Compost amendments to grasslands have been proposed as a strategy to mitigate climate change through carbon (C) sequestration, yet little research exists exploring the net mitigation potential or the long-term impacts of this strategy. We used field data and the DAYCENT biogeochemical model to investigate the climate change mitigation potential of compost amendments to grasslands in California, USA. The model was used to test ecosystem C and greenhouse gas responses to a range of compost qualities (carbon to nitrogen [C:N] ratios of 11.1, 20, or 30) and application rates (single addition of 14 Mg C/ha or 10 annual additions of 1.4 Mg C · ha(-1) · yr(-1)). The model was parameterized using site-specific weather, vegetation, and edaphic characteristics and was validated by comparing simulated soil C, nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) fluxes, and net primary production (NPP) with three years of field data. All compost amendment scenarios led to net greenhouse gas sinks that persisted for several decades. Rates of climate change mitigation potential ranged from 130 ± 3 g to 158 ± 8 g CO2-eq · m(-2) ·yr(-1) (where "eq" stands for "equivalents") when assessed over a 10-year time period and 63 ± 2 g to 84 ± 10 g CO2- eq · m(-2) · yr(-1) over a 30-year time period. Both C storage and greenhouse gas emissions increased rapidly following amendments. Compost amendments with lower C:N led to higher C sequestration rates over time. However, these soils also experienced greater N20 fluxes. Multiple smaller compost additions resulted in similar cumulative C sequestration rates, albeit with a time lag, and lower cumulative N2O emissions. These results identify a trade-off between maximizing C sequestration and minimizing N2O emissions following amendments, and suggest that compost additions to grassland soils can have a long-term impact on C and greenhouse gas dynamics that contributes to climate change mitigation.

In the face of rapidly advancing climate change, biodiversity loss, and water scarcity, it is clear that global agriculture must swiftly and decisively shift toward sustainability. Fortunately, farmers and researchers have developed a thoroughly studied pathway to this transition: agroecological farming systems that mimic natural ecosystems, creating tightly coupled cycles of energy, water, and nutrients. A critical and underappreciated feature of agroecological systems is that they replace fossil fuel- and chemical -intensive management with knowledge-intensive management. Hence, the greatest sustainability challenge for agriculture may well be that of replacing non-renewable resources with ecologically-skilled people, and doing so in ways that create and support desirable rural livelihoods. Yet over the past century, US agriculture has been trending in the opposite direction, rapidly replacing knowledgeable people with non-renewable resources and eroding rural economies in the process. Below, we suggest how US policy could pivot to enable and support the ecologically skilled workforce needed to achieve food security in the face of climate change.

Sustainable agriculture is among the most urgently needed work in the United States, for at least three reasons: we face an environmental crisis, a health crisis, and a rural economic crisis. Addressing these pressing crises through sustainability transition will require growing our agricultural workforce: both because the current farm population is aging, and because sustainable agriculture is knowledge-intensive work that substitutes experiential knowledge of farm ecosystems for harmful industrial inputs. Given its social value, sustainable agriculture ought to be a welcoming profession. But at present, US agriculture is decidedly unwelcoming for nearly all who work in it – and it puts new entry and sustainable farmers at a distinct disadvantage. In this paper, we first examine why it is so hard to enter and succeed in sustainable farming. We find that new entrants struggle to gain critical access, assets, and assistance, encountering substantial barriers that stand between them and the land, capital, markets, equipment, water, labor, and training and technical assistance they need to succeed. Secondly, we review promising policy and civil society interventions targeted at addressing these barriers, nearly all of which have already been piloted at the local and state levels or through modest public funding. These interventions are most effective, we find, when they are linked up through robustly governed networks to provide “wraparound” coverage for new entry sustainable farmers. Such networks can help patch together complementary sources of support (e.g. federal, state, local, NGO, cooperative) and synergistically address multiple barriers at once. Finally, we propose additional interventions that are more aspirational today, but that could offer important pathways to support new sustainable farmers in the longer term.