Building Soils for Better Crops, Third Edition

Active Organic Matter

SARE Outreach
Fred Magdoff and Harold van Es | 2010 | 294 pages
PDF (6.8 MB)

This title is temporarily out of print. We expect to publish an updated edition in the spring/summer of 2021.

Most of the discussion in this chapter so far has been about the factors that control the quantity and location of total organic matter in soils. However, we should keep in mind that we are also interested in balancing the different types of organic matter in soils—the living, the dead (active), and the very dead (humus). We don’t want just a lot of humus in soil, we also want a lot of active organic matter to provide nutrients and aggregating glues when it decomposes. It also supplies food to keep a diverse population of organisms present. As mentioned earlier, when forest or grassland soils were first cultivated, organic matter decreased rapidly. Almost the entire decline in organic matter was due to a loss of the active (“dead”) part of the organic matter. Although it decreases fastest when intensive tillage is used, the active portion increases relatively quickly when practices such as reduced tillage, rotations, cover crops, and applying manures and composts are used to increase soil organic matter.