The primary source of organic matter is plants, although animals and the uncountable microorganisms also contribute. Whan organic matter decomposes, important nutrients are supplied to plants, as well as to animals and microorganisms living in the soil.Consequently, soil fertility depends in part on the amount of organic matter present. Furthermore, the decay of plant and animal remains causes the formation various organic acids. These conplex acids hasten the weathering process. Organic matter also has a high water holding ability and thus aids water retention in a soil.