Reducing ammonia emissions

Producers can reduce the emission of NH₃ from farms in a number of ways. In general, these methods rely on absorbing NH₃ in water or acid, preventing excessive N excretion by livestock, and minimizing exposure of NH₃ sources to the air. Specific examples of control methods include the following:

Use improved methods of fertilizer application: Farmers can reduce ammonia loss from fertilizer by ensuring good contact between the applied fertilizer and moist soil. They should place urea either below the soil surface or till it into the soil immediately after applying it to the surface. Injecting anhydrous ammonia into moist soil at sufficient depth prevents it from diffusing to the surface.

Minimize nitrogen excretion from livestock: The most basic way of reducing NH₃ emission from animal wastes is to produce less manure N in the first place. Although animals cannot avoid excreting N, farmers can reduce the N content of the manure by using rations with a better N balance, by avoiding excessive N in the diet, or, possibly, by adding bacteria that help convert uric acid (a forerunner of urea) to nitrate. Use of these practices could reduce N excretion by up to 25% in cattle, pig, and broiler poultry operations. Indeed, simulation models suggest that, for Quebec conditions, better diets could reduce the N content of pig manure by up to 60%. Nitrogen excretion can also be reduced, indirectly, by using breeds of livestock, feed formulations, or other practices that improve animal performance and, hence, the product yield per unit of manure N.

Improve manure handling in the barn: Large amounts of NH₃ can be emitted in the barn when the manure is exposed to air. Farmers can minimize this exposure by removing manure frequently; washing barns with water, which absorbs NH₃; collecting liquid wastes in deep, narrow channels, to reduce surface exposure; and, in poultry barns, maintaining a deep layer of litter. As well, maintaining cool temperatures can reduce emission of gaseous NH₃. In Europe, changes in handling procedures (including diet) have reduced NH₃ release from pig barns by 45%.

Improve manure storage: Farmers can reduce ammonia loss during manure storage by minimizing exposure to air and lowering temperature. For example, applying a cover of mineral oil, straw, or peat over lagoons or tanks holding pig manure can reduce losses. Covers placed on tanks can cut NH₃ losses by two-thirds, and a thin layer of mineral oil on a slurry can reduce emissions by more than 30%. As well, adding acids to manure or covering composting manures with mildly acidic peat can minimize NH₃ loss. Ammonia is readily absorbed and held by acid, preventing escape to the atmosphere. Farmers can achieve reductions of at least 75% by using peat moss, sulfuric acid, or phosphoric acid during storage.

Use more effective application procedures: Ensuring quick and effective mixing with soil can minimize losses of NH₃ during application. For example, tillage or irrigation immediately after application drastically cuts emissions (Fig. 34). Farmers can also reduce losses by applying manure before rain, injecting slurry directly into soil, or using diluted slurry for irrigation. Where they must apply slurry to grassland, banding it on the surface, rather than spraying it, can reduce losses. Finally, since rate of gaseous loss is related to temperature, applying NH₃ in cool weather (though not on frozen soil) can curtail emission.

This list shows several ways of cutting NH₃ emissions from agriculture. Not all these are practical or even advisable in all cases. For example, incorporating manure by ploughing is not compatible with the no-till systems advocated elsewhere. Nevertheless, given the number of options available, large cuts in emissions are probably easier for NH₃ than for some of the other gases, notably N₂O. With increasing attention to health, environmental, and odor issues related to NH₃, efforts to achieve such reductions will likely increase in the future.

The Netherlands has decided that, by 2000, NH₃ emissions must be no more than half of those in 1980. There, the annual N deposition has reached 85 kg/ha in parts of the country. Though deposition rates in Canada are usually much lower, high rates of deposition may already occur in local areas of intensive livestock production.