Housed Livestock, Manure Storage, Manure Processing Draft Section for a Guidance Document

Housed livestock, manure storage, manure processing Draft section for a Guidance Document

Prepared by Barbara Amon and Lars Stoumann Jensen (session chairs)

For discussion at the workshop on integrated sustainable nitrogen management,

Brussels 30 September – 1 October 2019

This draft chapter to a planned Guidance Document on integrated sustainable nitrogen management has been prepared for the Task Force on Reactive Nitrogen under the UNECE Air Convention, with support from the European Commission. The process of drafting the Guidance Document started in connection to a workshop “Towards joined-up nitrogen guidance for air, water and climate co-benefits”, hosted in Brussels, 11-12 October 2016. The current chapter draft is based on the results from that workshop and on discussions and developments since then. It will be presented and discussed in Brussels on 30 September – 1 October at a second workshop jointly organised by the Task Force on Reactive Nitrogen and the European Commission.

The content of the draft paper reflects the views only of the authors and the European Commission cannot be held responsible for any use which may be made of the information.

Housed livestock, manure storage, manure processing

1. Introduction and background

2. Why do we have emissions and how can they be influenced – the basics behind emission processes Nitrogen can take various forms (Fig. 1). Reactive nitrogen (Nr) includes all forms of nitrogen that are biologically, photochemically, and radiatively active. Compounds of nitrogen that are - - reactive include the following: nitrous oxide (N2O), nitrate (NO3 ), nitrite (NO2 ), ammonia + (NH3), and ammonium (NH4 ). Reactive forms of nitrogen are those capable of cascading through the environment and causing an impact through smog, acid rain, biodiversity loss, etc.1. The design of mitigation measures requires a sound knowledge of the processes that influence formation and emission of ammonia (NH3), nitrous oxide (N2O) and dinitrogen (N2).

Figure 1: Forms of reactive nitrogen 1.1 Ammonia The principles of ammonia formation and its influencing factors are well known. Degradation + of nitrogen containing organic substance results in ammonium formation (NH4 ). There is an equilibrium between ammonium and ammonia: − + H2O + NH3 ⇌ OH + NH4 The degree to which ammonia forms the ammonium ion depends on the pH of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high, the equilibrium shifts to the left: the hydroxide ion abstracts a proton from the ammonium ion, generating ammonia.

1 http://www.n-print.org/node/5 3

Ammonia emissions are governed by the difference between solution and atmosphere NH3 partial pressure. High NH3 concentrations in the solution and low NH3 concentrations in the surrounding atmosphere increase NH3 emissions. According to Henry´s Law, ammonia emissions are also temperature dependent with rising temperatures increasing emissions (Fig. 2). Denmead et al. (1982) give the following equation: 0.09018+(2729.92/T)- pH NH3(solution) = (NH3(solution) + NH4 (solution) )/(1 + 10 ) where

NH3(solution) = NH3 concentration in the solution + NH3(solution) + NH4 (solution) = The sum NH3 and NH4 in the solution T = Temperature in the solution [K] pH = pH value in the solution

Figure 2: NH3 concentration in the solution depending on temperature for pH 7.0 and pH 7.5 (after Denmead at al. 1982)

1.2 N2O and N2 The principles of microbial formation of N2O and N2 are well known and have been described by a range of authors. N2O, NOx and N2 are formed both during the nitrification and the denitrification processes. The “Leakage“ model developed by Firestone & Davidson (1989) shows N2O, and NOx losses as leakage flows during nitrification and denitrification (Fig. 3).

Figure 3: “Leakage model for N2O and NOx losses during nitrification and denitrification” (after Firestone & Davidson 1989) Nitrification oxidises ammonia via nitrite to nitrate. This process is strictly aerobic. Autotrophic nitrifying bacteria belong to the widespread group of nitrosomonas, nitrospira + + and nitrobacter, which are capable of growing on CO2, O2 and NH4 . Availability of NH4 is mostly the limiting factor as CO2 and O2 are available in abundance. Low pH, lack of P and temperatures below 5°C or above 40 °C lead to a reduction in nitrification activities. A water content of 60% of soil water holding capacity is optimal for the nitrification process. At low pH values, nitrification is carried out by bacteria and funghi. In contrast to the autotrophic nitrifiers, they need carbon sources for their growth. Their turnover rate is much lower compared to the autotrophic nitrifiers, but still a substantial total turnover can be achieved as a wider range of species have the ability for heterotrophic nitrification. N2O production during nitrification is around 1%, NO production ranges between 1 and 4 %. - Denitrification reduces nitrate to N2O, NO or N2 when oxygen availability is low. NO3 , NO and N2O serve as alternative electron acceptors when O2 is lacking, and hence the denitrification occurs only under strictly anaerobic conditions. Molecular N2 is the last part of the denitrification reaction chain and it is the only biological process that can turn reactive nitrogen into molecular N2. Denitrifying bacteria are heterotrophic and facultative anaerobic. This means that they use O2 as electron acceptor and switch to alternative electron acceptors - (NO3 , NO and N2O) when oxygen availability is low. Denitrifying bacteria are wide spread and show a high biodiversity. Controlling factors for denitrification have been extensively investigated, mainly under lab conditions. Complex interactions exist between the various influencing factors which make a prediction of N2O emissions difficult under practical conditions.

Denitrification is mainly governed by oxygen availability. Denitrification starts when the O2 concentration decreases to below 5%. This may be the case in poorly aerated soils (e.g. high water content), but also in soils where a high biological turnover consumes the oxygen faster than the supply. Easily degradable carbon sources and high nitrate concentrations also enhances denitrification rate. Low temperature and low pH value limit denitrification.

The relationship between N2 and N2O formation is mainly governed by the relationship between electron acceptor and reducing agent and by the O2 concentration in the substrate. N2 - is only formed under strictly anaerobic conditions and a wide C : NO3 ratio. High nitrate concentrations or some O2 availability increase the rate of N2O production.

