Building Fertile Soil

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PERMANENT BEDS AND NO-TILL

Every time the soil is tilled, surface-layer organisms are buried, threads of beneficial fungi are broken and earthworm tunnels are destroyed. Steve Diver, an agriculture specialist with National Sustainable Agriculture Information Service (ATTRA), says plowing can bury plant debris and topsoil up to 14 inches deep—where oxygen levels are too low for decomposition.

The buried debris then acts as a physical barrier to the movement of water upward and downward. Tilling or plowing also introduces excess oxygen that causes organic matter to decay too fast, and tilling causes plants to give off more carbon dioxide, contributing to global climate change.

"Even if you cultivate only 2 to 3 inches deep," says Weil, "more damage is done than good." Worm channels and root paths that facilitate water absorption are destroyed, and soil clumps or aggregates are broken up, leaving little air space in the top layer. Then, raindrops pound on the soil particles, pushing them even closer together, creating an impenetrable, crusty surface.

Weil says good garden soil should be about half porous space occupied by air and water. Compacted soil, created by rainfall on bare ground and the use of heavy equip ment or repeated walking upon the ground, has much less space for air and water. That's a recipe for crop failure.

Weil's specialty is managing microbes on farmland, but he handles the soil food web in his home garden the same way. He makes permanent beds that are 4 feet across, so all work can be done from the sides without having to ever step on the soil.

The object is to avoid walking on the soil in the beds, or disturbing it or any plant roots in other ways. Diver says, "The roots left in the ground are food and shelter for microbes and earthworms." To incorporate compost into the soil, he suggests spreading it across the surface with a rake and covering it immediately with mulch. "The worms will move the compost into the soil."

Weil advocates a no-till/cover-crop approach to microbe management. "Start by applying a layer of compost and mulch if the soil is decent," he says. "The soil is not compacted if you can push a wire flag 12 inches into wet ground."

If the soil is severely compacted or poorly drained, build raised beds (see directions for building your own, "For Compacted Soil," below). Weil likes to begin in late summer or early fall by staking out the beds and planting a cover crop of a mixture of rye and hairy vetch.

The following spring, he uses a scythe to cut the cover crop (electric or gas-powered weed trimmers work well, too), cutting as close to the surface as he can and spreading the debris to an even thickness over the bed with a rake. [You also could let Mother Nature handle this job by using a less winter-hardy crop such as oats, which will grow strongly in the fall and die in the winter in U.S. Department of Agriculture Hardiness Zone 6 and north, and in much of Zone 7.]

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