ROTATIONS FOR PROBLEM FIELDS

R. Y. Bailey, W. M. Nixon

THE IDEAL rotation is the one that achieves complete harmony between the farmer's demand for cultivated crops and the needs of the land for protection.

A good soil-conserving rotation includes enough grass and legumes to reduce losses of soil through erosion; reduce losses of plant nutrients through leaching; improve the structure of the soil so that it will absorb water readily; increase and maintain organic matter and nitrogen in the soil; and increase yields of the cultivated crops grown in the rotation.

Grass and legumes in rotation improve the structure of the soil by making it more granular and thus increasing its ability to absorb water. Residues from grass and legumes that are returned to the soil as green manure increase organic matter and nitrogen in the soil.

Samples taken at the Southern Piedmont Conservation Experiment Station at Watkinsville, Ga., from Cecil clay at the ends of the first and second cycles of a 3-year rotation of cotton, oats, and lespedeza showed on analysis that there was little increase in soil aggregation, nitrogen, or organic matter in the soil during the first cycle, but after the second cycle aggregation was increased, the nitrogen was almost doubled, and organic matter was more than doubled. These results illustrate the need for continuing rotations for more than one cycle.

Larger crop yields are often obtained from fewer acres as a result of rotations including grass and legumes.

Drayton Hopkins, who farms in the Fork Shoals Road community in the Greenville County Soil Conservation District of South Carolina, had 134 acres in cotton, 183 acres in corn, and 87 in small grain before he began using soil-conserving rotations. He was producing an average of 77 bales of cotton, 1,830 bushels of corn, and 1,670bushels of oats and wheat. Under the rotation plan, he had 100 acres in cotton, 50 in corn, and 160 in small grain. The farm then produced 100 bales of cotton, 1,500 bushels of corn, and 10,300 bushels of oats, wheat, and barley. Annual lespedeza following small grain produced 70,000 pounds of seed. Fifty-five steep acres formerly in row crops were growing a perennial sericea lespedeza for seed and grazing, or kudzu for hay and grazing.

Soil-conserving rotations must be fitted to the land.

Kinds of ground cover, the extent of their use, and patterns of arrangement in rotations are determined by slope, soil type, drainage conditions, extent of erosion, and other characteristics of the land, which are the basis for land capability classification a physical guide for assisting farmers in soil conservation districts to plan the use of their land and to determine its needed treatment. Of the eight classes of land, four can be cultivated safely; consequently, we are concerned here with grass and legumes in rotations on those four classes.

Such factors as rainfall and the system of farming affect the types of rotations recommended for the various classes of land in different regions and farming areas. Kinds of rotations recommended in the Southeast for the four classes of cropland are illustrative. The type of cropping system is determined by the crop needs of the farm.

Land in Class 1 well-drained land of a desirable soil type, and flat enough so that erosion is not a problem can be maintained in a productive condition under intensive use for cultivated crops, if such cover crops as vetch, crimson clover, bur-clover, or crotalaria are included in the cropping system. Cotton, if it is the main cash crop, can be grown on it each year, with a winter cover crop like vetch or crimson clover seeded between the cotton rows in the fall. On livestock farms, the cultivated land may be used for winter grazing and summer grain crops.

Short rotations may include mixtures of small grain or ryegrass and crimson clover or button clover for winter grazing and grain sorghum for grain production. Where ryegrass and hard-seeded crimson clover or button clover are grazed until late spring and followed by grain sorghum after seed is harvested, thick volunteer stands of ryegrass and clover come up between the sorghum rows in the fall. Such a rotation requires no land preparation for the winter grazing crop, because the summer cultivation of the grain sorghum leaves the soil in condition for the germination of grass and clover seed.

Several annual winter legumes make enough hard seed to fit into a cropping system that includes two or three successive years of corn and one year of grain sorghum following a legume seed crop. Such a cropping system permits a grain crop to be grown each year with a green legume to be turned under for corn and a heavy, dry legume residue for grain sorghum.

Land in Class II needs terraces, water disposal at terrace ends, contour tillage, and a rotation that keeps half the land covered while the other half is cultivated.

The effectiveness of a simple 2-year rotation in reducing erosion on Class II land was shown at Watkinsville. A rotation of peanuts the first year and a vetch-oats mixture for hay followed by a summer crop of crotalaria the second year was compared with continuous peanuts on runoff plots 105 feet long on a 3-percent slope in 1944, 1945, and 1946. The average annual soil loss from the 2-year rotation was 1.37 tons an acre. The value of the residue from the protective crops in the rotation is illustrated by the loss of only 1.52 tons an acre from peanuts in rotation, as compared with the loss of 6.97 tons where peanuts were grown continually. Peanuts in the rotation made an average yield of1,634 pounds of nuts per acre, as compared with 1,079 pounds under continuous cropping.

Besides the protection that can be provided by terracing, proper water disposal at terrace ends, and contour tillage, Class III land, which is moderately good but subject to severe erosion, needs rotations that provide effective ground cover on at least two-thirds of the land while the remainder is under cultivation.

A rotation effective in controlling erosion at Watkinsville on Class II land did not control erosion on Class III land.

Soil losses under a simple 2-year cropping system of cotton and vetch the first year and corn and crotalaria the second year were measured on runoff plots on both Class II and Class III land. On a 105-foot plot of Class 11 land with a 3-percent slope, this cropping system lost only 3.45 tons of soil per acre annually during a 3-year period. During the same period, plots of Class III land 70 feet long on a 7-percent slope lost an average of 10.98 tons of soil an acre. Continuous cotton lost an average of 5.35 tons on Class 11 and 23.92 tons on Class III land.

Under a 3-year rotation of oats and lespedeza the first year, volunteer lespedeza hay the second year, and cotton the third year, on Class III land, average soil losses were only 3.79 tons an acre for the rotation. The average loss during a 4-year period under cotton in the rotation was 7.67 tons an acre, compared to 32.23 tons under continuous cotton.

Rotations that include a mixture of orchardgrass and red clover in a 3-year cycle with corn and small grain are effective on land in this class. Rotations that include more cover than either of the 3-year cropping systems described here are desirable. The high soil loss during the cultivated year should be as widely spaced as conditions permit.

Where livestock is a major source of income, a rotation that includes a cycle of alfalfa followed by a grass sod, or a mixture of perennial grasses and clovers, reduces soil losses and increases yields of other crops in the rotation.