3. Livestock feeding and housing Chadwick et al. (2011) state in their paper on “Manure management: Implications for greenhouse gas emissions”: Manure management is a continuum from generation by livestock to storage and treatment and finally to land spreading. There is the potential for NH3, N2O and CH4 emissions at each stage of this continuum. For describing and estimating NH3 emissions from the manure management continuum, a mass flow approach has been used (Webb and Misselbrook, 2004) as this allows effects of management at one phase that reduces emissions and conserves manure N to be considered as the manure passes to the next stage in the continuum. Other gaseous N losses, including N2O, are included in this mass flow in a manner similar to that of Dämmgen and Hutchings (2008). The importance of this whole system approach is that effects of mitigation methods at one stage are considered in downstream stages (Sommer et al., 2009; 2013). 2.1 Livestock feeding Ammonia emissions result from the degradation of urea by the ubiquitary enzyme urease + which results in NH4 formation. Urea is mainly excreted in the urine and once it is hydrolysed it is much more prone to ammonia losses than organic nitrogen excreted in the faeces. The crude protein content and composition of the animal diet is the main driver of urine excretion. Excess crude protein (CP) is excreted and can easily be lost in the manure management chain. Adaptation of crude protein in the diet to the animals´ needs is therefore the first and most efficient measure to mitigate nitrogen emissions.

Reduction of CP in animal feed is one of the most cost-effective ways of reducing NH3 emissions throughout the entire manure management chain. For each percent (absolute value) decrease in protein content of the animal feed, NH3 emissions from animal housing, manure storage and the application of animal manure to land are decreased by 5%–15%, depending also on the pH of the urine and dung. Low-protein animal feeding also decreases N2O emissions, and increases the efficiency of N use in animal production. Moreover, there are no animal health and animal welfare implications as long as the requirements for all amino acids are met. Low-protein animal feeding is most applicable to housed animals and less for grassland-based systems with grazing animals, because grass is eaten by the animls in an early physiological growth stage and thus high in degradable protein, and grassland with leguminous species (e.g., clover and lucerne) also have a relatively high protein content. While there are strategies to lower the protein content in herbage (balanced N fertilization, grazing/harvesting the grassland at later physiological growth stage, etc.), as well as in the ration of grassland-based systems (supplemental feeding with low-protein feeds), these strategies are not always fully applicable. 2.1.1 Mitigation measures: Feeding strategies for dairy and beef cattle Lowering CP of ruminant diets is an effective strategy for decreasing NH3 loss. The following guidelines hold: (a) The average CP content of diets for dairy cattle should not exceed 15%–16% in the dry matter (DM) (Broderick, 2003; Swensson, 2003). For beef cattle older than 6 months this could be further reduced to 12%; (b) Phase feeding can be applied in such a way that the CP content of dairy diets is gradually decreased from 16% of DM just before parturition and in early lactation to below 14% in late lactation and the main part of the dry period; (c) Phase feeding can also be applied in beef cattle in such a way that the CP content of the diets is gradually decreased from 16% to 12% over time. 6

In many parts of the world, cattle production is grassland-based or partly grassland-based. In such systems, protein-rich grass and grass products form a significant proportion of the diet, and the target values for CP may be difficult to achieve, given the high CP content of grass from managed grasslands. The CP content of fresh grass in the grazing stage (2,000–2,500 kg DM/ha) is often in the range of 18%–20% (or even higher, especially when legumes are present), whereas the CP content of grass silage is often between 16% and 18% and the CP content of hay is between 12% and 15% (e.g., Whitehead, 2000). In contrast, the CP content of maize silage is only in the range of 7%–8%. Hence, grass-based diets often contain a surplus of protein and the magnitude of the resulting high N excretion strongly depends on the proportions of grass, grass silage and hay in the ration and the protein content of these feeds. The protein surplus and the resulting N excretion and NH3 losses will be highest for grass (or grass-legume)-only summer rations with grazing of young, intensively fertilized grass or grass legume mixtures. However, urine excreted by grazing animals typically infiltrates into the soil before substantial NH3 emissions can occur and overall NH3 emissions per animal are therefore typically less for grazing animals than for those housed where the excreta is collected, stored and applied to land.

The NH3 emission reduction achieved by increasing the proportion of the year the cattle spent grazing outdoors will depend on the baseline (emission from non-grazing animals), the time the animals are grazing, and the N fertilizer level of the pasture. The potential to increase grazing is often limited by soil type, topography, farm size and structure (distances), climatic conditions, etc. It should be noted that grazing of animals may increase other forms of N emissions (e.g., nitrate-N leaching and N2O emissions). However, given the clear and well quantified effect on NH3 emissions, increasing the period that animals are grazing all day can be considered as a strategy to reduce emissions, but depending on grazing time. The actual abatement potential will depend on the base situation of each animal sector in each country. Changing from a fully housed period to grazing for part of the day is less effective in reducing NH3 emissions than switching to complete (24-hour) grazing, since buildings and stores remain dirty and continue to emit NH3; however, the feasibility of such a strategy also depends on climatic conditions (too cold or too hot). In general, increasing the energy/protein ratio in the diet by using “older” grass (higher sward surface height) or swathed forage cereal and/or supplementing grass by high energy feeds (e.g., silage maize) is a well proven strategy. However, for grassland-based ruminant production systems, the feasibility of these strategies may be limited, as older grass may reduce feeding quality, especially when conditions for growing high energy feeds are poor (e.g., warm climates), and therefore have to be purchased. Hence, full use of the grass production would no longer be guaranteed. 2.1.2 Mitigation measures: Feeding strategies for pigs Feeding measures in pig production include phase feeding, formulating diets based on digestible/available nutrients, using low-protein amino acid-supplemented diets, and feed additives/supplements. Further techniques are currently being investigated (e.g., different feeds for males (boars and castrated males) and females) and might be additionally available in the future. The CP content of the pig ration can be reduced if the amino acid supply is optimized through the addition of synthetic amino acids (e.g., lysine, methionine, threonine, tryptophan, typically limiting amino acids, which are in too low in normal grain rations) or special feed components, using the best available information on “ideal protein” combined with dietary supplementation. A CP reduction of 2%–3% in the feed can be achieved, depending on pig production category and the current starting point. It has been shown that a decrease of 1% CP in the diet of 7

