Cover crop mixture diversity, biomass productivity, weed suppression, and stability

Abstract

16 The diversity-productivity, diversity-invasibility, and diversity-stability hypotheses 17 propose that increasing species diversity should lead, respectively, to increased average 18 biomass productivity, increased invasion resistance, and increased stability. We tested 19 these three hypotheses in the context of cover crop mixtures, evaluating the effects of 20 increasing cover crop mixture diversity on aboveground biomass, weed suppression, and 21 biomass stability. Twenty to forty cover crop treatments were replicated three or four 22 times at eleven sites using eighteen species representing three cover crop species each 23 from six pre-defined functional groups: cool-season grasses, cool-season legumes, cool-24 season brassicas, warm-season grasses, warm-season legumes, and warm-season 25 broadleaves. Each species was planted in monoculture, and the most diverse treatment 26 contained all eighteen species. Remaining treatments included treatments representing 27 intermediate levels of cover crop species and functional richness and a no cover crop 28 control. Cover crop planting dates ranged from late July to late September with both 29 cover crop and weed aboveground biomass being sampled prior to winterkill. Stability 30 was assessed by evaluating the variability in cover crop biomass for each treatment 31 across plots within each site. While increasing cover crop mixture diversity was 32 associated with increased average aboveground biomass, this was the result of the 33 average biomass of the monocultures being drawn down by low yielding species rather 34 than due to niche complementarity or increased resource use efficiency. At no site did the 35 highest yielding mixture out-yield the highest yielding monoculture. Furthermore, while 36 increases in cover crop mixture diversity were correlated with increases in weed 37 suppression and increases in biomass stability, we argue that this was largely the result of 3 38 diversity co-varying with aboveground biomass, and that differences in aboveground 39 biomass rather than differences in diversity drove the differences observed in weed 40 suppression and stability. The results of this study contradict popular interpretations of 41 the diversity-productivity, diversity-invasibility, and diversity-stability hypotheses. 43 Introduction44 Increasing species diversity is thought to lead to increased average productivity, 45 increased invasion resistance, and increased stability [1,2]. Respectively named the 46 diversity-productivity, diversity-invasibility, and diversity-stability hypotheses, these 47 three hypotheses, while contested in the field of ecology [3][4][5], have often been treated in 48 the field of agriculture as proven principle with regard to mixed cropping. Increasing crop 49 mixture diversity is often assumed to be associated with increased productivity, increased 50 weed suppression, and increased stability despite a lack of compelling empirical evidence 51 in favor of these assertions [6][7][8][9]. The goal of this study is to test these three...

Are cover crop mixtures better at suppressing weeds than cover crop monocultures?

“…Plant diversity has also been shown to influence the stability of these ecosystem functions, with more diverse communities tending to be more temporally stable (less variable) compared with less diverse communities (Tilman et al 2014). Extending these observations to cover crops, speciesdiverse cover crop mixtures should therefore be expected to provide these same functions in agroecosystems and at higher levels than cover crops grown as monocultures (Couëdel et al 2018;Florence et al 2019;MacLaren et al 2019).…”

Winter cover crops effects on soil properties and sweet corn yield in semi‐arid irrigated systems

“…To enhance benefits derived from WCCs, they are often planted in mixtures that include combinations of grasses, mustards, and legumes. This practice is founded on research that has shown positive relationships between WCC functional biodiversity and cropping system benefits (Finney, White, & Kaye, ; Florence, Higley, Drijber, Francis, & Jindquist, ). For example, combinations of specific grass and legume cover crops were determined to increase levels of nitrogen‐sequestration and nitrogen contributions to the subsequent cash crop compared to monocultures of the constituent grasses or legumes (Kaye et al., ; Ranells & Wagger, ).…”

Advancing cover cropping in temperate integrated weed management

“…Mixtures of cover crops performed better under dry and warm conditions than the before‐mentioned single cover crop species . Cover crop mixtures better compensate temporal and spatial variation in growing conditions, and thus tend to outperform single species in the long term by ensuring that at least some species grow every year at every site .…”

“…Cover crop mixtures better compensate temporal and spatial variation in growing conditions, and thus tend to outperform single species in the long term by ensuring that at least some species grow every year at every site . This hypothesis was proven in a 4‐year field study at 11 locations testing 18 cover crop species in mixtures and as a pure stand . Cover crop mixtures, on average, produced more aboveground biomass and suppressed more weeds than the average of single cover crops.…”

“…Cover crop mixtures, on average, produced more aboveground biomass and suppressed more weeds than the average of single cover crops. However, highest biomass was always achieved in a pure stand . Mixtures may not necessarily be optimal if weed suppression is the only goal, but can provide multiple services simultaneously, such as weed suppression, N fixation and pollination, which may be preferable to farmers overall …”