The state soil conservation field staff of USDA's Natural Resources Conservation Service in Iowa is discouraging farmers from doing fall tillage. "There is a lot of unnecessary tillage done in the fall," says Barb Stewart, state agronomist for NRCS in Iowa. "Unless you like wasting fuel or destroying good soil structure, I'd ask you to do something else this fall and leave that crop residue alone so that it will protect the soil quality characteristics you've built over the last year."
Whether landowners planted corn or beans in 2007, leaving crop residue on the soil surface over winter is a valuable contribution to the quality of the soil and the erosion protection available on the farm. For landowners committed to a no-till operation, reduced-tillage or any conservation tillage system, resisting the urge to till saves money and offers other environmental benefits.
"It means fewer trips across the field, less wear and tear on equipment, better soil erosion control, improved soil quality, wildlife habitat establishment and water quality enhancement - just to name a few," notes Stewart.
Be careful with fall nitrogen application
Some farmers are convinced they must apply nitrogen in the fall instead of waiting until spring to do that job. Stewart urges farmers to delay nitrogen application until soils are cooler. Applying nitrogen to warm soils creates a high potential for losses to occur and then the nitrogen isn't available next year to the following corn crop. Part of the nitrogen lost can leach into the groundwater or be drained from the field through tile lines.
"Nitrogen loss represents an economic loss to farmers and is detrimental to water quality at the same time," says Stewart. According to ISU Extension guidelines, applications of anhydrous ammonia should not start until mid-day soil temperatures, at a 4-inch depth, are below 50 degrees F and trending lower.
Historically, soil temperatures at a 4-inch depth cool below 50 degrees in the northern third of the state during the first week of November. In central and southern Iowa, soil temperatures cool below 50 degrees during the second and third weeks of November, says ISU Extension soil fertility specialist John Sawyer.
"Cooler soil temperatures slow biological activity," says Stewart, "allowing nitrogen to stay in the ammonium form longer. Then it has a better chance of being retained in the soil. Don't be tempted to apply nitrogen too early in the fall. Better yet, apply your N in the spring instead of the fall. Losses can occur in the spring, too, but there's less risk of loss with spring application or sidedressing."