Didier Stilmant

Assessment of energy crops alternative to maize for biogas production in the Greater Region

The biomethane yield of various energy crops, selected among potential alternatives to maize in the Greater Region, was assessed. The biomass yield, the volatile solids (VS) content and the biochemical methane potential (BMP) were measured to calculate the biomethane yield per hectare of all plant species. For all species, the dry matter biomass yield and the VS content were the main factors that influence, respectively, the biomethane yield and the BMP. Both values were predicted with good accuracy by linear regressions using the biomass yield and the VS as independent variable. The perennial crop miscanthus appeared to be the most promising alternative to maize when harvested as green matter in autumn and ensiled. Miscanthus reached a biomethane yield of 5.5 ± 1 × 10(3)m(3)ha(-1) during the second year after the establishment, as compared to 5.3 ± 1 × 10(3)m(3)ha(-1) for maize under similar crop conditions.

Chemical characteristics and biofuels potentials of various plant biomasses: influence of the harvesting date.

BACKGROUND An optimal valorization of plant biomasses to produce biofuels requires a good knowledge of the available contents and molecular composition of the main chemical components, which changes with the harvesting date. Therefore, we assessed the influence of harvesting date on the chemical characteristics of various energy crops in the context of their conversion to biofuels. RESULTS We showed that the biomass chemical composition, enzymatic digestible organic matter, bioethanol and thermal energy production potential for each species are impacted by the harvesting date. The proportion of enzymatically digestible organic matter decreases as the harvesting date is delayed. This is related to the increase in cellulose and lignin contents. The suitability of the biomasses for bioethanol production increases with harvest stage, as the total carbohydrates content increases. The suitability of the biomasses as a source of thermal energy increases according to the harvesting date as the proportion of organic matter increases and the content of mineral compounds decreases. For all investigated energy conversions, the best harvesting period is autumn, because the significantly higher crop dry matter yield largely compensates for the sometimes slightly less favorable chemical characteristics. CONCLUSION While the biomass composition of energy crops changes with harvest stage, the dry biomass yield per unit area is the main factor that controls the total amount of chemical components, digestible organic matter, bioethanol and thermal energy that can be expected to be harvested per unit area. The biomass compositions presented in this paper are essential to investigate their suitability for bioenergy conversion.

Consequential environmental life cycle assessment of a farm-scale biogas plant.

Producing biogas via anaerobic digestion is a promising technology for meeting European and regional goals on energy production from renewable sources. It offers interesting opportunities for the agricultural sector, allowing waste and by-products to be converted into bioenergy and bio-based materials. A consequential life cycle assessment (cLCA) was conducted to examine the consequences of the installation of a farm-scale biogas plant, taking account of assumptions about processes displaced by biogas plant co-products (power, heat and digestate) and the uses of the biogas plant feedstock prior to plant installation. Inventory data were collected on an existing farm-scale biogas plant. The plant inputs are maize cultivated for energy, solid cattle manure and various by-products from surrounding agro-food industries. Based on hypotheses about displaced electricity production (oil or gas) and the initial uses of the plant feedstock (animal feed, compost or incineration), six scenarios were analyzed and compared. Digested feedstock previously used in animal feed was replaced with other feed ingredients in equivalent feed diets, designed to take account of various nutritional parameters for bovine feeding. The displaced production of mineral fertilizers and field emissions due to the use of digestate as organic fertilizer was balanced against the avoided use of manure and compost. For all of the envisaged scenarios, the installation of the biogas plant led to reduced impacts on water depletion and aquatic ecotoxicity (thanks mainly to the displaced mineral fertilizer production). However, with the additional animal feed ingredients required to replace digested feedstock in the bovine diets, extra agricultural land was needed in all scenarios. Field emissions from the digestate used as organic fertilizer also had a significant impact on acidification and eutrophication. The choice of displaced marginal technologies has a huge influence on the results, as have the assumptions about the previous uses of the biogas plant inputs. The main finding emerging from this study was that the biogas plant should not use feedstock that is intended for animal feed because their replacement in animal diets involves additional impacts mostly in terms of extra agricultural land. cLCA appears to be a useful instrument for giving decision-makers information on the consequences of introducing new multifunctional systems such as farm-scale biogas plants, provided that the study uses specific local data and identifies displaced reference systems on a case-by-case basis.

Role of input self-sufficiency in the economic and environmental sustainability of specialised dairy farms

