Well, I decided to do it myself. Here’s the distribution of “iron-rich soils” in Nigeria and potentially affected rice area (the paper’s Fig. 8b), the latter coming from the SPAM project we have alluded to before as a source of data on crop cultivation.
The yellow rings are African rice landraces, the red dots all rice landraces, both from Genesys. If you click on the map, you’ll see it much better, and notice that there’s not much rice germplasm from the more brownish areas, denoting rice cultivation areas with Fe-richer soils. Should these be targets for collecting? Kind of depends if landraces are still grown in those places, but it’s a start.