finishing pigs results in a 10% lower total ammoniacal nitrogen (TAN) content of the pig slurry and 10% lower NH3 emissions (Canh and others, 1998). 2.1.3 Mitigation measures: Feeding strategies for poultry For poultry, the potential for reducing N excretion through feeding measures is more limited than for pigs because the conversion efficiency currently achieved on average is already high and the variability within a flock of birds is greater. A CP reduction of 1%–2% may be achieved depending on the species and the current starting point, but is already a well proven measure for growers and finishers. Further applied nutrition research is currently being carried out in EU member States and North America and this may support further possible reductions in the future.. 2.2 Livestock housing When using measures to abate emission from livestock houses, it is important to minimize loss of the conserved NH3 during downstream handling of the manure, in storage and spreading to maximize the benefit from the cost of abatement. 2.2.1 Cattle housing Housing systems for cattle vary across the ECE region. While loose housing is most common, dairy cattle are still kept in tied stalls in some countries. In loose housing systems all or part of the excreta is collected in the form of slurry. In systems where solid manure is produced (such as straw-based systems), it may be removed from the house daily or it remain there for up to the whole season, such as in deep litter stables. The system most commonly researched is the “cubicle house” for dairy cows, where NH3 emissions arise from fouled slatted and/or solid floors and from manure in pits and channels beneath the slats/floor. Animal welfare considerations tend to lead to an increase of soiled walking area per animal, increased ventilation, possibly cooler winter temperatures and an overall increase in emissions. Changes in building design to meet the new animal welfare regulations in some countries (e.g., changing from tied stall to cubicle housing) will therefore increase NH3 emissions unless abatement measures are introduced at the same time to combat this increase. Solid versus slurry manure systems. Straw-based systems producing solid manure for cattle are likely to emit more NH3 in the animal houses than slurry-based systems. Further, N2O and di-nitrogen (N2) losses due to (de)nitrification tend to be larger in litter-based systems than slurry-based systems.

While straw-based solid manure can emit less NH3 than slurry after surface spreading on fields (e.g., Powell and others, 2008), slurry provides a greater opportunity for reduced emissions applications. A physical separation of faeces (which contains urease) and urine in the housing system reduces hydrolysis of urea, resulting in reduced emissions from both housing and manure spreading (Burton, 2007; Fangueiro and others, 2008a, 2008b; Møller and others, 2007). Verification of any NH3 emission reductions from using solid-manure versus slurry-based systems and from solid-liquid separation should consider all the stages of emission (housing, storage and land application). 2.2.2 Mitigation measures for cattle housing Mitigation options can be grouped into the following types:  Floor based systems and related management techniques (including scrapers and cleaning robots);  Litter based systems (use of alternative organic material);  Slurry management techniques at pit level;

 Indoor climate control techniques;  End-of-pipe techniques (hybrid ventilation + air cleaning techniques) and GHGs mitigation techniques. Several pathways can be identified to further optimize existing and develop new mitigation techniques. In this respect emission reduction techniques at animal housing level should aim to affect one or more of the following important key factors and/or driving forces of the ammonia emission process:  Draining capacity of the floor for direct transportation of urine to the manure storage  Residence time of open urine/manure sources;  Emitting surface area of open urine/manure sources;  Urease activity in urine puddles;  Urine/manure pH and temperature;  Indoor air temperature;  Air velocities at emitting surfaces (urine puddles and manure surface in the pit);  Air exchange between pit headspace and indoor air;  Exhaust of indoor air. The “grooved floor” system for dairy and beef cattle housing, employing “toothed” scrapers running over a grooved floor, is a reliable technique to abate NH3 emissions. Grooves should be equipped with perforations to allow drainage of urine. This results in a clean, low-emission floor surface with good traction for cattle to prevent slipping. Ammonia emission reduction ranges from 25% to 46% relative to the reference system (Smits, 1998; Swierstra, Bram and Smits, 2001). In houses with traditional slats (either non-sloping, 1% sloping or grooved), optimal barn climatization with roof insulation (RI) and/or automatically controlled natural ventilation (ACNV) can achieve a moderate emission reduction (20%) due to the decreased temperature (especially in summer) and reduced air velocities (Braam, Ketelaars and Smits 1997; Bram and others, 1997; Smits, 1998; Monteny, 2000). Decreasing the amount of animal excrement in animal housing systems through increased grazing is an effective measure to decrease NH3 emissions. Though emissions from grazing will increase when animals are kept outside, NH3 emissions from animal housing systems will decrease much more, provided surfaces in the house are clean while the animals are grazing outside. Total annual emissions (from housing, storage and spreading) from dairy systems may decrease by up to 50% with nearly all-day grazing (Bracher and others, forthcoming), as compared with animals that are fully confined. While increased grazing is a reliable emission reduction measure for dairy cows, the amount of emission reduction depends on the daily grazing time and the cleanliness of the house and holding area. Grazing is efficient in reducing NH3 emissions, if the animals are grazed all day or if very little floor area is contaminated with manure each day. Less than 18 grazing hours per day must be considered as category 2 (UNECE) because of the uncertainty in quantifying emissions. In some cases grazing may also contribute to increased leaching or increased pathogen and nutrient loading to surface waters. Different improved floor types based on slats or solid, profiled concrete elements have been tested. These designs combine emission reduction from the floor (increased run-off of urine)

and from the pit (reduction of air exchange by rubber flaps in the floor slots). The emission abatement efficiency depends on the specific technical characteristics of the system.

Bedding material in animal housing can affect NH3 emission. The physical characteristics (urine absorbance capacity, bulk density) of bedding materials are of more importance than their chemical characteristics (pH, cation exchange capacity, carbon to nitrogen ratio) in determining NH3 emissions from dairy barn floors (Misselbrook and Powell, 2005; Powell, Misselbrook and Casler, 2008; Gilhespy and others, 2009). However, further assessment is needed on the effect of bedding on emissions for specific systems while taking into account the whole manure management path.

Chemical or acid air scrubbers, while effective in decreasing NH3 emissions from force- ventilated pig housing, cannot generally be implemented in cattle housing which are mostly naturally ventilated across the ECE region. Also, there are few data for scrubbers on cattle (Ellen and others, 2008). 2.3.1 Pig housing Designs to reduce NH3 emissions from pig housing systems have been described in detail in European Commission (2003) and in the IPPC “BAT” document, and apply the following principles:  Reducing manure surfaces such as soiled floors, slurry surfaces in channels with sloped walls. Partly slatted floors (~50% area), generally emit less NH3, particularly if the slats are metal- or plastic-coated rather than concrete, allowing the manure to fall rapidly and completely into the pit below. Emissions from the non-slatted areas are reduced by inclined, smooth surfaces, by locating the feeding and watering facilities to minimize fouling of these areas, and by good climate control in the building;  Removing the slurry from the pit frequently to an external slurry store with vacuum or gravity removal systems or by flushing systems at least twice a week;  Additional treatment, such as liquid/solid separation; provided that the storage of the separated fractions maintains low emissions.  Circulating groundwater or other cooling agents in floating heat exchangers or walls of slurry pits to cool the surface of the manure in the under-floor pit to at least below12°C. Constraints include costs and need to locate a source of groundwater away from the source of drinking water;  Changing the chemical/physical properties of the manure, such as decreasing pH;  Using surfaces which are smooth and easy to clean (see above);  Treatment of exhaust air by acid scrubbers or biotrickling filters;  Lowering the indoor temperature and ventilation rate, taking into account animal welfare and production considerations, especially in winter;  Reducing air flow over the manure surface. For a given floor slat width, manure drains from concrete slats less efficiently than from steel- and plastic-covered slats and this is associated with greater emissions of NH3. Note that steel slats are not allowed in some countries for animal welfare reasons. These cross-media effects have been taken into account in defining BAT for the various housing designs. For example, frequent flushing of slurry (normally once in the morning and once in the evening) causes nuisance odour events. Flushing slurry also consumes energy unless manually operated passive systems are used.

