On the stability of mixed grasslands

Recent years have seen a renewed interest in the use of white clover (Trifolium repens) in grasslands, as a more sustainable alternative to fertiliser nitrogen inputs. However, mixtures of grasses and white clover have frequently been associated with unstable and hence unreliable herbage yields. The maintenance of a stable production from mixed grasslands requires the prototyping of new grassland management strategies.Temporal yield fluctuations may result from intrinsic ecosystem fluctuations, from environmental fluctuations, or from both. The stability of ecosystems in isolation of their environment is defined as the intrinsic stability. The stability of systems subjected to seasonal environmental fluctuation only is defined as the extrinsic stability, while the stability of systems under a regime of both seasonal and stochastic environmental fluctuations, as measured in field experiments, is defined as the actual stability. The actual stability depends on coincidental weather events and is hence an unreliable reflection of the grassland ecosystem or of the management imposed.A mathematical framework is presented with which the extrinsic and intrinsic stability levels of grassland ecosystems can be deducted from their yields during a large number of years, and with which the effects of intrinsic system properties and of environmental fluctuations on the stability of their yields can be segregated. Intrinsically stable systems remain stable in the face of seasonal environmental fluctuations, but are destabilised by stochastic environmental events. Intrinsically unstable systems are instead stabilised by environmental seasonality, and may be further destabilised or stabilised by stochastic fluctuations, depending on the timing of individual environmental events.This framework was applied to the yield data of two long-term experiments. Regular lime applications and a grazing regime increased the extrinsic stability of grassland ecosystems, whereas fertiliser treatments only had small or inconsistent effects. It was consequently hypothesised that the extrinsic stability of ecosystems depends largely on the availability and turnover rate of nutrients.Vertical spatial interactions between grass species and white clover depend on the vertical distributions of their lamina and total leaf material. A mechanistic model is presented, with which the distributions of perennial ryegrass (Lolium perenne) and white clover can be accurately simulated for a wide range of sward types subjected to various management regimes. This model uses simple morphological features of both species as input variables.The lateral spatial heterogeneity of mixed grasslands was quantified, using data generated by the Dry Weight Rank method for botanical assessment of grasslands. The heterogeneity of the total herbage mass was highest after cutting and topping events, and under lenient grazing, and lowest under strip-grazing. Opposite responses to the grassland management were found for the heterogeneity of the white clover herbage mass.The performance of white clover may be compromised by infestations of creeping bentgrass (Agrostis stolonifera). A mathematical methodology, based on the Dry Weight Rank method, is presented with which the effects of niche-differentiation and direct competition between white clover and creeping bentgrass can be discriminated. The exclusion of white clover by creeping bentgrass foremost resulted from direct competition. Both species only showed niche-differentiation in response to two extreme management strategies. Whereas the clover performance was enhanced under a permanent cutting regime, creeping bentgrass prevailed under a regime of lenient grazing.Finally, two types of management strategies were proposed to maintain the production stability of mixed grasslands. Structural management strategies, such as lime applications, the maximisation of the grazed area, and the targeted use of mixtures of grassland species and varieties, aim to increase the extrinsic stability of ecosystems, and can be prototyped. Dynamic management strategies are required to counteract the fluctuations of the abiotic and the biotic environment, and cannot be generalised due to the individuality of each farm ecosystem.Additional key-words: stability, variability, ecosystem, grassland, white clover, Trifolium repens, legumes, mixtures, model, competition, methodology, dry weight rank, organic farming.</p

Growing grass for a green biorefinery - an option for Ireland?

