It contains only microbes. You can grow your own microbes by taking care of your soil, it needs manure, and the more the grass is fertilized, the more grass grows, and the more grass, the more roots and manure, thus more grass, and so on. If grassland does not produce sufficiently it likely needs more nutrients or longer rests between grazing.
If one applies microbes to land with poor nutrient status or overgrazed land, the microbes will just starve. And if the soil and plants are fed what it needs, you have microbes naturally.