Towards improving the manure management chain

Animal manures are major sources of nutrients and organic matter, to be used to fertilize crops and improve soil quality. However, when not properly managed, these manures release considerable amounts of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) into the air, and nitrogen (N) and phosphorus (P) to water bodies, which create a range of unwanted environment impacts. Nutrient losses from manure depend on the management activities and techniques used at different stages of the whole manure management chain, from animal feeding up to manure application to land. The trade-offs and co-benefits of emission mitigation measures and manure treatment technologies are as yet poorly understood, especially when taking the whole manure management chain into account. Moreover, the effects of combinations of measures and technologies have not been well analyzed, and analyses at national scales are lacking. The overall objective of this PhD thesis research is (i) to enhance the quantitative insight into the effects of emission mitigation measures and treatment technologies on emissions of NH3, N2O and CH4, and the recovery of N and P from animal manure in the whole management chain, and (ii) to explore the effects of combinations of measures and technologies to mitigate these emissions and to increase the N and P recovery. In Chapter 2, methodologies for estimating N excretion factors for the main animal categories in member states of the European Union (EU) were reviewed. In Chapter 3, a transparent and uniform methodology for estimating annual feed use and N excretion per animal category for all countries of the EU-27 was developed, based on the energy and protein requirements of the animals and statistics of feed use and composition, animal number and productivity. In Chapter 4, firstly the impacts of a suite of NH3 mitigation measures on emissions of NH3, N2O and CH4 at individual stages of the manure management chain were analyzed by means of a meta-analysis of published data. Secondly, the overall impacts of alternative combinations of mitigation measures on emissions from the whole chain were evaluated through scenario analysis. Chapter 5 reports on an integrated assessment of the effects of manure treatment on NH3, N2O and CH4 emissions from manure management chains in EU-27 at the national level for 2010, using the model MITERRA-Europe. Whole-chain effects of implementing twelve treatment technologies in EU-27 on emissions and N and P recovery were further explored through scenario analyses. Chapter 6 reports on a survey conducted under various stakeholder groups with expertise in the domain of manure treatment in four European countries that have regions of high animal density. The survey addressed questions related to i) which factors facilitate and hinder the implementation of treatment technologies in practice, ii) which technologies have the most potential for successful adoption, and iii) how farm characteristics and the scale of the treatment operation affect priorities for adoption. The main conclusions of this PhD thesis are as follows: In EU-27, the amounts of N and P in manure are as large as or larger than the total amounts of fertilizer N and P used annually. However, there is a huge spatial variation in manure production. Nutrient excretion factors per animal category also vary between countries, as a result of variations in feed use and animal productivity. Clearly, for accurate inventories of national emission there is a need for estimating nutrient excretion using country-specific feed use data. Increasing the effectiveness of measures to mitigate NH3 and GHG emissions from animal manure requires proper combination of measures in the manure management chain. Lowering the dietary protein content in animal feed is an effective measure to reduce NH3 emissions and other N emissions at all stages of the manure management chain. Other measures may reduce emissions of a specific gas or emissions source, by which there is a risk of unwanted trade-offs in the manure management chain. Joint adoption of these measures with low-N feeding strategies and slurry acidification can greatly decrease the risk of pollution swapping. Implementation of manure treatment is on average still limited in EU-27. Effects of manure treatment on NH3 and GHG emissions are therefore relatively small at EU level. Increasing the implementation of treatment technologies, including acidification, incineration and thermal drying, or optimized combinations of treatment technologies, can significantly contribute to achieving NH3 and GHG emission targets of EU environmental policies. Implementation of manure treatment technologies provides opportunities to improve the use of plant nutrients in manures, because of the release of manure products with different N/P ratios. Applying acidification technology and optimized combination of NH3 emission mitigation measures increase the N recovery from animal manure, and can decrease the demand of mineral fertilizers. However, some technologies decrease the N and P recovery and/or decrease the availability of the N and P in manure products to plants. Implementation of manure treatment in practice is forced by the pressure from EU environmental regulations, and is hindered by financial barriers. To encourage the adoption of manure treatment, policies must be economically appealing to attract new adopters (farmers and industries). Long-term financial support schemes (e.g. subsidies) seem to be necessary, especially with the current low prices for fossil fuels. Outreach strategies are required to convey the knowledge to stakeholders from both the supply and the demand side, with respect to the economic, technical and environmental aspects of manure treatment technologies.