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Breakout Session B

Biomass to Biochar: A Carbon Drawdown Solution
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Converting waste biomass from agroforestry practices to biochar provides an innovative climate change solution. Biomass thermally reduced to its elemental carbon in the form of char and then applied to soil not only sequesters carbon but improves soil and plant health and productivity. This scalable, practical biomimetic practice provides multiple benefits beyond carbon sequestration: primary productivity increase, soil moisture and retention/bio-availability, soil off-gassing reduction; waste-to-resource conversion and soil health.

Gloria Flora, Executive Director, Sustainable Obtainable Solutions; Founder, US Biochar Initiative; Proprietor, TerraFlora Permaculture Learning Center

Woody agriculture, but not woody polyculture, increased soil organic carbon at a Chinese chestnut farm in Iowa, USA
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Perennial cropping systems have the potential to produce food, while sequestering carbon in soils and biomass. We examined soil carbon storage at one woody Chinese chestnut – pawpaw farm in Iowa, USA. Soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen were greater in the woody agriculture than in the corn – soybean system, but less than in the secondary forests. Woody agriculture increased soil organic carbon sequestration down to 100 cm (39 inches), with most of this increase concentrated in the top 30 cm (12 inches). In the 24 years since conversion to woody agriculture, we estimate the soil carbon sequestration rate to be approximately 0.4 Mg C ha-1 yr-1. Within the woody agriculture system, we compared soil organic carbon across several woody crop guilds, including single and double density chestnut and pawpaw, and one guild that included both chestnut and pawpaw. Overall, we found few effects of guild on soil carbon, suggesting that modest increases in density and diversity did not improve soil carbon storage in this system, however, recognize that further study is needed to examine the effects of density, diversity, and species composition on soil carbon sequestration in woody agriculture systems.

William C. Eddy III, University of Illinois at Urbana – Champaign

Soil carbon sequestration in temperate agroforestry systems
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Sequestering atmospheric carbon (C) in the soil through enhanced agricultural practices is an acclaimed tactic in combating climate change. Nevertheless, the strategy sometimes encounters limitations, e.g., the leakage effect in food production associated to extensification, or higher nitrous oxide emissions followed higher nitrogen demand by an ambitious increase in biomass production. Agroforestry (AF) is seen as a promising land use option that can make a substantial contribution to C sequestration without simultaneously exacerbating the dilemmas described above. While a number of global meta-studies on AF and C sequestration exist, most of them are for the tropics and subtropics. Our meta-analysis focuses on the temperate zones of the Koeppen-Geiger climate map provides robust values for 34 observations in Europe, 17 in North America and two in Asia and tests for numerous possible control factors. The results show that AF has a great potential for C sequestration in temperate climates. Soil organic carbon (SOC) stocks were higher in the topsoil than in the control in 70% of the observations, and in 80% of the subsoil samples, albeit large variation in the data. The amount of C sequestrated during the duration of the experiments was slightly higher at 0-20 cm compared with 20-40 cm soil depth (mean 0.20 ± 0.83 and 0.13 ± 0.24 t OC yr-1). Hedgerows revealed statistically significant higher sequestration rates than silvopasture. Whereas the absolute amount of stored SOC did not differ between tree types, i.e. broadleaf or coniferous, sequestration rates in broadleaf were higher than in coniferous systems.

Rico Hübner, Chair, Strategic Landscape Planning and Management, TUM School of Life Sciences, Technical University of Munich, Freising, Germany; German Association for Agroforestry – DeFAF, Cottbus, Germany

Carbon sequestration potential of orchard meadows in the foothills of the Bavarian Alps
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Orchard meadows are fruit tree based traditional agroforestry systems (AFS) in Germany, characterized by a high diversity in tree species, varieties and age. Space between the irregularly planted trees is used for crop, pasture or fodder production. Marginalized and threatened in modern times, their cultural and ecological value are of great value and political concern. Their potential as a climate protection instrument through the sequestration of C is increasingly attracting attention; however, hardly any robust studies exist to date.

The aim of this study was to quantify the above- and below-ground C stocks of traditional orchard meadows of the Alpine foothills in Bavaria. C stocks in the woody biomass of five orchard plots were determined allometrically. The soil sampling design was applied to three representative trees in each plot plus three adjacent references. Soil samples were collected to a depth of 50 cm using a pile driver probe and C stocks were determined at 0-10, 10-30, and 30-50 cm.

First results indicate that within the realm of the Alpine foothills, orchard meadows on grassland do not store more C than grassland controls. However, their long-term ambition protects the grassland from C losses and conversion to arable land. Secondly, substantial amounts of C is stored in the roots and above ground biomass for decades, that bind CO2 in the long term, and thus has climate mitigation effects. This benefit may be worth accounting for in order to better protect and finance the remaining orchard stand in the Alpine foothills.

Elron Wiedermann, Technical University of Munich, TUM School of Life Sciences, Department of Soil Science, Freising, Germany

Rico Hübner, Technical University of Munich, TUM School of Life Sciences, Chair for Strategic Landscape Planning and Management, Freising, Germany; German Association for Agroforestry – DeFAF, Cottbus, Germany

Martin Wiesmeier, Technical University of Munich, TUM School of Life Sciences, Department of Soil Science, Freising, Germany; Bavarian State Institute of Agriculture, Institute of Organic Farming, Soil Science and Resource Conservation, Freising, Germany