Urs Niggli

Enhanced top soil carbon stocks under organic farming

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.

Arbuscular mycorrhizae in a long-term field trial comparing low-input (organic, biological) and high-input (conventional) farming systems in a crop rotation

Abstract Arbuscular mycorrhizal (AM) root colonization was studied in a long-term field trial in which four farming systems currently in use in Switzerland were continuously applied to a randomized set of plots at a single field site from 1978 till 1993. There were two low-input farming systems (organic and bio-dynamic) and two high-input (conventional) farming systems (according to Swiss guidelines of integrated plant production with and without farmyard manure). The systems had an identical 7-year crop rotation and tillage scheme and differed essentially only in the amount and type of fertilizer supplied and in plant protection management. The percentage of root colonization by AM fungi was determined in field samples 2–3 times over the growing season in crops in the rotation, namely in winter wheat (Triticum aestivum L. cv. Sardona), vetch-rye and grass-clover. We found the percentage of root length colonized by AM fungi to be 30–60% higher (P≤0.05) in the plants grown in soils from the low-input farming systems than in those grown in conventionally farmed soils. Approximately 50% of the variation of AM root colonization was explained by chemical properties of the soils (pH, soluble P and K, exchangeable Mg), the effect of soluble soil P being most pronounced. The potential of the field soils from the differently managed plots to cause symbiosis with AM fungi was tested in a glasshouse experiment, using wheat as a host plant. Soils from the low-input farming systems had a greatly enhanced capacity to initiate AM symbiosis. The relative differences in this capacity remained similar when propagules of the AM fungus Glomus mosseae were experimentally added to the soils, although overall root colonization by AM fungi was 2.8 times higher.

Greenhouse gas fluxes from agricultural soils under organic and non-organic management — A global meta-analysis

It is anticipated that organic farming systems provide benefits concerning soil conservation and climate protection. A literature search on measured soil-derived greenhouse gas (GHG) (nitrous oxide and methane) fluxes under organic and non-organic management from farming system comparisons was conducted and followed by a meta-analysis. Up to date only 19 studies based on field measurements could be retrieved. Based on 12 studies that cover annual measurements, it appeared with a high significance that area-scaled nitrous oxide emissions from organically managed soils are 492 ± 160 kg CO2 eq. ha(-1) a(-1) lower than from non-organically managed soils. For arable soils the difference amounts to 497 ± 162 kg CO2 eq. ha(-1) a(-1). However, yield-scaled nitrous oxide emissions are higher by 41 ± 34 kg CO2 eq. t(-1) DM under organic management (arable and use). To equalize this mean difference in yield-scaled nitrous oxide emissions between both farming systems, the yield gap has to be less than 17%. Emissions from conventionally managed soils seemed to be influenced mainly by total N inputs, whereas for organically managed soils other variables such as soil characteristics seemed to be more important. This can be explained by the higher bioavailability of the synthetic N fertilisers in non-organic farming systems while the necessary mineralisation of the N sources under organic management leads to lower and retarded availability. Furthermore, a higher methane uptake of 3.2 ± 2.5 kg CO2 eq. ha(-1) a(-1) for arable soils under organic management can be observed. Only one comparative study on rice paddies has been published up to date. All 19 retrieved studies were conducted in the Northern hemisphere under temperate climate. Further GHG flux measurements in farming system comparisons are required to confirm the results and close the existing knowledge gaps.

Mineralization and microbial assimilation of 14C-labeled straw in soils of organic and conventional agricultural systems

An incubation experiment on straw decomposition was carried out with soils from a long-term field trial at Therwil, Switzerland. Two conventional agricultural systems, one with (CONFYM) and one without manure, an organic system managed according to bio-dynamic farming practice (BIODYN) and an unfertilized control were compared. CONFYM received stacked manure and an additional mineral fertilizer. BIODYN received composted farmyard manure and no mineral fertilizers. Both systems received the same amount of manure based on 1.4 livestock units ha ˇ1 . The aim of the investigation was to explain the large diAerences in soil microbial biomass and activity between the systems, especially between the manured soils. DiAerences in microbial C-utilization eAciency were suggested to be the main reason. We followed the decomposition of 14 C-labeled plant material over a period of 177 days under controled incubation conditions. Prior to incubation, microbial biomass was 75% higher and qCO2 up to 43% lower in the BIODYN soil than in the conventional soils. At the end of the incubation period, 58% of the applied plant material was mineralized to CO2 in the BIODYN soil compared to 50% in the other soils. This diAerence became significant 2 weeks after application of plant material and is suggested to be due to decomposition of more recalcitrant compounds. After addition of plant material, the increase of microbial biomass in the unmanured systems was higher than in the manured systems, but with a higher loss rate thereafter. The amount of 14 C incorporated into Cmic as related to 14 CO2 evolved was markedly higher in the BIODYN soil. The results support the hypothesis that agricultural measures applied to the BIODYN system invoke a higher eAciency of the soil microbial community with respect to substrate use for growth. 7 2000 Elsevier Science Ltd. All rights reserved.

Impacts of feeding less food-competing feedstuffs to livestock on global food system sustainability.

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.

