This BBC article talks about the specifics of it but basically the amount of loan you can get goes up and the interest goes down if you pay on time and improve, not degrade, your soil.
"But now, a Kenyan company is offering loans to farmers where the interest rates charged are linked to the quality of the soil, providing an incentive for soil preservation" - from the article.
"Instead of Pay It Forward I prefer Plant It Forward" ~Howard Story / "God has cared for these trees, saved them from drought, disease, avalanches, and a thousand tempests and floods. But he cannot save them from fools." ~John Muir