Dissecting the complexities of ammonia emissions may be as easy as milking profit from a realizer, but it could go a long way toward helping feedlots keep pace with tougher water and air quality standards.
"Ammonia itself is not a regulated pollutant, but we do use the atmosphere as a sink for ammonia when we build lagoons and apply manure to farmland, and it's not likely that will be sustainable for the future," says Brent Auvermann, assistant professor of agricultural engineering at Texas A&M University (TAMU).
Specifically, Andy Cole, a research animal scientist at the USDA Agricultural Research Service (ARS) Conservation and Production Research Laboratory in Bushland, TX, explains, "Ammonia emissions are a challenge in the feedlot from two perspectives." First, he says, data from USDA's Meat Animal Research Center (MARC) suggests 50-60% of all nitrogen fed in the feedlot is lost to the atmosphere. "So, when we scrape manure out of the feedlot pen, it's much lower in nitrogen than it ought to be," says Cole.
Rather than the manure containing the 5:1 nitrogen-to-phosphorous ratio required of most plants, Cole explains it winds up being 1:1. In states where nutrient management requires phosphorous-based application of manure to land that means more land is required to spread the manure, besides making it less valuable as a fertilizer.
Incidentally, although ammonia is often perceived as a chief contributor to the feedlot odors some folks might consider unpleasant, both researchers point out its role is minor compared to other trace gases.
The Dust Problem "The second challenge is the concern about nitrogen in the air and its effect on the health of humans and livestock," says Cole. This is where the track starts to get slippery, for more reasons than the fact that nitrogen can move around through the air and water.
"Ammonia is known to be a precursor to the production of PM 2.5 (particulate matter of 2.5 microns or less)," says Auvermann. He explains stricter air quality standards implemented the past two years take aim at PM 10 and the smaller PM 2.5 dust that can be created when ammonia emissions combine with oxides of nitrogen and sulfur, which are byproducts of combustion.
Keep in mind, this is dust you can't see. For perspective, Ben Weinheimer, regulatory manager for the Texas Cattle Feeders Association (TCFA), explains that a human hair is 70 microns wide and the human eye can only see things as small as 40-50 microns. At 2.5 microns, you can't see the dust but you can ingest it into your lungs.
"There are new ambient air quality standards for PM 2.5. If regional monitoring discovers these regulations aren't being met, those regions will be forced to implement PM 2.5 reduction plans," says Auvermann. "To the extent livestock agriculture is fingered as a source of PM 2.5, livestock operations could conceivably be required to reduce ammonia emissions. These types of requirements are pretty far down the road, but we need to be prepared for them."
Current Reality As it is, the state of Washington already set a precedent for feedlots being considered major pollution sources and liable for penalty fees. "Traditionally, fugitive emissions (such as dust from feedlot corrals) have not been included when regulators determine major pollution sources, but now they have that authority," says Auvermann.
Auvermann explains, feedlots contributing 100 tons or more of particulate to the air, including PM 10 can be liable to pay a $30 emissions fee per ton. "Feedlots as small as 8,000 head would be considered a major source," says Auvermann. "If you believe EPA's numbers, and we think their numbers are too high, a 50,000-head feedyard would produce about 600 tons of PM 10 each year." Or about $18,000 worth of emission fees.
What's more, Auvermann says regulators are re-interpreting ambient air quality standards. It used to be as long as the air surrounding a feedlot measured up, things were fine. Now, in general terms, they're starting to say the air at the property line has to be as clean as it is miles from the property line.
Bottom line, Auvermann explains, "Permits for livestock operations could be held up or not renewed because computer modeling shows that air quality at the property line of a feedlot doesn't meet the same standards imposed on large cities." In fact, he says, a cotton gin in the Southwest was denied a permit last year on these grounds.
Clearing The Air That's one reason TCFA helped fund a current ammonia emissions study being conducted by ARS, TAMU and West Texas A&M University (WTAMU).
"Because ambient air quality standards continue to change, regarding total suspended particulates of 10 and 2.5 microns, we believe it's important we have available to us the best science when we enter the rule-making process," says Weinheimer.
"We're trying to get a jump on those things and help feedlots find solutions to these regulations," says David Parker, assistant professor of environmental science at WTAMU. He explains, "The study looks at using different chemical amendments that could be added to the feedlot surface, which could reduce ammonia emissions." Chances are these chemicals either would be spread across the feedlot surface or mixed with water and sprayed on the pen floor.
At least in laboratory-scale experiments, research efforts have proven successful, reducing ammonia emissions by as much as 75% using calcium chloride (Table 1). Unfortunately, they peg the cost at $2-4/head, obviously not economically practical. So far, urease inhibitors show the greatest cost-to-benefit promise, reducing emissions 60-65% at a cost of 12-25 cents/head.
"I think these urease inhibitors have some of the best potential because most of the ammonia in a feedlot is created by urea in the urine," says Vince Varel, a MARC research microbiologist who helped develop them. He explains as much as 70% of the nitrogen excreted by animals is in the urine.
But chemical amendments are still an unknown distance from perfection. "If we do find an economic chemical amendment solution, the next question is if we put it on the feedlot surface, what will it do to the cattle themselves, if anything?" asks Parker. "And, what will it do to the environment if we apply this to a pen, then scrape the manure and apply it to farmland?"
Even if a safe and cost-effective chemical amendment eludes scientists, Parker says that knowledge is valuable in itself. It could help prove to regulators that what they want cannot be achieved without driving the cost of production through the roof.
Cole also has been aiming for reduced emissions at the feedbunk. As an example, he says, "Through different feeding strategies we're trying to trick the animal's system into recycling more nitrogen from the lower gut back to the rumen so we can use less nitrogen in the feed, and more of it will be excreted as feces (instead of urine)."
Management Still Key While researchers ferret out these and other answers, Auvermann points out common management practices can help reduce dust and ammonia emissions.
First, Auvermann says, "In the long-run, I think solid set sprinklers can be an effective tool for controlling dust." While he says the sprinkler systems are less expensive when installed as part of new construction rather than retro-fitted to existing pens, the cost of operation runs 30-50 cents/head marketed.
As well, Auvermann explains, "Today, manure harvesting is one way to increase the value of manure and reduce dust emissions by keeping the manure base moist and firm. One way to do that is to harvest the manure frequently so it is less likely to become dry and loose." He believes harvesting pens every two weeks would accomplish that reasonably well.
Plus, Auvermann points out, maintaining a 4% grade in pens for drainage and taking care not to gouge holes in the pen when harvesting manure helps prevent the anaerobic environment that spawns ammonia.
Looking outside the pens, Auvermann says some feedlots are using petroleum and resin-based sealers to reduce dust from the caliche roads in and around the feedlot. "Another approach we're looking at is higher stocking density in the pens," says Auvermann. The notion is that the urine from more cattle in less space can help keep the dust down. The method can't keep pace with the evaporative demands of summertime heat, but in certain parts of the country, at certain times of the year, stocking density can play a role in dust suppressions, he says.
Moreover, there is a silver lining to these efforts. Auvermann says, "Manure quality and air quality are closely related. The same management techniques that increase manure quality also improve air quality."