Practices That Sequester Soil Carbon

DR. LARRY OLDHAM

MISSISSIPPI STATE, MISS.

   Soil carbon (C) sequestration is the practice of growing plants to capture atmospheric C and store it in the soil to mitigate climate change. Soil carbon sequestration is not a magic bullet for climate mitigation but has a role in the management toolbox. The Biden administration has made soil C sequestration a priority of the US Department of Agriculture under USDA Secretary Tom Vilsack.

   Private sector soil C markets had already started expanding in 2020 with Truterra (unit of Land O’Lakes, Inc.), and Indigo Ag, among others, identifying and working with potential buyers and sellers. 

   Crop input providers Bayer and Nutrien are fostering supply chain enhancements that increase C sequestration, with potential participation in the C market. This is not an endorsement of these companies – this information is to provide examples of the private sector activity in agricultural C sequestration markets.

   The farm management data needed to participate in these programs include the number of growing seasons the fields or farms have been operated employing certain conservation management practices. There usually is a lag time between changing to the conservation-oriented practice and measurable differences in soil C contents.

   If a farmer shares their information with a farm data management service, the service may identify C sequestration as a potential revenue source for the grower and begin a conversation about sequestration contracts.

   The science of soil organic matter evolved over the past two decades as advanced analytical technology found that end-products of residue breakdown are not large macromolecules. Rather the C we strive to sequester is identifiable as biological origin materials which have been ‘processed’. Residue decomposes due to activity from larger creatures (earthworms etc.) along a food chain down to the microbial community that use the material as an energy source. Practices that promote this soil biology increase soil C and improve soil health. The core ideas are:

   • keep soils covered as much as possible to reduce erosion,

   • minimize tillage operations that increase C release from the soil, • use crop rotations that alternate taproot and fibrous root growth patterns, and

   • employ cover crops to increase C entering the soil matrix.

   Organic nutrient sources (such as poultry litter) introduce diverse C sources to the soil system that may stimulate biological activities. 

   However, other production practices may limit soil biological activity and the subsequent capacity for soil decomposition and long-term C storage.

   Many farming operations implement Conservation Plans developed by the Natural Resource Conservation Service (NRCS) to address resource concerns (such as erosion) that the grower may have. Conservation Plans are developed using Practice Standards, in NRCS terminology. 

   These are Best Management Practices and are all available by individual state at their eFOTG. Operations following a NRCS Conservation Plan, or even if not via a plan, that are using these soil management practices may have a reason to explore the C sequestration marketplace.

   Some NRCS Conservation Practices, i.e. Best Management Practices that foster soil biological activity and increase soil C include:

   Practice Code 328, Conservation Crop Rotation. This is a planned sequence of crops grown on the same ground over a period of time (i.e. the rotation cycle) to maintain or increase soil health and organic matter content.

   Practice Code 340, Cover Crops. These are grasses, legumes, and forbs planted for seasonal vegetative cover to maintain or increase soil health and organic matter content.

   Practice Code 329, Residue and Tillage Management, No Till: Limiting soil disturbance to manage the amount, orientation and distribution of crop and plant residue the soil surface year around to maintain or increase soil health and organic matter content.

   Practice Code 345, Residue and Tillage Management, Reduced Till: For managing the amount, orientation, and distribution of crop and other plant residue on the soil surface year-round while limiting soil- disturbing activities used to grow and harvest crops in systems where the field surface is tilled prior to planting improve soil health and maintain or increase organic matter content.

   The other caveat, in addition to the time lag before results are readily apparent from adopting these practices, is that increasing soil disturbance in the production system releases stored C back to the atmosphere. An important component of the private sector soil C market will be verification that the C is being stored in the soil. 

   The exact nature of verification procedures seems to be developing.

   To summarize, commercial sector interest in C sequestration trading is increasing. Some basic soil management practices are known to increase C in soils that may attract commercial interest in a particular farm. 

   However, farm management must be committed to operating, and maintaining those practices in the operation to fulfill any agreement entered.

   The author appreciates the assistance of Drs. Beth Baker, Mike Cox, and Keri Jones. ∆

   DR.LARRY OLDHAM: Extension Soils Specialist, University of Mississippi

 Photo courtesy of Dr. Beth Baker