March 27, 2009

If you didn't get a chance to repair field gullies last fall, repairing them now, before April rains come, can help reduce further erosion and maintain farmability.

Field machines will be able to safely cross gullies that have been filled in and shaped appropriately. Unless fill soil is firmed into the gully and anchored, it's likely to wash away with next heavy rain, down to the depth of tillage.

Fall Gully Repair Preferable

Figure 1. After harvest, the gully was filled and shaped and a single pass of a drill was used to seed cereal rye on this concentrated flow area. Shown the next spring, the growing rye roots and the vegetative cover helps anchor the soil and dissipate the energy of the flowing water when the next rainfall event occurs.

Figure 2. With soybeans, the cover crop stabilizing the soil in the flow areas can be killed with the first postemerge spraying. This allows more growth of the cover crop and better protection of the soil, especially when using oats seeded in the spring as the cover crop.

Gullies should be repaired in the fall after harvest when the soil tends to be drier than in the spring. Producers should avoid using wide tillage tools as they destroy too much residue cover and loosen too much soil. Consider using a center pivot track filler or a rear-mounted blade to fill in and shape the gully and perhaps a harrow to smooth the soil. Pack the fill soil into the gully and drill a cover crop to protect the soil. The drill openers also will aid in packing and smoothing the soil.

Depending on the amount of soil disturbed when filling the gully, a single pass of the drill may be all that's needed, reducing seeding costs. Cereal rye, winter barley, or wheat will provide some fall growth to anchor the soil. When spring arrives, they'll continue growing, providing more root mass and additional residue cover. By the time the spring storms come in April, the soil should be fairly well protected and anchored.

Producers need to look at the long range weather forecasts when determining when to kill the cover crop and balance the need for cover versus the need to conserve or use water. These small grain cover crops should be sprayed two to three weeks before planting corn to avoid potential germination injury. As the green plants die, they suppress other grass species, a form of biological weed control used by some organic producers. If the plants are fairly brown when planting the corn, the chances of injury are greatly reduced. For soybeans, the cover crops could be killed anytime, even with the first post emergence spraying if additional cover is needed.

Spring Gully Repair

If you didn't get a chance to repair gullies last fall, make spring repairs as soon as conditions allow, before the erosion-causing spring rains. Fill and pack the soil into the gully and establish a cover crop like oats to anchor the soil. Oats, drilled in March, provide fairly quick growth and biomass to protect the soil. Also, oats won't use much soil moisture if they're killed before planting the spring crop. If you're planting a Roundup Ready® crop and it looks like it will be a wet spring, kill the cover crop after planting the crop. This allow the cover crop to grow for a longer time, creating more biomass and using some excess soil moisture.

Monitor and Repair as Necessary

These repaired areas should be monitored this growing season. Some additional filling and shaping may be required after harvest to better protect the soil. A fall-seeded cover crop should be used again to protect and anchor the soil. With root masses in place the year around, many gullies are stabilized and some smaller ones even become self-healing. Fall-seeded cover crops provide more growth and better protection than spring-seeded cover crops. With the additional growth, the cover crop can be killed earlier in the spring to conserve water for the regular crop.

Paul Jasa
Extension Engineer