51 
plant food given to it. But how shall we know what quantity to 
give? This we find outin the following way:—On Plot 1 we give 
a light dressing of the complete manure, on Plot 2 we give twice 
as much as on Plot 1, and on Plot 4 we give three times as much 
as on Plot 1. Now, suppose Plot 3, without manure, gives us at 
the rate of 60 bushels of fruit per acre, and Plot 1, with the light 
dressing of manure, gives us 90 bushels, we shall then know that 
30 bushels per acre increase has resulted from the light dressing 
of manure, If again from Plot 2 we get 120 bushels per acre, we 
shall see that twice the dressing of manure has given twice the 
increase of crop, namely, 60 bushels. Therefore, the money 
spent in the medium dressing has given just as profitable a return 
as that spent in the light dressing. Naturally, then, we should 
think it desirable to give not less than the medium dressing. 
Now, suppose that on Plot 4 we get a yield of 150 bushels, we 
should likewise see that the heavy dressing was just as profitable 
as the medium dressing. Suppose, however, we obtain from this 
plot only the same as from Plot 2, then we should conclude that 
the increase of manure over and above what was given on Plot 2 
was simply waste, and if we got a result intermediate between 
these two we should reason that the most profitable quantity of 
_INanure was somewhat between the medium and the heavy 
dressing. i 
Thus far, however, we shall not have learnt whether our soil 
‘needs all the three plant foods, or only one or two of them. How 
are we to find this out? How, for instance, must we find out if 
the soil needs nitrogen? Some people might suppose we should 
‘do this simply enough by putting just nitrogen on one plot and 
comparing the yield of that plot with the yield from the unmanured 
plot. But this plan would not answer at all, for suppose the soil 
needed potash and phosphoric acid as well as nitrogen, then no 
amount of nitrogen added by itself would give us an adequate 
inerease of crop. In such case, indeed, by disturbing the balance 
of growth, it might result in a decrease of crop. We should have 
to supply the phosphoric acid and potash to one plot, and then to 
another plot the phosphoric acid and potash together with the 
nitrogen. This is arranged in the case of Plots 2 and 5 of the 
above plan. Now, if Plot 2 with the nitrogen gives us an increased. 
yield of 60 bushels of fruit, and Plot 5 without the nitrogen gives 
us an increase of only 10 or 20 bushels, we learn at once that 
the soil needs nitrogen manuring, though perhaps not the whole 
of the dressing given in Plot 2. Similarly Plots 6 and 7 tell us 
about the phosphoric acid and the potash. 
Let me here quote from some actual results of these test plots as 
applied to fruit trees by Mr. Ewers, of Childers, on his raspberry 
plantation. The test was made upon some young raspberry 
bushes in their third season; and striking as were the results 
D2 