Growing grass for a green biorefinery – an option for Ireland? Mind the gap: deciphering the gap between good intentions and healthy eating behaviour Halting biodiversity loss by 2020 – implications for agriculture A milk processing sector model for Irelan

Agroforestry systems can mitigate the impacts of climate change on coffee production: A spatially explicit assessment in Brazil

Climate change may impose severe challenges to farmers to maintain agricultural production levels in the future. In this study we analysed the effect of projected changes in climate on the area suitable for coffee production in 2050, and the potential of agroforestry systems to mitigate these effects in a major coffee production region in southeast Brazil. We conducted a spatially explicit analysis with the bioclimatic model MaxEnt to explore the area that is suitable for coffee production in 2050 when coffee is grown in unshaded plantations and in agroforestry systems. The projected climate in 2050 was assessed using 19 global circulation models, and we accounted for the altered microclimate in agroforestry systems by adjusting the maximum and minimum air temperature. The climate models indicated that the annual mean air temperature is expected to increase 1.7 °C ± 0.3 in the study region, which will lead to almost 60 % reduction in the area suitable for coffee production in unshaded plantations by 2050. However, the adoption of agroforestry systems with 50 % shade cover can reduce the mean temperatures and maintain 75 % of the area suitable for coffee production in 2050, especially between 600 and 800 m altitude. Our study indicates that major shifts in areas suitable for coffee production may take place within three decades, potentially leading to land conflicts for coffee production and nature conservation. Incentives that contribute to the development of coffee agroforestry systems at appropriate locations may be essential to safeguard coffee production in the southeast of Brazil.</p

Scenarios to limit environmental nitrogen losses from dairy expansion

peer-reviewedIncreased global demand for dairy produce and the abolition of EU milk quotas have resulted in expansion in dairy production across Europe and particularly in Ireland. Simultaneously, there is increasing pressure to reduce the impact of nitrogen (N) losses to air and groundwater on the environment. In order to develop grassland management strategies for grazing systems that meet environmental targets and are economically sustainable, it is imperative that individual mitigation measures for N efficiency are assessed at farm system level. To this end, we developed an excel-based N flow model simulating an Irish grass-based dairy farm, to evaluate the effect of farm management on N efficiency, N losses, production and economic performance. The model was applied to assess the effect of different strategies to achieve the increased production goals on N utilization, N loss pathways and economic performance at farm level. The three strategies investigated included increased milk production through increased grass production, through increased concentrate feeding and by applying a high profit grass-based system. Additionally, three mitigation measures; low ammonia emission slurry application, the use of urease and nitrification inhibitors and the combination of both were applied to the three strategies. Absolute N emissions were higher for all intensification scenarios (up to 124 kg N ha−1) compared to the baseline (80 kg N ha−1) due to increased animal numbers and higher feed and/or fertiliser inputs. However, some intensification strategies showed the potential to reduce the emissions per ton milk produced for some of the N-loss pathways. The model showed that the assessed mitigation measures can play an important role in ameliorating the increased emissions associated with intensification, but may not be adequate to entirely offset absolute increases. Further improvements in farm N use efficiency and alternatives to mineral fertilisers will be required to decouple production from reactive N emissions

Analysis of the production stability of mixed grasslands. II. A mathematical framework for the quantification of production stability of grassland ecosystems

The analysis of the intrinsic properties and processes of ecosystems, which regulate the production stability of mixed grasslands, has been complicated by the environmental noise caused by stochastic weather fluctuations. A mathematical framework is presented to deduct the actual, the extrinsic and the intrinsic stability of grassland ecosystems, as defined in the companion paper, from their yield patterns and the environmental patterns during a long time-course. Intrinsically stable grassland ecosystems remain stable when subjected to structured environmental fluctuations, yet are destabilised by stochastic environmental fluctuations. Contrastingly, intrinsically oscillating grassland ecosystems are on average somewhat stabilised by stochastic environmental fluctuations in temperate climates. Structured environmental fluctuations may fully stabilise these systems in continental climates. However, in these climates these ecosystems are destabilised by stochastic environmental fluctuations. As in some cases the actual stability of yields may be higher in intrinsically oscillating systems than in intrinsically stable systems, the stability of yields observed in short-term experiments is a poor reflection of the intrinsic ecosystem properties. Subsequently, this mathematical framework is applied to a number of experimental ecosystems in the Park Grass Experiment (UK) and at the Ossekampen (The Netherlands), which were subjected to various fertiliser and lime applications, and to a regime of either cutting or grazing, respectively. In the Park Grass Experiment, the yields of all plots studied appeared to be extrinsically unstable, with only small differences between fertiliser treatments. However, plots receiving lime showed a higher extrinsic stability than unlined plots. The extrinsic stability of the plot receiving farmyard manure (FYM) was lower than that of the plot receiving an equivalent of mineral nitrogen. Also at the Ossekampen, only small differences arose between the extrinsic stability of plots receiving various fertiliser treatments. Instead, the grassland management of the plots had an overriding effect on these stability levels. Whereas the extrinsic stability of all cut plots was low, all grazed plots were nearly entirely stable. It is argued that the nitrogen dynamics in grassland ecosystems have only a small impact on their extrinsic stability levels, in spite of the predictions by simulation models. Instead, pH-related soil processes and the grassland management play an overriding role in the maintenance of the production stability of mixed grassland. It is conceivable that a large number of other processes, which regulate ecosystem stability, could be identified in other plots and experiments, using the same mathematical framework

