Slurry Acidification Research Articles

An Incubation System for the Simulation of Ammonia Emissions from Soil Surface-Applied Slurry: Effect of pH and Acid Type

Acidification of slurry is a promising approach for reducing ammonia emissions during the application procedure. Since only a few studies have been conducted focusing on ammonia emissions during the application of liquid organic fertilizers on the soil surface, a suitable incubation system was developed to evaluate the effects of acidification under controlled conditions. This incubation system was used to measure the ammonia emissions of various liquid organic fertilizers. The substrates were acidified with sulfuric and citric acid to different pH values to determine both the influence of the pH value of the substrates and of the type of acid on the ammonia emissions. The emissions decreased with declining pH value, and the reduction in emissions compared to the initial pH of the substrate was over 86% for pH 6.5 and over 98% for pH 6.0 and below. At the same pH value, the ammonia emissions did not differ between substrates acidified with citric acid and sulfuric acid, although more than twice as much 50% citric acid was required compared to 96% sulfuric acid to achieve the same pH value. Overall, our results demonstrate that the incubation system used is suitable for measuring ammonia emissions from surface-applied liquid organic fertilizers. The system allows for the differentiation of emission levels at various pH levels and is therefore suitable for testing the effectiveness of additives for reducing ammonia emissions from liquid organic fertilizers.

Modeling the environmental impacts of Asparagopsis as feed, a cow toilet and slurry acidification in two synthetic dairy farms

Intensive dairy farming, particularly enteric fermentation and manure management, is a major contributor to negative impacts on the local and global environment. A wide range of abatement measures has been proposed to reduce livestock-related emissions, yet the individual and combined effects of these innovations are often unknown. In this study, we performed an attributional life cycle assessment of three innovative measures modeled in two synthetic German dairy farm systems: Feeding of the seaweed Asparagopsis, installing an in-house cow toilet system, and performing on-field slurry acidification. These measures were modeled both individually and in combination to account for single and cumulative effects and compared to a reference scenario under current practices. Our results showed that feeding high levels of Asparagopsis and the combination of all three measures were most effective at reducing global warming potential (20–30 %), while only the latter mitigated eutrophication (6–9%) and acidification potential (14–17 %). The cow toilet required additional adapted manure management (separated storage and injection of urine) to effectively reduce eutrophication (8–10 %) and acidification potential (19–23 %) and to decrease global warming potential (3–4%) and abiotic depletion (4–5%). Slurry acidification slightly affected all considered environmental impact categories. All three measures involved trade-offs, either between LCA impact categories (global warming potential vs. abiotic depletion), the location of impacts (off- vs. on-farm), or the emission reduction in individual gases (ammonia vs. nitrous oxide). Measure combinations could compensate for the observed trade-offs. Our study highlights the potential of novel abatement measures but also shows the interdependencies of measures in different stages. This calls for a revisiting of current priorities in funding and legislation, which often focus on single objectives and measures (e.g. ammonia reduction) toward the preferential use of measures that are effective without driving trade-offs or improving resource efficiency.

Slurry acidification is as effective as slurry injection at reducing ammonia emissions without increasing N2O emissions: A short-term mesocosm study

Agriculture currently accounts for 90% of UK ammonia (NH3) emissions, however, national legally-binding targets are seeking to reduce this by 16% by 2030, relative to 2005 levels. One area which has been targeted to help achieve this target is the lowering of NH3 emissions during livestock manure handling and storage. Slurry acidification represents one potential strategy to abate NH3 throughout the slurry management chain, however, is not currently used in the UK. To address this knowledge gap, two mesocosm-scale experiments were set up to assess the potential for slurry acidification to reduce NH3 emissions at application and to measure impacts on NH3 emissions and short-term changes to soil mineral dynamics and N2O emissions. Experiment 1 determined the impacts of acidified cattle slurry (pH 6.5, 5.5, and 4.8) to conventional (non-acidified) slurry when simulating surface broadcasting. Experiment 2 assessed the impact of conventional and acidified slurry (pH 5.5) using simulated surface broadcasting and shallow injection of cattle slurry. Our results showed that acidification significantly abated NH3 (% of NH4-N applied) from 61.6% for conventional slurry to 26.6% at pH 5.5, and 2.5% at pH 4.8. Acidified surface broadcast was as effective at abating NH3 emissions to injected conventional slurry, and also delayed nitrification, while not significantly altering N2O emissions from conventional slurry. Our results strongly suggest that slurry acidification could be a viable strategy to help the UK reach its NH3 reduction target and exceed the current abatement potential through combining low emissions spreading techniques with acidification.

