The field regrows biomass continuously between harvests following logistic growth: fast when the stock is small relative to what the soil can support, slowing as it approaches the land's carrying capacity. Every harvest cycle removes a fraction of the standing biomass and sends it to the biorefinery, which splits it into two useful product streams (biofuel and bioplastic) plus a residue stream. A share of that residue is recycled back to the field as fertiliser — nudging the soil's carrying capacity up over time — while the rest is lost as low-value waste.
dB/dt = r·B·(1 − B/K) (regrowth between harvests)
H = h·B (biomass harvested this cycle)
product = H·η waste = H·(1 − η)
recycled = waste·ρ → K += recycled·0.15
CO₂ avoided += product·(e_fossil − e_bio)
- Growth rate (r) — how quickly the biomass field regenerates between harvests; too low and harvesting outpaces regrowth, collapsing the stock.
- Harvest rate (h) — the fraction of standing biomass cut each cycle; higher throughput but less left to regrow.
- Conversion efficiency (η) — the biorefinery's yield of usable biofuel + bioplastic per tonne of feedstock; the rest becomes residue.
- Recycling rate (ρ) — the share of refinery residue returned to the field as fertiliser instead of discarded, closing the loop and slowly raising soil capacity K.
Real-world relevance: this loop mirrors how an actual biorefinery is run — feedstock has to regrow faster than it is cut or the supply chain collapses, conversion efficiency sets how much fossil fuel and fossil-based plastic each tonne of biomass can displace, and recycling residue back to the land is what keeps a bioeconomy circular rather than just extractive.