A functional diversity approach of crop sequences reveals that weed diversity and abundance show different responses to environmental variability

Abstract

1.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. 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. Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Mahaut L, Gaba S, Fried G. A functional diversity approach of crop sequences reveals that weed diversity and abundance show different responses to environmental variability.

Long‐term farming systems and last crop sown shape the species and functional composition of the arable weed seed bank

“…The different long-term farming systems, under the same crop rotation sequence and tillage practices, resulted in significant differences in the seedbank weed community. Although previous studies pointed out to a strong influence of crop rotation and tillage on weed communities (Mahaut, Gaba, & Fried, 2019), here we found that other farming practices determined significant differences in the abundance, diversity and floristic composition of the weed seedbank, as well as in the functional diversity, redundancy and composition. Besides, we found that not only long-term farming but also the yearly management associated to the last crop sown were important determinants of the functional and species composition of the soil seedbank.…”

Seasonal and interannual variations in functional traits of sown and spontaneous species in vineyard inter‐rows

“…The trait‐based approach allows for the comparison of various cropping systems involving different crop and spontaneous species (Mahaut et al 2019), using continuums of trait variations as explanatory or predictive variables for agroecosystem services (Duarte et al 1995, Mouquet 2015). It seems therefore important to multiply trait‐based experiments involving ITV in various agrosystems to assess their potential to provide ecosystem services (Martin and Isaac 2015).…”

Weed seedbank diversity and sustainability indicators for simple and more diverse cropping systems

“…Variations in disturbance timing, as reflected in crop sowing and harvest dates, and in functional attributes of crops, such as height and competitive ability for light, are important determinants of cropping system effects on weeds, and may have stronger effects than crop species richness per se Mahaut et al, (2019). examined data from 473 fields in France collected over five consecutive seasons and found that when evaluated over multiple phases of the rota-…”