Ammonia emission factors from cattle production systems in Ireland – a review

Ammonia (NH3) emissions from livestock production contribute to environmental pollution. To address this challenge, the European Union (EU) National Emission Reduction Commitments Directive 2016/2284 (NECD) sets NH3 reduction targets for EU member states. In order to achieve these targets, several strategies have been evaluated under Irish conditions. A compilation of emission factors (EFs) from studies which evaluated these strategies is necessary to assess their effectiveness. This paper reports NH3 EFs from cattle production under Irish conditions. The results from the review show that the mean EFs from the deposition of dung, urine and urea applied to urine patches on grasslands were 4%, 9% and 8% total nitrogen (TN), respectively. EFs from the application of urea to urine patches were reduced by 28% after the addition of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) to urea. The mean EF of 28% TN reported for urea fertiliser was almost 7 times higher than calcium ammonium nitrate (CAN). The inclusion of urease inhibitors with urea fertilisation on grassland led to EF reduction of up to 86%. The mean EFs from cattle houses, concrete yards, slurry storage pits and slurry landspreading were approximately 13%, 35%, 60% and 59% total ammoniacal nitrogen (TAN), respectively. The most effective NH3 abatement strategies for concrete yards and slurry storage were immediate cleaning of concrete floors (up to 89% reduction) after excreta deposition and the application of chemical amendments (sulphuric acid, acetic acid, alum and ferric chloride) to slurry in storage pits (up to 98% reduction), respectively. Low-emission spreading strategies and slurry acidification were effective at abating EFs after slurry application to land.

Nitrogen Enriched Organic fertilizer (NEO) elevates nitrification rates shortly after application but has no lasting effect on nitrification in agricultural soils

Amidst population growth, escalating food costs, limited arable land, and farmland degradation, the adoption of innovative technologies—like organic waste recycling and nutrient recovery—is crucial for enhancing the resilience of global agri-food systems. Nitrogen-Enriched Organic fertilizer (NEO) is produced using a new method, where dinitrogen (N2) is captured from the air through a plasma process and mixed with slurries or digestates as nitrate (NO3-) and nitrite (NO2-). This process leads to solid slurry acidification and a high NO2- content, potentially yielding toxic inorganic or organic N compounds. This study investigated the impact of NEO derived from cattle slurry and biogas digestate on soil nitrification—conversion of NH4+ to NO2- and NO3- by aerobic autotrophic bacteria and archaea. We investigated and compared the potential nitrification rates in soil samples from two agricultural trials (cereal and grass) treated with NEO and other fertilizers after two consecutive fertilization years. Additionally, we examined the immediate nitrification response to NEO through 73-hour soil incubations. Our results revealed that NEO significantly stimulated nitrification rates in agitated soil slurries, regardless of the feedstock used, surpassing rates observed in ammonium controls. Similarly, this pattern was also observed in loosely placed soil samples, with high nitrification rates occurring with NEO and ammonium chloride. Interestingly, the differences in nitrification rates between field-fertilized soil samples were minimal and inconsequential, suggesting that while NEO exhibits a rapid boost in nitrification rates shortly after application, this effect is not sustained ≈ six months after fertilization under field conditions. Consequently, NEO indicates its potential as an environmentally benign fertilizer without adversely affecting soil nitrification.

