When a soil is well supplied with lime there are three things that are liable to be deficient.  If it is not well supplied with lime there may be four, but the bulk of your soils are good enough so far as lime is concerned.  Those three are potash, which is abundant and will be abundant 100 years from now, phosphoric acid, or phosphorus, with which our soils are fairly well supplied, and nitrogen, which comes from the vegetable matter.  In nitrogen our prairie soils are remarkably rich when first plowed up.  The phosphoric acid and the potash you can not lose unless they are taken away in the form of crops, but the nitrogen may be lost without even taking off crops.  All you have to do is to cultivate your soil, when part of the nitrogen becomes soluble in water and is carried down by the rain into the water-table unless you have plants growing with roots to take it up; a large part escapes into the air.  So when your black prairie soil has been under cultivation for twenty years, as an orchard, usually from one-half to one-third of the original nitrogen has escaped, most of it into the air, only the smaller part being carried off in the crops.  That is the one thing that orchardists and horticulturists have to concern themselves about first of all, so far as soil fertility is concerned.

I see that the first of the questions for me to answer deals with that.  “What crop do you consider the best green manure?” There are two kinds of green manures.  One is represented by rye.  Rye takes up the nitrogen that is in the soil, and when it dies leaves behind what it took out of the soil; the next crop can get this.  By plowing under the rye crop you do not increase the amount of nitrogen, the most important element of fertility in the soil.

We have a better green manure than that, better than rye or oats or barley or any of those plants that properly belong to the grass family; namely, the members of the clover, bean or pea family—­all of these plants which are called legumes, which have pods and which have flowers shaped like butterflies.

As these grow they take up nitrogen from the air; the bacteria which make their home on the roots of those plants take the nitrogen from the air and give it to their host plants.  The plants receive this nitrogen, store it in themselves, and when the crop is plowed under you have a great amount of nitrogen added to the soil.  Now, a clover crop of an acre growing from spring until the freeze-up in the fall may take out of the air as much as 120 pounds of nitrogen.  One hundred and twenty pounds of nitrogen, bought in the form of commercial fertilizer from Swift & Company, or Northrup, King & Company, would cost you $24.00.  The clover has taken that much out of the air.  If the crop were pastured off, the greater part of this nitrogen would be returned to the soil; when you plow the clover under still more nitrogen is taken from the air by bacteria that live upon the decaying plant material, and you may have $48.00 worth of nitrogen per acre added to the soil by simply growing clover for one year.