THE TRIENNIAL CROP ROTATION SYSTEM After the red-clay lands of the southern cotton belt have been protected from erosion by terracing (Vol. I, page 402), experience has proved that a simple three-year crop rotation will rapidly restore their original fertility without materially derang ing existing conditions or interrupting the contin uous production of the three principal staples of that section cotton, corn and oats. The two fac tors which simplify the process are (1) the reten tive clay subsoil and (2) the rapid growth and effective service (both chemical and mechanical) of the cowpea. This valuable legume, in the space of 90 days, not only stores in the soil, through its decaying roots and stubble, a large quantity of vegetable matter for subsequent conversion into humus, and transfers from the atmosphere a con siderable supply of immediately available nitrogen, but it also "pays its own way" while so doing. In principle, the process is of course not new, but its adoption as a practice is recent and by no means universal, as yet, though making rapid headway, particularly in Georgia.
Details of the system.
In brief, the details of the process are as follows: An equal farm area is devoted to each of the three staple crops. The best third is planted in cotton, the next best in corn and the poorest third in fall oats. The three areas need not be all in one body; indeed, it is seldom found possible, at the start, so to locate them. After the oats are harvested in June, the stubble is turned under and the area sowed broad cast with cowpeas, which are later cut and con verted into either hay or ensilage, leaving only the roots and stubble to be turned under, since there would be no economy in utilizing a feeding material for a fertilizer at forage prices. The cowpea area is planted the second season in cotton, and the former cotton area is put in corn, while oats occupy the previous corn plat. With the corn, cowpeas are also generally planted, either in the drill after the corn is waist-high or upward, or sowed broadcast on "lay ing by," thus introducing a legume or nitrogen-. gatherer into the rotation two years in three. The rotation is invariably (1) corn (with peas) after cotton, (2) oats and peas after corn, and (3) cotton after oats and peas—the grossest feeding crop, cotton, thus following the nitrogen-gatherer, the cowpea. The result, after two or three complete rotations, is an impressive increase in yield all around. Each crop, however, is, when planted, given
its own specific fertilization, the formulas for which in the South are well-established standards.
Results.
At the end of the first rotation, that is to say in the fourth year, when the area first planted in cot ton is again occupied by that crop, the increase in yield is always marked and frequently surprising (100 per cent is by no means uncommon); and the poorer the land originally the more likely is the percentage to be attained. For example, an initial yield of one-third of a bale, or 500 pounds of seed cotton per acre (the average output), often reaches two-thirds of a bale or 1,000 pounds of seed cotton, after the first rotation; one bale, or 1,500 pounds of seed cotton, after the second rotation ; and one and one-third bales, or 2,000 pounds of seed cotton, after the third rotation. Here uniform increase seems to stop. Given a sufficient supply of moisture there would be, theoretically, no limit to the in crease in yield, since the mechanical condition of the soil would be steadily improving under its en larging content of humus, which would of course render possible a corresponding increase in the ap plication of commercial fertilizers for each staple. As the water-supply, however, is a most erratic factor, it is found in practice that after the third rotation (or tenth year), the yield fluctuates con siderably, yet seldom falls short of one and one third bales as a minimum and frequently, in more propitious seasons, attains a maximum of one and three-fourths to two bales per acre, in which there is a most satisfactory profit.
The increase in the yield of the other two staple crops is neither so uniform nor so large, relatively, as the increase for cotton, yet it is nevertheless very obvious.
When the available supply of lot manure, usually limited in the South, is distributed broadcast over the poorer spots, or "galls," in order to bring their fertility up to the average of the surrounding area, a terraced cotton-farm, subjected to the "triennial rotation" for ten or twelve years, presents a high type of progress, and becomes, with little cost or inconvenience, an impressive and profitable object lesson, and one that is fortunately placed each year more and more in evidence. The general adoption of the system throughout the entire cotton-belt is unquestionably assured.