Influence of slurry acidification with H2SO4 on soil pH, N, P, S, and C dynamics: Incubation experiment

Acidifying slurry with sulfuric acid (H2SO4) is practiced in some countries for reducing ammonia (NH3) emissions during slurry storage and spreading to land. However, knowledge on how the application of acidified slurry affects soil health and nutrient cycling is lacking. This is particularly important since acidification with H2SO4 can substitute a sulfur (S) mineral fertilizer to increasingly S-deficient agricultural soils. We hypothesized that (ⅰ) slurry acidification would decrease the soil pH over a prolonged period, and as a result (ⅱ) would increase the extractable N, P, C and S concentrations, (ⅲ) and decrease greenhouse gas emissions. By using laboratory mesocosms, the nutrient (C, N, P and S) dynamics were monitored in an arable sandy clay loam soil receiving acidified and non-acidified cattle slurry in a 2-month incubation. Estimations of greenhouse gas emissions (CO2, CH4, N2O), soil-pore- water components (NO3−, NH4+, PO43−, SO42−, DOC, DON, pH) were performed on static mesocosms. In addition, a parallel set of mesocosms were used for soil extractions using distilled water and 0.5 M K2SO4. There were six treatments: (1) soil (control), (2) soil + slurry, (3) soil + acidified slurry (with H2SO4, pH =5.5), (4) soil + HCl, (5) soil + K2SO4, and (6) soil + K2SO4 + H2SO4. Our results showed that over the incubation, slurry acidification reduced soil pH by at least 0.4 units. Water soluble PO43−-P concentration was also reduced, whilst extractable DOC and NO3—N concentrations were increased; the latter as a result of stimulated N mineralization in the acidification treatments (3, 4 and 6). Differences in water soluble SO42- -S concentrations per treatment were not significant over time.Slurry acidification did not significantly affect N2O emissions but decreased net CO2 and CH4 emissions leading to an overall reduction in the soil's total greenhouse gas footprint (expressed as CO2e). We conclude that application of acidified slurry to soil can reduce soil pH by at least 0.4 pH units for up to 2-months before it is buffered back to the pH level of the soil that received the non-acidified slurry. In addition to increasing organic N mineralization with limited impacts on P and S dynamics of the soil and the slurry.

Analysis of Manure Separation Technology Efficiency into Fractions Followed by Liquid Fraction Rectification

Introduction. There is not enough data on the used intensive technologies of processing pig manure into organic fertilizer to accurately calculate the content of nutrients in the final products and, accordingly, their doses of application. Aim of the Article. To determine the efficiency of pig manure processing technology, which includes liquid fraction rectification, by the quantitative and qualitative characteristics of manure and final products, and to trace the redistributing total nitrogen between the final products on the example of a pilot pig breeding complex production. Materials and Methods. For the study, there was chosen a typical pig-breeding complex, where the pig manure processing included slurry acidification, flocculation, separation into fractions in a decanter centrifuge, rectification of liquid fraction, passive composting of solid fraction, and long-term storing of liquid fraction. The technology allows producing three types of end products: solid organic fertilizer, concentrated liquid (ammonia water), and fertilizer solution. Quantity and quality of pig manure and the end products were calculated by the known methods. Experimental studies were performed to compare the results. Samples were analyzed in the analytical laboratory of Institute for Engineering and Environmental Problems in Agricultural Production in 2022. Three replications were carried out for each sample. The experimental data were statistically analysed in MS Excel. Results. Quantitative and qualitative characteristics of pig manure, its solid and liquid fractions, and end products were calculated. The difference between the calculated and actual values does not exceed 10.2% that indicates the reliability of calculations. Discussion and Conclusion. The introduction of a new technology at the pig-breeding complex has reduced atmospheric emissions by 10% due to the nitrogen conservation, has reduced operating costs for transporting organic fertilizer by 47% due to the concentration of nutrients in a smaller volume and has improved soil fertility through fertilizer irrigation.

