“The Doctor is in the main correct,” said I; “but he does not fully answer the question, ‘What is manure?’ To say that manure is plant-food, does not cover the whole ground. All soils on which plants grow, contain more or less plant-food. A plant can not create an atom of potash. It can not get it from the atmosphere. We find potash in the plant, and we know that it got it from the soil and we are certain, therefore, that the soil contains potash. And so of all the other mineral elements of plants. A soil that will produce a thistle, or a pig-weed, contains plant-food. And so the definition of the Doctor is defective, inasmuch as it makes no distinction between soil and manure. Both contain plant-food.”
“What is your definition of manure?” asked Charley; “it would seem as though we all knew what manure was. We have got a great heap of it in the yard, and it is fermenting nicely.”
“Yes,” I replied, “we are making more manure on the farm this winter than ever before. Two hundred pigs, 120 large sheep, 8 horses, 11 cows, and a hundred head of poultry make considerable manure; and it is a good deal of work to clean out the pens, pile the manure, draw it to the field, and apply it to the crops. We ought to know something about it; but we might work among manure all our lives, and not know what manure is. At any rate, we might not be able to define it accurately. I will, however, try my hand at a definition.
“Let us assume that we have a field that is free from stagnant water at all seasons of the year; that the soil is clean, mellow, and well worked seven inches deep, and in good order for putting in a crop. What the coming ‘season’ will be we know not. It may be what we call a hot, dry summer, or it may be cool and moist, or it may be partly one and partly the other. The ‘season’ is a great element of uncertainty in all our farming calculations; but we know that we shall have a season of some kind. We have the promise of seed-time and harvest, and we have never known the promise to fail us. Crops, however, vary very much, according to the season; and it is necessary to bear this fact in mind. Let us say that the sun and heat, and rain and dews, or what we call ‘the season,’ is capable of producing 50 bushels of wheat per acre, but that the soil I have described above, does not produce over 20 bushels per acre. There is no mechanical defect in the soil. The seed is good, it is put in properly, and at the right time, and in the best manner. No weeds choke the wheat plants or rob them of their food; but that field does not produce as much wheat by 30 bushels per acre as the season is capable of producing. Why? The answer is evident. Because the wheat plants do not find food enough in the soil. Now, anything that will furnish this food, anything that will cause that field to produce what the climate or season is capable of producing, is manure. A gardener may increase his crops by artificial heat, or by an increased supply of water, but this is not manure. The effect is due to improved climatic conditions. It has nothing to do with the question of manure. We often read in the agricultural papers about ‘shade as manure.’ We might just as well talk about sunlight as ‘manure.’ The effects observed should be referred to modifications of the climate or season; and so in regard to mulching. A good mulch may often produce a larger increase of growth than an application of manure. But mulch, proper, is not manure. It is climate. It checks evaporation of moisture from the soil. We might as well speak of rain as manure as to call a mulch manure. In fact, an ordinary shower in summer is little more than a mulch. It does not reach the roots of plants; and yet we see the effect of the shower immediately in the increased vigor of the plants. They are full of sap, and the drooping leaves look refreshed. We say the rain has revived them, and so it has; but probably not a particle of the rain has entered into the circulation of the plant. The rain checked evaporation from the soil and from the leaves. A cool night refreshes the plants, and fills the leaves with sap, precisely in the same way. All these fertilizing effects, however, belong to climate. It is inaccurate to associate either mulching, sunshine, shade, heat, dews, or rain, with the question of manure, though the effect may in certain circumstances be precisely the same.”
Charley evidently thought I was wandering from the point. “You think, then,” said he, “manure is plant-food that the soil needs?”
“Yes,” said I, “that is a very good definition—very good, indeed, though not absolutely accurate, because manure is manure, whether a particular soil needs it or not.” Unobserved by us, the Deacon and the Doctor had been listening to our talk. —“I would like,” said the Deacon, “to hear you give a better definition than Charley has given.” —“Manure,” said I, “is anything containing an element or elements of plant-food, which, if the soil needed it, would, if supplied in sufficient quantity, and in an available condition, produce, according to soil, season, climate, and variety, a maximum crop.”