good tilth. In both fields the soils were at the outset moderately acid. 

 In the first mentioned hme at the rate of a ton to the acre was applied 

 once during the progress of the experiment. In the other two, similar 

 applications of lime have been made. The quantity in both fields was 

 considerably short of that required to completely neutralize the free 

 acids present. 



In both experiments most of the principal crops common in our agri- 

 culture have found a place, and some of them for several years. In neither 

 series of experiments has any manure been applied. In both, chemical 

 fertihzers containing nitrogen and potash in quantities beheved to be 

 adequate for large crops have been equally applied to all plots. 



In one series of experiments the basis of comparison of the phosphates 

 used was "equal money's worth;" in the other, "equal phosphoric acid." 



Comparison of Phosphates on the Basis of Equal Money's Worth. 

 A full account of this experiment has already been published. ^ De- 

 tailed reference to it at this time, therefore, is unnecessary. I may go 

 further and say that any reference to the results of this series of experi- 

 ments might lead to the formation of absolutely misleading conclusions. 

 The experiment was clearly not of such a character as to afford a fair 

 basis of comparison between the more soluble phosphates and the rock 

 phosphates, for, as is shown by our other series of experiments as well as 



1 Fourteenth annual report, Hatch Experiment Station, pp. 24-28. 



