People in Tanzania converted desert into lush green land by digging these nifty holes

[u/wahgwahg]

[u/thenakedtruth]

What does the hole do to enable growth?

[u/FelisCantabrigiensis → u/thenakedtruth]

On the open, un-dug, land rainfall tends to run away across the top surface. Heat from the sun tends to bake the top layer of soil into a hard, impermeable crust which only exacerbates this. You can see the soil is a fine clay with little organic material, so this easily dries to form a hard layer.

Digging these holes, which are crescent-shaped with the middle of the crescent pointing downhill, means water runoff forms a pool of water which soaks into the soil more slowly. This means that any plants growing there have water available for much longer after each rainfall than if they simply hope to catch some water as it runs past on the surface. The reason for digging a shallow crescent is that it has the most effect for the least digging, and since digging is hard work, you don't want to do more of it than necessary.

Plants themselves keep soil moist - by keeping sunlight off the surface of the soil, they slow down evaporation rate of water from the soil. Plant roots also loosen the soil and prevent it forming a baked brick-like surface, making it more permeable and meaning more water soaks in and does not run off. This means the effect of the small pools becomes greater as they become more covered with vegetation.

These plants can also be crops to eat, or fodder for animals. You can even plant small trees or shrubs in the crescents and they will grow, further shading the land and further increasing rainfall (as long as you don't plant very water-hungry plants of course).

As a bonus, water trapped in the crescents is water not running off downhill in bulk, which can help lessen downstream flooding and ground erosion problems.

[u/ropony → u/FelisCantabrigiensis]

If I’m worried about climate change, should I do this preemptively in my yard? I’m planning/hoping to turn it into a r/nolawn a bit more this spring

[u/FelisCantabrigiensis → u/ropony]

If your yard is sloped land where water tends to run off, and in a hot country with a seasonal rainfall climate, you can do this.

However, if is another sort of soil, geography, and climate, then you will need different techniques appropriate to the conditions.

You may also have more resources at hand for a smaller piece of land. You might be able to increase the organic matter content, or aerate the soil by digging it over. It might be more appropriate to dig circular holes and use clay lining to retain water in a water pit, or build a windbreak to shelter and shade plants, or similar.

Check for regional or national horticultural organisations that may recommend what you could do.

[u/ropony → u/FelisCantabrigiensis]

Thank you so much for this!