Simple Management Changes Drastically Reduce Pig House Methane Emission in Combined Experimental and Modeling Study.

Reducing methane from livestock slurry is one of the quickest ways to counteract global warming. A straightforward strategy is to reduce slurry retention time inside pig houses by frequent transfer to outside storages, where temperature and therefore microbial activity are lower. We demonstrate three frequent slurry removal strategies in pig houses in a year-round continuous measurement campaign. Slurry funnels, slurry trays, and weekly flushing reduced slurry methane emission by 89, 81, and 53%, respectively. Slurry funnels and slurry trays reduced ammonia emission by 25-30%. An extended version of the anaerobic biodegradation model (ABM) was fitted and validated using barn measurements. It was then applied for predicting storage emission and shows that there is a risk of negating barn methane reductions due to increased emission from outside storage. Therefore, we recommend combining the removal strategies with anaerobic digestion pre-storage or storage mitigation technologies such as slurry acidification. However, even without storage mitigation technologies, predicted net methane reduction from pig houses and following outside storage was at least 30% for all slurry removal strategies.

Acidification of slurry to reduce ammonia and methane emissions: Deployment of a retrofittable system in fattening pig barns

Livestock farming, and in particular slurry management, is a major contributor to ammonia (NH3) and methane (CH4) emissions in Europe. Furthermore, reduced NH3 and CH4 emissions are also relevant in licensing procedures and the management of livestock buildings. Therefore, the aim is to keep emissions from the barn as low as possible. Acidification of slurry in the barn can reduce these environmental and climate-relevant emissions by a pH value of 5.5. In this study, an acidification technology was retrofitted in an existing fattening pig barn equipped with a partially slatted floor. The slurry in a compartment with 32 animals was acidified. An identical compartment was used for reference investigations (case-control approach). Several times a week slurry was pumped for acidification in a process tank outside the barn compartment in a central corridor, where sulphuric acid (H2SO4) was added. Then the slurry was pumped back into the barn. In contrast to other systems, where acidified slurry was stored mainly in external storage tanks, in this study the slurry was completely stored in the slurry channels under the slatted floor, during the entire fattening period. The emission mass flow of NH3 and CH4 was measured continuously over three fattening periods, with one period in spring and two periods in summer. On average 17.1 kg H2SO4 (96%) (m³ slurry)−1 were used for acidification during the three fattening periods. NH3 and CH4 emissions were reduced by 39 and 67%, respectively. The hydrogen sulphide (H2S) concentration in the barn air of the acidification compartment was harmlessly low (0.02 ppm). Thus, despite the storage of the acidified slurry in the barn, the system leads to a lower concentration of detrimental gases, which is beneficial for the animals' as well as for the workers’ health. The study shows that it is possible to retrofit acidification technology into existing pig barns. Further investigations shall identify possible measures to reduce the amount of H2SO4 used and thus minimise the sulphur input into the slurry.

Impacts of slurry acidification and injection on fertilizer nitrogen fates in grassland

Low nitrogen (N) use efficiency of broadcast slurry application leads to nutrient losses, air and water pollution, greenhouse gas emissions and—in particular in a warming climate—to soil N mining. Here we test the alternative slurry acidification and injection techniques for their mitigation potential compared to broadcast spreading in montane grassland. We determined (1) the fate of 15N labelled slurry in the plant-soil-microbe system and soil-atmosphere exchange of greenhouse gases over one fertilization/harvest cycle and (2) assessed the longer-term contribution of fertilizer 15N to soil organic N formation by the end of the growing season. The isotope tracing approach was combined with a space for time climate change experiment. Simulated climate change increased productivity, ecosystem respiration, and net methane uptake irrespective of management, but the generally low N2O fluxes remained unchanged. Compared to the broadcast spreading, slurry acidification showed lowest N losses, thus increased productivity and fertilizer N use efficiency (38% 15N recovery in plant aboveground plant biomass). In contrast, slurry injection showed highest total fertilizer N losses, but increased fertilization-induced soil organic N formation by 9–12 kg N ha−1 season−1. Slurry management effects on N2O and CH4 fluxes remained negligible. In sum, our study shows that the tested alternative slurry application techniques can increase N use efficiency and/or promote soil organic N formation from applied fertilizer to a remarkable extent. However, this is still not sufficient to prevent soil N mining mostly resulting from large plant N exports that even exceed total fertilizer N inputs.

