“9. There is strong presumptive evidence that the nitrogen which exists in the air, in shape of ammonia and nitric acid, and descends, in these combinations, with the rain which falls on the ground, satisfies, under ordinary circumstances, the requirements of the clover-crop. This crop causes a large accumulation of nitrogenous matters, which are gradually changed in the soil into nitrates. The atmosphere thus furnishes nitrogenous food to the succeeding wheat indirectly, and, so to say, gratis.
“10. Clover not only provides abundance of nitrogenous food, but delivers this food in a readily available form (as nitrates), more gradually and continuously, and, consequently, with more certainty of a good result, than such food can be applied to the land in the shape of nitrogenous spring top-dressings.”
“Thank you Charley,” said the Doctor, “that is the most remarkable paper I ever listened to. I do not quite know what to think of it. We shall have to examine it carefully.”
“The first three propositions in the Summary,” said I, “are unquestionably true. Proposition No. 4, is equally true, but we must be careful what meaning we attach to the word ‘accumulate.’ The idea is, that clover gathers up the nitrogen in the soil. It does not increase the absolute amount of nitrogen. It accumulates it—brings it together.
“Proposition No. 5, will not be disputed; and I think we may accept No. 6, also, though we can not be sure that allowing clover to go to seed, had anything to do with the increased quantity of clover-roots.
“Proposition No. 7, may or may not be true. We have no proof, only a ‘probability;’ and the same may be said in regard to propositions Nos. 8, 9, and 10.”
The Deacon seemed uneasy. He did not like these remarks. He had got the impression, while Charley was reading, that much more was proved than Dr. Vœlcker claims in his Summary.
“I thought,” said he, “that on the part of the field where the clover was allowed to go to seed, Dr. Vœlcker found a great increase in the amount of nitrogen.”
“That seems to be the general impression,” said the Doctor, “but in point of fact, we have no proof that the growth of clover, either for hay or for seed, had anything to do with the quantity of nitrogen and phosphoric acid found in the soil. The facts given by Dr. Vœlcker, are exceedingly interesting. Let us look at them: