After looking at the above figures, the Deacon remarked: “You say 10 tons of dry earth before being used in the closet contained 62 lbs. of nitrogen. How much nitrogen does 10 tons of barn-yard manure contain?”
“That depends a good deal on what food the animals eat. Ten tons of average fresh manure would contain about 80 lbs. of nitrogen.”
“Great are the mysteries of chemistry!” exclaimed the Deacon. “Ten tons of dry earth contain almost as much nitrogen as 10 tons of barn-yard manure, and yet you think that nitrogen is the most valuable thing in manure. What shall we be told next?”
“You will be told, Deacon, that the nitrogen in the soil is in such a form that the plants can take up only a small portion of it. But if you will plow such land in the fall, and expose it to the disintegrating effects of the frost, and plow it again in the spring, and let the sun and air act upon it, more or less of the organic matter in the soil will be decomposed, and the nitrogen rendered soluble. And then if you sow this land to wheat after a good summer-fallow, you will stand a chance of having a great crop.”
This dry earth which Dr. Vœlcker analyzed appeared, he says, “to be ordinary garden soil, containing a considerable portion of clay.” After it had been passed once through the closet, one ton of it was spread on an acre of grass-land, which produced 2 tons 8 cwt. of hay. In a second experiment, one ton, once passed through the closet, produced 2 tons 7 cwt. of hay per acre. We are not told how much hay the land produced without any dressing at all. Still we may infer that this top-dressing did considerable good. Of one thing, however, there can be no doubt. This one ton of earth manure contained only 1¼ lb. more nitrogen and 1½ lb. more phosphoric acid than a ton of the dry earth itself. Why then did it prove so valuable as a top-dressing for grass? I will not say that it was due solely to the decomposition of the nitrogenous matter and other plant-food in the earth, caused by the working over and sifting and exposure to the air, and to the action of the night-soil. Still it would seem that, so far as the beneficial effect was due to the supply of plant-food, we must attribute it to the earth itself rather than to the small amount of night-soil which it contained.
It is a very common thing in England, as I have said before, for farmers to make a compost of the sods and earth from an old hedge-row, ditch, or fence, and mix with it some lime or barn-yard manure. Then, after turning it once or twice, and allowing it to remain in the heap for a few months, to spread it on meadow-land. I have seen great benefit apparently derived from such a top-dressing. The young grass in the spring assumed a rich, dark green color. I have observed the same effect where coal-ashes were spread on grass-land; and I have thought that the apparent benefit was due largely to the material acting as a kind of mulch, rather than to its supplying plant-food to the grass.
I doubt very much whether we can afford to make such a compost of earth with lime, ashes, or manure in this country. But I feel sure that those of us having rich clay land containing, in an inert form, as much nitrogen and phosphoric acid as Dr. Vœlcker found in the soil to be used in the earth-closet at Wakefield, can well afford to stir it freely, and expose it to the disintegrating and decomposing action of the atmosphere.
An acre of dry soil six inches deep weighs about 1,000 tons; and consequently an acre of such soil as we are talking about would contain 6,200 lbs. of nitrogen, and 3,600 lbs. of phosphoric acid. In other words, it contains to the depth of only six inches as much nitrogen as would be furnished by 775 tons of common barn-yard manure, and as much phosphoric acid as 900 tons of manure. With such facts as these before us, am I to blame for urging farmers to cultivate their land more thoroughly? I do not know that my land or the Deacon’s is as rich as this English soil; but, at any rate, I see no reason why such should not be the case.