Organic matter is the key factor for soil quality and fertility. It relates to chemical, physic and biological soil quality. According to the chemical soil quality, nutrients can be bound on and released by soil organic matter.
Organic matter has a low density. This makes it of high importance when it comes to soil structure (physic soil quality): it gives the soil a lighter structure in which roots can develop more easily and the soil is less susceptible to soil compaction. Organic matter also gives the soil spongy properties. This means there is a better water infiltration by a soil with high organic matter content, which leads to less puddles on the field and less run-off. In this way the organic matter reduces water pollution. But the water is also better stored which makes it longer available for the crop in dry periods. As the last part of the physic soil quality, organic matter leads to better forming of granules, which are less susceptible to erosion, both from wind and water, and soil sealing.
Finally organic matter plays a key role in the soil food web. On the one hand larger animals, like worms, are important in the forming of organic matter, on the other hand the organic matter itself is food for the microbial soil life. A good balance in soil life makes the soil less sensitive for pests and diseases. Therefore organic matter input can be beneficial for natural pest control.