Bio-Acidification of Cattle Slurry with Whey Reduces Gaseous Emission during Storage with Positive Effects on Biogas Production

Livestock manure is the main source of ammonia (NH3) and greenhouse gases emissions (GHG), which can be reduced by acidifying manure. This work assessed the effect of acidification of cattle slurry using whey on NH3 and GHG emissions during storage, followed by its usage for biogas production. Tests were conducted to optimize the dose and the frequency at which whey was applied to cattle slurry. Two of the analyzed treatments, AS1-100 and AS1-10, showed reduced emissions when compared with the control AS1-0 without whey. In AS1-100, 100% of the optimized amount of whey was added to the slurry at the beginning of the test, while in AS1-10 whey was fractioned in 10 applications (one per day) corresponding to 10% of the total. Batch-type anaerobic digestion assays using AS1-100 and AS1-10 as feedstock resulted in a significant increase in methane production when compared with the anaerobic digestion of AS1-0 (+33% and +53%, respectively). The best results in terms of gas emissions abatement and methane production during anaerobic digestion were obtained when a low organic loading rate of whey was used. These results demonstrate that the use of whey for slurry acidification is a viable approach for potentially solving the economic and environmental problems of GHG and NH3 emissions during slurry storage, whereby increasing energy and environmental sustainability.

Effect of natural and regulatory conditions on the environmental impacts of pig slurry acidification across different regions in Europe: A life cycle assessment

Animal manure handling is an essential but challenging part of Europe's intensive agriculture. To safeguard the environment and facilitate sustainable livestock production, lower-impact manure management technologies need to be identified, evaluated and implemented. Slurry acidification has been developed to address some of the environmental challenges faced by pig farmers, such as methane and ammonia emissions, that contribute to environmental impacts such as climate change, terrestrial acidification and air fine particulate matter formation. However, the efficiency of this technology has been found to depend on local environmental and regulatory conditions. The current study compared two slurry treatment options (no treatment versus slurry acidification in storage tanks) under the climatic, agronomic and legislative conditions found in Denmark, the Netherlands and Spain using Life Cycle Assessment (LCA). Data for the LCA model was collected from various sources and emissions following field application and crop yields were simulated over a 100-year period using the Daisy agricultural model. To address the uncertainty in LCA modelling, parameter analyses and Monte Carlo simulations with 1000 iterations were conducted followed by pairwise statistical tests. The results indicated that slurry acidification reduces the impact in all countries in impact categories mostly related to direct emissions from agriculture, such as methane and ammonia. For impact categories related to the provision of materials and energy to the farm, acidification increased the impacts in some cases. Additional requirements for lime application to counteract potential soil acidification did not result in significant changes in the performance of slurry acidification. The sulphur in the applied acid as an alternative to mineral S fertiliser can in some cases reduce the environmental impact of slurry acidification, but should not be advertised as doing so per se. Introducing stricter P application limits would seem to be the preferred option compared with slurry acidification in the Netherlands, while the opposite appeared true for Denmark.

Bio-acidification of animal slurry: Efficiency, stability and the mechanisms involved

Slurry acidification is effective for reducing gaseous emissions during slurry storage. However, an alternative to sulfuric acid traditionally used is needed. This study investigated the efficiency of slurry bio-acidification treatment by adding different types and amounts of fermentable substrates to initiate and sustain the fermentation process. The carbon pools in the slurry were quantified to understand the mechanisms involved during the bio-acidification. Substrate addition efficiently reduced slurry pH during storage via lactic acid production. Substrates with a low pH proved beneficial in initiating the fermentation process, but higher glucose dosage did not produce the highest lactic acid concentration. Once the treated slurries reached pH 4.2 during the fermentation process, the production of lactic acid was promoted and provided substrate was still available, the weaker volatile fatty acids were avoided, resulting in lower CH4 emissions. In conclusion, bio-acidification could replace the sulfuric acid to reduce gaseous emissions during slurry storage.

