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Ju
ne, 1999One of the new methods for controlling odors from earthen manure storages is to create a cover by blowing a 12-inch depth of straw on the liquid surface during late spring. During the summer of 1998, straw was applied to six demonstration sites in southern Minnesota. One observation was a distinct reduction in odor from the storages after the straw was applied. The straw cover reduces odor release by providing a physical barrier between the liquid surface and the air. Within the straw mat that forms, a biologically active zone develops that is well aerated and is inhabited by aerobic organisms that consume odorous gases and release low-odor by-products. The light colored straw also reflects sunlight and acts as an insulator to the liquid. This tends to slow biological activity within the manure and somewhat reduces odorous gas production.
In the Minnesota experiment, the length of time the straw covers remained intact and functioning ranged from 1½ to 5 months. An 11-inch rainfall caused the cover that lasted 1½ months to become totally saturated and to sink prematurely. The remaining storages remained functional for 3 to 5 months. By fall, the straw became decomposed, the storage was agitated and the manure was removed with a chopper pump.
The straw cover is created with either wheat or barley straw. While earlier research in Canada indicated that barley straw was superior to wheat straw, the Minnesota experiment indicated both functioned equally well. A depth of 12-inch seems to be the minimum depth to prevent winds from creating openings in the straw cover. This requires approximately 100 large round bales (800 to 1100 lbs.) per acre of liquid surface or approximately 2200 lbs. of straw per 1000 square feet of liquid surface. The cost for the straw ranges from 5 to 10 cents per square foot per year or $2200 to $4400 per acre of liquid surface per year.
Using long stems of straw helps maintain the integrity of the straw cover. The straw is applied to the liquid surface with a tub grinder equipped with a blower. During the season there are likely to be patches of straw that sink. Additional straw should be applied at these locations. Plan to apply additional straw (20% of the original amount) for maintenance.
Howard Person
