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[Display omitted] • Hedgerows and adjacent croplands at 23 sites across Germany were sampled. • Under hedgerows, 36 ± 49 % more soil organic carbon (SOC) was stored compared to cropland. • 41 % of absolute SOC stock increase was found in subsoil below 30 cm soil depth. • SOC stocks were also increased along the transect from the hedgerow to the cropland. • Planting hedgerows on 3 % of German cropland could increase SOC stocks by 13 Tg C. Carbon dioxide removal strategies are becoming increasingly important as a fundamental component of comprehensive climate policies. One strategy to increase carbon (C) sinks is the integration of hedgerows into agricultural landscapes. Besides additional C storage in above-ground and below-ground hedgerow biomass, the establishment of hedgerows has the potential to increase soil organic carbon (SOC) stocks. However, empirical data regarding the magnitude of SOC accrual with hedgerow establishment are still limited. We sampled 23 sites across Germany in a paired-plot approach with the aim of estimating SOC stock change with hedgerow establishment on cropland. At 21 sites, SOC stocks were higher beneath hedgerows than in the reference cropland. On average, SOC stock accrual was 29 ± 22 Mg ha−1 (36 ± 49 %) in 0–100 cm soil depth. SOC stocks were significantly different in both topsoil and subsoil. Subsoils below 30 cm depth contributed 41 % (12 ± 17 Mg C ha−1) of the total SOC stock change, stressing the importance of subsoil SOC for the total SOC stocks of hedgerow systems. The positive effect of hedgerows on SOC stocks extended laterally beyond the hedgerow area itself. SOC stock in the grassy hedgerow edge also increased significantly by 22 ± 22 Mg C ha−1 (28 ± 30 %) and SOC stock in the cropland directly adjacent to the hedgerow were 9 ± 19 Mg C ha−1 (12 ± 25 %) higher than in the reference cropland. Particularly high C stock differences between hedgerows and reference cropland soils were found in old hedgerows (>200 years) planted on hedgebanks, which are typically found in northern Germany. Our study confirmed that SOC stocks increase with hedgerow establishment on cropland throughout the whole soil profile. If hedgerows were to be established on 3 % of Germany's cropland area, SOC stocks would increase by 13 Tg C equivalent 48 Mio. t CO 2 , highlighting that hedgerows are a promising and multi-functional climate change mitigation option. [ABSTRACT FROM AUTHOR]

Soil-based carbon farming has been identified in previous research as a win-win for farm productivity and the mitigation of climate change through carbon sequestration. However, it faces numerous barriers to adoption, including low carbon prices, high transaction costs, information barriers and high uncertainty around future outcomes, markets and policy conditions. Collaboration between landholders and other stakeholders has been proposed as a potential means of overcoming some of these barriers, while maximising the benefits of soil-based carbon farming. In this article, we present the results of a two-stage process investigating collaborative soil-based carbon farming in Australia, involving national-scale key informant interviews and a regional-scale Participatory Rural Appraisal. Fifty-three interviews were undertaken with key carbon farming stakeholders, including landholders, landholder groups, carbon service providers, government, researchers and the financial sector. Collaboration was seen to offer the greatest advantages in relation to knowledge-sharing and social support, followed by its potential to increase carbon income through enhanced bargaining power and the optimisation of co-benefits. The advantages of collaboration were less clear in relation to reducing costs or maximising farm productivity and collaboration also presents new challenges around risk and complexity. Under current conditions, informal collaboration models were seen to offer the best balance between the benefits and risks, with existing cooperatives also well-placed to diversify into carbon. Alternative conditions in the future or in other locations would be needed to facilitate models involving joint projects, pooled credits, shared land management and/or the creation of new carbon-specific cooperatives. • Soil-based carbon farming benefits both carbon sequestration and farm productivity. • Advantages of collaboration are greatest for knowledge-sharing and social support. • Collaboration less beneficial in relation to cost-reduction and farm productivity. • Informal models for collaboration preferred by study participants. • Existing agricultural cooperatives are well-placed to diversify into carbon farming. [ABSTRACT FROM AUTHOR]

