Impotence of Crop Rotation

Crop Rotation

By : Ron Heiniger, Crop Science Extension Specialist, NC State University and Molly Hamilton, Extension Assistant, NC State University

The importance of crop rotation in an organic production systems cannot be overemphasized. Select a rotation sequence of production crops and cover crops based on the specific characteristics of the field. This is particularly important in the first few years of an organic production system because the transition period will set the conditions for success. Rotation sequences should be designed to:

• reduce weed pressure by minimizing the amount of weed seed produced and reducing perennial weeds;
• increase the amount of mineralizable nitrogen in the soil;
• reduce the incidence of insect and disease pests by eliminating hosts and interrupting pest life cycles.

This usually requires combinations or rotations of crops that attract or harbor different insects and diseases, fix nitrogen, inhibit weed growth, and enhance the soil. The following crop sequences are recommended for organic grain crop production in North Carolina:

Wheat – Red clover (or other forage legume) – Corn. Wheat and the legume provide continuous ground cover, help break up pest cycles, reduce warm-season weeds through the mowing of clover, and increase available nitrogen. Tilling the clover into the soil makes nitrogen available for the succeeding corn crop. Growing the legume for two seasons rather than one will result in more nitrogen return to the soil and a longer period between corn crops to break pest insect and disease cycles. However, in systems without livestock, the legume cover crop might have little economic value unless it can be cut and sold for hay as an organic forage crop. Cutting for hay will reduce the amount of biomass from residue and may reduce the amount of nitrogen available to subsequent crops.

Wheat – Soybean – Corn. This rotation has many of the same advantages as the above rotation, but the soybean crop can be harvested and marketed. One disadvantage of this rotation is longer soil exposure since soybean is planted after wheat and harvested before corn. Weeds emerging in the soybean crop may be difficult to control, and less nitrogen will be fixed by the soybean crop. However, a cover crop could be incorporated into this rotation to provide ground cover when needed, to expand the rotation beyond two years, or both. A short, two-year rotation will need to be approved by a certification agency.

Farmers who have long-established organic fields usually use a longer rotation of four or five years. A longer crop rotation in North Carolina could rely on one of these sequences:

• Corn – rye cover crop – soybeans – rye or crimson clover cover crop – wheat – cowpea cover crop

• Corn – wheat – (double cropped) soybeans – crimson clover cover crop – sunflowers or summer production or cover crop – small grain (oats, barley, triticale)

Legumes or other broadleaf crops should be grown at least two of every five years. A well-developed cropping sequence should result in minimal problems with insects and plant diseases