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Breakout Session B
Soil Organic Carbon Spatial and Temporal Variability on a Corn-Soybean Rotation Watershed with 23 Years of Agroforestry
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Unsustainable agricultural practices deplete soil organic carbon (SOC), affecting ecosystem services, land productivity, soil health, and water quality. This study evaluated the long-term effects of row crop (RC), agroforestry buffers (AB), grass buffers (GB), and grassed waterways (GWW) on SOC. Agroforestry buffers (grass and tree) and grass buffer treatments were established in 1997 on a corn (Zea Mays L.)-soybean (Glycine Max [L]. Merr.) rotation. Grid soil samples from 86 locations were collected in 10 transects to determine SOC at 0-10 and 10-20 cm depths. Geospatial statistics and ANOVA were conducted to evaluate treatment, landscape, soil depth and series on SOC. The mean SOC% in the top 10 cm depth for the RC, AB, GB, and GWW areas was 1.94%, 2.19% 2.41%, and 2.51%, respectively (𝜌 < 0.001). The soil depth caused significant differences (𝜌 < 0.001) between samples from 0-10 cm and 10-20 cm. The mean SOC% among soil series showed no significant differences at the studied depths. The mean SOC% from 0-10 cm for RC, AB, GWW were 1.85%, 1.88%, and 2.30% in 2000, and 1.94%, 2.19%, and 2.51% in 2020. In overall, the foot slope position had the highest (2.41%) and the summit position had the lowest SOC (2.02%). The SOC% in the RC treatment from 0-10 cm at the summit, backslope and foot slope positions were ranked 1.83% < 2.22% < 2.31%, respectively. Perennial vegetation and undisturbed land management practices increased SOC compared to the RC areas.
Miguel Salceda G., School of Natural Resources, University of Missouri
Evaluating regression models for predicting carbon sequestration in aboveground biomass in hybrid poplar clones under afforestation plantation management in Southern Ontario, Canada
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Estimation of the accumulated biomass in woody cropping systems is essential for tracking carbon (C) stocks based on temporal changes in biomass and can help evaluate the potential C sequestration in the aboveground biomass of the system. This study was conducted in two high-yield hybrid poplar afforestation sites planted with a variety of poplar clones [DN-34, DN-182, NM-6, DN-132, DN-154, 2293-19, DN-136, DN-2, and DN-74] established in 2005 and 2009 to evaluate three regression models for predicting C sequestration in aboveground biomass in Southern Ontario, Canada. The study measured actual (observed) and predicted biomass to validate the model. The 72 representative poplar trees were selectively harvested and weighed, and their heights, diameters at breast height (DBH), and moisture content were determined. C content in each tree sample was quantified by combustion method and actual C content in aboveground biomass was calculated. Analysis in this study showed the proven ability of GenOnBio model in providing a reasonable estimate of C content in aboveground biomass in hybrid poplar. Predicted biomass C by GenOnBio model and Observed biomass C in harvested poplar trees in both 2005 and 2009 systems had a significant linear relationship (yielded adjusted R2 = 0.835** and 0.821**, respectively), and RMSE were lowest in this model for 2009 planted afforestation system (2.83 Kg C tree -1). Regression of predicted vs. observed values and comparing the slope and intercept parameters against the 1:1 line also showed that GenOnBio had nonsignificant differences from 1:1 line among three predictive models. Results showed that GenOnBio model had the least deviation of prediction in both 2005 and 2009 systems (13.5 and 11.9 percent, respectively) compare to the other models and produced very similar C sequestration predictions in aboveground biomass. Therefore, this model was chosen for use in the subsequent analysis to quantify C sequestered in aboveground biomass of afforestation poplar plantations in southern Ontario, Canada.
