Rotations for Improving Eroded Land

Much of the cropland in different sections of the United States has lost a large part of its topsoil. The productive capacity of severely eroded lands can be increased, although it cannot be fully restored. The Ohio experiment station initiated a study in 1937 to determine the relative crop production of topsoil and subsoil. Measurements were made of yields of hay in 1940 and corn in 1941 on topsoil and subsoil under different systems of cropping and management. Higher yields of hay and corn on both topsoil and subsoil were obtained through combined soil treatments. Yields on subsoil remained substantially lower than those on topsoil, a fact that emphasizes the desirability of initiating good rotations and whatever other conservation practices are needed before serious erosion or soil deterioration takes place.

In preliminary studies at McCredie, Mo., rotations including deep-rooting legumes proved effective in deepening the feeding zone for crops in Putnam silt loam. Placing lime and fertilizer deep in this soil facilitated deepening of the root zone. When lime and fertilizer had been placed at a depth of 9 to 18 inches in the shattered claypan soil, sweetclover roots penetrated to a depth of 20 inches, compared with 6 or 8 inches where only the topsoil was treated. Corn following sweetclover on this specially treated soil in 1945 yielded 6 to 9 bushels more to the acre than corn following sweetclover on adjacent plots where subsurface treatment had not been given.

The part played by crop rotations and soil management in rebuilding eroded soils is further illustrated by the results of an experiment carried out at Bethany, Mo., in 1932-42 to find how rapidly the organic-matter content of exposed subsoil of Shelby loam and crop yields from this soil might be increased. Seven plots were subjected to four cropping systems, with and without soil treatments. The topsoil of the experimental area had been eroded to about half its original depth. Except on plot 1, the remaining topsoil was removed artificially. Plots 3-7 were treated with lime and with superphosphate, which was applied on oats at the rate of 200 pounds per acre. Manure was applied on plot 6 before corn, at the rate of 8 tons per acre. Rainfall during the experimental period was scanty. In 1942 corn was grown on all the plots, to find how corn yields might be affected by past cropping and management. The cropping system and the 1942 corn yields were as follows:

The 1942 corn yield of plot 2, untreated subsoil, was 48 percent of that of plot 1, untreated topsoil. Plot 3, exposed subsoil that was limed and fertilized, yielded 80 percent as much corn as the untreated topsoil. Plot 5, with a 3-year rotation including sweetclover which was turned under in the spring before corn was planted, yielded 102 percent as much corn as plot 1. ( Fields with topsoil comparable to that of plot 1 that were treated with lime and superphosphate yielded about 80 bushels of corn an acre, or almost twice as much as plot 1.) Where manure was applied before sweetclover grown on exposed subsoil was turned under for corn, the corn yield was 150 percent of the yield from the comparable plot where manure was not applied. On plot 7, which was limed and fertilized and seeded to a grass-legume mixture that occupied the land for 10 years, the 1942 corn yield was 102 percent of the yield of untreated topsoil and 215 percent of that of untreated subsoil.

In this Missouri experiment runoff and soil loss averaged markedly lower for the higher-yielding subsoil plots. For example, for plot 2 the water loss was 1.63 times as great as for plot 3 and the soil loss was 2.3 times as great. These results emphasize the desirability of using needed soil amendments to rebuild eroded soils. The highest gains in soil organic matter were recorded for plot 6, on which sweetclover was turned under and manure was applied, and plot 7, where a good grass-legume cover was maintained for 10 years without being harvested.

On many eroded areas, crop rotations cannot satisfactorily be used until large quantities of lime have been applied, along with needed mineral fertilizers. Figures compiled in 1945 by C. E. Carter, of the Production and Marketing Administration, indicate that cropland in the United States needs 36,618,000 tons of limestone a year and pasture land needs 14,762,000 tons. In the North Central States alone, the limestone needed annually for cropland and pasture land together was estimated at more than 25 million tons.

A farmer who grows only a single crop, such as corn, cotton, or wheat, not only exposes his soil to serious erosion and robs it of its stored plant nutrients but fails to provide steady employment for himself and his help throughout the year. A good rotation usually provides for cash crops, feed crops, and pasture. For this reason and because it improves the quantity and quality of crop yields, a good rotation makes possible the fullest and best use, all year, not only of soil, livestock, and equipment but also of labor, one of the largest items of cost in producing crops. Well-planned crop rotations, supported by other soil conservation practices and supplemented by the growing of livestock of the types that will best utilize the feed crops, provide steady employment and insure a more dependable farm income.

THE AUTHOR