Crop rotation and its ability to suppress perennial weeds (OK-Net Arable Practice abstract)

Summary

The appropriate combination of crops and green manures prevents spread of perennial weeds and increases crop yields and quality. Weed-suppressing crop rotations are absolutely essential for sustainable organic arable farming.
Practical recommendation
Basic rules
• Implement green manures, such as clover or lucerne, in at least 20 % of the rotation.
• Do not grow more than 50 % of cereals with low weed competitiveness in the rotation. Do not cultivate such crops for more than 2 consecutive years.
• In fields with prevalent high weed pressure cultivate only crops with high weed competitiveness.
Points to consider in case of high weed pressure:
• Do not grow grain legumes where perennial weeds are a problem. Late harvest in combination with loose plant stands (light) and high nutrient availability before harvest further propagates the growth of perennial weeds.
• Do not sow winter crops after lupine or broad beans, as winter crops leave perennial weeds undisturbed during a long period of time. Instead, undersow a cover crop in the legumes to hold-back the nutrients and then sow a competitive crop in spring.
• Do not sow spring barley after grass-clover, as spring barley does not take up the available nitrogen effectively and thus creates a high risk of nitrogen leaching. Instead, grow oats or spring wheat undersown with cover crops two years in succession. On clayey soils and in dry climates though, winter crops are better than spring crops.
• Do not leave a badly established crop unmanaged until harvest, as weeds might take over. Decide before beginning of June, whether to leave the crop or better control the weeds effectively and lay the foundation for a successful crop next year.
• Do not leave a badly established cover crop unmanaged in autumn, as perennial weeds might flourish. In autumn weeds can be controlled with relatively low cost. You may concentrate on weed control measures on infested parts of a field only.
• On sandy soils, sow rye, triticale or winter spelt instead of winter wheat, as winter wheat does not grow well on such soils and encourages propagation of perennial weeds.