SOIL AND ITS PRODUCTIVENESS. 949 
We will therefore assign half the value to the subsoil plant 
foods that we do to the soil plant foods, and regard the nitrogen 
used, or which might have been used, as in the following pro- 
portions :— 
Plot 3.  Plot7. Plot il. Plot 14. 
DOs easvdacaesenesneroees 525 463 307 315 
Sulbsoileeeenmcenceeeeeee 108 135 135 103 
633 598 492 418 
In the same way we may regard the phosphoric acid available 
as being in the following proportions :— 
Plot 3. Plot 7. Plot 11. Plot 14. 
113 101 111 124 
31 45 39 20 
144 146 150 144 
The phosphoric acid at the command of the plants was, it will 
be seen, practically the same in all the plots. 
The results of a number of manure experiments in the soils on 
Mr. Goldie’s farm have shown that the manuring which has the 
most marked effect on these soils is phosphoric acid manuring, 
and next to that comes nitrogen manuring. Potash manuring 
has little or no effect, so far, at least, as the quantity of the crop 
is concerned. These facts correspond with the results of analysis. 
Of these three main plant foods the analysis shows the phosphoric 
acid to be present in least quantity, and in conformity with 
Liebig’s law of minimum—which, though it is not strictly is yet 
in the main true—we should expect to find this soil respond most 
markedly to phosphoric acid manuring. As regards the potash, 
one might, on first glancing at the results of analysis, be inclined 
to suppose that potash manuring would have more effect than 
nitrogen manuring ; but it is to be considered, firstly, that most 
plants make a greater demand on the nitrogen of the soil than on_ 
the potash, and secondly, that the potash was in this soil more 
readily available than the nitrogen, for the nitrogen was present 
to a great extent in the form of peaty matter, the soil being a 
peaty, marly, clay loam, whereas the potash was present to a 
considerable extent in the form of soluble salts. We must there- 
fore consider that the variations in the productiveness of this soil 
were dependent mainly on the phosphoric acid, and after that on 
the nitrogen, and that the other constituents were responsible for 
these variations in a very minor degree. 
