Merced, CA | bharrison4@ucmerced.edu

Brendan Harrison is a Ph.D. candidate at the University of California, Merced and is a member of Dr. Rebecca Ryals’ Agroecology Lab. His dissertation work investigates the potential of biochar co-composting as an untapped natural climate solution. He received his B.A. in Environmental Studies and B.S. in Earth and Planetary Sciences from UC Santa Cruz where he was a Gliessman Fellow in Water Resources and Food System Sustainability.

Session Code: A2

Track: Current Research (hosted by CREF)

Session Name: Biological Indicators, Biochar Co-composting, Increasing SOC

Session Time: Wednesday, Jan 25, 1:45 to 3:15 PM

Presentation Title: Biochar Co-Composting of Dairy Manure Substantially Reduces Methane and Can Play a Critical Role in Meeting Climate Goals

Presentation Description: Livestock manure is a leading source of anthropogenic methane (CH_4) emissions. In intensive dairy systems, manure management can account for half of livestock CH_4. Recent policies targeting CH_4 emissions will require a significant reduction in livestock CH_4 by 2030. However, strategies aimed at reducing CH_4 from dairy manure typically focus on the liquid portion, whereas stockpiled solids can remain a large source of CH_4. We address this problem by asking the question: what role can biochar-composting of dairy manure solids, a novel methane (CH_4) mitigation strategy, play in meeting California’s short-lived climate pollutant reduction law (SB 1383) and the Global Methane Pledge? We answered this question by measuring daily greenhouse gas (GHG) fluxes during a field-scale biochar-composting experiment and conducting the first life-cycle assessment (LCA) of a biochar-composting dairy manure management system. We found that adding 6% biochar to composting dairy manure reduces CH_4 by 79% compared to compost without biochar. From our LCA, we show that biochar-composting has a net global warming potential of -535 kg CO_2e Mg^-1 manure compared to -194 kg CO_2e Mg^-1 for composting and 102 kg CO_2e Mg^-1 for stockpiling. In addition to substantially reducing CH_4 from manure, the persistent biochar carbon in biochar-compost enhances its climate benefit by sequestering carbon in soils after being applied in agroecosystems. Using our LCA results, we estimate that when biochar-composting is scaled up in intensive dairy systems globally, 1.59 Tg CH_4 yr^-1 is reduced, and the technical net greenhouse gas mitigation potential nearly doubles, increasing from 154 Tg CO_2e yr^-1 to 297 Tg CO_2e yr^-1. Biochar-composting could offer governments a powerful CH_4 mitigation tool to help achieve climate goals by the end of the decade.