Weed dynamics in the Danish long-term experiments on organic arable crop rotation systems

Summary

Summary of main findings on perennial weeds:
1. Gradual increase of perennial weeds over time, predominantly in the O4 rotation (without green manure)
2. Perennial green manures suppressed Creeping thistle and Sowthistle but caused Couch to increase
3. Cover crops hindered effective cultivation campaigns against perennials, especially Couch
4. Legume crops and mixtures with cereals and legumes caused perennials to proliferate, particularly Couch
5. Fertilisation had inconsistent effects
6. Summer fallow was effective st perennials, especially against Couch in particular
Summary of main findings on annual weeds:
1. No major problems encountered at all three sites
2. Skillfull operations of weed harrows, inter hoes and other mechanical tools improved over time
3. Hemp, spring oat and winter rye were particularly suppressive
4. Green manuring with grass clover or lucerne reduced the pressure of annual weeds in the first years after termination of the green manure