Managing Soil Carbon

Soil organic matter, or soil carbon, is the organic component of soil. This can consist of three primary parts that include small fresh plant particles and small living soil organisms, active decomposing organic matter, and stable organic matter, usually bound onto soil minerals. Soil carbon is generally known to be beneficial for crops and the environment because it helps retain moisture and nutrients. When organic material is added to soils that have been degraded, productivity increases. But it’s not clear how much carbon is the optimal amount. Soils also have the ability to act as a filter for water systems, and soils using practices that build carbon--like cover crops--can improve water quality. 

Soil scientists need to be able to produce practical recommendations on how soil should be managed, but studies lead to different conclusions based on differences in soil type, crop type, and other properties. The Managing Soil Carbon working group is a Science for Nature and People Partnership (SNAPP) team that has worked to synthesize these different studies into more generalizable relationships that could help conservation organizations better promote sustainable soil management.

The central focus of this working group was to synthesize and analyze existing data to provide new insight into how soils can be managed for agronomic and environmental outcomes. The group has published three journal articles that provide these new insights, with one more in review. 

The working group explored two case studies: grazing lands in California and row crop agriculture in the Midwest. California has a lot of actively managed grazing land that is essential for productive cattle ranching. The state is encouraging grazing managers to increase soil carbon as part of the state's “Healthy Soils Initiative” and the working group wanted to ensure that increasing soil carbon would be done in a way that would not compromise other environmental goals, like biodiversity. One of the working group’s goals was to determine if and how soil management and indices could benefit California grazing systems. 

The team also looked at row crop management in the Midwest. A primary concern with current soil management is the loss of fertilizer and nutrients into nearby water systems like the Mississippi River watershed. The excess nutrients in the water systems encourage a phenomenon (known as “eutrophication”) in which algae blooms cause declines in biodiversity affecting ecosystems far from the farms from which the nutrients came. The SNAPP team wants to showcase management schemes that will increase crop productivity and resilience to climate change while taking positive steps to minimize environmental damage from these management practices. 

The team also created an online tool called “AgEvidence” that stores scientific papers and data related to soil management in the US, organized by agricultural practice and outcome. Stephen Wood, the lead scientist of the Managing Soil Carbon working group, states “We set ambitious goals to push the field into a different way of thinking about soil conservation. We want to help agriculture practitioners by showing them where the data is coming from and how we can fill the gaps to make predictions.”

Published articles from the working group:

Bradford MA, Carey CJ, Atwood L, Bossio D, Fenichel EP, Gennet S, Fargione J, Fisher JRB, Fuller E, Kane DA, Lehmann J, Oldfield EE, Ordway EM, Rudek J, Sanderman J, Wood SA (2020) Soil carbon science for policy and practice. Nature Sustainability 2: 1070-1072. doi: 10.1038/s41893-019-0431-y

Gravuer K, Gennet S, Throop HL (2019) Organic amendment additions to rangelands: A meta-analysis of multiple ecosystem outcomes. Global Change Biology 25: 1152-1170. doi: 10.1111/gcb.14535

Oldfield EE, Bradford MA, Wood SA (2019) Global meta-analysis of the relationship between soil organic matter and crop yields. SOIL 5: 15-32. doi: 10.5194/soil-5-15-2019