Agricultural management can influence soil organic carbon (SOC) stocks and thus may contribute to carbon sequestration and climate change mitigation. The soil depth to which agricultural management practices affect SOC is uncertain. Soil depth may have an important bearing on soil carbon dynamics, so it is important to consider depth effects to capture fully changes in SOC stocks. This applies in particular to the evaluation of carbon farming measures, which are becoming increasingly important due to climate change. We sampled and analysed the upper metre of mineral cropland soils from ten long-term experiments (LTEs) in Germany to quantify depth-specific effects on SOC stocks of common agricultural management practices: mineral nitrogen (N) fertilisation, a combination of N, phosphorus (P) and potassium (K) fertilisation, irrigation, a crop rotation with preceding crops (pre-crops), straw incorporation, application of farmyard manure (FYM), liming, and reduced tillage. In addition, the effects of soil compaction on SOC stocks were examined as a negative side effect of agricultural management. Results showed that 19 ± 3 % of total management effects on SOC stocks were found in the upper subsoil (30–50 cm) and 3 ± 4 % in the lower subsoil (50–100 cm), including all agricultural management practices with significant topsoil SOC effects, while 79 ± 7 % of management effects were in the topsoil (0–30 cm). Nitrogen and NPK fertilisation were the treatments that had the greatest effect on subsoil organic carbon (OC) stocks, followed by irrigation, FYM application and straw incorporation. Sampling down to a depth of 50 cm resulted in significantly higher SOC effects than when considering topsoil only. A crop rotation with pre-crops, liming, reduced tillage and soil compaction did not significantly affect SOC stocks at any depth increment. Since approximately 20 % of the impact of agricultural management on SOC stocks occurs in the subsoil, we recommend soil monitoring programs and carbon farming schemes extend their standard soil sampling down to 50 cm depth to capture fully agricultural management effects on SOC. • Ten 32- to 112-year-old long-term experiments were sampled down to 100 cm depth. • Sampling only topsoil ignores 20 % of agricultural management effects on SOC stocks. • Mineral fertilisation had the greatest effect on subsoil organic carbon stocks. • None of the agricultural measures had significant effects deeper than 50 cm. • Standard soil sampling should therefore be extended to 50 cm depth. [ABSTRACT FROM AUTHOR]

Transition towards soil-health sustaining crop production is at the core of climate change mitigation and adaptation efforts in agriculture. Improving soil conditions for resilience to variable and extreme weather conditions are among the main expectations of farmers implementing sustainable management practices. In this study, we evaluate whether the transition from conventional arable towards soil-health oriented farming systems restores soil pore characteristics towards non-arable natural soils and identify factors predominantly shaping different pore domains. Pore size distributions (PSD) at 20 sites with diverse soil types from adjacent fields of (1) standard arable, (2) soil health-oriented pioneer farming and (3) non-arable natural reference soils were measured. Based on parametric PSD descriptors, management-responsive functional pore classes and the role of textural, biochemical and structural drivers in different pore domains were analysed by a novel data-driven evaluation method. Parametric descriptors indicate an evolution from non-disturbed natural to intensively disturbed standard arable soils towards larger structural pores within a less heterogeneous structural domain. These shifts go along with less medium-sized storage pores, which overall was the most management sensitive pore fraction. Our novel data-driven approach confirmed a partial regeneration of natural pore characteristics with soil-health oriented practices. The most responsive pore domain was found in the range of ∼0.3–0.5 µm. The SOC-to-clay ratio was the predominant driver for structural porosity in both pioneer arable and natural reference soils. On the contrary, soil texture exerted the main control on the PSD pattern over the entire range of pore classes for standard farming systems. Overall, our study demonstrated that soil-health oriented pioneer farmers could effectively advance in managing functionally relevant pore domains for climate change resilience by promoting biological agents of structure formation. • Soil health-oriented farming partly restores pore characteristics of natural soils. • Functionally relevant pore domains for water storage were also restored. • Pore formation in soil health-oriented farming systems overcomes texture dependency. • We present a novel method for evaluating management-responsive pore domains. [ABSTRACT FROM AUTHOR]

