BULLETIN OF THE BUSSEY INSTITUTION. 155 
It will be remembered that the original motive (page 81) of the 
experiments was to determine, if possible, what kinds of fertilizers 
among those readily procurable in Boston were best fitted to increase 
the yield of crops grown upon a field that had been chosen as the 
typical representative of the light and hungry soils resting upon 
drift gravel that are so common in New England. This question has 
been clearly answered by the results that have been tabulated in 
the present report and in the reports of the two previous years. It 
is plain that the soil of the experimental field needs fertilizers that 
are rich in potash, and that, under the existing condition of things, 
no advantage can be gained by applying mere phosphatic or nitro- 
genous fertilizers to the land. The soil evidently contains a much 
larger store of phosphatic and nitrogenous substances that are avail- 
able for the use of plants than it does of potash compounds. Hence 
very little useful effect has been gained by adding phosphates and 
nitrogen compounds to the potassic manures. If only potash enough 
be given to this soil, the latter can of itself supply all the other in- 
gredients that compose the food of plants, at least for the term of 
years during which the experiments have lasted, and for as many 
more, of course, as the store of phosphates and nitrogen may hold 
out. Consequently until such time as the natural supply of these 
substances shall begin to fail, it would be wise to apply but little of 
them. The crying want of the land is for potash, and it is the 
potassic manures that should be applied to it, to the wellnigh com- 
plete exclusion of other fertilizers, until an equilibrium has been 
reached. 
This conclusion is most directly and clearly enforced by the ex- 
periments above recorded, in so far as regards the soil of the experi- 
mental field ; and from analogy it would naturally be inferred that the 
same conclusion would apply to other New England soils similarly com- 
posed and situated. But in order to establish this general conclusion 
beyond all chance of doubt, it would be necessary to make many 
other experiments in different localities, were there not already a mass 
of confirmatory evidence bearing upon the subject. There are, in 
fact, already available a number of observations, usages, and tradi- 
tions that go far to prove that the potassic manures are specially 
needed in New England. It has long been believed, for example, — 
for a century probably, and perhaps for a still longer period, — by the 
