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Rotations and Corn
Crop rotations and crop sequences are management tools that can be used to exploit available resources more efficiently. Evaluation of cropping systems is complex with rotations and crop sequences only one part of the system. Research on corn rotations usually compares mono-cropping (continuous corn) to various other cropping sequences with some legume crop or small grain. Biological systems research usually show an advantage to rotation of crop species. The factors involved include but not limited to are: soil fertility, H20 use, soil tilth, soil erosion, crop residues, weed control, insect control and disease. Differences between continuous corn and rotational corn yields are greatly reduced as N rates are increased to attain maximum yield productivity in non-legume cropping sequences. However in many rotations, the difference in yields can't be made up by N application alone. Factors which causes these additional rotational benefits include reduced disease problems, less insect pressure, improved soil physical properties, elimination of phytotoxic substances in corn residues and the addition of growth promoting substances in legume residues.
One exception to the advantage of using legumes in a corn rotation can occur in years when a perennial legume, such as alfalfa can deplete soil moisture during the fall, prior to spring corn planting. Disease pathogen populations can be reduced or suppressed by rotations to certain broadleaf or legume crops. The key function of a rotation with corn is not to eradicate the pathogen but to reduce it to a low enough level so as a profitable yield can be produced when the susceptible crop (corn) is replanted into the crop sequence at a later time.
A mystery does remain, however, in that most research data show higher corn yields using rotations even when all factors known are equal such as fertility, pest pressures, water available, and hybrids are the same. Yield benefits have been obtained by rotating to legumes, from non-row crop to corn, from row-crop to corn, and even from one hybrid to another hybrid the second year in a sequence. In a recent national survey, corn yield increases due to rotations ranged from 6 to 30 bushels per acre. The best recommendation is to rotate, rotate, rotate.
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