Simulation of Long-Term Carbon and Nitrogen Dynamics in Grassland-Based Dairy Farming Systems to Evaluate Mitigation Strategies for Nutrient Losses

Many measures have been proposed to mitigate gaseous emissions and other nutrient losses from agroecosystems, which can have large detrimental effects for the quality of soils, water and air, and contribute to eutrophication and global warming. Due to complexities in farm management, biological interactions and emission measurements, most experiments focus on analysis of short-term effects of isolated mitigation practices. Here we present a model that allows simulating long-term effects at the whole-farm level of combined measures related to grassland management, animal housing and manure handling after excretion, during storage and after field application. The model describes the dynamics of pools of organic carbon and nitrogen (N), and of inorganic N, as affected by farm management in grassland-based dairy systems. We assessed the long-term effects of delayed grass mowing, housing type (cubicle and sloping floor barns, resulting in production of slurry and solid cattle manure, respectively), manure additives, contrasting manure storage methods and irrigation after application of covered manure. Simulations demonstrated that individually applied practices often result in compensatory loss pathways. For instance, methods to reduce ammonia emissions during storage like roofing or covering of manure led to larger losses through ammonia volatilization, nitrate leaching or denitrification after application, unless extra measures like irrigation were used. A strategy of combined management practices of delayed mowing and fertilization with solid cattle manure that is treated with zeolite, stored under an impermeable sheet and irrigated after application was effective to increase soil carbon stocks, increase feed self-sufficiency and reduce losses by ammonia volatilization and soil N losses. Although long-term datasets (>25 years) of farm nutrient dynamics and loss flows are not available to validate the model, the model is firmly based on knowledge of processes and measured effects of individual practices, and allows the integrated exploration of effective emission mitigation strategies.     

Sustainable intensive livestock production demands manure and exhaust air treatment technologies

Intensive livestock production is connected with a number of environmental effects, including discharges to soils and surface waters and emissions to the atmosphere. In areas with a high livestock density the low availability of nearby arable land, together with the preferred use of chemical fertilizer by arable farmers, results in high off-farm disposal costs for manure. Furthermore, ammonia abatement technologies, such as treatment of exhaust air, are important as ammonia emissions may account up to a quarter of the total nitrogen flux.     

Ammonia volatilization from cattle slurry following surface application to grassland

Three experiments were conducted using a system of small wind tunnels to measure ammonia (NH₃) volatilization from cattle slurry after surface application to land. In each experiment slurry was applied at a rate equivalent to 80 m³ ha^-1, providing the equivalent of approximately 100 kg NH₄ ⁺-N ha^-1. The first experiment compared NH₃ volatilization from the liquid fraction obtained by mechanical separation of slurry with that from unseparated slurry. The total NH₃ loss over six days from unseparated and separated slurry were very similar, being 38 and 35% respectively of the NH₄ ⁺-N applied. For the first five hours, the rate of NH₃ loss was higher from the unseparated slurry, thereafter it was consistently lower. In the second experiment, slurry was ponded in a tray to examine whether impeded infiltration or changes in the NH₄ ⁺ concentration or overall pH of the slurry influenced the rapid decline in rate soon after application that is characteristic of NH₃ volatilization from animal slurries applied to land. It appeared, however, that other factors such as resistance to diffusion within the slurry and/or at the slurry surface were mostly responsible for the rapid decline in rate. In the third experiment, in which NH₃ volatilization was measured from slurry applied to grassland or bare soil, the total loss from slurry applied to grassland was approximately 1.5 times that from slurry applied to bare soil.     

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

Ammonia emissions from the agricultural sector give rise to numerous environmental and societal concerns and represent an economic challenge in crop farming, causing a loss of fertilizer nitrogen. Ammonia emissions from agriculture originate from manure slurry (livestock housing, storage, and fertilization of fields) as well as urea-based mineral fertilizers. Consequently, political attention has been given to ammonia volatilization, and regulations of ammonia emissions have been implemented in several countries. The molecular cause of the emission is the enzyme urease, which catalyzes the hydrolysis of urea to ammonia and carbonic acid. Urease is present in many different organisms, encompassing bacteria, fungi, and plants. In agriculture, microorganisms found in animal fecal matter and soil are responsible for urea hydrolysis. One strategy to reduce ammonia emissions is the application of urease inhibitors as additives to urea-based synthetic fertilizers and manure slurry to block the formation of ammonia. However, treatment of the manure slurry with urease inhibitors is associated with increased livestock production costs and has not yet been commercialized. Thus, development of novel, environmentally friendly and cost-effective technologies for ammonia emission mitigation is important. This mini-review describes the challenges associated with the volatilization of ammonia in agriculture and provides an overview of the molecular processes of urea hydrolysis and ammonia emissions. Different technologies and strategies to reduce ammonia emissions are described with a special focus on the use of urease inhibitors. The mechanisms of action and efficiency of the most important urease inhibitors in relation to agriculture will be briefly discussed.     

