BULLETIN OF THE BUSSEY INSTITUTION. 311 
have been. It will be seen from the calculations on page 116, that 
enough of each kind of plant food was taken to have supplied a consid- 
erably larger crop than was actually obtained in any one instance. 
The. calculations in question were based upon results that had been 
obtained in previous years upon a strip of land that proved to be 
decidedly deeper and richer than the section devoted to the experi- 
ments with mixed fertilizers. We are ignorant as to how much more, 
or how much less of a fertilizer than can be removed from the land, 
by the largest crop that could possibly grow there, should be added to 
the land in any given case in order to obtain the maximum crop. ‘The 
amount needed would vary not only with the chemical composition, 
and the mechanical texture of the soil, and with the amount of moisture 
accessible to the crop, but with the seasons also, accordingly as they 
were more or less wet or dry, warm or cold. It was partly because 
of this uncertainty, and partly in the hope of obtaining a still larger 
crop than any that had been got bythe use of single fertilizers, that 
no deduction was made on account of the natural strength of the land 
from the data which served as the basis of the calculations on page 116. 
The argument there developed, would plainly have been more logical 
if the yield of the squares, numbered “5,” that had not received any 
manure, had been subtracted from the amounts harvested on the 
squares that yielded the best crops, before making the calculations. 
In point of fact, experience has shown that the argument and my 
- expectations were both pitched too high. ‘The crops obtained by the 
use of mixed fertilizers in 1873. and 1874, and those obtained by 
means of heavy dressings of dung and of wood-ashes in 1871, ’72, ’73, 
and ’74, show very clearly that the power or ability of the land of the 
experimental field to yield crops is limited to the amount of five or six 
kilogrammes of grain, whether of barley or beans and the correspond- 
ing amount of straw; that is to say, under the conditions of climate 
and tillage that have obtained in these years. Although this subject 
has been discussed quite fully already on page 129, it should again be 
said that in view of the poor character of the surface soil of the exper- 
imental field, of the great distance of that soil from the ground water 
(see page 80), and of the coarseness of the gravel upon which the soil 
rests, it may fairly be held, that the crops actually obtained in 1874, 
were in general as good or very nearly as good as could have been 
obtained from this particular soil and field by any process of mere 