Reducing greenhouse gas emissions from pig slurry by acidification with organic and inorganic acids.

Methane (CH4) emission from pig slurry is a large contributor to the climate footprint of livestock production. Acidification of excreta from livestock animals with sulfuric acid, reduce CH4 emission and is practiced at many Danish farms. Possible interaction effects with other acidic agents or management practices (e.g. frequent slurry removal and residual slurry acidification) have not been fully investigated. Here we assessed the effect of pig slurry acidification with a range of organic and inorganic acids with respect to their CH4 inhibitor potential in several batch experiments (BS). After careful selection of promising CH4 inhibitors, three continuous headspace experiments (CHS) were carried out to simulate management of manure in pig houses. In BS experiments, more than <99% CH4 reduction was observed with HNO3 treatment to pH 5.5. Treatments with HNO3, H2SO4, and H3PO4 reduced CH4 production more than acetic acid and other organic acids when acidified to the same initial pH of 5.5. Synergistic effects were not observed when mixing inorganic and organic acids as otherwise proposed in the literature, which was attributed to the high amount of acetic acid in the slurry to start with. In the CHS experiments, HNO3 treatment reduced CH4 more than H2SO4, but increased nitrous oxide (N2O) emission, particularly when the acidification target pH was above 6, suggesting considerable denitrification activity. Due to increased N2O emission from HNO3 treatments, HNO3 reduced total CO2-eq by 67%, whereas H2SO4 reduced CO2-eq by 91.5% compared to untreated slurry. In experiments with daily slurry addition, weekly slurry removal, and residual acidification, HNO3 and H2SO4 treatments reduced CO2-eq by 27% and 48%, respectively (not significant). More cycles of residual acidification are recommended in future research. The study provides solid evidence that HNO3 treatment is not suitable for reducing CO2-eq and H2SO4 should be the preferred acidic agent for slurry acidification.

Incentivising ammonia emission abatement through in-house slurry acidification: Evidence from a discrete choice experiment in Germany

This article assesses farmers' willingness to participate in a stylised scheme supporting the adoption of slurry acidification techniques in livestock facilities. Slurry acidification is a novel technique, developed in Denmark, to reduce ammonia emissions. In a discrete choice survey of 129 German livestock farmers, the respondents were asked to choose among different support schemes and the status quo. The attributes presented in the choice sets were the expected emission reduction, the cost share on offer, a factor by which the additional nitrogen in acidified slurry must be accounted for in fertiliser plans, and concessions on current fertiliser regulations. A mixed logit model showed that the majority of respondents valued emission reductions, a higher cost share and concessions on the statutory requirements of the Fertiliser Ordinance. A latent-class model was applied to reveal preference heterogeneity. It identified three preference classes with different perceptions of the scheme's attributes.

Slurry acidification outperformed injection as an ammonia emission-reducing technique in boreal grass cultivation

Ammonia (NH3) constitutes the single largest loss of manure nitrogen (N), making measures targeted at reducing its emissions meaningful for the environment and the overall efficiency of manure N use. In this study, the performance of two emission-reducing techniques, acidification and injection, were studied in a field experiment with grass ley over two growing seasons. Emissions of NH3, crop growth, and N use efficiency were determined from plots fertilized with cattle slurry either band spread, injected or band spread after acidification. The approximate cumulative NH3 losses from the plots with band-spread untreated slurry amounted to about 22 kg NH3-N ha−1 over the observation periods in 2017 and 10 kg NH3-N ha−1 in 2018. The injection and acidification reduced the estimated cumulative NH3 emissions by 43 and 95% respectively in 2018, and both by 97% in 2017. In 2017, the emission-reducing techniques had no impacts on crop growth, but in 2018, acidification increased dry matter yield by 29% and apparent N recovery by 65% compared with band-spread untreated slurry. According to the current results, acidification consistently produced the lowest NH3 emissions and a discernible positive yield effect. It can therefore be recommended instead of injection for reducing NH3 emissions in boreal grass cultivation.

