HEARINGS BEFORE COMMITTEE ON AGRICULTURE. 127 
Mr. Woops. Yes; they will work, but they do not show the same 
effect of restoring the soil; that is, if you have a crop that has a large 
amount of available nitrogen in it—that is, a quantity required by that 
crop—then these organisms simply produce a small amount of ‘nitro- 
gen; but just as soon as the amount of nitrogen available in the soil 
falls below the requirements of the crop, then these organisms begin 
to work, and they stand there as a guard against the reduction of 
the nitrogen in that soil below the requirements of the crop. 
The Cuarrman. What is the most common proof that your soil is 
exhausted. What shows to the ordinary farmer that there is no nitrogen 
left—is it land exhaustion? 
Mr. Woops. It is what the farmer calls land exhaustion. It means 
that the nitrogen is exhausted; the other materials ure there in suffi- 
cient quantities, but when the nitrogen is lacking the crop will be low 
and yellow and very slow in maturing. There are all gradations; it 
depends on the amount that is lacking. 
Mr. Grarr. Is that the reason why leguminous plants like clover 
are found to be good in restoring soil? 
Mr. Woops. That is just exactly the reason. 
‘i Me Henry. What is meant by “clover sickness,” as we term it down 
ast ¢ 
Mr. Woops. It is caused by many different things. The term is 
applied to any soil that refuses to produce a crop of clover. 
Mr. Henry. Can you give the reason why that soil refuses to 
produce a crop of clover? 
Mr. Woops. Yes; in New England the main reason is that the soils 
accumulate organic acids and have to be limed. 
The Cuarrman. That does not apply to limestone soils, then ? 
Mr. Woops. No; unless the lime is pretty far down and completely 
formed into carbonate, and if it is too far below the roots of the plants. 
Sometimes you can have a lack of lime in a limestone country. I saw 
the greatest lime starvation in soils underlaid by limestone. 
The Cuarrman. That was too deep? 
Mr. Woops. Yes. 
Mr. Haueen. We can not get clover unless we use fertilizer in such 
cases. 
Mr. Woops. That means that the organic acids are present in the soil. 
Mr. Grarr. Can this condition of the soil be determined by analysis, 
either chemical or physical? 
Mr. Woops. It can not be determined by a chemical or a physical 
analysis; it can only be determined by trying the plant on the soil. 
Mr. Grarr. When you try it, how do you know whether that is the 
trouble or not? 
Mr. Woops. We tell by the behavior of plants; we can tell by the 
effect of the soil on the plant whether it is due to acidity. If it is due 
to acidity, the plant will turn brown and the root hairs will refuse to 
grow. Very often the acidity is not soluble except to the roots of the 
plant, and can be detected only by the plant. ; 
The importance of this new form of nitrogen-fixing organisms, I 
think, will be apparent, and we want to concentrate our scientific work 
this year upon that new crop of organisms. We have quite a number 
of them a we know that they will fix nitrogens in any soil that con- 
tains decaying organic matter, the roots of any crop, or the decaying 
roots of any previous crop, and if we can breed those up to the same 
