It has been suggested that conversion to organic farming contributes to soil carbon sequestration, but until now a comprehensive quantitative assessment has been lacking. Therefore, datasets from 74 studies from pairwise comparisons of organic vs. nonorganic farming systems were subjected to metaanalysis to identify differences in soil organic carbon (SOC). We found significant differences and higher values for organically farmed soils of 0.18 ± 0.06% points (mean ± 95% confidence interval) for SOC concentrations, 3.50 ± 1.08 Mg C ha −1 for stocks, and 0.45 ± 0.21 Mg C ha −1 y −1 for sequestration rates compared with nonorganic management. Metaregression did not deliver clear results on drivers, but differences in external C inputs and crop rotations seemed important. Restricting the analysis to zero net input organic systems and retaining only the datasets with highest data quality (measured soil bulk densities and external C and N inputs), the mean difference in SOC stocks between the farming systems was still significant (1.98 ± 1.50 Mg C ha −1 ), whereas the difference in sequestration rates became insignificant (0.07 ± 0.08 Mg C ha −1 y −1 ). Analyzing zero net input systems for all data without this quality requirement revealed significant, positive differences in SOC concentrations and stocks (0.13 ± 0.09% points and 2.16 ± 1.65 Mg C ha −1 , respectively) and insignificant differences for sequestration rates (0.27 ± 0.37 Mg C ha −1 y −1 ). The data mainly cover top soil and temperate zones, whereas only few data from tropical regions and subsoil horizons exist. Summarizing, this study shows that organic farming has the potential to accumulate soil carbon.climate change | soil quality | agricultural systems

Organic agriculture is proposed as a promising approach to achieving sustainable food systems, but its feasibility is also contested. We use a food systems model that addresses agronomic characteristics of organic agriculture to analyze the role that organic agriculture could play in sustainable food systems. Here we show that a 100% conversion to organic agriculture needs more land than conventional agriculture but reduces N-surplus and pesticide use. However, in combination with reductions of food wastage and food-competing feed from arable land, with correspondingly reduced production and consumption of animal products, land use under organic agriculture remains below the reference scenario. Other indicators such as greenhouse gas emissions also improve, but adequate nitrogen supply is challenging. Besides focusing on production, sustainable food systems need to address waste, crop–grass–livestock interdependencies and human consumption. None of the corresponding strategies needs full implementation and their combined partial implementation delivers a more sustainable food future.

Increasing efficiency in livestock production and reducing the share of animal products in human consumption are two strategies to curb the adverse environmental impacts of the livestock sector. Here, we explore the room for sustainable livestock production by modelling the impacts and constraints of a third strategy in which livestock feed components that compete with direct human food crop production are reduced. Thus, in the outmost scenario, animals are fed only from grassland and by-products from food production. We show that this strategy could provide sufficient food (equal amounts of human-digestible energy and a similar protein/calorie ratio as in the reference scenario for 2050) and reduce environmental impacts compared with the reference scenario (in the most extreme case of zero human-edible concentrate feed: greenhouse gas emissions −18%; arable land occupation −26%, N-surplus −46%; P-surplus −40%; non-renewable energy use −36%, pesticide use intensity −22%, freshwater use −21%, soil erosion potential −12%). These results occur despite the fact that environmental efficiency of livestock production is reduced compared with the reference scenario, which is the consequence of the grassland-based feed for ruminants and the less optimal feeding rations based on by-products for non-ruminants. This apparent contradiction results from considerable reductions of animal products in human diets (protein intake per capita from livestock products reduced by 71%). We show that such a strategy focusing on feed components which do not compete with direct human food consumption offers a viable complement to strategies focusing on increased efficiency in production or reduced shares of animal products in consumption.

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ABSTRACT. With sustainability within food systems becoming an increasingly important issue, several approaches that claim to assess the sustainability of farms, farming systems, and supply chains have been developed. Looking more closely at these sustainability impact assessment approaches, we discerned considerable differences between them in terms of scope, the level of assessment, and the precision of indicators used for impact assessment. Our aim was to classify and analyze a range of available sustainability impact assessment approaches with respect to scope and precision. From a total of 35 sustainability assessment approaches, we selected 6 for a detailed comparison. From our analysis, we concluded that there are 3 different types of trade-offs in these approaches: between different kinds of scope, between different indicators for precision and trade-offs, and between the scope and precision. Thus, one-sizefits-all solutions, with respect to tool selection, are rarely feasible. Furthermore, as indicator selection determines the assessment results, different and inconsistent indicators can lead to contradictory assessment results that may not be comparable. To overcome these shortcomings, sustainability impact assessments should include a precise definition of the notion of "sustainability" along with a description of the methodological approach and the indicator sets and should aim for harmonization of indicators and assumptions. Global initiatives such as the Sustainability Assessment in Food and Agriculture Systems (SAFA) Guidelines are a helpful step toward shedding light on the differences of these approaches and making the assessment results more comparable.

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This paper describes the findings from a consumer survey conducted as part of the EU-funded research project QualityLowInputFood (QLIF). The objective was to segment occasional organic consumers with regard to their preferences for organic, conventional and conventional-plus products, i.e., conventional products with a specific attribute that also applies to organic products. In other words, these conventional-plus products are placed between organic and conventional food products. In addition, we aimed at analysing differences between consumer segments regarding their price sensitivity and attitudes towards food. The survey used choice experiments to investigate occasional organic consumer preferences for the different types of products. In subsequent standardized face-to-face interviews we collected data on consumer attitudes towards food that could explain the observed preferences. The attitudes were summarized in attitude factors, using factor analysis. The responses from the interviews and choice experiments were analysed by latent class models. These econometric models were used to identify segments within a group of individuals for their preference structure and to relate membership in each segment to consumer characteristics. Two segments of occasional organic consumers were identified. Consumers in segment 1 strongly preferred organic products and were less price sensitive. Furthermore, consumers in this segment showed a significantly higher level of agreement with most of the investigated attitude factors than consumers in segment 2. The latter consisted of consumers who were significantly more price sensitive and preferred conventional-plus and conventional products rather than organic products. Communicating quality attributes represents a promising marketing tool of product differentiation and information for both organic and conventional food marketers. The price sensitivity of parts of occasional organic consumers suggests that the perceived price-performance ratio of organic products needs to be increased by targeted pricing and communication strategies integrating product-relevant information. If not, conventional-plus products, representing a cheaper alternative, might be preferred by parts of the occasional organic consumers

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