1. Microbes in the soil decompose dead plants and animals and convert it into humus. This humus supplies nutrients to the soil.
2. Humus also aerates soil and holds water in it. It makes the soil more fertile.
3. If microbes are destroyed, humus will not be formed and the soil will not become fertile, making it unsuitable for growth of plants.
Also dead and decaying matter will accumulate on land.