Although neglected in scientific research and development, bamboo based family forests (BBFF) have traditionally been managed on family farms because of their great socioeconomic value in India and other parts of Asia. Recently, there has been increasing interest in their role in biomass production and climate change mitigation. However, our knowledge of the contribution of BBFF at village and landscape level to biomass production and terrestrial carbon is very limited. Therefore, the objectives of this paper are to (1) quantify occurrence of bamboo resources in BBFF,(2) develop appropriate models for estimation of biomass of thick walled bamboos, and (3) estimate biomass and carbon stock in BBFFs in North East India. Occurrence of bamboo resources in BBFF was quantified through survey of 2850 households selected from 95 villages of Barak valley, North East India. Allometric models for biomass estimation were developed through destructive harvesting of 268 bamboo culms from Bambusa cacharensis , B. vulgaris and B. balcooa . The height-diameter relationships and allometric scaling between above-ground biomass (AGB), culm height (H) and diameter at breast height (D) were examined using various models.Culm height, D and AGB were allometrically related in all the three species, but the exponents were significantly larger than those expected under a geometric and stress similarity growth models. The above-ground biomass carbon density in BBFF was estimated at 16.38 Mg ha −1 for B. cacharensis , 38.42 Mg ha −1 for B. vulgaris and 19.64 Mg ha −1 for B. balcooa . In addition to the various ecosystem services provided by village grown bamboo, total biomass (52.8 Mg ha −1 ) and carbon (25.8 Mg ha −1 ) storage in BBFFs can offer an opportunity for carbon farming. [ABSTRACT FROM AUTHOR]

• We evaluated on-farm management and site predictors for soil organic carbon storage. • Soil texture strongly predicted soil organic carbon sequestration potentials. • Conservation management practices were overall of less importance. • Future carbon farming schemes need to properly account for biophysical constraints. Although conservation agriculture practices evidently facilitate the build-up of soil organic carbon (SOC), the sequestration potential of arable soils is strongly mediated by edaphic attributes; so far, their interplay is not well understood. Deciphering these drivers is however important to correctly estimate SOC storage potentials in arable soils and to derive effective strategies for the implementation of successful measures. By using an on-farm approach, we conducted a pairwise comparison of 21 conventional and highly innovative 'pioneer' farms across a wide range of arable soil types and evaluated the leverage of site attributes and management practices such as crop diversity, reduced tillage, organic fertilization, cover cropping and inter cropping on the SOC sequestration potential. While most pioneer management practices proved beneficial for the sequestration of SOC – particularly cover cropping and crop diversity – our results clearly show that soil texture was the most significant shaping factor. Coarse-textured soils had a significantly higher potential for SOC accrual compared to medium- and fine-textured soils. The initial SOC content also had a significant effect on prevalent sequestration potentials. Based on the fact of a clear predominance of natural site conditions over management impacts in enhancing SOC storage of arable soils, we call for a critical discussion of carbon farming schemes. As similar efforts and costs of implementing carbon farming measures will have distinctive carbon gains, dependent on environmental constraints beyond farmers' influence, we advocate for strategies harmonizing both activity- and results-based approaches to maximize the ecological effectiveness and the spatial dissemination of soil health innovations. Carbon farming schemes thus need reconsideration within the state-of-the-art scientific framework of carbon saturation behaviour in order to properly account for biophysical constraints when formulating soil-related climate change mitigation policies. [ABSTRACT FROM AUTHOR]