The volatilization of ammonia from cattle urine applied to soils as influenced by soil properties

The amounts of ammonia volatilized, following the application of cattle urine to 22 soils, were measured in the laboratory during an incubation period of 10 days. The urine contained 12.0 g N dm^-3 and was applied to small columns of soil at a rate equivalent to 26.5 g N m^-2. The soils were from fields of both grassland and arable cultivation and varied widely in properties. Ammonia volatilization ranged from 6.8 to 41.3% of the total urinary N, with a mean value of 26.4%. The soil property most closely related to the extent of volatilization was cation exchange capacity (CEC), and this was so whether all 22 soils were considered together or whether the 14 grassland and 8 arable soils were considered separately. In general, the higher the CEC the less the amount of ammonia volatilized. However, for a given value of CEC, volatilization tended to be greater from a grassland than from an arable soil. The pH of a soil/urine mixture measured after 24 hours was also quite closely correlated with the amount of ammonia volatilized, but the initial pH and titratable acidity of the soil were poorly correlated with ammonia volatilization. ei]H Marschner ei]H Lambers     

Pathogen survival during livestock manure storage and following land application

This paper reports the first year results of field experiments to determine the survival times of pathogens in livestock manures during storage and following land application, using viable count methods. E. coli O157, Salmonella and Campylobacter survived in stored slurries and dirty water for up to three months, with Listeria surviving for up to three months. In contrast, all these pathogens survived for less than one month in solid manure heaps where temperatures greater than 55 degrees C were obtained. Following manure spreading to land, E. coli O157, Salmonella and Campylobacter generally survived in the soil for up to one month after application to both the sandy arable and clay loam grassland soils, whereas Listeria commonly survived for more than one month. These data are being used to develop guidelines on the management of manures to minimize the risks of pathogen transfer from animal manures to the human food chain.     

Modelling of manure production by pigs and NH3, N2O and CH4 emissions. Part II: effect of animal housing, manure storage and treatment practices

A model has been developed to predict pig manure evolution (mass, dry and organic matter, N, P, K, Cu and Zn contents) and related gaseous emissions (methane (CH4), nitrous oxide (N2O) and ammonia (NH3)) from pig excreta up to manure stored before spreading. This model forms part of a more comprehensive model including the prediction of pig excretion. The model simulates contrasted management systems, including different options for housing (slatted floor or deep litter), outside storage of manure and treatment (anaerobic digestion, biological N removal processes, slurry composting (SC) with straw and solid manure composting). Farmer practices and climatic conditions, which have significant effects on gaseous emissions within each option, have also been identified. The quantification of their effects was based on expert judgement from literature and local experiments, relations from mechanistic models or simple emission factors, depending on existing knowledge. The model helps to identify relative advantages and weaknesses for each system. For example, deep-litter with standard management practices is associated with high-greenhouse gas (GHG) production (+125% compared to slatted floor) and SC on straw is associated with high NH3 emission (+15% compared to slatted floor). Another important result from model building and first simulations is that farmer practices and the climate induce an intra-system (for a given infrastructure) variability of NH3 and GHG emissions nearly as high as inter-system variability. For example, in deep-litter housing systems, NH3 and N2O emissions from animal housing may vary between 6% and 53%, and between 1% and 19% of total N excreted, respectively. Thus, the model could be useful to identify and quantify improvement margins on farms, more precisely or more easily than current methodologies.     