Composition differences between organic and conventional meat: a systematic literature review and meta-analysis

Demand for organic meat is partially driven by consumer perceptions that organic foods are more nutritious than non-organic foods. However, there have been no systematic reviews comparing specifically the nutrient content of organic and conventionally produced meat. In this study, we report results of a meta-analysis based on sixty-seven published studies comparing the composition of organic and non-organic meat products. For many nutritionally relevant compounds (e.g. minerals, antioxidants and most individual fatty acids (FA)), the evidence base was too weak for meaningful meta-analyses. However, significant differences in FA profiles were detected when data from all livestock species were pooled. Concentrations of SFA and MUFA were similar or slightly lower, respectively, in organic compared with conventional meat. Larger differences were detected for total PUFA and n-3 PUFA, which were an estimated 23 (95 % CI 11, 35) % and 47 (95 % CI 10, 84) % higher in organic meat, respectively. However, for these and many other composition parameters, for which meta-analyses found significant differences, heterogeneity was high, and this could be explained by differences between animal species/meat types. Evidence from controlled experimental studies indicates that the high grazing/forage-based diets prescribed under organic farming standards may be the main reason for differences in FA profiles. Further studies are required to enable meta-analyses for a wider range of parameters (e.g. antioxidant, vitamin and mineral concentrations) and to improve both precision and consistency of results for FA profiles for all species. Potential impacts of composition differences on human health are discussed.

Strategies for feeding the world more sustainably with organic agriculture

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.Organic agriculture requires fewer inputs but produces lower yields than conventional farming. Here, via a modeling approach, Muller et al. predict that if food waste and meat consumption are reduced, organic agriculture could feed the world without requiring cropland expansion.

Sustainability of organic food production: challenges and innovations.

The greatest challenge for agriculture is to reduce the trade-offs between productivity and long-term sustainability. Therefore, it is interesting to analyse organic agriculture which is a given set of farm practices that emphasise ecological sustainability. Organic agriculture can be characterised as being less driven by off-farm inputs and being better embedded in ecosystem functions. The literature on public goods and non-commodity outputs of organic farms is overwhelming. Most publications address the positive effects of organic farming on soil fertility, biodiversity maintenance and protection of the natural resources of soil, water and air. As a consequence of focusing on public goods, organic agriculture is less productive. Meta-analyses show that organic agriculture yields range between 0·75 and 0·8 of conventional agriculture. Best practice examples from disadvantaged sites and climate conditions show equal or, in the case of subsistence farming in Sub-Saharan Africa, higher productivity of organic agriculture. Hence, organic agriculture is likely to be a good model for productive and sustainable food production. Underfunding in R&D addressing specific bottlenecks of organic agriculture are the main cause for both crop and livestock yield gaps. Therefore, the potential for improving the performance of organic agriculture through agricultural research is huge. Although organic farming is a niche in most countries, it is at the verge of becoming mainstream in leading European countries. Consumer demand has grown over the past two decades and does not seem to be a limiting factor for the future development of organic agriculture.

How the organic food system supports sustainable diets and translates these into practice

Organic production and consumption provide a delineated food system that can be explored for its potential contribution to sustainable diets. While organic agriculture improves the sustainability performance on the production side, critical reflections are made on how organic consumption patterns, understood as the practice of people consuming significant amounts of organic produce, may also be taken as an example for sustainable food consumption. The consumption patterns of regular organic consumers seem to be close to the sustainable diet concept of FAO. Certain organic-related measures might therefore be useful in the sustainability assessment of diets, e.g., organic production and organic consumption. Since diets play a central role in shaping food systems and food systems shape diets, the role of organic consumption emerges as an essential topic to be addressed. This role may be based on four important organic achievements: organic agriculture and food production has a definition, well-established principles, public standards, and useful metrics. By 2015, data for organic production and consumption are recorded annually from more than 160 countries, and regulations are in force in more than 80 countries or regions. The organic food system puts the land (agri-cultura) back into the diet; it is the land from which the diet in toto is shaped. Therefore, the organic food system provides essential components of a sustainable diet.

Organic Agriculture - Driving Innovations in Crop Research

Food security is threatened by a growing human population, depletion of natural resources, and mounting environmental degradation. Agricultural research faces a crossroad: continue down a path dominated by proprietary technologies produced by high-input systems, or design farming systems that conserve natural resources and work with ecological processes. Soil fertility is the foundation of sustainable agriculture. Land in agricultural production is being degraded by intensive farming practices. Reliance on non-renewable resources to provide soluble nutrients to crops is inherently unsustainable as it proves to be destructive to soils and the environment. Crop nutrients will need to be efficiently recycled if soils are to remain productive, particularly in tropical regions. Crops grown in low-input conditions will need to be bred to be efficient feeders resistant to pests and diseases. Continued focus on yield supported by increasing use of fertilizers and pesticides will not meet the needs of farmers who lack access to those inputs. As conventional farming practices continue to reduce biodiversity at an accelerating pace through a narrower gene pool and fewer species cultivated, agricultural ecosystems become more vulnerable to ecological disruptions. Productivity is only one dimension of sustainability. A greater understanding and application of functional biodiversity can be used to design site-specific systems that provide for current needs, while conserving resources and maintaining options for future generations. Ecosystem management also involves nutrient cycling, the ecological food web, and the flow of genetic resources. Research in the ecology of farming systems is needed to develop cultural and biological practices that prevent production problems. Technological development and diffusion will need to be restructured to give resource-constrained farmers access to the tools needed to meet the challenge. The reductionist paradigm has increased short-run productivity, but at a social and environmental cost. A narrow, reductionist, disciplinary approach to research is incapable of answering complex systems questions. Transdisciplinary research is proposed to address the challenges that are raised by a holistic approach to science. Farmers are crucial participants in the research process, to identify research priorities, to collaborate with scientists in conducting research, and to adopt and disseminate the results of research. As organic agriculture continues to grow and improve, organic agricultural research has not kept pace and is under-served. Organic farmers innovated and pioneered many techniques used in integrated systems. Organic farming systems research offers the most promising way forward to meet the challenges of food production and environmental quality.