Effect of Sudan Grass and of Soybeans on Yield of Corn 1

Three 2-year rotations in which sudan grass, soybeans, and oats were alternated with corn were compared between 1919 and 1933, inclusive. All crops were removed except corn stalks and some fallen soybean leaves. On O'Neill black fertile soil corn yielded 50.8 bushels per acre after sudan grass, 49.0 bushels after soybeans, and 47.8 bushels after oats. The differences are not statistically significant. The results were not changed by superphosphate applied at corn planting time to half of each plat in the later years. It is believed the soil was well supplied with other minerals. Sudan grass removed over twice as much dry matter as soybeans or oats, over twice as much nitrogen as oats, and appreciably more than soybeans. Despite these heavier withdrawals the sudan grass plats appeared to be just as productive after 13 years of cropping as the soybean and oat plats. On soil similar to that used for the other test, fall plowing sudan grass stubble increased the yield of corn 10.7% over spring plowing. Yields obtained in dry years and water determinations of the soil indicate that moisture deficiency is not a cause of the depressed yields sometimes obtained following sudan grass.