Greenhouse gas emissions from four bioenergy crops in England and Wales: Integrating spatial estimates of yield and soil carbon balance in life cycle analyses

Accurate estimation of the greenhouse gas (GHG) mitigation potential of bioenergy crops requires the integration of a significant component of spatially varying information. In particular, crop yield and soil carbon (C) stocks are variables which are generally soil type and climate dependent. Since gaseous emissions from soil C depend on current C stocks, which in turn are related to previous land management it is important to consider both previous and proposed future land use in any C accounting assessment. We have conducted a spatially explicit study for England and Wales, coupling empirical yield maps with the RothC soil C turnover model to simulate soil C dynamics. We estimate soil C changes under proposed planting of four bioenergy crops, Miscanthus ( Miscanthus × giganteus ), short rotation coppice (SRC) poplar ( Populus trichocarpa Torr. & Gray × P. trichocarpa , var. Trichobel), winter wheat, and oilseed rape. This is then related to the former land use – arable, pasture, or forest/seminatural, and the outputs are then assessed in the context of a life cycle analysis (LCA) for each crop. By offsetting emissions from management under the previous land use, and considering fossil fuel C displaced, the GHG balance is estimated for each of the 12 land use change transitions associated with replacing arable, grassland, or forest/seminatural land, with each of the four bioenergy crops. Miscanthus and SRC are likely to have a mostly beneficial impact in reducing GHG emissions, while oilseed rape and winter wheat have either a net GHG cost, or only a marginal benefit. Previous land use is important and can make the difference between the bioenergy crop being beneficial or worse than the existing land use in terms of GHG balance.     

Turning, compacting and the addition of water as factors affecting gaseous emissions in farm manure composting

Composting allows simple management of animal manure but excessive aeration can increase emissions of polluting gases such as ammonia or nitrous oxide. The aim of the present work was to determine the effect of three techniques--turning, compacting and the addition of water--on gaseous emissions. One ton of cattle manure and 3 tons of turkey manure were composted in two and four cells for 46 and 51 days respectively. The manure was either turned, wetted, or compacted. Emissions of carbon dioxide, water vapor, ammonia and nitrous oxide were monitored. The results show that turning did not alter the free air space. Compacting can be used specifically to reduce the water loss. A reduction of free air space by 20-60%, either by compacting or adding water (or both), reduced the ammonia and nitrous oxide emissions by 30-70%.     

Stimulation of N2O emission by manure application to agricultural soils may largely offset carbon benefits: a global meta‐analysis

Animal manure application as organic fertilizer does not only sustain agricultural productivity and increase soil organic carbon (SOC) stocks, but also affects soil nitrogen cycling and nitrous oxide (N₂O) emissions. However, given that the sign and magnitude of manure effects on soil N₂O emissions is uncertain, the net climatic impact of manure application in arable land is unknown. Here, we performed a global meta‐analysis using field experimental data published in peer‐reviewed journals prior to December 2015. In this meta‐analysis, we quantified the responses of N₂O emissions to manure application relative to synthetic N fertilizer application from individual studies and analyzed manure characteristics, experimental duration, climate, and soil properties as explanatory factors. Manure application significantly increased N₂O emissions by an average 32.7% (95% confidence interval: 5.1–58.2%) compared to application of synthetic N fertilizer alone. The significant stimulation of N₂O emissions occurred following cattle and poultry manure applications, subsurface manure application, and raw manure application. Furthermore, the significant stimulatory effects on N₂O emissions were also observed for warm temperate climate, acid soils (pH < 6.5), and soil texture classes of sandy loam and clay loam. Average direct N₂O emission factors (EFs) of 1.87% and 0.24% were estimated for upland soils and rice paddy soils receiving manure application, respectively. Although manure application increased SOC stocks, our study suggested that the benefit of increasing SOC stocks as GHG sinks could be largely offset by stimulation of soil N₂O emissions and aggravated by CH₄ emissions if, particularly for rice paddy soils, the stimulation of CH₄ emissions by manure application was taken into account.     

Effect of covering pig slurry stores on the ammonia emission processes

The aim of this study was to evaluate the effects of different covers (oil, plastic film, perforated polystyrene float, peat and zeolites) on slurry settling characteristics and ammonia emission during storage and following surface application in the field. Laboratory trials were carried out for 15 days using a pilot scale device. Samples of 5 kg slurry were used. At the end of the storage period, distributions of dry matter, pH, total ammoniacal nitrogen and total Kjeldahl nitrogen in slurry were characterized. In the field, ammonia volatilisation was measured for three days using a wind tunnel system. Oil and plastic film retained all ammoniacal nitrogen forms in the slurry, whereas the others reduced ammonia volatilisation by reducing the emitting surface or by adsorbing/absorbing ammonia. Over the whole process studied (storage plus application) ammonia emissions were reduced by 40% by oil up to 65-71% by zeolites with different particle sizes.     