Use of straw litter in pig housing is expected to increase due to concern for the welfare of the pigs. In conjunction with (automatically controlled) naturally ventilated housing systems, straw allows the animals to self-regulate their temperature with less ventilation and heating, reducing energy consumption. In systems with litter, the pen is sometimes divided into solid areas with litter and slatted dunging areas. However, pigs do not always use these areas in the desired way, using the littered area to dung and the slatted area to cool off in warm weather. Generally, pens should be designed to accommodate desired excreting behaviour of pigs to minimize fouling of solid floors. This is however more difficult in regions with a warm climate. Note that integrated evaluation of straw use should consider the added cost of the straw and mucking out the pens; possible increased emissions from storage and application of manure with straw; as well as the benefit of adding organic matter to the soil. 2.3.2 Mitigation measures for pig housing The reference system, used commonly in Europe, is a fully slatted floor with a deep manure pit underneath and mechanical ventilation; emission ranges from 2.4 to 3.2 kg NH3 per pig place per year. Since growers/finishers are always housed in a group, most systems used for group housing of sows are applicable to growers. Ammonia emission can be reduced by 25% by reduction of emitting surface area through frequent and complete vacuum-assisted drainage of slurry from the floor of the pit. Where this is possible to do, this technique has no cost. Partly slatted floors covering 50% of floor area generally emit 15%–20% less NH3, particularly if the slats are metal or plastic-coated which is less sticky for manure than concrete. Decreasing risk of emissions from the solid part of the floor can be achieved by using an inclined (or convex), smoothly finished surface; by appropriate siting of the feeding and watering facilities to minimize fouling of the solid areas; and by good climate control (Aarnink and others, 1996; Guigand and Courboulay, 2007; Ye and others, 2008a, 2008b). Further reduction of the emitting area can be achieved by making both the partly slatted area and the pit underneath smaller. With the smaller slatted area, the risk of greater fouling of the solid area can be mitigated by installing a small second slatted area with a water canal underneath at the other side of the pen where the pigs tend to eat and drink. The canal is filled with about two centimetres (cm) of water to dilute any manure that might eventually drop into it. This slatted area will have low emissions because any manure dropped here will be diluted. This combined manure-canal and water-canal system can reduce NH3 emissions by 40%–50% depending on the size of the water canal. Reducing the emitting surface area by having one or two slanted pit walls, in combination with partly slatted floors and frequent manure removal, can reduce emissions by up to 65%. Reducing the emitting surface area with shallow V-shaped gutters (maximum 60 cm wide, 20 cm deep) can reduce emission in pig houses by 40% to 65%, depending on pig category and the presence of partly slatted floors. The gutters should be flushed twice a day with the liquid (thin) fraction of the slurry rather than water; flushing with water dilutes the manure and increases the cost of transporting and applying it in the field.

Reducing NH3 emissions can also be achieved by acidifying the slurry to shift the chemical + balance from NH3 to NH4 . The manure (especially the liquid fraction) is collected into a tank with acidified liquid (usually using sulphuric acid, but organic acids can be used as well, though at higher cost) maintaining a pH of less than 6. In piglet housing emission reduction of 60% has been observed. Surface cooling of manure with fans using a closed heat exchange system is a technique with a reduction efficiency of 45%–75% depending on animal category and surface of cooling fins. This technique is most economical if the collected heat can be exchanged to warm other facilities such as weaner houses (Huynh and others, 2004). In slurry systems this technique can often be retrofitted into existing buildings. This system is however

not applicable when straw bedding is used or when the feed contains a lot of roughage because a layer of floating residue may develop on top of the slurry. Treatment of exhaust air by acid scrubbers (mainly using sulphuric acid) or biotrickling filters has proven to be practical and effective for large-scale operations in Denmark, Germany, France and the Netherlands (e.g., Melse and Ogink, 2005; Guingand, 2009). This is most economical when installed in new houses, because retrofitting in existing housing requires costly modification of ventilation systems. Acid scrubbers have demonstrated NH3 removal efficiencies of 70%–90%, depending on their pH-set values. Scrubbers and biotrickling filters also reduce odour and particulate matter by 75% and 70%, respectively (Guingand, 2009). Further information is needed on the suitability of these systems in South and Central Europe. Operational costs of both acid scrubbers and trickling filters are especially dependent on the extra energy use for water recirculation and to overcome increased back pressure on the fans. Optimization methods are available to minimize costs (Melse, Hofschereuder and Ogink, 2012) and costs will be lower for large operations. 2.4.1 Poultry housing Designs to reduce NH3 emissions from poultry housing systems apply the following principles:  Reducing emitting manure surfaces;  Removing the manure frequently to an external slurry store (e.g., with belt removal systems);  Quickly drying the manure;  Using surfaces which are smooth and easy to clean;  Treatment of exhaust air by acid scrubbers or biotrickling filters;  Lowering the indoor temperature and ventilation as animal welfare and/or production allow.

