Abstract
Plant species diversity may benefit natural grassland productivity, but its effect in managed grassland systems is not well understood. A four-year multispecies grassland experiment was conducted to investigate the effect of species diversity–legumes and non-leguminous forbs–on productivity, persistence and sward quality under cutting or grazing regimes and with or without slurry application. Three mixtures were established– 3-mix: grass, red and white clover, 10-mix: 3-mix plus birdsfoot trefoil and six non-leguminous forbs, and 12-mix: 10-mix plus lucerne and festulolium. Species diversity increased sward production and yield persistence under cutting regime. The 12-mix had the highest yield from the second year onwards and no statistically significant yield reduction over four years, while annual yields in the 3-mix and 10-mix decreased significantly with increasing grassland age. The higher yield in the 12-mix was mainly due to the inclusion of high-yielding lucerne. The 10-mix and 12-mix had lower proportions of unsown species than the 3-mix, the difference being dependent on grassland age. Generally, the 3-mix had higher concentrations of in-vitro organic matter digestibility (IVOMD), neutral detergent fiber (NDF) and crude protein (CP), and a lower concentration of ash than the 10-mix and 12-mix. Slurry application increased annual yield production by 10% and changed the botanical composition, increasing the proportion of grass and decreasing the proportion of legumes. Compared to cutting, grazing increased forage production by 9% per cut on average and lowered legume and forb proportions in the mixtures, but yields did not differ among the three mixtures. Overall, our results suggest that species diversity increases sward productivity and persistence only under an ungrazed cutting regime. We conclude that increasing species diversity by selecting appropriate species with compatible management is key to achieving both high yields and high persistence in managed grasslands.
Highlights
Plant diversity has often been shown to increase productivity and stability in natural grasslands [1,2,3,4]
A primary conclusion drawn from these contrasting results is that the effect of species diversity on forage production per se is not as important as that of certain plant functional groups and/or the combination of these functional groups [12], probably because functional trait diversity and composition in complex forage mixtures can be a strong driver of resource utilization and yield production [13]
The effect of diversity on productivity and persistence under cutting Our study demonstrated that herbage productivity increased with richer species diversity under the cutting regime (Fig 1), which is consistent with previous studies on natural grasslands and forage mixtures [5, 36, 37]
Summary
Plant diversity has often been shown to increase productivity and stability in natural grasslands [1,2,3,4]. There is a growing interest for exploring the potential of a higher species diversity to promote forage production, persistence and nutritive value in European agricultural grasslands. Previous studies have shown contrasting effects of plant diversity on forage yield, ranging from positive effects [6,7,8,9] to no effects [10], or even negative effects [11]. A primary conclusion drawn from these contrasting results is that the effect of species diversity on forage production per se is not as important as that of certain plant functional groups and/or the combination of these functional groups [12], probably because functional trait diversity and composition in complex forage mixtures can be a strong driver of resource utilization and yield production [13]
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