Mechanistic simulation of the vertical structure of mixed swards

The vertical structure is an important feature of mixed swards, as it influences the inter-species competition for light, as well as the patterns of grazing. Although the experimental measurement of the vertical sward structure is relatively straightforward, the mechanistic and dynamic modelling of the leaf density and lamina density profiles is complicated by the unpredictability of leaf angles. Therefore only static, descriptive profiles have been incorporated in grassland simulation models to date. Two mechanistic models are presented which predict the leaf and lamina density profiles of perennial ryegrass and white clover, based on variables which can readily be measured or produced by simulation models. The `basic model' for grass requires only three input variables: the average leaf length, the average sheath length, and either the total herbage mass or the Leaf Area Index. For clover, only the average petiole length, and either the total weights or areas of petiole and lamina material are required. Use of this basic model is restricted to the simulation of homogeneous swards in which all herbage material shows a random spatial orientation. The `extended model' is more flexible and capable of simulating a wide range of different sward types. However, it requires variables which have not been produced by simulation so far such as the distributions of leaf top heights, sheath top heights, and petiole top heights. Both models were evaluated against a measured profile of a grass–clover sward. The leaf density and lamina density profiles of both perennial ryegrass and white clover, as predicted by the extended model, closely matched the observed profiles. However, the predictions of the basic model were significantly inaccurate for both ryegrass and clover. The extended model can be incorporated as a sub-model into dynamic grassland simulation models in order to enhance the accuracy of simulation of both competition for light and of grazing

Advanced analysis of dry-weight-rank data to discriminate direct and indirect interactions between white clover and grasses in a multi-species pasture under a range of management strategies

Infestations of pastures by species, such as creeping bentgrass (Agrostis stolonifera), may compromise the white clover (Trifolium repens) content in perennial ryegrass (Lolium perenne) mixtures. However, the interactions between white clover and species other than perennial ryegrass are not well understood. Strategies to prevent creeping bentgrass infestations require an understanding of its interactions with white clover, as the exclusion of white clover from infested pastures could be the result of either direct interaction or niche-differentiation in response to management. A methodology is presented which enables the segregation of the effects of direct interaction and niche-differentiation, based on existing dry-weight-rank measurements of a number of experimental pastures, subjected to a range of management strategies. Only between the two management extremities, i.e. permanent cutting of silage and lax grazing for long periods, did niche-differentiation occur between white clover and creeping bentgrass. The white clover content was enhanced under the cutting regime, whereas lax grazing for long periods stimulated the content of creeping bentgrass. White clover was actively excluded from creeping-bentgrass-dominated patches by direct interaction, whereas it showed a high compatibility with perennial ryegrass. This direct interaction presents challenges to the prevention of creeping bentgrass by management, as creeping bentgrass and white clover showed nearly identical requirements in terms of environmental conditions and grassland management

Modelling the concentrations of nitrogen and water-soluble carbohydrates in grass herbage ingested by cattle under strip-grazing management