2.4.2 Mitigation measures for Housing systems for laying hens The evaluation of housing systems for layers in the EU member States has to consider the requirements laid down by Council Directive 1999/74/EC of 19 July 1999 setting minimum standards for the protection of laying hens. This Directive prohibits the use of conventional cage systems in effect since 2012). Instead, only enriched cages (also called furniture cages), or non-cage systems, such as litter (or deep litter) housing systems or aviary systems, are allowed. Ammonia emissions from battery deep-pit or channel systems can be lowered by reducing the moisture content of the manure by ventilating the manure pit. The collection of manure on belts and the subsequent removal of manure to covered storage outside the building can also reduce NH3 emissions, particularly if the manure has been dried on the belts through forced ventilation. The manure should be dried to 60%–70% DM to minimize the subsequent formation of NH3. Manure collected from the belts into intensively ventilated drying tunnels, inside or outside the building, can reach 60%–80% DM content in less than 48 hours, but in this case exposure to air and emissions are increased. Weekly removal from the manure belts to covered storages reduces emissions by 50% compared with bi-weekly removal. In general, emission from laying hen houses with manure belts will depend on: (a) the length of time that the manure is present on the belts; (b) the drying systems; (c) the poultry breed; (d) the ventilation rate at the belt (low rate = high emissions); and (e) the feed composition. Aviary

systems with manure belts for frequent collection and removal of manure to closed storages reduce emission by more than 70% compared with the deep litter housing system. Treatment of exhaust air by acid scrubber or biotrickling filters has been successfully employed in several countries (Melse and Ogink, 2005; Ritz and others, 2006; Patterson and Adrizal, 2005; Melse, Hofschreuder and Ogink, 2012). Acid scrubbers remove 70%–90% of NH3, while biological scrubbers remove 70%; both also remove fine dust and odour. To deal with the high dust loads, multistage air scrubbers with prefiltering of coarse particles have been developed (Ogink and Bosma, 2007; Melse, Ogink and Bosma, 2008). Yet some Parties consider this technique as only category 2 (UNECE) because of the dust loading issue. 2.4.1 Mitigation measures for housing systems for broilers To minimize NH3 emission in broiler housing, it is important to keep the litter dry. Litter moisture and emissions are influenced by:  Drinking-water design and function (leakage and spills);  Animal weight and density, and duration of the growing period;  Ventilation rate, use of in-house air purification and ambient weather;  Use of floor insulation;  Type and amount of litter;  Feed. Reducing spillage of water from the drinking system: A simple way to reduce spillage of water from the drinking system is using a nipple instead of bell drinkers.

Air scrubber technology to remove NH3 from ventilation air is highly effective, but not widely implemented because of costs. Packed-bed filters and acid scrubbers currently available in the Netherlands and Germany remove 70%–90% of NH3 from exhaust air. Questions about long- term reliability due to high dust loads must be further clarified. Various multi-pollutant scrubbers have been developed to also remove odor and particulate matter (PM10 and PM2.5) from the exhaust air (Zhao and others, 2011; Ritz and others, 2006; Patterson and Adrizal, 2005). 4. Manure storage, treatment and processing In order for livestock agriculture to become sustainable an optimal and efficient use of manure nutrients and organic matter is a must. However, manure nitrogen may be easily lost via via gaseous emissions (NH3, N2O, NOx, N2) and nitrate leaching. Besides nitrogen losses, animal and manure methane emissions to the atmosphere must be reduced as far as possible, to limit climate change impacts. Animal slurry composition is typically not ideal with regard to low emission handling and crop fertilizing properties. In particular, the high dry matter and carbon content pose several problems during slurry storage, application and crop utilisation (Table 1). Table 1. Problems and benefits resulting from slurry high dry matter and carbon content, low nutrient content Problem Storage  natural crust formation and sedimentation of solids  high energy consumption per unit of nutrient for pumping and mixing

 potentially higher emissions of NH3, N2O, CH4, and odour

Field  high potential risk of NH3 losses due to slow infiltration application  high technical effort required (at high economic cost) for even and low emission application  suffering of plants due to scorching by broadspread slurry Crop  less effective crop uptake of slurry N than from mineral utilisation fertilizer  Crop N effect less predictable / more variable than from mineral fertilizer  Increased temporary N immobilisation in the soil, increasing risk of lower crop N effect

 Higher risk of denitrification and subsequent N2O emissions Benefits Storage  Natural crust formation may serve as a natural barrier, inhibiting NH3 transport to the atmosphere; furthermore, the crust may have significant capacity for CH4 oxidation, due to it’s partial aerobic conditions and high microbial activity Field / soil  High dry matter and carbon contributes to maintenance of soil organic matter content and biologically active soil

Slurry dry matter tends to crust formation on the slurry surface and/or to sedimentation on the bottom of the slurry tank. In order to achieve an even distribution of nutrients in the slurry, slurry must be homogenised prior to application. Homogenisation of slurry with high dry matter content is energy consuming and increases NH3 emissions as slurry comes to close contact with the atmosphere. Thus, slurry homogenisation is to be reduced as far as possible which is only possible if slurry dry matter content is reduced. Slurry contains considerable amounts of easily degradable carbon that serves as nutrient source to microbes. During slurry storage a continuous degradation of organic matter can be observed. Degradation intensity is strongly dependent on the slurry dry matter content. Amon et al. (1995) investigated changes in slurry composition over a 200-day storage period. Cattle, beef and pig slurry was stored in 250-l-tanks. The influence of slurry dry matter content on changes in slurry composition was tested with three different dry matter contents. Degradation of organic matter was significantly greater with higher slurry dry matter content. As conditions in the slurry are anaerobic, degradation of organic matter must always occur with anaerobic pathways. This means, that CH4 and CO2 are formed as end products of the degradation process. It is thus to be assumed that high dry matter slurry bears a greater risk for CH4 emissions.

After surface application of slurry NH3 emissions increase with an increase in slurry dry matter content, due to slower soil infiltration. Ammonia emissions not only have negative environmental impacts, but also represents a loss of a valuable plant nutrient which in consequence has to be bought as mineral fertiliser.

Figure 4. Effect of changes in slurry composition achieved by manure treatment. Environmentally friendly slurry application in the field requires that the slurry is more evenly applied near or under the soil surface. It is much more complicated to fulfil this requirement when the slurry has a higher dry matter Content, causing a higher viscosity and less easy flow through band spreading hoses. The N availability to plants is difficult to calculate with high dry matter slurry, because a high dry matter content drives increased microbial immobilization right after application. The more narrow the C/N-ratio, and the higher NH4-N content the more N is available to plants, whereas with a wide C/N-ratio, part of slurry N is immobilised in the soil N pool and becomes available only at a later and often unpredictable stage. In addition, an increase in slurry dry matter and subsequent soil N content has the potential to increase the denitrification rate and subsequent N2O losses (Dosch 1996). It may thus be beneficiary to reduce slurry dry matter and carbon content at an early stage of manure management. This leads to several manure treatment options that have to be evaluated against the requirements listed in Figure 4. There are various techniques of simple manure treatment that can be first classified as physical, chemical or biological ways of treatment (Figure 5). Furthermore, a number of different options/technologies are available for further processing of raw or treated manures for recovering and upgrading nutrients and organic matter from different manure types (Figure 6). For slurries or other liquid manures such as digestate from anaerobic digestion of manure and other biowaste, basically all treatment steps start with mechanical separation into a relatively organic N- and P-rich solid fraction, and a liquid fraction, with low P, but relatively high mineral N and K contents.

