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soil does not have the same ability to produce year after year. One of these experi- 
ments was accidental, but the result is of great interest, and I am sure you will pardon 
me for mentioning it. We were troubled with certain fungi in these soils. We did 
not want to apply fungicides for fear it might change the character of the soil, which 
should remain constant, so the soils were sterilized. All the soils of one pot were 
placed in a pan, covered with another pan, and exposed for several successive days 
to the temperature of steam, even above the temperature of boiling water. In this 
way beyond doubt all the fungi were killed and also all the bacteria, so that when the 
experiment was started again we had to resort to inoculation. But, much to our 
surprise, the soils were restored almost to their former condition of fertility after 
being sterilized, nothing else having been done, which seems to show that a high 
temperature has the power of unlocking additional sources of plant food. And this is 
demonstrated in every one of the thirty-seven and more soils with which these 
experiments were made. This shows that if there were a way of sterilizing the soils 
and then reinoculating them, we could restore fertility for a certain length of time by 
unlocking these additional plant foods. This experiment was made in 1900. We 
find also a diminution of the crop again the succeeding year. The increased solu- 
bility of the plant foods was determined immediately by chemical analysis of the 
ordinary fertilizing ingredients, and it was shown that certain of these were con- 
siderably more soluble in our ordinary reagents than before, which proved the fact 
that these were unlocked. 
Of course, we understand perfectly well that this process could not go on indefi- 
nitely. No matter how large your bank account may be, if you check against it 
again and again and again it will gradually grow smaller, until at last your deposit is 
exhausted. The same is true of the soil. You may draw upon it every year, but 
finally there will be nothing left and your check will be dishonored. 
I will not detain you by going into the details of these experiments, but will pass 
over the results rapidly. The chemists, as you know, have been trying for years to 
find some way to gauge the fertility of the soil by chemical analysis. We know how 
to determine the total amount of the constituents of a soil. That process is easy and 
accurate. But how can we determine (if it is possible to do so) by chemical analysis 
what portion of the fertilizing constituents of the soil the plant takes out of the soil 
during its growth? Every agricultural chemist here present understands, without 
any explanation, the immense difficulty of such a problem, because the fertility of 
the soil is the sum of a number of conditions. You may say of a soil that it is as 
infertile as its weakest constituent, no matter how abundant the other constituents 
may be. You may have a soil abundantly supplied with a certain number of fertil- 
izing ingredients — nature is usually extravagant; she makes a thousand seeds for 
one complete plant, and she furnishes to the soil a hundred times more plant food 
than the crop takes out of it in any one season; she is extremely extravagant in her 
supplies, is not a very good housewife in many respects — but, I say, that if a single 
essential ingredient is absent, I do not care what it is, you can produce no crop at 
all. Suppose a crop takes out of the soil 100 pounds of potash per acre. You might 
devise a method which, when applied to the soil, would extract 100 pounds of pot- 
ash, so as to meet exactly the requirements of the crop; but that method, if applied, 
might not extract the correct amount of phosphoric acid or of nitrogen. That is to 
say, every one of the elements of plant food must have a method of its own, When 
the crop is changed you must change the method, because each crop acts differently 
toward the elements of plant food in the soil. 
Nitrogen presents a more complicated problem, because a plant uses it only in one 
form; no matter how much nitrogen you may give the plant in another form it will 
not eat it. You may feed a growing green plant with all the free nitrogen you please 
and with all theammoniathe soil will hold, and the plant will not take a single molecule 
of them. The nitrogen must be in the form of nitric acid before the crop can eat it. 
Hence the available nitrogen in a soil is not by any means determined by an analysis 
which determines nitrogen in the various forms in which it exists. The only nitrogen 
in the soil that the green plant can eat at any time is that which exists as nitric acid. 
Nitric acid and nitrates are the most soluble of all the plant foods, and they are 
the only plant foods which the soil has no power to hold back when a solvent is 
placed on the soil. There is no tendency on the part of the soil to hold nitric acid 
when water is thrown upon it, while there is a tendency to hold other fertilizing 
elements. Hence nitric acid is the most evanescent as well as the most important in 
point of cost of all the plant foods. Now, the total amount of nitrogen which is 
available at any time in a soil is the amount which happens to be nitrified, and 
which is not washed out nor appropriated for other purposes. 
Hence you may find the means of measuring the amount of phosphoric acid which 
a plant will takeout in an ordinary crop; you may find methods of determining how 
much lime a plant will take out of the soil in a certain crop; you may find out how 
