We just shipped a ton (literally) of soil samples to Nairobi to be be analyzed, covering about 150 of our farmers. I'm looking forward to seeing the results, which should tell us something about how to use fertilizer most effectively, as well as a bunch of other potential interventions. Soil fertility is a major issue around here. Most farmers don't have enough land to leave part of it fallow, so the land is gradually being leached of its nutrients, while the repeated use of chemical fertilizer tends to increase the acidity of the soil.

The challenge is how to intervene in a way that increases farmer income while also increasing sustainability. And the solution needs to be simple enough that we can quickly scale to serve thousands of people. It's the last part that's the most difficult: really customized solutions can work wonders, but at the cost of reducing the number of people you reach.