Risk

Aflatoxin and fumonisin contamination of corn costs the United States up to an estimated $1.66 billion a year, yet the forecasting models used elsewhere have no US counterpart. Machine learning models were trained on 1,772 mycotoxin measurements from Illinois corn between 2003 and 2021, paired with daily rather than monthly weather, satellite greenness and county soil properties, which sets them apart from an earlier attempt in the state. High contamination events were rare. Even so, the best models reached 96% and 92% balanced accuracy on withheld data. Carbonate-rich soils tracked lower aflatoxin and wetter soils higher fumonisin, relationships that remain correlational.

Attributing a smallholder harvest to the farmer’s decisions rather than to soil and weather has been difficult, since field records are scarce. A process-based crop model simulated maize yields across all 72 of Zambia’s districts from 1979 to 2016, varying cultivar, fertilizer rate and planting date, which resolves those three choices separately for the first time nationally. Management explained 53% of yield variance overall, from 27% in the drier south to 82% in the wetter north, where fertilizer alone accounted for 72%.

While potential maize yields in Zambia are 9 t per hectare (t/ha), the average farmer produces only 1–2. We evaluate the contribution of responses to weather risk to that gap by decomposing the yield gap in maize in Zambia. Risk aversion explained 24% of the average gap, varying widely by location, implying 6.75 tons per hectare attainable without added risk against 8.84 when maximizing profit.