Measures to reduce ammonia emissions in pig production
In this literature review, measures of reducing the ammonia (NH3) emissions from pig production are described, with focus on systems that can be used under Swedish conditions. The entire production chain with feed, housing, manure storage and application on the field is described and taken into consideration. However, in order to limit the study, the production of crops for feed is not included. As compared to many other countries, emissions of NH3 in Swedish pig production are already low, due to low protein levels in the feed, housing systems with a small excretory area, and storage of slurry outside the building. Lowering the crude protein level from 14.5 % to 12.5 % would reduce NH3 emission by 20 % from the pig house. Including fiber in the feed, leads to a shift from nitrogen in the urine towards more nitrogen in the faeces. In combination with removing the manure daily from the pig house, this might give opportunities for reducing NH3 emissions. A reduction in NH3 emission of up to 50 % might be possible. However, using fiber leads to higher methane (CH4) emissions (from animal and housing), and therefore this should be combined with biogas production. More research is needed in this field. Adding acids or salts to the feed could reduce NH3 emission by up to 40 %, while also improving feed conversion efficiency. Of course, good practice when preparing the feed must be followed. By applying multi-phase feeding and feeding according to the sex of the animals, NH3 emissions could be reduced by 5-15 %. By reducing feed spillage, offering a good environment for the pigs and maintaining good pig health, nitrogen losses could also be reduced with about 5 – 15 %. The importance of having clean pens is also discussed in this literature survey. Swedish housing systems, having a relatively high percentage of solid flooring (with some bedding) and a small excretory area in the pen, provides an opportunity for reducing NH3 emissions from the housing system. However, one prerequisite for this is that the pigs keep the pens clean, and therefore the room temperature should not be too high. This means that during hot periods, the air has to be conditioned before entering the pig house, e.g., by taking in the air via channels under the building. Removing manure daily by means of scrapers (reduction up to 40 %) and cooling the manure under the slats (reduction up to 50 %) are measures that are already implemented in Swedish pig production. The effect of air temperature, air flow and ventilation system are also discussed. Cleaning the exhaust air using bio-filters (up to 65 % reduction), bio-scrubbers (up to 70 % reduction) and chemical scrubbers (up to 96 % reduction) is also an option. By only purifying the exhaust air from the manure channels, the costs for this method can be reduced substantially. The emissions of CH4 and nitrous oxide (N2O) from the housing system are also discussed. Removal of the manure under the slats appears to reduce CH4 emission from the building. The use of deep-litter bedding may in many cases result in high N2O emissions. More research is needed in this field. Treating the manure with sulphuric acid, in combination with aeration and re-circulation in the pig house, can reduce NH3 emissions by up to 70 %. Pumping slurry between different compartments in a pig house is not allowed according to the Swedish Welfare Legislation. Therefore it is not certain that the acidification of slurry, inside the pig house, can be applied in Sweden. Anaerobic treatment of biogas production, as another treatment of manure, may not reduce NH3 emissions when storing and spreading the manure, but it results in increasing the nitrogen availability for the crops. In that way nitrogen losses can be reduced since less nitrogen has to be spread per hectare. Besides, biogas production reduces odour problems as well as emissions of green house gas (GHG) by the production of energy and lower CH4 emissions. Aerobic treatment of manure, can reduce the emissions of NH3 and GHG. However, poorly controlled aeration processes can have the opposite effect. Storage of slurry in a tank having a cover lid has been pointed out in many investigations, to be the easiest and most effective way of reducing NH3 and CH4 emissions. The straw used for fattening pigs is mainly consumed by the pigs, and it is rare that a naturally stable crust will be developed on the slurry. However, within piglet production a crust on the slurry tank is often found. This crust can cause problems when the slurry tank is covered. Technical solutions have to be developed to solve this problem. On pig farms, the main crops are cereals, and the slurry is mainly applied either in the spring during tillage work, or band spread in the early summer on growing cereals. Incorporation of the slurry, e.g., by harrowing in the spring, effectively reduces the NH3 losses if it takes place as soon as possible after spreading, preferably directly or at least within 4 hours after spreading. Another possibility is to band spread the slurry onto the growing cereals because the canopy provides a microclimate which reduces the NH3 losses, as compared to spreading on a bare field. Late application during the vegetation period or spreading before the autumn sowing, often results in lower nitrogen utilization by the plants, and thereby higher risks of nitrogen leakage. Due to interactions between different sources on a farm, reduction in NH3 emission from the individual sections of the livestock production system cannot be simply added to give the net reduction in emission from the total system. Thus a whole farm system approach is needed for devising control strategies for reducing NH3 emission. Four scenarios were evaluated in this report. Scenario 1 consists of: Reduction of the crude protein in the feed from 14.5 % to 12.5 %, relatively simple technique inside the pig house to reduce NH3 emission, covering the slurry tank and new technique when spreading manure. Scenario 2 consists of: Using biproducts from industry (16.5 % crude protein instead of 14.5 %) and cleaning of exhausting air, covering the slurry tank and new technique when spreading manure. Scenario 3 comprises conditions similar to those of Scenario 1, including high dietary feed fiber content in combination with biogas production. Scenario 4 comprises conditions similar to those of Scenario 2, including high dietary feed fiber content and in combination with biogas production. Preliminary calculations indicate that the scenarios may reduce emissions by 47-68 %. It should be pointed out that the calculations are still very uncertain. The calculations show that Scenario 3 appears to be the most effective way of reducing NH3 emissions. So the combination of using low protein feed with high fiber content together with the production of biogas appears to be a promising method for future development. Even Scenario 1, which used only simple techniques, has a significant result: lowering the protein content affects the entire chain from feed to the field. From the literature review, it can be concluded that one should consider whole farm systems when trying to reduce NH3 emissions. Having a roof on the manure storage, using band spreading together with incorporation, e.g. harrowing, within a few hours after spreading, are the most important and easiest ways of reducing NH3losses. When discussing the method of animal keeping, feeding and housing, a low protein level in the feed has a positive effect along the entire production chain, and appears to be the most effective means of reducing NH3 emissions. Using more fiber or acids/salts in the feed will reduce the NH3 emission even more. When biproducts from industry are used in the pig feed, cleaning the exhausting air from the manure channel may be an option. More research is needed before recommendations can be given.