Soil Impacts and Improvements

There are many ways that 20th century agricultural practices have made soils unhealthy. The first till of a field releases a huge proportion of the carbon stored in the soil as organic matter. And removing residues (e.g. corn stalks and leaves) from a field after the corn kernels have been harvested can drive erosion, degrade soil structure, starve soil microbiome, reduce soil carbon, reduce key nutrients like nitrogen, phosphorus and potassium, and reduce micronutrients like boron, zinc, manganese, iron, copper, molybdenum, and chlorine.

And since we use ag residues as a feedstock, people sometimes ask: what the hell are you thinking? Aren’t you destroying the soil?

Actually, we’re striving for the opposite.

The key is that we’ve designed our process to improve soil carbon and soil structure by returning char to the soil, maintain nutrients and micronutrients by returning ash with that char, and avoid negative erosion and microbiome impacts by only processing a portion of the residue on the field.

Erosion & Microbiome

If the residue take rate is too high, the soil is exposed to rain and wind, and the microbiome won’t have anything to munch on. Both topsoil erosion and microbiome are protected by leaving 60% of the residue on the field (Nunes 2021).

Soil Structure

Soil structure is important for retaining water and nutrients. Biochar improves soil structure (Wang 2018).

Soil Carbon

While removing residue without char replacement would have an obvious negative impact on soil carbon, we’re specifically excited about our process because it will leave behind increased soil carbon relative to baseline. More specifically, at scale:

• 25% of C will be used for pyrolysis heat and power via syngas, re-emitted as CO₂
• 50% of C will be bio-oil for sequestration, ironmaking, SAF, etc.
• 25% of C will be left as char, 3x'ing soil C relative to a no-till at 15 yrs (Woolf 2021: Figure 1 on biochar vs. Beyaert 2011: Table 2 on no-till)

Nutrients

Nitrogen

The nitrogen in the residue ends up in the volatiles and condensate, so it is 99% removed from the soil and needs to be replaced. We account for the additional emissions in our life cycle analyses (see the bio-oil sequestration protocol and our registry).

Phosphorus

Our testing shows that roughly 60% of the phosphorus in the residue ends up back in the char and soil. The remainder will need to be replaced. We account for the additional emissions associated with the partial replacement in our life cycle analyses (see the bio-oil sequestration protocol and our registry).

Potassium

Our testing shows that 99% of the potassium ends up in the char/ash and back in the soil.

Micronutrients

Since metals in biomass end up in the ash, and most micronutrients are metals (like Fe, Zn and Mn), we expect that trace metal micronutrients will end up in the char/ash, and then back in the soil.