Earthworm effects on gaseous emissions during vermifiltration of pig fresh slurry

Treatment of liquid manure can result in the production of ammonia, nitrous oxide and methane. Earthworms mix and transform nitrogen and carbon without consuming additional energy. The objective of this paper is to analyse whether earthworms modify the emissions of NH₃, N₂O, CH₄ and CO₂ during vermifiltration of pig slurry.The experiment used mesocosms of around 50 L, made from a vermifilter treating the diluted manure of a swine house. Three levels of slurry were added to the mesocosms, with or without earthworms, during one month, in triplicate. Earthworm abundance and gas emissions were measured three and five times, respectively.There was a decrease in emissions of ammonia and nitrous oxide and a sink of methane in treatments with earthworms. We suggest that earthworm abundance can be used as a bioindicator of low energy input, and low greenhouse gas and ammonia output in systems using fresh slurry with water recycling.     

Strategies for optimizing recovery of the biogas process following ammonia inhibition

Strategies for recovery of ammonia-inhibited thermophilic biogas process, were evaluated in batch and lab-scale reactors. Active methane producing biomass (digested cattle manure) was inhibited with NH(4)Cl and subsequently, 3-5 days later, diluted with 50% of water, or with 50% digested manure, or with 50% fresh manure or kept undiluted. Dilution with fresh cattle manure resulted in the highest methane production rate during the recovery period while dilution with digested cattle manure gave a more balanced recovery according to the fluctuations in volatile fatty acids. Furthermore, the process recovery of a 7600m(3) biogas plant suffering from ammonia inhibition was observed. The ammonia concentration was only gradually lowered via the daily feeding with cattle manure, as is the normal procedure at Danish full-scale biogas plants. Recovery took 31 days with a 40% methane loss and illustrates the need for development of efficient process recovery strategies.     

Managing ammonia emissions from dairy cows by amending slurry with alum or zeolite or by diet modification

Animal agriculture is a significant source of atmospheric ammonia. Ammonia (NH3) volatilization represents a loss of plant available N to the farmer and a potential contributor to eutrophication in low-nitrogen input ecosystems. This research evaluated on-farm slurry treatments of alum or zeolite and compared three diets for lactating dairy cows in their effectiveness to reduce NH3 emissions. NH3 emissions were compared using a group of mobile wind tunnels. The addition of 2.5% alum or 6.25% zeolite to barn-stored dairy slurry reduced NH3 volatilization by 60% and 55%, respectively, compared to untreated slurry. The alum conserved NH3 by acidifying the slurry to below pH 5, while the zeolite conserved ammonia by lowering the solution-phase nitrogen through cation exchange. The use of alum or zeolite also reduced soluble phosphorus in the slurry. NH3 loss from fresh manure collected from lactating dairy cows was not affected by three diets containing the same level of crude protein but differing in forage source (orchardgrass silage vs. alfalfa silage) or neutral detergent fiber (NDF) content (30% vs. 35% NDF). NH3 losses from the freshly excreted manures occurred very rapidly and included the urea component plus some unidentified labile organic nitrogen sources. NH3 conservation strategies for fresh manures will have to be active within the first few hours after excretion in order to be most effective. The use of alum or zeolites as an on-farm amendment to dairy slurry offers the potential for significantly reducing NH3 emissions.     

土地利用变化对沙地土壤全氮空间分布格局的影响

利用经典统计学和地统计学相结合的方法,分析了科尔沁沙地东南缘草地和8年前开垦的耕地土壤全氮含量和空间分布格局．结果表明,草地与耕地表层(O～10cm)土壤全氮含量差异不显著,亚表层(10～20cm)含量差异显著(P     

Quantification,sources, and control of ammonia emissions in the Czech Republic

The exact quantification of ammonia (NH3) emissions is the basic presumption for the fulfillment of obligations set by the CLRTAP (Convention on Long Range Transboundary Air Pollution) Protocol which was signed by the Czech Republic in 1999. Most NH 3 emissions in the Czech Republic are produced during the breeding of cattle, pigs, and poultry; therefore, determinating emission factors for these kinds of animals by studying their total number, type of breeding, and subsequent disposal of manure is the solution to the problem of NH 3 emissions quantification. This paper summarizes the results of 4 years of research in this area, determining the emission factors and ways of decreasing emissions from the breeding of cattle, pigs, and poultry.     