Agricultural activities through conventional and intensive practices contribute to climate change by increasing emission of reactive carbon (C) and nitrogen (N) from soils to the atmosphere. Minimum soil disturbance, appropriate residue management and cover cropping as conservation practices are perceived as key strategies to limit GHGs emissions by increasing soil C and N sequestration as soil organic matter (SOM), thus promoting soil aggregation and enhancing soil fertility. Yet, the actual contribution of conservation practices to C and N sequestration, as well as mechanisms behind chemical and biochemical stabilization of SOM in the long-term are still controversial. In the present 9-year field study on a wheat-maize-soybean rotation we investigated the effect of no-till (NT) coupled with grass vs. legume cover crop (i.e., rye [ Secale cereale L., NT-R] or hairy vetch [ Vicia villosa Roth, NT-V]) on main crop yields, C and N input by cover and main crops, soil aggregation and C and N sequestration rates, in comparison with conventional tillage (CT). We hypothesized that NT-R may lead to higher biomass input, C sequestration and comparable yield to CT, while NT-V may increase N input, N sequestration and lead to comparable yield to CT. We found that yield of winter wheat, maize, and soybean were never reduced under both NT treatments, neither during the transition phase, nor afterwards. Rye and hairy vetch provided the same amount of biomass and C input, although vetch doubled N input compared with rye. Moreover NT-V increased cumulative biomass and C input from main crop residues compared with NT-R. Both NT-R and NT-V promoted C (+0.4 Mg ha−1 y−1 and +0.6 Mg ha−1 y−1, respectively) and N (+88 kg ha−1 y−1 and +145 kg ha−1 y−1, respectively) soil sequestration, mainly due to the increase of macroaggregate-associated C and N, thus corroborating a major role of NT for macroaggregates formation and SOM stabilization within macroaggregates. Since no difference was found between cover crops in terms of biomass input, and C and N sequestration potential, we concluded that cover crop biomass production (rather than biomass quality) and retention onto the soil as residue were the main drivers of soil C and N sequestration. Therefore, both rye and hairy vetch may be combined with NT and promise significant potential as effective C farming practices. • Main crop yield under NT treatments was comparable to that under CT during and following the transition period. • Rye and hairy vetch produced the same amount of biomass and C input. • C and N sequestration rates and efficiencies were higher under NT-R and NT-V than under CT. • Biomass input rate was the main driver of SOM sequestration rather than residue quality. [ABSTRACT FROM AUTHOR]

Carbon farming policies aim to contribute to climate change mitigation, but their success strongly depends on whether landholders actually adopt desired practices or participate in offered programs. The Australian Government’s Carbon Farming Initiative and Emissions Reduction Fund policies were designed to incentivise the adoption of carbon farming practices. Although these policies have been active since December 2011, farmer engagement has been limited, and net emissions reductions low as a result. We surveyed broad-acre farmers in the Western Australian wheatbelt to explore their drivers and barriers to adopting carbon farming practices and participating in carbon farming policy programs. Drivers of adoption included knowledge and perception of co-benefits (for yield, productivity, and the environment), knowing another adopter, and believing that changes to farm management are an appropriate method to reduce Australia’s greenhouse gas emissions. Barriers to adoption included lack of information, uncertainty and costs. The key barrier to participation was policy and political uncertainty. The determinants of adoption and participation that we identify in our study offer important insights into how to best ensure the success of Australia’s land sector-based climate change policies. We conclude that, to increase landholder engagement, the co-benefits and climate change benefits of carbon farming practices must be actively promoted, and additional information is needed about the costs associated with adoption. Information diffusion is best achieved if it actively leverages landholder social networks. Finally, our results indicate that landholder buy-in to carbon farming could be greatly enhanced by achieving more continuity in Australian climate change policies and politics. [ABSTRACT FROM AUTHOR]

