Ammonia Nitrogen Loss Studied at Dairy Research Center

By Ron Johnson, Dairy Editor
Thursday, September 13, 2007 7:37 AM CDT

To trim ammonia losses into the air, the general advice is to incorporate manure as soon as possible. But do that and what happens in the soil?

Does more ammonia nitrogen end up running off during the next rain? Does more of it end up leaching out of the crop’s root zone and ending up in groundwater?

Those are questions researchers at the USDA Dairy Forage Research Center are investigating. Bill Jokela, a soil scientist at the center, talked about this ongoing research during the recent Upper Midwest Manure Handling Expo at Prairie du Sac.

Jokela reminded his audience of manure applicators and farmers that the ammonia nitrogen in manure is readily available to plants, while the organic portion is released over time. And, some nitrogen volatilizes, or escapes into the air, while some also stays in the soil, some is prone to leaching, and some can run off.

But why care about ammonia losses anyway? First, the soil scientist explained, lost ammonia nitrogen is lost crop nutrients.

Second, lost nitrogen alters the nitrogen to phosphorus ratio in manure. That means that if a farm’s manure applications are being managed for nitrogen, phosphorus can build up in the soil. Conversely, if manure applications are being managed for phosphorus levels, nitrogen will need to be purchased.

A third reason to care about ammonia losses is what the nutrient can do to lakes and streams. Excess amounts can cause eutrophication - an excess of plant growth resulting in low levels of dissolved oxygen.

Then there’s the air quality component. Ammonia in the atmosphere has been linked to smog.

Jokela cited a study from the United Kingdom showing that most ammonia that escapes into the air from farms comes from land applications of manure. Fully 50 percent was found to stem from land applications, he said, with 28 percent emanating from barns, 17 percent coming from manure storage structures, and 5 percent due to cattle grazing.

Farmers and manure applicators have long been told that there are three main ways to trim ammonia nitrogen losses. One, noted Jokela, is to simply match the amount of manure applied - and at the same time the nutrients in it - to the needs of crop.

Another way is to time the manure application for the soil type, soil conditions, weather, and time of year. Little or no manure applied on wet ground, little or none applied to frozen ground, for example.

A third way to manage manure applications to reduce ammonia losses is to cover the manure with soil right away. This can mean tilling the soil soon after the application, or injecting the manure right into the ground.

Ammonia loss measured

Jokela went on to talk about the research he and colleagues at the dairy forage research center are doing. He explained that the pattern of ammonia loss is highest right after a manure application.

It can hit nine to 10 pounds an hour, then fall and level off. Because of this high ammonia nitrogen loss right away, incorporation has long been recommended.

But, as noted earlier, that brings up a couple of new questions. Since less ammonia is lost into the air, that means more of it is in the ground, where it could leach or run off.

Does that actually happen? If it does, what conditions are needed for it to happen?

Those are complicated questions. Right now, the dairy forage research center scientists are seeking answers to just one aspect. They’re trying to find out what happens to ammonia losses when corn for silage is grown. Furthermore, they’re looking at no-till silage corn.

The ground involved in this study grew a cover crop of rye, Jokela explained. First they killed the rye. Then they applied 1,600 gallons of liquid dairy manure per acre.

Next they made three comparisons. In the first one, the manure was simply applied to the soil surface. In the next one, it was surface applied using a machine called an Aerway that provided partial incorporation. For the third method the manure was shallowly injected, then covered.

Then they measured the amount of ammonia entering the air and the amount leaching through the soil. A device called a “rainfall simulator” provided the water for the leaching aspect.

Jokela emphasized that the results so far are only preliminary. The study is in its fourth year.

Conclusions mixed

So far, they’ve arrived at mixed conclusions.

During the first year of the study, they found that - as might be expected - ammonia losses were greatest from the area that received a simple broadcast application of manure. Applying it with the Aerway produced less ammonia loss, while injecting it produced even less.

But during the second year of the study, applying manure with the Aerway produced the least amount of lost ammonia. Jokela admitted that they’re still trying to figure out why that happened.

Last year - the study’s third year - yielded the same results as the first year did. The broadcast application lost the most ammonia, followed by the Aerway application, followed by injecting.

The soil scientist was asked about corn silage yields each year. He answered that there was “not much” difference during the first year. But applying manure via the Aerway machine and injecting it both presented a “slight (yield) increase” during the second year.

Phosphorus

Jokela wrapped up by mentioning that USDA Forage Research Center scientists are also measuring the amount of phosphorus that is running off these test fields. So far, he said, there’s “not much” to report.

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