Nitrogen transformations during biological aerobic treatment of pig slurry: effect of intermittent aeration on nitrous oxide emissions

A laboratory scale aeration treatment system was built to study the fate of nitrogen during aeration of pig slurry. For each run evaluated, the nitrogen mass balance was determined including measurement of the nitrous oxide gas emissions. Intermittent aeration led to a nitrogen removal of about 53% of the total nitrogen content of the raw slurry. About 18% of the total nitrogen content of the raw slurry was emitted as N2O during aeration with an aerobic to anoxic ratio equal to 0.625. In contrast, the extension of the anoxic period (aerobic to anoxic ratio = 0.375) allowed complete denitrification and avoided N2O emissions.     

Survival of Escherichia coli O157:H7 and Salmonella typhimurium in cow manure and cow manure slurry

An exponential linear destruction was observed for Escherichia coli O157:H7 and Salmonella typhimurium in cattle manure and manure slurry stored at 4, 20 or 37 degrees C. The resulting decimal reduction times ranged from 6 days to 3 weeks in manure and from 2 days to 5 weeks in manure slurry. The main effects of time as well as temperature were pronounced with the most rapid destruction at 37 degrees C. The ammonia concentration in manure increased slightly during storage but did not exceed 0.1%. pH values in the deeper layers of manure remained constant except at 37 degrees C when the pH increased by 1 unit in 60 days. In the surface layers of manure, pH increased by 1.5-2 units, the oxidation-reduction potential of the manure declined rapidly to values below -200 mV. These changes do not seem to be reflected in changing rates of bacterial destruction. The observed order of destruction makes it possible to predict storage conditions (temperature and time) that will lead to a predetermined level of reduction of the two pathogens.     

京津冀地区碳排放时空格局变化及其驱动因子

人类对陆地生态系统的改变是碳排放增加的主要原因。在“双碳”目标背景下探索土地利用变化与碳排放的动态关系,有助于区域土地低碳可持续利用。研究基于土地利用转移视角,采用重心-标准差椭圆方法揭示了京津冀地区土地利用碳排放时空格局演化特征,评估了碳排放与生态环境、社会经济发展的协调程度,并借助改进的Kaya模型和LMDI分解模型定量分析了土地利用变化对碳排放的影响程度。结果表明：(1)建设用地的转入是土地利用碳排放增加的主要来源,引起碳排放量增加15844.36万t;耕地、草地向林地、水域的转变促进了地区固碳能力的提升。(2)土地利用碳排放空间分布格局呈现出东北-西南方向向中心进一步聚集的趋势,并且东-西向聚集趋势大于南-北向。(3)京津冀地区整体碳排放与生态环境的协调性呈向好趋势发展,但大部分地区碳排放与社会经济发展出现失衡现象,地区间碳生产力差异逐渐增大。(4)经济水平是促进碳排放增加的最显著因素,单位GDP用地强度是抑制碳排放增加的最主要因素。分析结果表明,严格控制建设用地的无序扩张是促进低碳土地利用的基础,低碳经济发展是促进地区减碳的重要途径。     

Mitigation of ammonia,nitrous oxide and methane emissions from manure management chains: a meta‐analysis and integrated assessment

Livestock manure contributes considerably to global emissions of ammonia (NH₃) and greenhouse gases (GHG), especially methane (CH₄) and nitrous oxide (N₂O). Various measures have been developed to mitigate these emissions, but most of these focus on one specific gas and/or emission source. Here, we present a meta‐analysis and integrated assessment of the effects of mitigation measures on NH₃, CH₄ and (direct and indirect) N₂O emissions from the whole manure management chain. We analysed the effects of mitigation technologies on NH₃, CH₄ and N₂O emissions from individual sources statistically using results of 126 published studies. Whole‐chain effects on NH₃ and GHG emissions were assessed through scenario analysis. Significant NH₃ reduction efficiencies were observed for (i) housing via lowering the dietary crude protein (CP) content (24–65%, compared to the reference situation), for (ii) external slurry storages via acidification (83%) and covers of straw (78%) or artificial films (98%), for (iii) solid manure storages via compaction and covering (61%, compared to composting), and for (iv) manure application through band spreading (55%, compared to surface application), incorporation (70%) and injection (80%). Acidification decreased CH₄ emissions from stored slurry by 87%. Significant increases in N₂O emissions were found for straw‐covered slurry storages (by two orders of magnitude) and manure injection (by 26–199%). These side‐effects of straw covers and slurry injection on N₂O emission were relatively small when considering the total GHG emissions from the manure chain. Lowering the CP content of feed and acidifying slurry are strategies that consistently reduce NH₃ and GHG emissions in the whole chain. Other strategies 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. Proper farm‐scale combinations of mitigation measures are important to minimize impacts of livestock production on global emissions of NH₃ and GHG.