Figure 5. Options of simple manure treatment (source? Own?)

Figure 6. Options for further processing of manures to recover and upgrade nutrient and energy, resulting in widely different bio-based fertilisers (Jensen, 2013) Manure treatment and processing options presented in this chapter will be evaluated against the following criteria:  reduction in dry matter content  reduction in carbon content  narrowing of the C/N ratio

 impact on potential for NH3, N2O and CH4 emissions  energy consumption for treatment  impact on effort (energy, equipment) for slurry application  influence on effectiveness of treated manure as a fertiliser  costs of treatment

3.1 Mitigation measures for slurry storage and treatment and processing

Slurry mixing is one of the most commonly applied manure treatment technology. Slurry is thereby homogenised prior to application in order to achieve an even distribution of nutrients. Apart from this, mixing does not offer any additional benefits compared to untreated slurry. Neither dry matter nor carbon content are reduced. The C/N-ratio is not altered. No significant changes in NH3, N2O or CH4 emissions are to be expected, though NH3 may tend to increase a little, depending on the extent and timing of mixing (Table 2). Table 2. Assessment of impacts achieved by slurry mixing criteria result achieved by mixing energy consumption cattle slurry: 0.91 kWh m-3 pig slurry: 3.25 kWh m-3 DM and C content not changed C/N-ratio not changed pH not changed, though may tend to increase (depending on air exposure)

NH3, N2O and CH4 losses not significantly changed, maybe slight increase for NH3 N losses 11—22 % (during mixing) costs 0.41- 0.64 EURO m-3 effort for slurry application high, not changed fertilising effectiveness not significantly changed, though more homogenous, possibly less variable effect

Slurry dilution with water can be used to reduce NH3 losses after slurry application. However, a significant effect it only achieved if water-to-slurry-ratio is at least 2:1 (Beudert et al. 1988). This would result in a dramatic increase in slurry volume that has to be stored and applied, and hence increased economic cost. Nutrient ratios stays unchanged and thus slurry fertiliser quality is not greatly improved, though slightly higher N effectiveness may be achieved. Water dilution has positive effects only in a few criteria and generally cannot be recommended as very effective manure treatment option (Table 3). Table 3. Assessment of impacts achieved by dilution with water criteria result achieved dilution with water energy consumption Increase (due to an increase in efforts for mixing and transport increase) DM and C content reduction C/N-ratio not changed

pH not changed

NH3, N2O and CH4 losses reduction N losses reduction (if water-to-slurry-ratio is 2:1 or greater) costs Increase (water, mixing, volume to be applied) effort for slurry application reduction fertilising effectiveness not changed, perhaps slightly higher N effect

Slurry additives can act on a chemical, physical or biological basis.

Clay/zeolite mineral additives are meant to adsorb NH4-N and thus reduce NH3 losses. However, this can only be achieved with high amount of additives. E.g. 25 kg of Zeolite per 3 m slurry have been shown necessary to adsorb 55 % of NH4-N (ref?). On most commercial farms it is neither logistically possible nor economic profitable to add such enormous amounts of slurry additives. An obvious way to minimize ammonia emissions from slurry is to decrease slurry pH by addition of acids or other substances. This solution has been used commercially since 2010 in countries such as Denmark (by 2018, around 15-20% of all slurry applied in Denmark was acidified), and its efficiency for minimizing NH3 emissions haved been documented in many studies (see review by Fangueiro et al. 2015). Table 4. Assessment of impacts achieved by slurry acidification criteria result achieved by slurry acidification energy consumption Increase (for due to an increase in efforts for mixing and transport increase) DM and C content Not significantly changed C/N-ratio Slightly lower, due to higher NH4-N content pH Reduced to 5.5-6

NH3, N2O and CH4 losses Siginficant reduction N losses 50-70% reduction (if pH<5.5 in animal house, <6 during application) Costs Increase (sulfuric acid, mixing, high investment in safe and reliable dosing equipment for animal house or slurry tanker). In Denmark, contractors carry out online acidification during application for an additional cost of 1- 1,25 €/ton, incl. acid costs) effort for slurry application Enables high capacity, low N emission application on grasslands and bare soils, where injection may be only other low N emissions technology fertilising effectiveness Significantly higher N fertiliser replacement value, typically 15-25% (abs.) more mineral N fertiliser replacement value

Additives on an enzymatic basis are intended to increase biological degradation of organic matter with the aim to reduce slurry dry matter content and thus avoid crust formation and sedimentation. In addition, odour nuisance may be reduced, as well. An increase in degradation of organic matter during slurry storage improves slurry viscosity and reduces the potential for NH3 losses upon application. However, as organic matter is anaerobically degraded, potentials for CH4 emissions during storage may increase. Mode of action and composition of such commercial biological additives are in most cases not known and it may be questioned whether the claimed effects have actually been achieved on commercial farms. Research has so far generally not been able to proove significant and reproducible effects of biological slurry additives (Owusu-Twuma et al., 2017). Slurry aeration introduces oxygen rapidly into the slurry in order to allow aerobic microbes to develop. Oxidation of organic matter to CO2 and H2O increases. Odorous compounds are degraded. Slurry dry matter content decreases. Thus, less mixing is needed and technical properties of slurry are often improved. However, successful aeration requires 200 m-3 oxygen per t of slurry (Burton 1998).

