New and improved manure
If a liquid manure system eliminated agitation, saved fuel, increased manure value and created safer working conditions by eliminating deadly gases, would farmers be willing to try it?
Farmers in Ireland tried it and liked it, and now farmers in the U.S. can benefit from a manure management system based on continuous aeration.
Grant Troop, Certified Crop Advisor based in Oxford, PA, helps farmers improve soil structure and crop yields through the diligent use of manure. Odor management, soil health, nutrient management and watershed protection are all important aspects. A system that involves continuous aeration improves manure value and creates a safer working environment.
The system Troop explains is almost too simple: an electric motor powers a blower pump that powers rotary valves, pushing air through non-return outlet valves. Air is pulled into the pump, creating a high-volume/low-pressure air supply that’s distributed through a series of manifolds and outlet valves. Air from the outlet valves mixes, moves and aerates manure in the lagoon and maintains it in a mixed state through the action of rising air bubbles. The fully automated system operates on a timer and runs three to four times a day.
“Toxic gases are all oxidized out of the system,” Troop explained. “People ask me, ‘Doesn’t the action of aerating force the hydrogen sulfide and methane out?’ but the chemistry behind putting air through is that it oxidizes the compounds in manure. Manure issues come from reduced compounds: hydrogen sulfide is reduced sulfur; methane is reduced carbon. What makes manure stink and causes neighbor issues are reduced compounds generated from organic matter rotting in an oxygen-starved environment.”
In the system, the pipes in the manure are long lifespan uPVC (unplasticized polyvinyl chloride) manufactured under high pressure. At the end of each pipe is a soft rubber flap valve where air exits without allowing manure to enter.
“The weight of the manure seals it off,” Troop said. “There’s no backflushing. A little bit of air causes a lot of turbulence, which is what we’re looking for. It’s stirring and mixing to keep everything homogenized.”
The system is suitable on livestock farms that use organic bedding. Materials such as sand or limestone can’t be broken down by microbes in storage. However, gypsum (hydrated calcium sulfate) bedding will break down in the manure solution.
Gypsum can present a serious health risk in a traditional pit because it increases sulfur content in manure, but with continuous aeration, sulfur is oxidized and the risk is greatly reduced.
A continuous aeration system can be installed with a new build or retrofitted in an existing pit or tank. Manure storage with a concrete bottom is ideal but the system can be installed in lined lagoons.
Aeration results in a significant increase in manure microbial populations. In anaerobic (lacking oxygen) pit manure, some microbes struggle to survive. With the large volume of air injected in continuous aeration, more of the aerobic microbes thrive, quickly breaking down solids and liquifying the manure much faster.
After the pit is emptied, Troop advised leaving some manure in the bottom for a “starter” microbial population to initiate microbial breakdown as more manure is added.
“Manure is homogenized from top to bottom,” said Troop. “It’s that way all the time. If farmers want to topdress hay or alfalfa fields, the challenge is doing it quickly after cutting so there isn’t a lot of regrowth. Scheduling can be an issue because with regular pit manure an agitator must be present, then someone hauls manure to the field. Continuous aeration leaves manure field-ready at all times. If you cut and bale hay, manure can be spread as a fertilizer source immediately.”
The nutrient value in most traditional pit manure is variable among loads, and even with extended agitation, it isn’t always fully homogenized. Continuous aeration allows farmers to apply manure with consistent nutrient value that remains the same from the first load to the last.
Safety is one of the reasons farmers in Ireland and other European countries are willing to try continuous aeration. Although all farmers are aware that hydrogen sulfide is deadly, there are still numerous incidents every year resulting in deaths from this manure gas.
“When it’s running, oxygen is added to the system,” Troop said. “It’s oxidizing the sulfur so it’s sulfite sulfur, and oxidizing methane so the microbes use the carbon. When there’s a tremendous increase in microbial population in manure, they use the carbon and nitrogen.”
Advantages of continuous aeration go beyond safety and efficiency. Manure is pumpable, spreadable and ready to go year-round. There’s no need for an additional tractor for agitation because the manure is constantly aerated. Farmers using aerated manure have reduced the need for fertilizer by up to 50%. Fuel costs are lower because no fuel is used for agitation and the aerated manure is easier to pump than slurry.
Troop said farmers can have a more balanced fertility program with aerated manure, and most can expect a 15% increase in grass regrowth on hay fields. When spread on growing crops, those crops have improved regrowth rate because the manure is fully homogenized and highly spreadable.
“In high animal ag areas, we are capped out on phosphorus levels,” Troop said. “We want as much nitrogen in manure because there’s a lower application rate. With regular pit manure, ammonium nitrogen has to be broken down and eventually oxidized to nitrate, so starting with ammonium is much more efficient.”
There’s at least a 40% reduction in methane levels around the pit, and because there’s no crust on top of the storage, fly breeding habitat is eliminated.
Based on the added value of applied manure and less nitrogen brought to the farm, the return on investment is four to six years. Some states, including Pennsylvania and New York, offer funding assistance for manure systems.
For more information on manure aeration, visit dp1973.com/smart-slurry-aeration-system.
by Sally Colby
