A win-win for legume mixtures

The inter-relationship between food production and biodiversity is now well established. The ecosystem services provided by the organisms within the environment include, for example, nutrient cycling, pest regulation and pollination, to name but a few. However, perhaps the greatest challenge now facing agricultural production is to find ways of enhancing these ecosystem services, while at the same time increasing food production – particularly in light of food security issues. A range of farm and landscape management options include ‘setting aside’ land for wildlife. However, some proponents argue that such land should be used for food production. While the debate continues, there is no doubt that a large body of scientific evidence from the last three decades highlights the wildlife benefits of organic farming. This article will describe how the Legume LINK project has identified a win-win system for biodiversity conservation and increased productivity through legume-base fertility building. Although this project has focused on organic farming systems, it is of direct relevance to non-organic production, particularly with the increasing interest in legumes across the industry

Modelling the ability of legumes to suppress weeds

The ability of different legume cover crops to suppress annual weeds during the early establishment phase was compared using a simulation model of inter-plant competition and field observations. Height, partitioning parameters, extinction coefficients, crop density and time of emergence were recorded for 11 species sown in monocultures. A naturally occurring population of fat hen (Chenopodium album) was present on the experiment. The competition model was run to compare the expected suppressive ability of the different species on this weed. Samples of C. album were also taken from each plot immediately prior to cutting to provide some empirical observations. Predicted suppressive ability was correlated with seed size and height with large seeded, tall species such as white sweet clover being the most competitive. However, these species may recover poorly from mowing compromising their potential to suppress perennial weeds and a mixture of contrasting species may provide the optimum weed control

Using simulation models to investigate the cumulative effects of sowing rate, sowing date and cultivar choice on weed competition

With the increasing pressure on crop production from the evolution of herbicide resistance, farmers are increasingly adopting Integrated Weed Management (IWM) strategies to augment their weed control. These include measures to increase the competitiveness of the crop canopy such as increased sowing rate and the use of more competitive cultivars. While there are data on the relative impact of these non-chemical weed control methods assessed in isolation, there is uncertainty about their combined contribution, which may be hindering their adoption. In this article, the INTERCOM simulation model of crop / weed competition was used to examine the combined impact of crop density, sowing date and cultivar choice on the outcomes of competition between wheat (Triticum aestivum) and Alopecurus myosuroides. Alopecurus myosuroides is a problematic weed of cereal crops in North-Western Europe and the primary target for IWM in the UK because it has evolved resistance to a range of herbicides. The model was parameterised for two cultivars with contrasting competitive ability, and simulations run across 10 years at different crop densities and two sowing dates. The results suggest that sowing date, sowing density and cultivar choice largely work in a complementary fashion, allowing enhanced competitive ability against weeds when used in combination. However, the relative benefit of choosing a more competitive cultivar decreases at later sowing dates and higher crop densities. Modelling approaches could be further employed to examine the effectiveness of IWM, reducing the need for more expensive and cumbersome long-term in situ experimentation

Livestock in diverse cropping systems improve weed management and sustain yields whilst reducing inputs

<p>Dataset used for the article: </p> <p>MacLaren, C.; Storkey, J.; Strauss, J.; Swanepoel, P.; and Dehnen-Schmutz, K. (2018). Livestock in diverse cropping systems improve weed management and sustain yields whilst reducing inputs. <em>Journal of Applied Ecology.</em></p> <p> </p

An Integrated Weed Management framework: A pan-European perspective

Initiatives to reduce the reliance of agriculture on pesticides, including the European Union (EU) Directive 2009/128/EC on the sustainable use of pesticides (SUD), have yet to lead to widespread implementation of Integrated Pest Management (IPM) principles. Developments in weed management have strongly focused on increasing the efficiency of herbicides or substituting herbicides with other single tactics such as mechanical control. To increase sustainability of agricultural systems in practice, a paradigm shift in weed management is needed: from a single tactic and single growing season approach towards holistic integrated weed management (IWM) considering more than a single cropping season and focusing on management of weed communities, rather than on control of single species. To support this transition, an IWM framework for implementing a system level approach is presented. The framework consists of five pillars: diverse cropping systems, cultivar choice and establishment, field and soil management, direct control and the cross-cutting pillar monitoring and evaluation. IWM is an integral part of integrated pest management (IPM) and adopting IWM will serve as a driver for the development of sustainable agricultural systems of the future

The implications of spatially variable pre-emergence herbicide efficacy for weed management

BACKGROUND The efficacy of pre-emergence herbicides within fields is spatially variable due to soil heterogeneity. We quantified the effect of soil organic matter on the efficacy of two pre-emergence herbicides; flufenacet and pendimethalin, against A. myosuroides and investigated the implications of variation in organic matter for weed management using a crop-weed competition model. RESULTS Soil organic matter played a critical role in determining the level of control achieved. The high organic matter soil had more surviving weeds with higher biomass than the low organic matter soil. In the absence of competition, surviving plants recovered to produce the same amount of seed as if no herbicide were applied. The competition model predicted that weeds surviving pre-emergence herbicides could compensate for sub-lethal effects even when competing with the crop. The ED50 was higher for weed seed production than seedling mortality or biomass. This difference was greatest on high organic matter soil. CONCLUSION These results show that the application rate of herbicides should be adjusted to account for within-field variation in soil organic matter. The results from the modelling emphasised the importance of crop competition in limiting the capacity of weeds surviving pre-emergence herbicides to compensate and replenish the seedbank