Slurry aeration results in an increase in NH3 emissions and in energy consumption. The potential for N2O emissions is likely to increases, as well. The extent of these increases has so far not been exactly quantified. This has to be done in order to allow a complete evaluation of slurry aeration (Table 5). Table 5. Assessment of impacts achieved by slurry aeration Criteria result achieved by slurry aeration energy consumption 3.6 - 17.6 kWh m-3(depending on slurry dry matter content) DM and C content reduction C/N-ratio not changed pH increase

NH3, N2O and CH4 losses NH3: strong increase

N2O, CH4: unknown effect N losses strong increase costs 2.03 - 2.54 EURO m-3 effort for slurry application reduction fertilising effectiveness improvement

During slurry separation, solids and liquids are mechanically separated from slurry. This results in two fractions: a liquid slurry fraction with low dry matter content and a solid fraction that can be stored in heaps. Energy consumption for slurry separation is low, though depends on the technology used for separation. Dry matter content in the liquid fraction is reduced by 40 - 45%, and vice-versa for the solid. Carbon content in the liquid is reduced by 45-50 %. C/N-ratio of the liquid therefore decreases from about 10:1 to about 5:1 (Amon 1995). As carbon is removed from the slurry, microbial degradation of organic matter during slurry storage is reduced. However, the opposite may be the case for the solid fraction, depending on storage conditions. The removal of solids reduces crust formation and sedimentation. Thus, less intensive mixing is necessary to homogenise the slurry prior to application. Efforts for low emission 19

application techniques are reduced as separated slurry has a lower viscosity and flows more easily through band spreading hoses. Slurries with very low dry matter content can be spread with simple nozzle-beam-dischargers that can be operated on slopes > 10 %, which is not possible with other band spreading techniques. Separated slurry liquid fraction infiltrates rapidly into the soil. Thus, plants get less dirty and ammonia emissions after liquid fraction spreading are reduced. A reduction of ammonia emissions by slurry separation of up to 63 % is possible for the liquid. Separated slurry has a narrow C/N-ratio which reduces the potential for N immobilisation in the soil. N availability is more predictable and can be better calculated in order to match nutrient requirements of plants to fertilisation. Dosch (1996) investigated fertilisation with untreated and separated slurries. He found significantly higher denitrification rates with untreated slurry. Separated slurry resulted in significantly higher crop yield. Slurry separation fulfils all requirements of manure treatment (Table 6). Costs for slurry separation could be further reduced if the technology was more wide spread and more separators were built. As fertiliser value of separated slurry is improved, mineral fertiliser input can be reduced. Slurry application near the soil can be done with very simple low cost slurry spreaders. Table 6. Assessment of impacts achieved by slurry separation criteria result achieved by slurry separation energy consumption cattle slurry: 0.10- 2.20 kWh m-3 pig slurry : 0.06 – 0.40 kWh m-3 DM and C content 40 – 45 % reduction in liquid; opposite in solid fraction C/N-ratio Reduction in liquid, increase in solids pH not significantly changed

NH3, N2O and CH4 losses Reduction from the liquid, increase in the solids N losses strong increase in potential N loss from solids costs 1.02 -2.03 EURO m-3 effort for slurry application Reduction for the liquid, increase for the solids fertilising effectiveness Improvement for the liquid, less for the solids. If applied to the same type of soil/crops, the overall effectiveness is not really improved; if applied to different soils/crops, matching demands may be better (i.e. solids to P deficient soils, no overload of N)

Anaerobic digestion of animal manures is mainly implemented for energy production reasons. Improvement of manure quality is a "by-product" of anaerobic digestion. Biogas production from animal manures aims at maximising the biomethane yield. Whereas anaerobic degradation of organic substances into methane during manure storage should be prohibited as far as possible to prevent emission to the atmosphere as this potent greenhouse gas, methane production in an agricultural biogas plant is enhanced and collected and transformed to electricity and heat in a combined heat and power plant. Anaerobic digestion not only reduces methane emissions from subsequent storage of the manure digestate, but the energy produced substitutes consumption of fossil energy as well. Both processes reduce anthropogenic greenhouse gas emissions. 20

Anaerobic digestion reduces manure carbon and dry matter content by about 50 % (Amon & Boxberger 2000). NH4-N content and pH in digested slurry are higher than in untreated slurry. Thus, potential for ammonia emissions during slurry storage are increased. Digested slurry therefore has to be stored in covered slurry stores that should be connected to the gas bearing system of the biogas plant, as methane is still formed after the main digestion took place in the heated digester and emission to the atmosphere should be prevented. Due to the reduced dry matter content, biogas slurry can infiltrate more rapidly into the soil which reduces ammonia emissions after slurry application. However, the increased NH4-N content and pH give rise to higher potential for ammonia loss especially after surface application. It is to be recommended to apply biogas slurry with low emission techniques near the soil surface, e.g. band application or injection. This considerably reduces ammonia emissions. N immobilization and N2O losses are likely to be smaller than from untreated slurry, due to digestion of easily degradable organic substances. Energy consumption for pumping and mixing is considerably reduced due to the reduced dry matter content. Anaerobic digestion therefore has multiple positive effects on environmental impacts of manure management (Table 7). Table 7. Assessment of impacts achieved by anaerobic digestion Criteria result achieved by anaerobic digestion energy consumption energy is produced DM and C content up to 50 % reduction C/N-ratio Reduction pH Increase

NH3, N2O and CH4 losses Reduction N losses reduction (if low emission spreading techniques are applied) costs for electricity 0.15 - 0.20 EURO kWh-1 production effort for slurry application Reduction fertilising effectiveness Significantly higher N fertiliser replacement value, typically 10-15% (abs.) more mineral N fertiliser replacement value

Some further processing depicted in Fig. 5 and 6 may be implemented for further upgrading manure products (Jensen, 2013): Composting of manure is done in order to create a stable and odourless bio-based fertiliser product, with lower moisture content and most of the initial nutrients, free of pathogens and seeds. Composting significantly reduces mass (water evaporation and volatile solids decomposition) and hence transport costs; however, it is difficult to avoid some loss of manure N in the form of NH3 and the process may also emit some GHGs. Furthermore, the N fertiliser value of composts is often significant lower than the N rich manure components it is made from. Composting is typicaly low-technology, but implies space and energy consumption. Overall, it can therefore usually not be recommend from a nitrogen point of view, but may be preferred on other criteria, like stability, odour, marketability or soil amelioration. 21

Drying and pelletising of solid manures, slurry or digestate solids can be done to to create a more stable and odourless bio-based fertiliser product. Drying is energy intensive and thereby relatively expensive, unless excess energy (e.g. from the power plant engine on a biogas plant) is freely or cheaply available. Ammonia loss is inevitable in the process, unless exhaust filtering or scrubbing and recovery is applied or the solids are acidified prior to drying. Drying is usually combined with a pelletising process to facilitate handling. The pelleted material can be marketed as an organic matter and P-rich soil amendment; if acidified prior to dryig, the resulting product may also be rich in plant available N (Pantelopoulos et al. 2017) Combustion, thermal gasification or pyrolysis of manure and digestate solids in a power plant to generate a net energy output for heat and/or electricity production, but also producing ash or biochar residuals. These contain the non-volatile nutrients, concentrated relative to the solids, and can be used as an ash-based, P- and K-rich soil amendment or bio-based fertiliser, but with a more or less complete loss of the manure N, which is converted into N2 or NOx gaseous forms. Availability of the remaining nutrients in the ash is generally much lower than for the raw manure, whereas for biochar it is in between ash and raw manure. The biochar organics are very recalcitrant to biological decay and have a very large specific surface area, potentially charged; hence. biochar may be used for soil amendment, ameliorating soil pH and organic matter positively.

