Grass and Rotations

GRASS AND THE YIELDS OF CASH CROPS

R. E. Uhland

FARMERS generally recognize that continuous cropping to the Fame crop lowers the productive power of the soil. Data from tests at State and Federal agricultural experiment stations prove that when corn is grown after grass the yields may be several times greater than when corn is grown year after year.

In 1927 the Illinois Agricultural Experiment Station reported an experiment it had been carrying on for 39 years. For the last 9 years of the investigation the average yield of corn when the crop was grown continually on the same land was 24 bushels per acre. The average yield for the first 9 years was 41 bushels per acre showing that the yield for the last 9-year period was 41.5 percent less than that for the first 9-year period. The average yield for the last 22 years was 25.1 bushels per acre, compared with a yield of 50 bushels for corn grown in a 3-year rotation following clover. When fertilizer and manure were applied, the Yield of corn grown year after year on the same land averaged 40.5 bushels per acre. The same treatment applied to rotated land produced a yield of 66.6 bushels. The yield of corn on treated land following clover was 2.65 tunes as great as that for continuous corn grown on untreated land.

Research at the Indiana Agricultural Experiment Station, at La Fayette, offered proof that after 20 years of continuous cropping with corn, yields were reduced from 62 bushels per acre to 40 bushels. This decrease of 22 bushels occurred even though ample fertilization was practiced. When corn was grown in a rotation following clover and grass, the yield for the same period increased from 56 bushels to 65 bushels to the acre.

The accompanying figure on corn yields shows the importance of legumes and grasses in boosting yields in a number of sections of the country. For example, in a 14-year test at Wooster, Ohio, the yield of corn grown in a 3-year and a 5-year rotation with alfalfa was approximately three times as high as when corn was grown continually. That is, by following a good crop rotation, farmers in the Corn Belt can produce as much corn on a given acreage in 1 year as in 3 years of growing corn year after year.

The largest percentage increase in yield was obtained in a 3-year test at Auburn, Ala. Corn grown annually on untreated land yielded an average of 3.3 bushels an acre. This yield is in contrast with an average yield of 33.7 bushels when corn followed well-established kudzu. This land had been fertilized. When corn following kudzu received an application of sodium nitrate in addition to regular fertilizer, the yield was 39.1 bushels.

The data from Clarinda, Iowa, show that this decline in corn yields was quickly checked by substituting a good crop rotation. The corn yield in 1945 for the fourteenth consecutive crop was 24.3 bushels an acre. On an adjacent area that had been cropped to corn for 11 years, then to oats in 1943,and clover-and-timothy meadow in 1944, the 1945 corn yield was 56.8 bushels. That yield, however, was only 60 percent as great as the yield of 94.4 bushels on the field where a rotation had been followed for the 14 years.

It should be pointed out that the soil on this continuous corn plot at Clarinda had suffered a great deal because of erosion and deterioration. In-sects and diseases had become more injurious. The land, however, still possessed enormous soil resources, which made possible the 32.5-bushel increase in corn yield. This fact emphasizes the urgency of using rotations, including grasses and legumes, while there is still soil to conserve.