Conservation agriculture is a lot about taking care of your soil - having healthy soil will help you to have healthy crops. In a hilly place like where we're living in Kenya it's especially important to take special care of your soil because it's so easy to lose your all-important topsoil to erosion when there's a heavy rain.
I saw some examples of erosion after a rainstorm a while back and took pictures to show the results. First of all, I have a couple pictures of where soil got washed about 200 meters down a hill to an area just off a gravel road. The farms up the hill had ploughed right to the edge of the road and planted up and down the slope instead of along the contour of the hill, so when it rained, the soil went down the field, off the edge, and along down the road to here:
Later, I saw another field that had lots of soil washed down to the bottom of it. In this picture, you can see how there is so much soil that it covered up the crops growing there at the bottom:
That field, which is the same one in the picture below, was at least planted along the contour of the slope instead of up and down it. I did watch the field get ploughed, though, and it was ploughed up and down the slope before planting. Possibly that contributed to these gullies forming when it rained:
This slope kind of sloughed off in the rain, so you can see the roots of the plants that are exposed where the soil went away:
What can a person do to avoid these kinds of problems? For one, it is good to leave grass or other plants growing around the edges of the field to keep soil and water from running off the field.
Planting along the line of the slope (on the contour) rather than against it also helps catch water and soil. Some people even plant lines of grass or trees at intervals along a slope, or make terraces so there isn't such a long, steep slope for water to rush down when it rains.
And, practices from conservation agriculture, like keeping the soil covered (by mulch or living plants), helps prevent erosion, as does minimum or non-tillage.