5. Best practices and priority measures Best practices and priorities for the selection of mitigation measures must be based on the following criteria: (i) Implementability; (ii) Effectiveness; (iii) Impact on environmental emissions; (iv) Secondary effects; (v) Controllability; (vi) Cost efficiency. Based on these criteria, we suggest the following priority measures: 5.1 Livestock feeding  Avoid N surplus from the very beginning of the manure management continuum  Adjust animal diet to animal performance (in line with existing guidance in the Ammonia Framework Code)  Reduce N excretion with the urine  Dairy cattle: o reduction of crude protein content in the diet o adapt diet and dairy productiony system to site specific conditions o increase milk yield with moderate level of concentrates o increase production cycles per cow  Pigs: o reduction of crude protein content in the diet o multiphase feeding 5.2 Livestock housing  reduction of indoor temperature  reduction of emitting surfaces, reduction of soiled areas  reduction of air flow over soiled surfaces

 use of additives (e.g. urease inhibitors, acidification)  regular removal of slurry to an outside store  in the longer term: smart barns with optimised ventilation 5.3 Manure storage, treatment and processing  manure storage outside the barn  cover of slurry stores  manure treatment/processing to o reduce slurry dry matter content o increase slurry NH4 content o lower pH e.g. anaerobic digestion, separation (but only valid for liquid fraction), acidification

6. Conclusions, final remarks and research questions

It is clear that manure management impacts quantities of NH3, direct and indirect N2O emissions and CH4 emissions at each stage of the manure management continuum (Chadwick et al. 2011). Since production of these gases is of microbial origin, the DM content and temperature of manure and soil are key factors for farm manure management decisions that influence the magnitude of N and GHG losses. There remains a degree of uncertainty in emission rates of N and GHG gases from different stages of manure management, and researchers continue to investigate interactions of the management and environmental factors which control emissions. Some specific approaches to reducing N and GHG emissions from livestock housing and manure storage include optimising diet formulation, low emission housing technologies, air scrubbers, manure storage outside the barn, cover of slurry stores, slurry separation, and anaerobic digestion. Some legislation may result in ‘win–win’ scenarios, such as the Nitrates Directive (91/676/EEC) which has led to development of Nitrate Vulnerable Zone action plans to prevent application of (high available N content manures slurry and poultry manure) in autumn, a practice which reduces N losses and direct and indirect N2O losses. Whereas, other legislation may result in potential ‘pollution swapping’, as is sometimes the case with use of slurry injection to reduce NH3 emissions at the expense of an increase in N2O emissions. However, in this latter example there is no clear understanding of why this pollution swapping only occurs on some occasions. The nature of the N cycle and its interaction with the C cycle demands a holistic approach to addressing N and GHG emissions and mitigation research at a process level of understanding. Systems based modelling must play a key role in integrating the complexity of management and environmental controls on emissions. Progress has been made to this end (Sommer et al., 2009), with some studies producing whole farm models encompassing livestock production (del Prado et al., 2010). An evidence based database is required to validate and test such models to determine the scope to which management practices can be used to reduce N and GHG from livestock manure. Concepts for Best practices addressing environmental needs require: A) Integrated concepts  relationship between nitrogen and GHG emissions  influence of climate change on nitrogen emissions

 interaction between mitigation and adaptation measures  interaction between nitrogen emissions and animal welfare  integrated assessment of the whole manure management continuum  integrated assessment considering the three pillars of sustainability: economy, environment, society  interaction between consumer demand and nitrogen emissions  development of region specific concepts for sustainable intensification  modelling of livestock production at regional, national and global scale B) Detailed understanding at process level  assessment of emissions from naturally ventilated barns  assessment of emissions from new, animal friendly housing systems  development of mitigation measures esp. for naturally ventilated dairy barns (e.g. targeted ventilation and air scrubber, manure acidification)  interaction between climate change and heat stress / animal behaviour / emissions  interaction between low protein diets and N and GHG emissions  life cycle assessment: grass based dairy feeding versus low protein dairy feeding  feed and manure additives for improved N use efficiency  manure treatment for higher N use efficiency (increase of nutrient availability, decrease of emissions) We conclude that the development of best practice concepts is challenging. Climate and site specific conditions are highly variable. The influence emission level and at the same time set the framework conditions for potential mitigation measures. It is essential to consider the three columns of sustainability and to address potential conflicts of interest as well as synergies. This inevitably leads to the conclusion that there will be no “one size fits all solution”, but best practice concepts need to give guidance on the development of flexible measures which are targeted for the specific region. 7. References Aarnink, A. J. A., and others. (1996). Effect of slatted floor area on ammonia emission and on the excretory and lying behaviour of growing pigs. Journal of Agriculture Engineering Research, vol. 64, pp. 299–310. Amon, T., Boxberger, J. (2000). Biogas production from farmyard manure. In: Management Strategies for Organic Wastes in Agriculture, FAO European Cooperative Research (ed.), Network on Recycling of Agricultural, Municipal and Industrial Residues in Agriculture (RAMIRAN), 9th International Conference, 6 - 9th September 2000, Gargnano, Italy. Amon, T., Boxberger, J., Gronauer, A. , Neser, S. (1995). Einflüsse auf das Entmischungsverhalten, Abbauvorgänge und Stickstoffverluste von Flüssigmist während der Lagerung. In: Bau und Technik in der landwirtschaftlichen Nutztierhaltung, Beiträge zur 2. Internationalen Tagung am 14./15. März 1995 in Potsdam. Institut für Agrartechnik Bornim, MEG, KTBL, AEL (eds), pp 91 – 98. Beudert, B.; Döhler, H.; Aldag, r. (1988): Ammoniakverluste aus mit Wasser verdünnter Rindergülle im Modellversuch. Schriftenreihe 28, VDLUFA, Kongreßband Teil II. Bittman, S., Dedina, M., Howard C.M., Oenema, O., Sutton, M.A., (eds), 2014, Options for Ammonia Mitigation: Guidance from the UNECE Task Force on Reactive Nitrogen, Centre for Ecology and Hydrology, Edinburgh, UK.

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