The science: At pH 5.1, aluminium and manganese toxicity is active in the root zone, directly stunting root development in maize. Microbial activity drops 60% below pH 5.5. Every nutrient input applied at this pH is operating at 40–60% efficiency. Dolomitic lime also adds magnesium — critical for chlorophyll production and often deficient in Free State soils.

The science: SOC of 1.8% is critically low for the Free State — the region historically supported 3–4% SOC under natural Highveld grassland. Bare-fallowed monoculture maize has depleted carbon at approximately 0.15%/yr over 20 years. Below 2% SOC, the soil lacks the water-holding capacity to buffer the summer rainfall variability that is intensifying with climate change.

The science: Limestone ammonium nitrate (LAN) at 145 kg N/ha is causing active soil carbon priming in already-depleted soil. The high application rate, combined with low SOC, creates a C:N imbalance that forces microbial burndown of what little soil carbon remains. Priming risk score is currently 7/9.