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. 2 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). 4 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. 5 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.

Load more