Net greenhouse gas balances of South African pasture-based dairy farms using the DESTiny biogenic carbon model

Riana Reinecke^1,2*James N Blignaut^1,2,3Heinz MEISSNER⁴Pieter Swanepoel¹

• ¹Stellenbosch University, Stellenbosch, South Africa
• ²ASSET Research, Pretoria, South Africa
• ³South African Environmental Observation Network, Pretoria, South Africa
• ⁴Milk SA, Pretoria, South Africa

The DESTiny framework was used to calculate net greenhouse gas balances for 12 pasture-based dairy farms in South Africa's Garden Route. Farms were grouped as low-, moderate-, or high-input based on fertiliser use, purchased feed, stocking rate, conservation tillage, and forage self-sufficiency. Eleven of the 12 farms exhibited negative net GHG balances. Farm balances ranged from –15,211 to +6,764 t CO₂e year⁻¹, and carbon intensity per kg of fat-and-protein-corrected milk (FPCM) ranged from –2.21 to +0.53 kg CO₂e kg⁻¹ FPCM (median – 0.83 kg CO₂e kg⁻¹ FPCM). Low-input farms showed the most negative intensities (median – 1.09 kg CO₂e kg⁻¹ FPCM), followed by moderate-input farms (–0.94 kg CO₂e kg⁻¹ FPCM). High-input farms varied widely and included the only net source. External inputs (mostly purchased feed) and enteric methane each contributed approximately 40% of gross emissions. Farms achieving the greatest carbon accumulation potential typically combine high feed efficiency, strong milk solids, legume-rich pastures, conservation tillage, and near-complete reliance on home-grown forage. The results show that management decisions matter far more than input intensity, and that well-managed pasture-based dairies in this region generally maintain a negative net carbon flux. By fully integrating on-farm biogenic carbon fluxes, this work reveals that pasture-based dairy systems in temperate climates can have a strongly negative net carbon flux, transforming them from traditional emitters into verifiable climate assets.