We know how vital moisture is, and the recent drought drove home soil aggregates’ key role in storing soil moisture more efficiently.

Underground highways, or pore spaces, are also vital storehouses of moisture. Organic matter (OM) evens out soil’s water distribution for future access and reduces ponding. Research by USDA-SCS Soil Scientist Beman Hudson correlates soil’s available water-holding capacity more closely with OM content than any other soil property. As soil OM increases from 1% to 3%, its available water-holding capacity doubles, regardless of soil texture.

Soil OM content has more of a “pronounced effect on water-holding capacity” than previously realized. For example, the available water-holding capacity of a silt loam with 4% OM by weight (about 15% by volume) was more than twice that of a silt loam containing 1%OM by weight in his research. The surface layers of most cultivated soils in the U.S. contain from 1to 6% OM by weight. For every 1% increase in soil OM, water-holding capacity increased by 3.2 times that much, Hudson concludes. “Organic matter’s pronounced effect on soil available water-holding capacity suggests that soil OM’s a key factor in agricultural productivity.”

At today’s fertilizer prices, each 1% of soil OM provides $750/acre of soil nutrients…free, according to Jim Hoorman, Ohio Extension assistant professor, cover crops and water quality.

Your “soil factory” needs as much continuous soil cover as possible, because those living roots provide food for soil microbes. That food is carbon. This complex system banks a lot of carbon in your soil, the key to soil fertility.

Soil pore spaces are also vital pathways for soil carbon, the major feedstock for soil microbes. During the growing season, 10-35% of the total soil carbon is provided by crops fromroot material, microorganism wastes and other soluble products (Juma, 1993).

Each plant species provides different nutrients to different soil organisms because each plant species has a different carbon-to-nitrogen ratio. This is the rationale behind cover-crop cocktails, which diversify the aboveground species to expand underground.

“This interplay of the biological, physical and chemical soil components continues unless altered by tillage,” Nichols says. Tillage reduces your bank of soil carbon and destroys soil highways.

Another benefit of soil cover is reduced soil temperature on hot summer days. In the scorching summer of 2006, uncovered soil near Mandan, N.D. registered 107.4 degrees F, versus 87.6 degrees, Nichols says. “High soil temperatures kill soil microbes and reduce your nutrient supply.”