Increasing input self-sufficiency is often viewed as a target to improve sustainability of dairy farms. However, few studies have specifically analysed input self-sufficiency, by including several technical inputs and without only focussing on animal feeding, in order to explore its impact on farm sustainability. To address this gap, our work has three objectives as follows: (1) identifying the structural characteristics required by specialised dairy farms located in the grassland area to be self-sufficient; (2) analysing the relationships between input self-sufficiency, environmental and economic sustainability; and (3) studying how the farms react to a decrease in milk price according to their self-sufficiency degree. Based on farm accounting databases, we categorised 335 Walloon specialised conventional dairy farms into four classes according to their level of input self-sufficiency. To this end, we used as proxy the indicator of economic autonomy - that is, the ratio between costs of inputs related to animal production, crop production and energy use and the total gross product. Classes were then compared using multiple comparison tests and canonical discriminant analysis. A total of 30 organic farms - among which 63% had a high level of economic autonomy - were considered separately and compared with the most autonomous class. We showed that a high degree of economic autonomy is associated, in conventional farms, with a high proportion of permanent grassland in the agricultural area. The most autonomous farms used less input - especially animal feeding - for a same output level, and therefore combined good environmental and economic performances. Our results also underlined that, in a situation of decrease in milk price, the least autonomous farms had more latitude to decrease their input-related costs without decreasing milk production. Their incomes per work unit were, therefore, less impacted by falling prices, but remained lower than those of more autonomous farms. In such a situation, organic farms kept stable incomes, because of a slighter decrease in organic milk price. Our results pave the way to study the role of increasing input self-sufficiency in the transition of dairy farming systems towards sustainability. Further research is required to study a wide range of systems and agro-ecological contexts, as well as to consider the evolution of farm sustainability in the long term.

Sensitive parameters in local agricultural life cycle assessments: the illustrative case of cereal production in Wallonia, Belgium

PurposeLife cycle assessment (LCA) is a useful tool for investigating the environmental performance of agricultural products. For many crop-based products, the agricultural production step shows substantial impacts in LCA results. Using the illustrative case of cereal production in Wallonia, Belgium, the study uses sensitivity analyses to explore the parameters to be adjusted in priority when conducting a local LCA for crop production, taking into account uncertainties tied to input and output inventory data and impact characterization factors.MethodsThe analysis investigated local specificities in the production of eight cereal crops in Wallonia. Cropping systems were modeled according to accounting data from representative farms, including areas, yields, inputs, and machinery. Sensitivity and uncertainty analyses for input parameters and methodological choices were performed. The following parameters were evaluated: the influence of the functional unit (kg, ha, €), the link between yield and LCIA results, the relevance of using up-to-date data for mineral fertilizer production, the type of mineral fertilizer, the model for direct field emission calculation, and the allocation rules.Results and discussionWe observed that the use of several functional units embracing the multifunctional role of agriculture enables identifying crops with low impacts per kilogram, hectare, and euro at the same time. The cereal production steps with the greatest impact were mineral fertilizer production (up to 84% of the total impact, depending on crop and impact category) and emissions from the application of mineral (up to 65%) and organic (up to 94%) fertilizers. Sensitive parameters to be adjusted in priority were identified. Despite the high correlation between yield and results, simply extrapolating impacts on the basis of yield seemed mostly inappropriate. Using updated data for mineral fertilizer production reduced impacts by 6–160%. Shifting models for field emission calculation influenced acidification and eutrophication by 5–142%. Hypotheses on allocation factors affected results by 10–26%.Conclusions and recommendationsAn LCA for the production of major Walloon cereals was conducted taking into account local cropping practices and yields. The parameters relevant for conducting a regional LCA of crop production were identified and discussed in comparison with generic data and models. As LCA is an iterative process, further improvements would include the use of more specific models for direct field emission calculation. The results could serve as a reference for products using Walloon cereals and help enhance the quality of LCAs conducted for these products.

The Relevance of Fuzzy Cognitive Mapping Approaches for Assessing Adaptive Capacity and Resilience in Social{Ecological Systems?

Social–Ecological Systems (SES) are complex due to uncertainty related to their nature and their functions. In these systems, decision-making processes and practices of managers are often value-laden and subjective, dominated by their world-views and their own knowledge. People’s knowledge are central in building their adaptive capacity but are seldom taken into account by traditional decision-making approaches in modelling SES management. In this paper, we introduce a Fuzzy Cognitive Mapping approach to study the dynamic behaviour of managers’ systems of practices. As a case study, we aim to assess farmers’ forage management under different climatic scenarios. Results show that summer drought have varying consequences according to farmers’ systems of practices. Fuzzy Cognitive Mapping approaches are particularly relevant in studying systems of practices in SES. Their utilisation is promising for the evaluation of adaptive capacity and resilience in SES at local scale (exploitation, community) and regional scale (ecological areas, country).

Variation of greenhouse gas emissions and identification of their drivers during the fattening of Belgian Blue White bulls based on a LCA approach

Greenhouse gas emission intensity (GHGI; kilograms carbon dioxide equivalents/kilograms liveweight gain) have to be reduced so as to limit the impact of human activities on global warming while furnishing food to human. In this respect, performances of 654 Belgian Blue double-muscled bulls (BBdm) during their fattening phase were recorded. On this basis, their greenhouse gas emissions were modelled to estimate variation in GHGI and investigate mitigation options at that level. The relevance of theses option is discussed, taking into account the whole life and production system scales. Large variations (mean (s.d.)) were observed (from 7.2 (0.4) to 10.0 (0.7) kg carbon dioxide equivalents/kg liveweight gain) for, respectively, the 1st- and 4th-quantile groups defined for GHGI. Early culling, low liveweight and age at start of the fattening phase of the bulls would lead to a reduction of GHGI. Nevertheless, more than 32% of the variation remained unexplained. However, decision leading to reduction of GHG intensity at this stage of the life may be compensated in the early stage of BBdm. Attention is drawn on the necessity to encompass the whole life of BBdm for investigating mitigation options and on the sensitivity of the results on models and methodological choices.