Amir Bazrgar, School of Environmental Sciences, University of Guelph, ON, Canada
Enhancing soil organic carbon storage through forested buffers and biochar application in agricultural lands
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Tailoring agricultural management practices to increase soil organic carbon (SOC) storage and reduce greenhouse gas (GHG) emissions can help mitigate climate change and improve ecological goods and services generated by agriculture. We conducted a 3-yr field study in central Alberta, Canada in two common types of agroforestry systems: hedgerows (legacy woody perennial vegetation) and shelterbelts (planted woody perennial vegetation). In the cropland, we compared manure compost (MT) and biochar (BT, charred MT) applications with a control (CT, no treatment). We also compared SOC and GHG emissions between CT and adjacent perennial vegetated areas, either with (+WT) or without (-WT) a woody component or planted saplings (PT). Two years post treatment application, BT contained 12 Mg ha−1 more SOC in the surface soil relative to CT, +70% compared to the applied C rate. In 2018 and 2019, MT increased annual GHG emissions by 33%, on average, relative to CT and BT. In 2020, BT reduced annual GHG emissions by 21%, on average, relative to CT and MT. In the surface soil, +WT contained 74% (21 Mg ha−1) more SOC relative to CT. Cumulatively, +WT contained 64% (111 Mg ha−1) more SOC relative to CT, wherein the subsoil (~30–100 cm) comprised 66% of the total SOC difference between the land uses. Perennial vegetation contained more SOC in particulate form, while CT contained substantially less mineral SOC physically protected in aggregates. Our study shows that the application of biochar, rather than its manure compost precursor, increased surface SOC sequestration and had no effect or reduced GHG emissions relative to no treatment. Additionally, we show that established woody perennial vegetation increases SOC storage and protection in agricultural lands in both surface and deep soil. Policy and C sequestration initiatives should incentivize biochar application and agroforestry systems as viable climate change mitigation agricultural practices.
Cole D. Gross, Department of Renewable Resources, Faculty of Agricultural, Life and Environmental Sciences, University of Alberta
Edward W. Bork, Department of Agricultural, Food and Nutritional Science, Faculty of Agricultural, Life and Environmental Sciences, University of Alberta
Cameron N. Carlyle, Department of Agricultural, Food and Nutritional Science, Faculty of Agricultural, Life and Environmental Sciences, University of Alberta
Scott X. Chang, Department of Renewable Resources, Faculty of Agricultural, Life and Environmental Sciences, University of Alberta
Agave Power: Greening the Desert
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Organic Consumer Association’s Mexico affiliate, Via Organica, in a project sponsored by OCA and our sister project Regeneration International, operates a research farm and teaching center outside San Miguel de Allende, Guanajuato, in the semi-arid drylands of North Central Mexico. Over the past several years we have been working with a group of innovative small farmers and agronomists to develop a new system of organic and regenerative desert agriculture and holistic livestock management, utilizing native plants and trees (agave and mesquite). We believe that Agave Power has the potential to revolutionize farming and ranching in the arid and semi-arid farmlands and rangelands that constitute 40% of the world’s lands. We believe that we can green the desert, eliminate rural poverty, and sequester massive amounts of excess atmospheric CO2 both aboveground and below ground with this Agave Power agroforestry system, which builds upon native wisdom and small farmer innovation. The Billion Agave Project is a game-changing ecosystem-regeneration strategy recently adopted by several innovative Mexican farms in the high-desert region of Guanajuato. This strategy combines the growing of agave plants and nitrogen-fixing companion tree species (such as mesquite), with holistic rotational grazing of livestock. The result is a high-biomass, high forage-yielding system that works well even on degraded, semi-arid lands. A pioneering group of Mexican farmers are transforming their landscape and their livelihoods. How? By densely planting (1600-2500 per hectare), pruning, and inter-cropping a fast-growing, high-biomass, high forage-yielding species of agaves among pre-existing (500 per hectare) deep-rooted, nitrogen-fixing tree species (such as mesquite), or among planted tree seedlings. When the agaves are 3 years old, and for the following 5 – 7 years, farmers can prune the leaves or pencas, chop them up finely with a machine, and then ferment the agave in closed containers for 30 days, ideally combining the agave leaves with 20% of leguminous pods and branches by volume to give them a higher protein level. In Guanajuato, mesquite trees start to produce pods that can be harvested in 5 years. By year 7, the mesquite and agaves have grown into a fairly dense forest. In year 8 – 10, the root stem or pina (weighing between 100-200 pounds) of the agave is ready for harvesting to produce a distilled liquor called mescal. Meanwhile the hijuelos (or pups) put out by the mother agave plants are being continuously transplanted back into the agroforestry system, guaranteeing continuous biomass growth (and carbon storage). In this agroforesty, system farmers avoid overgrazing by integrating rotational grazing of their livestock across their rangelands. They feed their animals by supplementing pasture forage with fermented agave silage.A manifesto on Agave POwer4 is available in English and Español. The system produces large amounts of agave leaf and root stem—up to one ton of biomass over the 8-10-year life of the plant. When chopped and fermented in closed containers, this plant material produces an excellent, inexpensive (two cents per pound) animal fodder. This agroforestry system reduces the pressure to overgraze brittle rangelands and improves soil health and water retention, while drawing down and storing massive amounts of atmospheric CO2. The goal of the Billion Agave campaign is to plant one billion agaves globally to draw down and store one billion tons of climate-destabilizing CO2. The campaign will be funded by donations and public and private investments.
Ronnie Cummins, International Director of Organic Consumers Association