Emission metrics

• KPI value(s): (Direct N2O + indirect N2O + CH4) / (yield). The average kg CO2e/kg per crop per spatial unit per year for the soil related (field) components of agricultural activity.
• Metric calculation details: Key examples include the GHG impact from residue left on field (vs. removing through bailing) is included in this metric. Emissions associated from the fuel usage / tractor emissions of tillage events is NOT included.
• LCA crosswalk: This emission factor is the best aligned with generic LCA database components of direct and indirect N2O emissions.

Field emissions per acre/hectare

• Definition: greenhouse gas emissions from crop production, regenerative agriculture practices have the ability to reduce greenhouse gas emissions from crop production and this is generally referred to as “reductions”

• KPI value(s): The total GHG emissions (metric tons CO2e / acre) calculated per field level and aggregated at each geospatial aggregation unit

• Metric calculation details: Regrow utilizes the DNDC scientific model to model GHG emissions (measured in tonnes of CO2e) consisting of the following components: CH4, N20 (indirect/direct). Components are converted to CO2e by their global warming potential. The CO2e multiplier Regrow utilizes is from IPCC Climate Reports, specifically the AR6 values from the 2021 report:

  Version	N2O Multiplier	CH4 Multiplier
  AR6	44 / 28 * 273 = 429	16 / 12 * 29.8 = 39.733

Field SOC sequestration per acre/hectare

• Definition: the ability of soil to store carbon, regenerative agriculture practices have the ability to help accelerate the soil’s ability to remove greenhouse gas from the atmosphere and this is generally referred to as “removals”

• KPI value(s): Per geospatial aggregate unit, the change in soil carbon stocks (metric tons CO2e / acre) per year calculated per field level and aggregated at each geospatial aggregation unit

• Metric calculation details: SOC (soil organic carbon) sequestration is calculated by taking the difference of soil organic carbon stock values between 2 points in time (i.e. annual difference). The soil organic carbon stock values encompass the total soil carbon in the soil pools down to a specified depth, but does not include any residue (litter) pools. This dSOC (change in soil organic carbon) value is then converted into a GHG value (dSOC in co2e) by using a conversion factor of 44/12, a widely recognized conversion factor used for this purpose.
• Reversals: DNDC modeling captures year-over-year changes to soil carbon stocks, including losses of soil carbon and potential reversals. Any reversal in soil organic carbon is captured by the subsequent change in the Sustainability Insights dSOC Sequestration, Field dSOC and Field Net EF values for the following year.

Net emissions per acre/hectare

• Definition: Net emissions is the combination of GHG emissions less SOC sequestration. This represents the net impact from on field agricultural activities.
• Metric calculation details: Net emissions = GHG emissions per area - SOC sequestration per area.

Regrow’s Denitrification-Decomposition (DNDC) model is a biogeochemical model that is based on first principles of soil biogeochemistry and estimates nutrient cycling in the soil that drive GHG emissions, including how soil dynamics change with the adoption of new farming practices.

DNDC supports over 100 crop types, has been peer reviewed in over 500 academic publications, received the first ever ‘General Approval’ from the Climate Action Reserve for measuring soil GHG dynamics, and consistently received minimal (roughly 5%) deductions for model uncertainty when predicting soil organic carbon levels (per 100 fields, within .5mt/acre).

Regrow has a dedicated team that is responsible for ensuring that DNDC is calibrated for each crop, field, and region that we model. This team is responsible for finding the best available emissions data for a particular crop/geo combination, and using this data to ensure that the DNDC model is subsequently calibrated, and producing accurate results.

Additionally, Regrow has a package of publicly available peer-reviewed literature that a client can use in order to demonstrate DNDC’s accuracy for a particular context. CAR SEP also produced a validation report for DNDC (CAR SEP Validation of DNDC) that a customer can point an auditor towards. 

Model Calibration and Validation

DNDC is validated globally, and calibrated for different crop/geo combinations.  

Calibration

Regrow maintains a large database of experimental studies used for regular calibration and validation of DNDC. The database is populated through literature review of peer-reviewed studies and datasets that report changes in emission sources of interest within targeted validation domains. Additionally, the database is populated with thousands of soil samples that contribute the required ‘ground-truth’ information used to generate DNDC estimates. The database is then used to build and run DNDC simulations for relevant experimental treatments (i.e. longitudinal measurements of a target emissions source, like soil organic carbon, or nitrous oxide flux).

Independent Validation

Validation of DNDC simulations is demonstrated through the description of an uncertainty model, allowing for the propagation of the uncertainty quantified through the validation data to new modeling units in the validation domain. The uncertainty model is an empirical model that estimates the lack of fit between model estimates and measured values of differences (i.e. calibration data). According to the Climate Action Reserve, a leading third party independent validator of soil carbon claims, DNDC effectively meets the bias and error requirements needed for validation within specific geographies and for specific crops. (do we need to be more specific)?

Accounting for Model Uncertainty

When Regrow estimates a change in soil organic carbon (SOC), our model delivers a distribution of values as the distribution of estimated changes in soil carbon, reflecting model uncertainty. Most values fall near the middle value, but some fall far from the middle. This pattern (distribution) describes the model's uncertainty.

Uncertainty decreases as the number of fields or acreage size increases. Statistically, the more a sample size is expanded, the more likely it is that individual results align closely to the projected mean. Regrow has performed analyses that show our average uncertainty is quite small for simulations of a large number of fields.

IPCC Tiers

The Intergovernmental Panel on Climate Change (IPCC) defines three different methodological approaches for quantifying greenhouse gas emissions for carbon inventories. These approaches are ranked into categories of data quality: Tier 1, Tier 2 and Tier 3.

Regrow’s methodology and data from Sustainability Insights meets IPCC Tier 3 criteria, which is the highest level of rigor:

Process-Based Modeling

Sustainability Insights measurement data is calculated using the process-based DNDC soil model. DNDC simulates how microbes react to changes in soil conditions and the resulting greenhouse gas effects. The DNDC model takes into account site-specific conditions, incorporating data on cropping, fertilizer, tillage, irrigation, weather and soils, resulting in more accurate and location-specific results than Tier 1 and Tier 2 default values provide.

Location-Specific Data

Regrow uses remote sensing-based technology to identify crops and acreage at the field level. This data is then aggregated according to the user’s mapped regions in Sustainability Insights. Regions can be mapped at the county, state, watershed or country level. Custom regions, such as a radius or polygon, are also supported. This approach enables emissions calculations that are location-specific, rather than the use of default values that are often available only at the country level. 

CO2 Conversion Factors 

Regrow uses AR6 CO2 equivalent conversion factors for N2O and CH4 to reflect values published in the 2021 IPCC Report. 

The table below summarizes the changes between each version

Detailed values for AR6 can be found in Table 7.15 of the IPCC Technical Report, found here.