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⁻¹for stocks, and 0.45 ± 0.21 Mg C ha⁻¹y⁻¹for 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⁻¹y⁻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⁻¹y⁻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.

Agricultural practices contribute considerably to emissions of greenhouse gases. So far, knowledge on the impact of organic compared to non-organic farming on soil-derived nitrous oxide (N₂O) and methane (CH₄) emissions is limited. We investigated N₂O and CH₄ fluxes with manual chambers during 571 days in a grass-clover– silage maize – green manure cropping sequence in the long-term field trial “DOK” in Switzerland. We compared two organic farming systems – biodynamic (BIODYN) and bioorganic (BIOORG) – with two non-organic systems – solely mineral fertilisation (CONMIN) and mixed farming including farmyard manure (CONFYM) – all reflecting Swiss farming practices–together with an unfertilised control (NOFERT). We observed a 40.2% reduction of N₂O emissions per hectare for organic compared to non-organic systems. In contrast to current knowledge, yield-scaled cumulated N₂O emissions under silage maize were similar between organic and non-organic systems. Cumulated on area scale we recorded under silage maize a modest CH₄ uptake for BIODYN and CONMIN and high CH₄ emissions for CONFYM. We found that, in addition to N input, quality properties such as pH, soil organic carbon and microbial biomass significantly affected N₂O emissions. This study showed that organic farming systems can be a viable measure contributing to greenhouse gas mitigation in the agricultural sector.

In 2007 two long-term trials were established in Kenya to contribute research-based evidence to the global debate on the productivity, economic viability and sustainability of different agricultural production systems. These trials compare conventional (Conv) and organic (Org) farming systems at high and low input levels at two locations, i.e. Chuka, with Humic Nitisols, high inherent soil fertility and rainfall, and Thika, with Rhodic Nitisols with low soil fertility and rainfall. The high input systems (High) represent commercial-scale, export-oriented production that uses the recommended amounts of fertilisers, pesticides and irrigation water to generate high yields, whilst the low input systems (Low) represent local smallholder practices, using relatively few fertilisers and pesticides and operating under rain-fed conditions. The conventional systems received synthetic fertilisers and organic manure, whilst the organic systems only received organic inputs. The trials so far have consisted of a 6-season, 3-year, crop rotation with maize (Zea mays L.) planted in the long rainy seasons (March-September), and vegetables in the short rainy seasons (October – February). Generally, there were no significant differences in the dry matter yields and nutrient uptake by maize, baby corn or beans between the conventional and organic systems at either site. Similar maize grain and baby corn yields were also obtained at Chuka. However, at Thika, maize grain yields in Org-High in 2007 (at conversion) were lower than the yields in Conv High, but the yields became similar in 2010 (after conversion). At the same site the yields of maize grain under sole cropping in Org-Low were 3.2 times lower than the yields in Conv-Low in 2007 and 1.7 times lower in 2010. When intercropped with beans the yields of the two systems were similar. In the first two years profits from Conv-High were 0.5–1.8 times and 0.2–2.4 times higher than in Org-High when selling the produce at local (Chuka and Thika) and regional markets (Nairobi), but thereafter the profit from the two was similar, even when organic produce was sold at regular market prices. From the fifth year onwards Org-High attracted a price premium of 20 to 50% and this made it 1.3 to 4.1 times more profitable than Conv-High when selling on local and regional markets (in Chuka, Thika and Nairobi). Compared to Conv-High, partial N and K balances at the two sites were positive and higher in Org-High, except for N at Chuka. Our findings demonstrate that Org-High is productive, economically viable, resource-conserving and can contribute to sustainable agriculture production in Kenya depending on regional conditions and the crops cultivated

Although scientists have been researching the impacts of organic agriculture on the environment and animal welfare for decades, the conclusions drawn by the scientific community remain controversial. Against this background, this paper provides a comprehensive assessment of the benefits of organic farming in both areas by analysing results of all relevant scientific comparative studies between organic and conventional farming that have dealt with this topic over the last thirty years. So far, this study is the largest one of its kind and the first one that adds the aspect of animal welfare to a comprehensive array of impact categories. The systematic review of the scientific literature from pairwise comparisons found that organic management showed clear advantages over conventional management in the fields of environmental protection and resource conservation, which can be mainly explained by the system approach pursued in organic farming. No clear conclusion was drawn regarding animal welfare indicating that farm-specific management factors are of greater importance than the production system (organic vs conventional). Consequently, organic farming may contribute to solving current environmental and resource challenges and is rightly considered a key approach for sustainable land use. The positive effects should be further strengthened by decreasing the yield gaps between organic and conventional farming, i.e. by improving yields based on organic principles as well as by altering their relevance through changes in consumption as feed for livestock and food for humans.