A functional diversity approach of crop sequences reveals that weed diversity and abundance show different responses to environmental variability
Résumé
Combining several crop species and associated agricultural practices in a crop sequence
has the potential to control weed abundance while promoting weed diversity
in arable fields. However, how the variability in environmental conditions that
arise from crop sequences affects weed diversity and abundance remains poorly
understood, with most studies to‐date simply opposing weed communities in
monoculture and in crop rotation. Here, we describe crop sequences along gradients
of disturbance and resource variability using a crop functional trait and associated
agricultural practices. We tested the hypothesis that in disturbances
reduces weed abundance, whereas variability in resources promotes weed
diversity.
2. We used functional Hill's numbers to compute crop sequence functional diversity
based on sowing date, herbicide spectrum and crop height—these are the respective
proxies of disturbance timings, disturbance types and light availability. Using
a large‐scale weed monitoring database, we assessed crop sequence diversity for
1,045 crop sequences of five consecutive cropping seasons. We computed weed
richness and abundance at pluri‐annual (pool of weeds observed across five cropping
seasons) and annual (pool of weeds observed during a winter cereal cropping
season preceded by five cropping seasons) scales. We also accounted for herbicide
and tillage intensities to test whether management intensity affects the response
of weed diversity and abundance to crop sequence diversity.
3. At the pluri‐annual scale, weed richness increased with the diversity of crop height
and sowing date, whereas weed abundance decreased with sowing date diversity.
Annual weed richness decreased with sowing date diversity, whereas annual weed
abundance poorly relied on crop sequence diversity.
4. Synthesis and applications. This study establishes a scientific basis for designing
crop sequences according to specific weed management goals. We show that
farmers may enhance arable weed diversity on a pluri‐annual scale by sequentially
sowing crop species that differ in their competitive ability and sowing date. They
may also achieve a better control of weed abundance by increasing the diversity
of crop sowing dates across the crop sequence.