I agree with Mary that it can he necessary to add compost. I think that compost is what made my garden soils deep and black, and now they’re still deep and black every year ehen in patches where no compost is added. I also let weeds grow where perennials aren’t established, so no ground is bare for long.
Also, grasses are very good fertility-creating and preserving plants. They let you keep soil on the land better than any other sort of plant except trees.
I am suspicious, however, of importing fertility from elsewhere because I think at a landscape scale. Of course, if it’s a waste product like sawdust or bagged leaves, that can be a very helpful source.
It would be interesting to hear what people think of the difference between mulching (dry decomposition) versus piling together as a compost heap or in the digestive system of animals (wet decomposition). I have a suspicion that the more effective option for soil improvement is the wet decomposition in an appropriate microclimate with food scraps, humanure, etc., and then working that into the soil—as it seems like it would mimic best the way that grassland ecosystems are supposed to build their excellent soils.
