November’s CSA Paper of the Month is from Agriculture, Ecosystems & Environment and is entitled: Annual intercropping suppresses weeds: A meta-analysis (https://doi.org/10.1016/j.agee.2021.107658) by Chunfeng Gu, Lammert Bastiaans, Niels P.R. Anten, David Makowski, and Wopke van der Werf.
In agricultural systems, the aim is to produce the highest crop yield while minimizing costs. In comparison to pests and diseases, weeds have the potential largest adverse effect on crop growth and yield quality, and thus have high control costs. Intercropping is the cultivation of two or more crop species simultaneously in the same field for the whole or part of their growing period. This practice has been proposed as a promising way to improve weed management in agriculture.
The researchers did an overarching meta-analysis to quantify the weed suppressive effect of intercrops composed of two annual cash crops. They compared the observed weed biomass between intercrop and respective sole crop treatments. They found that in general, weed biomass in intercrops was substantially (58%) lower than that in the less weed-suppressive sole crop, and was similar to that in the more weed-suppressive sole crop. Findings were consistent across different groups of species combinations, such as maize/legume and small-grain cereal/legume intercrops.
They observed that the level of temporal segregation in intercrops was not an important factor for weed suppression. No evidence in this study showed that when two species sown and harvested together provided better weed suppression than situations when the second crop was sown or planted after the emergence of the first crop.
The researchers faced some challenges when analyzing the dataset. Intercrop design and management practices were commonly confounding within this meta-analysis and beyond. For instance, maize/legume intercrops were characterized by a high temporal niche differentiation, a row or strip arrangement, and an additive design, while small-grain cereal/legume intercrops were characterized by lower temporal niche differentiation, a mixed arrangement, and equally distributed over replacement and additive design. The implication is that it is not possible to identify in a meta-analysis unique factors driving weed suppressiveness, suggesting that the main driving force for weed suppression might be a combination of factors that co-occur rather than a single factor.
Chunfeng Gu is a PhD candidate in the Centre for Crop Systems Analysis group at Wageningen University. Her PhD project aims to investigate the contribution of crop diversification to weed control in agriculture and facilitate understanding of the possible mechanisms by using meta-analysis method and functional-structural plant modelling. Her project belongs to the EU’s Horizon 2020 Program - ReMIX project.