Compaction of a granular material under cyclic shear

In this paper we present experimental results concerning the compaction of a granular assembly of spheres under periodic shear deformation. The dynamic of the system is slow and continuous when the amplitude of the shear is constant, but exhibits rapid evolution of the volume fraction when a sudden change in shear amplitude is imposed. This rapid response is shown to be to be uncorrelated with the slow compaction process.Comment: 7 pages, 9 figures, accepted for publication in European Physical Journal

Diagnosing Nitrogen, Phosphorous and Potassium Status of Natural Grassland in the Presence of Legumes

In most temperate areas, sustainable management of grassland ecosystems has to deal with evaluation and management of N, P and K resources. For this purpose, appropriate diagnostic systems are needed in order to manage fertilisation accordingly. The nutrient index method based on nutrient concentrations in plant tissues relative to the degree of growth has been developed; it relies on critical curves which serve for diagnostic: for N, the critical curve gives the optimum N concentration for different levels of biomass accumulation in swards, for P and K optimum concentrations are a linear function of sward N concentration (Duru & Thélier-Huché, 1997). However limitations in the use of P nutrient index (PNI) were reported when the herbage contained a large proportion of white clover (Jouany et al., 2004). Our objectives were to verify whether similar behaviour were observed with other legumes and for K and N nutrition indices (KNI, NNI) as well

How to Simplify Tools for Natural Grassland Characterisation Based on Biological Measures Without Losing Too Much Information?

In marginal areas, such as the Pyrenees, natural grasslands are the only available resource for livestock feeding. Despite this, there is a lack of simple and efficient tools for advisers to aid the management of the complex vegetation of these grasslands. Therefore, we tested an approach derived from functional ecology, to construct such tools: using biological traits to inform on the agronomic characteristics and the way farmers’ practices act on them (Ansquer et al., 2004). Nevertheless, the required protocol of measurement is still time-consuming and difficult. In this paper, we test different ways of simplifying this protocol by reducing the number of species measured and not considering specific abundances

Are Leaf Traits Suitable for Assessing the Feeding Value of Native Grass Species?

Research on forage feeding value other than in vivo assessment can be roughly divided into three kinds of approach. The first aims to predict feeding value using a set of enzymatic or physical methods. A second approach is based on phenological stages of species. These approaches are mainly used for pure stands of improved grasses or legumes. However, for native grassland, a complex type of vegetation, a third approach, based on botanical records, has been proposed to rank grassland communities for their feeding value. The aim of this work concerns the third approach. We tested whether leaf traits (e.g. specific leaf area (SLA), leaf dry matter content (LDMC) and leaf life span (LLS)), assessed under non-limiting plant growth conditions, ranked the species in the same order as did chemical components and digestibility

Farming system design for innovative crop-livestock integration in Europe

The development of integrated crop-livestock systems (ICLS) is a major challenge for the ecological modernisation of agriculture but appears difficult to implement at a large scale. A participatory method for ICLS design has been developed and implemented in 15 case studies across Europe, representing a range of production systems, challenges, constraints and resources for innovation. Local stakeholders, primarily farmers, but also cooperatives, environmental-association representatives and natural-resource managers, were involved in the identification of challenges and existing initiatives of crop-livestock integration; in the design of new options at field, farm and territory levels; and then in qualitative multicriteria assessment of these options. A conceptual framework based on a conceptual model (crops, grasslands, animals) was developed to act as a boundary object in the design step and invite innovative thinking in 'metabolic' and 'ecosystemic' approaches. A diversity of crops and grasslands interacting with animals appeared central for designing sustainable farming systems at the territory level, providing and benefitting from ecosystem services. Within this diversity, we define three types of integrated systems according to their degrees of spatial and temporal coordination: complementarity, local synergy, territorial synergy. Moreover, the options for cooperation and collective organisation between farmers and other stakeholders in territories to organise and manage this diversity of land use revealed opportunities for smart social innovation. The qualitative multicriteria assessment identified farmer workload as the main issue of concern while demonstrating expected benefits of ICLS simultaneously for economic, agronomic, environmental and social criteria. This study concludes that participatory design of ICLS based on a generic multi-level and multi-domain framework and a methodology to deal with a local context can identify new systems to be tested. Further assessment and redesign work will be performed in later stages of the European FP7 CANTOGETHER project.authorsversionPeer reviewe

Potentialities of Near Infrared Spectroscopy to Assess Nitrogen, Phosphorus and Potassium Nutrient Status of Grasslands in the Reunion Island

Controlled mineral fertilisation practices are an important component for sustainable management of grasslands. The assessment of available nutrients for plants and the general recommendations on the level of phosphorus and potassium to apply to grasslands are classically based on classical soil analysis and average regional levels. For nitrogen, mid or long term recommendations cannot easily be derived solely from soil composition, because it may be rapidly leached from the soil. Recent approaches tended to show that herbage plant N (Lemaire & Gastal, 1997), P, K (Duru & Huché, 1997) mineral analyses associated with actual biomass measurement could be useful for the calculation of combined nutrient indices (IN, IP, IK). Expressing these indices along references curves with a standard optimum value of 100, indicates the limiting factors or excess in the mineral feeding of the plants. It provides a diagnosis of the main nutrient status at a specific local plot situation. The step has been successfully implemented to provide local advice in the management of grasslands on Reunion Island (Blanfort, 1998). Nitrogen content can be predicted from NIRs, but this technique is less used for the other elements. However, the concern is here more related to the development of a combined index, it appeared interesting to test the potential of NIRs to predict these or to rank grasslands according to nutrition levels

Assessing the Effect of N and P Supply on Dry Matter Yield of Three Tropical Grasses

The objectives are to study the effects of N and P supply and their interaction, on herbage dry matter yield and nutrient status of three tropical grasses. In order to estimate direct and indirect effects of P supply we express above-ground dry matter production as a function of the herbage nutrient status obtained from plant analysis. Results show that in absence of N, the significant increase in P nutrition status has only moderate consequences on herbage production and suggest that both N and P are limitant for herbage growth. P fertilization results in significant increase in dry matter yield only when N limitation is suppressed as well

Coarse-grained computations of demixing in dense gas-fluidized beds

We use an "equation-free", coarse-grained computational approach to accelerate molecular dynamics-based computations of demixing (segregation) of dissimilar particles subject to an upward gas flow (gas-fluidized beds). We explore the coarse-grained dynamics of these phenomena in gently fluidized beds of solid mixtures of different densities, typically a slow process for which reasonable continuum models are currently unavailable

A Herbage Growth Model for Different Types of Natural Grassland

The aim of this work was to extend existing growth models established for pure stands to a wide range of grassland communities. For this purpose we built a simple growth model, including sub-models for radiation interception and use. Parameters for the effect of nutrient rates (N, P) and defoliation regimes were based on a plant trait database. Senescence and reproductive processes were particularly considered because of their importance in late spring growth. The model makes it possible to simulate the daily biomass production as a function of both environmental factors and the functional type of the dominant species in the community