Population responses to observed climate variability across multiple organismal groups

A major challenge in ecology is to understand how populations are affected by increased climate variability. Here, we assessed the effects of observed climate variability on different organismal groups (amphibians, insects, mammals, herbaceous plants and reptiles) by estimating the extent to which interannual variation in the annual population growth rates (CV lambda) and the absolute value of the long-term population growth rate (|log lambda|) were associated with short-term climate variability. We used empirical data (>= 20 consecutive years of annual abundances) from 59 wild populations in the Northern Hemisphere, and quantified variabilities in population growth rates and climatic conditions (temperature and precipitation in active and inactive seasons) calculated over four- and eight-year sliding time windows. We observed a positive relationship between the variability of growth rate (CV lambda) and the variability of temperature in the active season at the shorter timescale only. Moreover, |log lambda| was positively associated with the variability of precipitation in the inactive season at both timescales. Otherwise, the direction of the relationships between population dynamics and climate variability (if any) depended largely on the season and organismal group in question. Both CV lambda and |log lambda| correlated negatively with species' lifespan, indicating general differences in population dynamics between short-lived and long-lived species that were not related to climate variability. Our results suggest that although temporal variation in population growth rates and the magnitude of long-term population growth rates are partially associated with short-term interannual climate variability, demographic responses to climate fluctuations might still be population-specific rather than specific to given organismal groups, and driven by other factors than the observed climate variability

Above‐ and below‐ground assessment of carabid community responses to crop type and tillage

Carabid beetles are major predators in agro‐ecosystems. The composition of their communities within crop environments governs the pest control services they provide. An understudied aspect is the distribution of predacious carabid larvae in the soil. We used novel subterranean trapping with standard pitfall trapping, within a multi‐crop rotation experiment, to assess the responses of above‐ and below‐ground carabid communities to management practices. Crop and trap type significantly affected pooled carabid abundance with an interaction of the two, the highest numbers of carabids were caught in subterranean traps in barley under sown with grass. Trap type accounted for the most variance observed in carabid community composition, followed by crop. Tillage responses were only apparent at the species level for three of the eight species modelled. Responses to crop type varied by species. Most species had higher abundance in under‐sown barley, than grass, wheat and barley. Crop differences were greater in the subterranean trap data. For predaceous larvae, standard pitfalls showed lowest abundances in under‐sown barley, yet subterranean traps revealed abundances to be highest in this crop. Comprehensive estimation of ecosystem services should incorporate both above‐ and below‐ground community appraisal, to inform appropriate management

Predicting intercrop competition, facilitation, and productivity from simple functional traits

Context: Recent meta-analyses demonstrate that intercropping can increase the land use efficiency of crop pro-duction by 20-30 % on average, indicating a strong potential contribution to sustainable intensification. How-ever, there is substantial variability around this average: individual studies range from half to double the land productivity of monocrops. Legume-cereal intercrops and intercrops with high temporal niche separation tend to be more productive than the average, but these two combination types are not always suitable. There is a need to explore other possibilities to achieve productive intercrops.Research question: We explored whether two simple functional traits involved in radiation use, plant vegetative height and specific leaf area (SLA), could be used to predict intercrop productivity. Height and SLA together are associated with key plant life-history and resource economy strategies determining competitiveness and toler-ance of competition, especially with regard to light, and could therefore be expected to underpin overyielding in intercrops. Methods: In the first year of our study, we grew crops as monocrops at one site in Kenya and measured their height and SLA. In the second year, we grew crops in monocrop, intercrop, and single plant treatments at two sites in Kenya and one site in Nigeria. Together, these treatments allowed us to identify whether each intercrop combination overyielded or underyielded, and whether any overyielding was driven by facilitation and/or dif-ferences in inter-vs intraspecific competition. We then related the strength of these interactions to the two traits.Results: We found that intercrop grain yields varied in relation to the height and SLA of each species in the intercrop, but together these traits explained less than a third of variation in intercrop land equivalence ratios (LER). More variation could be explained by allowing for the effect of site, suggesting that the two traits interact with site conditions to determine yield. Biomass LERs responded differently to grain LERs, suggesting that plasticity in resource allocation in response to intercropping conditions may further influence yields. Conclusions: Our study found some evidence that combining species with traits indicating contrasting responses to competition (an avoidant species with a tolerant species) could increase resource use complementarity and thus intercrop overyielding. However, it was clear that other factors (such as additional traits, or the trait by site interaction) are needed to refine our understanding of intercrop productivity.Implications: A trait-based framework has potential to predict intercrop productivity, but simple measures of height and SLA alone are insufficient