Long‐term climate change mitigation potential with organic matter management on grasslands

Abstract

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.

Effects of bio‐based residue amendments on greenhouse gas emission from agricultural soil are stronger than effects of soil type with different microbial community composition

“…Although seemingly having no net effect in the short term, the use of these residues is not without merit and may benefit other aspects of soil functioning. In particular, compost mineralization is slower than in fresh organic residues; hence, the extraneous carbon pool is sequestered in the soil for longer periods or is accumulated with recurring compost amendments (Ryals et al ., ). Previously, we showed a significant stimulation of soil methane uptake with compost addition (Ho et al ., ).…”

Nitrogen deposition and greenhouse gas emissions from grasslands: uncertainties and future directions

“…Model simulations were performed using DayCent (v. 4.5; Parton et al, 1998), the most recent daily time step version of CENTURY. DayCent has been used to simulate the effects of climate and land use change on C and nutrient cycling in terrestrial ecosystems including grasslands across the globe (Stehfest & M€ uller, 2004, Parton et al, 2007Ryals et al, 2015).…”

Gross nitrous oxide production drives net nitrous oxide fluxes across a salt marsh landscape

“…The climate is characterized as Mediterranean, with cool wet winters and warm dry summers. Mean annual rainfall reported for a nearby grassland is 950 mm, and seasonal temperatures range from 6°C in January to 20°C in July (Ryals et al 2015). This study was conducted in three adjacent marsh zones that differ in elevation and thus also in inundation regimes.…”