There is scope of increasing the nitrogen (N) efficiency of grazing cattle through manipulation of the energy and N concentrations in the herbage ingested. Because of asymmetric grazing by cattle between individual plant parts, it has not yet been established how this translates into the concentrations of N and water-soluble carbohydrates (WSC) in the herbage ingested. A model is described with the objective of assessing the efficacy of individual tools in grassland management in manipulating the WSC and N concentrations of the herbage ingested by cattle under strip-grazing management throughout the growing season. The model was calibrated and independently evaluated for early (April), mid- (June, regrowth phase) and late (September) parts of the growing season. There was a high correlation between predicted and observed WSC concentrations in the ingested herbage (R-2 = 0.78, P <0.001). The correlation between predicted and observed neutral-detergent fibre (NDF) concentrations in the ingested herbage was lower (R-2 = 0.49, P <0.05) with a small absolute bias. Differences in the N concentration between laminae and sheaths, and between clean patches and fouled patches, were adequately simulated and it was concluded that the model could be used to assess the efficacy of grassland management tools for manipulating the WSC and N concentrations in the ingested herbage. Model application showed that reduced rates of application of N fertilizer and longer rotation lengths were effective tools for manipulating herbage quality in early and mid-season. During the later part of the growing season, the large proportion of area affected by dung and urine reduced the effect of application rate of N fertilizer on herbage quality. In contrast, relative differences between high-sugar and low-sugar cultivars of perennial ryegrass were largest during this period. This suggests that high-sugar cultivars may be an important tool in increasing N efficiency by cattle when risks of N losses to water bodies are largest. The model output showed that defoliation height affects the chemical composition of the ingested herbage of both the current and the subsequent grazing period

A new family of Fisher-curves estimates Fisher's alpha more accurately

Fisher's alpha is a satisfactory scale-independent indicator of biodiversity. However, alpha may be underestimated in communities in which the spatial arrangement of individuals is strongly clustered, or in which the total number of species does not tend to infinity. We have extended Fisher's curve to allow for an accurate calibration of Fisher's alpha in Such communities. In spite of its good performance, the use of this extended curve is complicated by its optimization procedure. Therefore, we have simulated the extended Fisher curve by modifying the smooth expolinear curve, using three ecologically meaningful parameters only, i.e. Fisher's alpha, a coefficient describing the effects of clustering and the maximum number of species. The resulting equations successfully describe species-individual relationships from both spatial and temporal observations on both plant and animal communities. This family of equations combines three advantages: Fisher's alpha can be quantified more accurately, the number of estimated parameters is flexible and can be kept to a minimum, while all parameters can legitimately be compared across sites. (C) 2004 Elsevier Ltd. All rights reserved

Analysis of the production stability of mixed grasslands. I. A conceptual framework for the qualification of production stability in grassland ecosystems

The increased use of white clover in grasslands has led to new management challenges, as mixed pastures have been associated with unstable herbage production. The stability of mixed pastures depends on a complex of intrinsic ecosystem properties, on the variability of the environment, and on the spatial and temporal scale at which it is studied. In this paper, intrinsic ecosystem properties and processes are explored and illustrated using a simple dynamic simulation model of grass and clover interactions. Competition for light, the delayed availability of nitrogen fixed by white clover, grazing per se, preferential grazing for clover, and cutting were identified as destabilising processes. Instead, niche-differentiation, nitrogen dependence of grass and clover, and plant mechanisms to `escape¿ from grazing, were identified as stabilising processes. The intrinsic stability of mixed swards depended on the balance of, and the interactions between these processes. Including the temperature as an environmental variable into the model, unstable ecosystems were stabilised by seasonal temperature fluctuations, and were either further destabilised, or stabilised by stochastic temperature fluctuations. Stable ecosystems were always destabilised by these stochastic fluctuations. It is explained how spatial heterogeneity can stabilise ecosystems, which oscillate at patch scale. Heterogeneity can be maximised by increasing the incidence of small-scale disturbances and by minimising large-scale disturbances. Finally, three concepts of stability are presented. The actual stability is defined as the stability of grasslands as measured in the field, i.e. subjected to both seasonal and stochastic environmental fluctuations. The extrinsic stability presumes the presence of seasonal, yet the absence of stochastic environmental fluctuations. The intrinsic stability represents the stability of yields in a hypothetical constant environment. It is explained how these concepts of stability can bridge the gap between experimental and theoretical studies. It is demonstrated that long-term experiments are required for the experimental analysis of grassland stability, and it is argued that the development of spatially and environmentally explicit simulation models is a prerequisite for the prototyping of management systems for mixed grasslands