Summer 1998
Incorporate manure to reduce odor and maintain residue cover
by Mark Hanna, extension agricultural and biosystems engineer
Livestock producers who prefer incorporating manure often must balance their decisions with destroying residue cover, slowing field application, and using more tractor horsepower. While the benefit is reduced odor and limited nutrient losses, the decision is often a difficult one.
Iowa State University ag engineers have been conducting field experiments in both no-till soybean and corn residue to evaluate the effects of six liquid swine manure application methods on odor and residue cover retention.
The researchers recommend avoiding broadcast application if odor is the primary concern. Most methods involving some soil incorporation reduce odor levels to a fraction of the broadcast level. Odor levels decline over time and become indistinguishable from the odor of untreated soil.
The treatments in the field experiments include four commercial methods: injection with a two-inch-wide knife, injection with a 16-inch-wide sweep, surface broadcast application, and broadcast application with disk incorporation.
One alternate method, row cleaner, applies manure under surface residue and on the soil surface. This is accomplished by moving residue from a narrow strip with a row cleaner, applying manure in a narrow surface band, and then returning residue over the band with closing wheels. A second alternate method, narrow knife, injects manure in a shallow band behind a narrow-profile knife designed to minimize soil disturbance. The row cleaner and all injection treatments use finger-closing wheels.
Each treatment is tested both in the fall and in the spring. In addition to measuring residue cover, air samples over the soil surface are obtained both during application and one day later for evaluation by an odor panel.
Results thus far indicate that incorporation techniques typically reduce odor level by 20 percent to 90 percent, compared to broadcast application. One day after application, odor is greatly reduced and often indistinguishable from that of untreated soil.
The choice of a manure application method in soybean residue is more critical to maintaining cover than the choice of a method in corn residue.
In
soybean residue, the narrow knife and row cleaner methods have shown better
retention of residue cover than other incorporation treatments. The odor
they emit is comparable to commercial incorporation treatments. Among
the commercial incorporation techniques of knife, sweep, and disk incorporation,
the knife leaves more residue cover, with very little increase in odor
compared to the incorporation with sweep or tandem disk.
In corn residue, the sweep treatment leaves less cover than other incorporation treatments immediately after application. After planting, residue cover in the row cleaner and conventional knife treatments has been greater than other incorporation treatments. The tandem disk, knife, and sweep methods produce less odor than broadcast application.
Residue coverage and odor emission from the two alternative treatments do not seem to differ as much from other incorporation treatments in corn residue. Broadcast application has maintained the greatest residue cover in both crops, but has the highest odor levels. Although greater residue cover has been maintained with fall-applied treatments, cover is reduced by this application strategy during the winter and early spring.
