Agriculture guide
Reading a dry spell from orbit
In July, three weeks without rain hit maize across southern Kwara. Here is what vegetation indices showed field by field, and how an out grower programme decided who to visit first.
What a vegetation index measures
Healthy leaves reflect a lot of near infrared light and absorb red light. A vegetation index compares the two. When crops are stressed, the index drops, often a week before the change is visible from the road.
We calculate it every five days for every field in a programme, and compare it with the same field in normal years.
What July looked like
By the second week of the dry spell, about 14 percent of monitored fields had fallen well below their normal range. Fields on sandy soils near Offa fell first; fields near the river held up.
The pattern was not random. It followed soil type, planting date and whether the farmer had weeded.
The index dropped a week before anyone saw a problem from the road.
Who to visit first
The programme had 30 extension officers for 9,000 farmers. Insight ranked fields by how far they had fallen and how close they were to an officer's route. Officers visited 600 farms in ten days.
Where replanting was still possible, farmers received early maturing seed. Where it was not, the lender agreed to reschedule repayments before defaults began.
Limits to keep in mind
Indices show stress, not its cause. Pests, weeds and drought can look similar from orbit. That is why a visit still matters, and why we never present an index as a yield guarantee.
Figures in this guide are example figures for a COVORN demo site.