Slurry Acidification as a Solution to Minimize Ammonia Emissions from the Combined Application of Animal Manure and Synthetic Fertilizer in No-Tillage

The combined application of manure/slurry and synthetic fertilizer (SF) might be a solution to decrease transport and application costs involving those by-products as well as enable access to them in regions where availability is low. Moreover, their joint application can potentially reduce environmental pollution, enlarge the manure benefits to more areas, and enhance the SF efficiency. However, such a strategy might result in increased ammonia emissions when applied to crop residues. Two experiments were implemented to assess ammonia emissions from stubble-covered soil fertilized with manure amended with SF. In Experiment 1 (E1), urea (U) and calcium ammonium nitrate (AN) were applied combined with dairy manure (MAN). In Experiment 2 (E2), urea was combined with acidified pig slurry (APS) and applied just after sowing (T0) or eight days later (T8). The combinations U + MAN and AN + MAN increased the ammonia emissions, while APS decreased the emissions from U, in APS + U combination, by more than 75%. Therefore, manure combined with SF applied on stubble-covered soil should not be recommended. T8 reduced ammonia emissions from U. APS enhanced the efficiency of U, being then an interesting strategy to mitigate ammonia emissions when applied on stubble-covered soil, as in no-tillage.

Phosphorus Flows, Surpluses, and N/P Agronomic Balancing When Using Manure from Pig and Poultry Farms

The pig and poultry industries continue to grow across the world and together they provide the majority of meat consumed. The European Union (EU) in particular has the highest global relative meat production by monogastrics (i.e., pig and poultry). The fate of phosphorus (P) in pig and poultry farming was studied, accounting for P content in feed, animals, manure, soil, and runoff. P input from manure, and P offtake in crops receiving manure, were plotted against each other to arrive at “safe” P loading rates, in order to minimize soil P surpluses along the lines of the EU Nitrogen Expert Panel in their work with nitrogen (N). However, it was observed that it is the N/P ratio and the background soil P levels that determine whether a certain manure will end up producing surplus levels of soil P. Critical N/P weight ratios were derived over different crop P offtake rates when applying stored manure to croplands. At spreading rates of 170 and 250 kgN/ha/year and a crop P offtake of 15 or 30 kgP/ha/year, stored pig and chicken manure result in soil P surpluses. An important factor in determining effective N/P ratios is the plant availability of N in stored manure, which runs at around 47%, estimated from previously published results. The minimization of N losses to the atmosphere and to groundwater in housing, storage, and spreading of manure has a major impact on the N/P weight ratio of the manure that ends up on fields. In most cases, half of the ex-animal N content has been lost in stored or degraded manure, with N/P weight ratios running at two and less. Following only the EU Nitrates Directive, which allows for a maximum of 170 kgN/ha/year in NVZs (Nitrate Vulnerable Zones), will often result in soil P surpluses leading to runoff losses to adjacent water bodies. Therefore, for the pig and poultry industries to continue thriving, measures are required to better manage manure, including improved storage and spreading techniques, acidification, separation, struvite extraction and ammonia stripping of pig slurry, and drying and pelleting of poultry litter. This way, excess manure and derived biofertilizers from animal farms can find their way back into the commercial market, instead of ending up as legacy P in watersheds and coastal zones.

