The interface between the soil surface and the atmosphere above it is a critical juncture, and numerous measurements have shown that 60% of plant roots are within 4 inches of this critical zone.

Raindrops strike this area with the force of little bombs, exploding the soil surface into tiny particles that then plug the porosity of the interface, and stop air and water from crossing. If this wasn’t bad enough, most tillage systems are designed to pulverize the soil surface to kill weeds and to provide a fine seed-soil contact for rapid germination.

This makes the soil skin more susceptible to sealing of the surface pores. Except for semi-aquatic plants, oxygen at the root surface is critical for roots to use plant energy to grow and absorb nutrients. Air moves through the pores in the soil unless those pores are plugged. The water that can’t get in cannot be used by the crop to produce yield.

Adding insult to injury, the water that cannot penetrate will run off, taking the small, most fertile and productive soil particles loosened by the raindrops with it, leaving behind stones, and compacted lumps and subsoil.

Broadcast fertilizer applied to the surface can be lost if the initial rainfall comes too fast and the surface is sealed before it is absorbed. Perhaps the most egregious loss is that of surface-applied manure. It is easily entrained in water as floating lumps in bedded pack or as fine particles in liquid-applied manure.

This removes expensive fertilizer that you paid for when you grew the crops and shorts the crop it was applied. The final blow is that the runoff water becomes polluted with nutrients, helping to create algae blooms and deteriorating water quality.

Even if you are not directly concerned about this latter factor, you should be because of the dollars leaving your field in the form of nutrients.

Preserving worms

Any steps you take to protect the soil surface also protect one of its most important modifiers: earthworms. Worms drill air and water holes from the surface down into the soil. “Nightcrawlers” are one of the most important as they leave holes a quarter inch in diameter. We have measured them to continuously go 3 to 4 feet deep; alfalfa roots followed the holes down into the soil.

Not only do worms leave holes, but their castings (manure) leave a very stable soil structure on the surface, protecting the hole and keeping it open.

In one of our corn trials planted no-till on fall-killed sod — in a 4-foot-by-12-foot area — there was a worm hole every 6 inches. In the portion of the field that had one pass of a mole board plow, there were only two worms left in the same total area.

Protecting your soils

The good news is that there are clear management steps developed over the past 40 years that can greatly reduce the losses and increase the porosity of the soil skin. No-till and strip-till systems have clearly shown that this surface destruction is not necessary for high yields. A coulter or set of coulters, or a surface-clearing coulter, will work a thin zone where the corn can be planted with good seed-soil contact for rapid emergence.

The first step is to keep some type of residue on the surface year-round. Profitable farmers no longer leave their soil bare over winter. A cover crop or winter forage will provide surface protection in the offseason, so long as when it is removed or killed, the stubble residue remains on the surface.

SEALED SOIL: In this NRCS demonstration, the unprotected tilled soil surface only absorbed water 1 inch deep.

Thousands of acres are now protected as farmers have learned that they can grow a profitable triticale winter forage that acts like a cover crop on steroids, simultaneously protecting and enhancing the porosity of the soil surface.

Legumes such as soybeans, alfalfa and clover can be planted without any tillage as they are not affected by allelopathy. In fact, in New York, our best seedings have been no-tilled into triticale stubble in early June after haylage is finished.

The benefit extends for most of the season after winter forage is harvested if a no-till or narrow zone strip-till is used for the next row crop. This narrow strip breaks any allelopathic layer for the next crop. In addition to optimizing corn soil porosity, the critical inter-row is kept in winter forage stubble and massive root system. Anyone who has made the mistake of chisel-plowing or disking a good winter forage has learned, to their regret, of the huge root system under these crops.

Both the surface stubble and roots protect the soil surface. The bonus is that each stubble piece is connected to a root system. As the stubble dies, it leaves a hole protected by a surface stem that captures and channels water and air to rapidly move in the soil along the decaying winter forage root.

Planting green

For farms without livestock, more farmers are “planting green” where they directly plant into a living cover crop and then kill it afterwards. The resulting residue protects the soil surface. For farms that just grow grains, this has become a viable replacement for the above-harvested winter forage system.

Care must be taken to avoid “hair pinning” the residue in the slot with the seed. Planting deeper — 2 inches or more — can help alleviate that issue. The second concern with planting green is slug damage. A win-win option is for the grain farmer to sell the winter forage to a neighboring livestock farmer and then plant into the stubble without the above issues.

For farms with livestock, a harvested winter forage provides a profitable, high-quality forage and a protective surface cover for the soil.

Sign up for manure seminar

Manure management has a critical role on today’s farm. Register for an online manure seminar March 2, which will be led by Quirine Ketterings of Cornell University. Visit cornell.zoom.us.

Kilcer is a certified crop adviser in Rutledge, Tenn., formerly of Kinderhook, N.Y.