Ecology and management of weeds under conservation agriculture: A review

Tillage has been known to cause soil erosion and cost time and resources and this affects productivity and inflates the cost of production. Therefore, over the past few years in many countries, there has been a growing trend toward conservation agriculture (CA) to enhance sustainability without compromising land productivity. Three important pillars of CA are minimal tillage operations, permanent residue cover, and rotation of primary crops. Adoption of CA, however, influences weed populations differently from conventional agriculture. Weed control in CA is a greater challenge than in conventional agriculture because there is no weed seed burial by tillage operations and soil-applied herbicides are not incorporated, resulting in reduced efficacy. The behavior of weeds and their interaction with crops under CA tend to be complex and not fully understood. A large proportion of weed seed bank remains generally on or close to the soil surface after crop sowing under CA. Weed species, in which germination is stimulated by light, are likely to be more problematic in CA. In addition, in the absence of tillage, perennial weeds may also become more challenging in this system. On the other hand, weed seeds present on the soil surface are more prone to desiccation and greater predation activity of insects, especially ants. Crop residues, when uniformly and densely present, under CA could suppress weed seedling emergence, delay the time of emergence, and allow the crop to gain an initial advantage in terms of early vigor over weeds. Where pre-emergence herbicides are applied, crop residues may also intercept a considerable proportion of the applied herbicide and may result in lower herbicide efficacy. Approaches such as stale seedbed practice, uniform and dense crop establishment, use of cover crops and crop residues as mulch, crop rotations, and practices for enhanced crop competiveness with a combination of pre- and post-emergence herbicides could be integrated to develop sustainable and effective weed management strategies under CA systems.