Acidification Effects on In Situ Ammonia Emissions and Cereal Yields Depending on Slurry Type and Application Method

Field application of organic slurries contributes considerably to emissions of ammonia (NH3) which causes sever environmental damage and can result in lower nitrogen (N) fertilizer efficiency. In recent years, field acidification systems have been introduced to reduce such NH3 emissions. However, combined field data on ammonia emissions and N use efficiency of acidified slurries, in particular by practical acidification systems, are scarce. Here, we present for the first time a simultaneous in situ assessment of the effects of acidification of five different organic slurries with a commercial acidifications system combined with different application techniques. The analysis was performed in randomized plot trials in winter wheat and spring barley after two applications to each crop (before tillering and after flag leave emergence) in year 2014 in Denmark. Slurry types included cattle slurry, mink slurry, pig slurry, anaerobic digestate, and the liquid phase of anaerobic digestate. Tested application techniques were trail hose application with and without slurry acidification in winter wheat and slurry injection and incorporation compared to trail hose application with and without acidification in spring barley. Slurries were applied on 9 m × 9 m plots separated by buffer areas of the same dimension. Ammonia emission was determined by a combination of semi-quantitative acid traps scaled by absolute emissions obtained from Draeger Tube Method dynamic chamber measurements. Experimental results were analysed by mixed effects models and HSD post hoc test (p &lt; 0.05). Significant and almost quantitative NH3 emission reduction compared to trail hose application was observed in the barley trial by slurry incorporation of acidified slurry (89% reduction) and closed slot injection (96% reduction), while incorporation alone decreased emissions by 60%. In the two applications to winter wheat, compared to trail hose application of non-acidified slurry, acidification reduced NH3 emissions by 61% and 67% in cattle slurry, in anaerobic digestate by 45% and 57% and liquid phase of anaerobic digestate by 58%, respectively. Similar effects but on a lower emission level were observed in mink slurry, while acidification showed almost no effect in pig slurry. Acidifying animal manure with a commercial system was confirmed to consistently reduce NH3 emissions of most slurry types, and emission reductions were similar as from experimental acidification systems. However, failure to reduce ammonia emissions in pig slurry hint to technical limitations of such systems. Winter wheat and spring barley yields were only partly significantly increased by use of ammonia emission mitigation measures, while there were significant positive effects on apparent nitrogen use efficiency (+17–28%). The assessment of the agronomic effects of acidification requires further investigations.

Effects of slurry acidification on soil N2O fluxes and denitrification

AbstractBackgroundReductions of ammonia volatilization resulting from slurry applications to intensively managed grassland may be achieved via slurry acidification. However, it remains uncertain if this may result in pollution swapping, that is, due to reduced ammonia volatilization and increased soil N availability, emission of nitrous oxide from soils may increase.AimsIn this study, we compared control (no fertilizer) and slurry fertilized grassland treatments [not acidified (S) and acidified (AS)] to assess whether slurry acidification results in changes of soil N availability, denitrification potential and activity as well as soil fluxes of nitrous oxide.MethodsThe study was carried out in a montane grassland system in southern Germany, and parameters were followed over a 43‐days period with continuous measurements of soil GHG fluxes and biweekly measurements of microbial and soil parameters preceding and following two fertilizing events.ResultsOver the entire observation period cumulative N2O emissions were significantly elevated for treatments receiving slurry applications, with differences between acidified and non‐acidified slurry treatments being overall insignificant. Transcripts of the nirK type nitrite reductase showed significantly higher numbers in soils of the AS treatment. While soil potential denitrification rates (PDR) did not differ between treatments, there was a strong tendency of increased PDRs for the AS treatment.ConclusionsAgainst expectation, we did not find that application of AS affects PDR or soil N2O emissions significantly, though in tendency higher rates of soil N2O emissions as well as higher potential denitrification rates were found in treatments receiving acidified slurry as compared to the slurry only treatment. Our results indicate that longer observation periods and given the significant spatial variability, higher numbers of replicates are needed, to finally assess if slurry application indeed results in increased soil denitrification activity, soil N2O production and soil‐atmosphere N2O emissions.