Carbon farming in agricultural landscapes may provide a cost-effective mechanism for offsetting carbon emissions while delivering co-benefits for biodiversity through ecosystem restoration. Reforestation of landscapes using native tree and shrub species, termed environmental plantings, has been recognized as a carbon offset methodology which can contribute to biodiversity conservation as well as climate mitigation. However, far less attention has been paid to the potential for assisted natural regeneration in areas of low to intermediate levels of degradation, where regenerative capacity still remains and little intervention would be required to restore native vegetation. In this study, we considered the economics of carbon farming in the state of Queensland, Australia, where 30.6 million hectares of relatively recently deforested agricultural landscapes may be suitable for carbon farming. Using spatially explicit estimates of the rate of carbon sequestration and the opportunity cost of agricultural production, we used a discounted cash flow analysis to examine the economic viability of assisted natural regeneration relative to environmental plantings. We found that the average minimum carbon price required to make assisted natural regeneration viable was 60% lower than what was required to make environmental plantings viable ($65.8 t CO 2 e −1 compared to $108.8 t CO 2 e −1 ). Assisted natural regeneration could sequester 1.6 to 2.2 times the amount of carbon possible compared to environmental plantings alone over a range of hypothetical carbon prices and assuming a moderate 5% discount rate. Using a combination of methodologies, carbon farming was a viable land use in over 2.3% of our study extent with a low $5 t CO 2 e −1 carbon price, and up to 10.5 million hectares (34%) with a carbon price of $50 t CO 2 e −1 . Carbon sequestration supply and economic returns generated by assisted natural regeneration were relatively robust to variation in establishment costs and discount rates due to the utilization of low-cost techniques to reestablish native vegetation. Our study highlights the potential utility of assisted natural regeneration as a reforestation approach which can cost-effectively deliver both carbon and biodiversity benefits. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) sequestration by improved agricultural practices is an acclaimed strategy to combat climate change. Nevertheless, the aim of increasing of SOC encounters limitations, e.g. with regards to permanence of carbon storage or leakage effects in food production. Agroforestry systems (AFS) are a promising land use option that is able to sequester substantial amounts of SOC while addressing these challenges. With a focus on temperate climate zones worldwide, available information on SOC in AFS was reviewed to determine their SOC sequestration potential and respective controlling factors. From a total of 61 observations, SOC sequestration rates in soils of AFS were derived for alley cropping systems (n = 25), hedgerows (n = 26) and silvopastoral systems (n = 10). The results showed that AFS have a potential for substantial SOC sequestration in temperate climates. SOC stocks were higher in the topsoil (0–20 cm) than in the control in more than 70% of the observations, and higher within the subsoil (20–40 cm) for 81% of all observations, albeit large variation in the data. The mean SOC sequestration rates were slightly higher at 0–20 cm (0.21 ± 0.79 t ha-1 yr-1) compared to 20–40 cm soil depth (0.15 ± 0.26 t ha-1 yr-1). Hedgerows revealed highest SOC sequestration rates in topsoils and subsoils (0.32 ± 0.26 and 0.28 ± 0.15 t ha-1 yr-1, respectively), followed by alley cropping systems (0.26 ± 1.15 and 0.23 ± 0.25 t ha-1 yr-1) and silvopastoral systems showing a slight mean SOC loss (−0.17 ± 0.50 and −0.03 ± 0.26 t ha-1 yr-1). Moreover, SOC sequestration rates tended to be higher for AFS with broadleaf tree species compared to coniferous species. We conclude that temperate AFS sequester significant amounts of SOC in topsoils and subsoils and represent one of the most promising agricultural measures for climate change mitigation and adaption. • Agroforestry has a highly significant and positive effect on SOC sequestration in the temperate zone. • SOC stocks in temperate AFS are generally higher than in treeless agricultural sites. • The amount of sequestered SOC was slightly higher at 0–20 cm compared to 20–40 cm soil depth. • Hedgerows revealed higher SOC sequestration rates than alley cropping and silvopastoral systems. • SOC sequestration rates were higher for AFS with broadleaf tree species compared to coniferous species. [ABSTRACT FROM AUTHOR]

Abstract: Carbon sequestration in agricultural soil has been identified as a potential strategy to offset greenhouse gas emissions. Within the public debate, it has been claimed that provision of positive incentives for farmers to change their land management will result in substantial carbon sequestration in agricultural soils at a low carbon price. However, there is little information about the costs or benefits of carbon sequestration in agricultural soils to test these claims. In this study, the costeffectiveness of alternative land-use and land-management practices that can increase soil carbon sequestration is analysed by integrating biophysical modelling of carbon sequestration with wholefarm economic modelling. Results suggest that, for a case study model of a crop-livestock farm in the Western Australian wheatbelt, sequestering higher levels of soil carbon by changing rotations (to include longer pasture phases) incur considerable opportunity costs. Under current commodity prices, farmers would forego more than $80 in profit for every additional tonne of CO2-e stored in soil, depending on their adoption of crop residue retention practices. This is much higher than the initial carbon price of $23t−1 in Australia’s recently legislated carbon tax. This analysis does not incorporate the possibility that greenhouse gas emissions may increase as a result of including longer pasture phases. Accounting for emissions may substantially reduce the potential for net carbon sequestration at low carbon prices. [Copyright &y& Elsevier]