Weed dynamics and conservation agriculture principles: A review

Abstract

a b s t r a c tConservation agriculture (CA) is based on minimum soil disturbance, permanent soil cover, and crop rotation; it is promoted as a sustainable alternative to systems involving conventional tillage. Adoption of CA changes weed dynamics and communities and therefore necessitates adjusting weed control methods. The objectives of this review are to summarize literature concerning CA principles and their interactive effects on weed life cycles and community composition, briefly review CA-appropriate cultural practices for additional weed control, and identify areas where further research is needed. No-till systems accumulate seeds near the soil surface where they are more likely to germinate but are also exposed to greater mortality risks through weather variability and predation. Assuming no seed input into the system, germinable seedbanks under no-till decrease more rapidly than under conventional tillage. Reducing tillage may shift weed communities from annual dicots to grassy annuals and perennials. Surface residues lower average soil temperatures and may delay emergence of both crops and weeds. Germination and growth of small-seeded annuals will suffer from restricted light availability, physical growth barriers and potential allelopathic effects from surface residue. Crop rotation affects weeds via allelopathy and altered timing of both crop management and resource demands. Rotations should incorporate crops sown in varied seasons (e.g., autumn and spring), annuals and perennials, different herbicides, and/or various crop families. Literature indicates implementing no-till without crop rotation can result in severe weed problems; greater rotational crop diversity results in easier weed management. Additional cultural practices for CA include: (i) selecting highly competitive varieties; (ii) altering planting dates; (iii) preventing weed seed recruitment; (iv) adjusting planting arrangement, densities, and fertilizer placement; and (v) microbial bio-controls. Further research is needed concerning: (i) the interactive effects of tillage and surface residue on weeds; (ii) the use of models and/or meta-analyses to predict weed responses, and to identify intervention points in CA; and (iii) the weed-suppressive potential of longer (4+ years) rotations.

Soil management shapes ecosystem service provision and trade-offs in agricultural landscapes

“…[37]). Under conservation tillage, weed communities are richer in perennial species and volunteer crops, being more similar to those inhabiting grasslands, and are therefore more influenced by the immigration of seeds from semi-natural habitats [42]. Conventional tilled fields instead harboured mostly annual weed species typical of more disturbed environments.…”

Sustainable Weed Management for Conservation Agriculture: Options for Smallholder Farmers

“…A method of controlling the notoriously noxious weed of cereal crops-blackgrass (Alopecurus myosuroides Huds. )-with no-tillage practices is a good example [68,73]. Up to 80% of blackgrass seeds perish each year in undisturbed (i.e., direct-drilled) soil and so only 20% of the previous year's seed bank will germinate.…”

“…• Seed predation in ecological weed management Surface accumulation of seeds under no-tillage should increase their susceptibility to predation by insects, rodents and birds [68]. This can be a useful avenue for ecological weed management [69].…”

Allelopathy: driving mechanisms governing its activity in agriculture

“…Understanding allelopathy is helpful for planning and managing cropping systems (Gronle et al 2015). Reduced weed infestation in CA can be achieved with proper weed-suppressive cover crops (Altieri et al 2011;Jabran et al 2015;Nichols et al 2015), or via the use of allelopathic crop cultivars (Balbinot Junior et al 2003;Nichols et al 2015) or consortium systems that involve potential allelopathic species. Highly productive crop rotations should consider crop species that are tolerant to the allelochemicals released from previous crops.…”