During 25 years the four crops of maize, oats, wheat, timothy and clover hay have been taken in rotation from the four tiers of plats at the Pennsylvania State College, so that the influence of the soil has been entirely eliminated. At the December farm prices for the decade ending December 1, 1906, the value of these four crops per acre have been: Maize, $29.67; oats, $14.49; wheat, $18.49; and hay, $18.05. It will be noted that during 25 years the average income from an acre of maize has been almost exactly twice that from an acre of oats. The region where these results were obtained is relatively unfavorable to a large yield of maize. It is obvious, therefore, that a modification in the rotation may modify the average income from the farm materially, provided such modification does not reduce the fertility of the soil. Thus, while the average income per acre during 25 years for the four-course rotation above mentioned was $20.17, if the rotation were increased to a five-course rotation by the addition of another year of maize, the average income would be $22.45 an acre.
It may be desirable to modify the rotation in order to increase or decrease a certain crop usually fed upon the farm. Thus, with a four-course rotation of maize, oats, wheat, clover and timothy, one-fourth the area would produce hay; while with a six-course rotation, composed of maize, oats, wheat, each one year, and hay three years, one-half the area would produce hay. If it is desired to still further reduce the area in oats and wheat, a seven-course rotation could be arranged with maize, two years in succession. This is the rotation that would be desirable for a dairy farm where it is planned to keep as many cows as practicable and to buy the concentrates largely. Either the wheat or the oats could be taken out of this rotation if either the one or the other were thought undesirable and a still greater amount of roughage desired.
On the other hand, there are places where the minimum amount of roughage is wanted. There are certain sections of the central West where it is possible to sow oats on corn stubble without plowing and where occasionally a rotation is practiced of maize, oats and mammoth clover. The clover is plowed for maize, the oats are disked in upon the corn stubble and the next year the clover is pastured until about June 1, when it is allowed to go to seed. In this rotation the only roughage obtained is the corn stover and the oat straw.
Another result reached by this rotation is that only one-third the land is plowed annually. In the four-course rotation mentioned above three-fourths of the land must be plowed, while in the six-course rotation one-half is plowed each year. In other ways the character of the rotation modifies the labor. For example, the labor and cost of harvesting an acre of hay is much less than that of producing, harvesting and threshing an acre of wheat.
Rotations may often be planned with reference to the main or cash crop. Thus in the Aroostook (Maine) potato district the rotation is potatoes, oats and clover. The chief purpose of the oats and clover is to keep down the blight in potatoes and add through the clover nitrogen and organic matter to the soil.
A system of cropping that is best when the owner operates the farm may not be desirable when the farmer is a tenant. When a farm is rented, the lease should provide that clover or other legumes occur with sufficient frequency to keep up the supply of nitrogen without the purchase of a considerable quantity in chemical fertilizers. The lease should be so drawn as to make it necessary for the tenant to keep live stock in order to realize the largest profit. The landlord should provide an equitable proportion of the mineral fertilizers when such are required.
The provisions of the lease and the character of the rotation will necessarily vary with circumstances, but the following system of tenant farming which has been employed for many years in Maryland will illustrate the principles just stated:
The lease provides for a five-course rotation consisting of maize, wheat, clover, wheat, clover. The landlord and the tenant share the maize and wheat equally, but the clover for hay or pasture goes entirely to the tenant, unless hay is sold, when it is divided equally. They each provide one-half the commercial fertilizer and one-half the seed, except clover seed, which the tenant is required to furnish.
This lease provides for two clover crops out of every five crops raised, thus supplying nitrogen abundantly, and the terms of the lease are such that it is necessary for the tenant to keep live stock to consume these clover crops in order to secure the most profitable returns. The feeding of the clover makes it necessary to feed some or all the maize and may lead to buying additional concentrates.
Stable manure is thereby supplied for the field which is to raise maize, while mineral fertilizers may be applied to the fields sown to wheat. On the limestone soils of the eastern states 50 pounds each of phosphoric acid and potash per acre applied to the wheat, and 10 loads of stable manure per acre to the maize will probably be found sufficient to maintain the crop producing power of the soil.