soil of all important elements of fertility, and on normal soils always results ultimately in land ruin, unless some system of restoration is practised. Clover takes large amounts of calcium and phosphorus from the soil, and does not increase the nitrogen content if only the roots and stubble are left, because they contain no more nitrogen than the clover itself will take from soils of normal productive power.
To increase or maintain the nitrogen and organic matter of the soil is the greatest practical problem in American agriculture. In an hour's time one can spread enough limestone or phosphate on an acre of land to provide for large crops of wheat, corn, oats and clover, for ten or twenty years, while to supply the nitrogen for the same length of time would require from 20 to 40 tons of clover, or from 80 to 160 tons of farm manure, to be added to the same acre of land, even though one of the four crops harvested secured its nitrogen from the air.
Certainly we are making no such additions to the soil in average corn-belt agriculture, and one may well ask, How then is it possible to grow the crops now produced in this country? In the simplest language the answer to this question is: By "skinning" the soil—by working the land for all that's in it—by following the example of our ancestors, who brought agricultural ruin to millions of acres of once fertile farm land in the original thirteen states.
To provide nitrogen in the Illinois system of permanent agriculture requires the use of common sense and positive knowledge, the same as in providing limestone and phosphorus.
For the live-stock farmer I would suggest a five-field system—a four-year rotation of-corn, corn, oats and clover, grown upon four fields for five years, while the fifth field is kept in alfalfa. At the end of the fifth year the alfalfa field is brought into the rotation and one of the four fields seeded to alfalfa for another five-year period, and so on.
If the crop yields are 50 bushels each of corn and oats, 2 tons of clover and 3 tons of alfalfa; if the straw and half the corn stalks are used for bedding and all other produce for feed, and if 60 per cent, of the nitrogen in the manure is used for the production of crops, then a system is provided which will permanently maintain the supply of nitrogen.
For the farmer who sells grain, a 25-bushel wheat crop may well be substituted for the first corn crop, clover being seeded on the wheat for plowing under next year before planting com. If the fall and spring growths of this clover aggregate 112 tons, and if only the grain and clover seed and the alfalfa hay are sold, all clover, stalks and straw being turned to the land, this also provides a system for the permanent maintenance of nitrogen.
If the crop yields are all increased by 50 per cent., or even by 100 per cent., these systems still provide for the nitrogen supply, unless with the larger yields on richer land a somewhat greater amount is likely to
