Manfred Trimborn’s research while affiliated with University of Bonn and other places

Background Silage emits climate- and environment-relevant gases during fermentation and feed-out periods. This trial aimed to determine the unknown carbon dioxide (CO2), methane, nitrous oxide, ethanol, and ethyl acetate emissions of constant maize silage material over both periods. The results will be published in two consecutive articles (Part A: anaerobic fermentation period, Part B: aerobic storage period). Methods The untreated control (CON) was compared with the chemical additive treatment (CHE; 0.5 g sodium benzoate and 0.3 g potassium sorbate per kg fresh matter) and the biological additive treatment (BIO; 10⁸ colony-forming units (CFU) Lentilactobacillus buchneri and 10⁷ CFU Lactiplantibacillus plantarum per kg fresh matter). Barrel silos (n = 4) were connected to gas bags to quantify gas formation during anaerobic fermentation (30 or 135 ensiling days). Glass jar silos (n = 12) were used for laboratory silage analysis. Results CHE produced significantly (p < 0.05) less gas (6.7 ± 0.3 L per kg dry matter ensiled material (kgDM) until ensiling day 14.0 ± 0.0) and ethanol (8.6 ± 1.5 mg kgDM–1) than CON did (8.5 ± 0.2 L kgDM–1 until ensiling day 19.5 ± 6.4; 12.2 ± 1.5 (mg ethanol) kgDM–1). BIO indicates prolonged gas formation (9.1 ± 0.9 L kgDM–1 until ensiling day 61.3 ± 51.9; 12.0 ± 2.1 mg kgDM–1). CO2 is the main component of the gas formed. All treatments formed methane and nitrous oxide in small quantities. CON emitted significantly more CO2eq emissions than BIO and less than CHE (p < 0.05). Additives had no effect on ethyl acetate gas emissions. For BIO, ethanol concentrations in the material (rS = 0.609, p < 0.05) and gas quantities (rS = 0.691, p < 0.05) correlate with ethyl acetate gas quantities. All the treatments exhibited decreasing gas and CO2 quantities, and the dry matter mass increased between ensiling days 14 and 30 (− 0.810 ≤ rS ≤ 0.442; p < 0.05 to p = 0.20). Conclusion Silage generates climate- and environmental-relevant gases during fermentation and silage additives affect this pattern. Gas formation exceeds the fixation potential, and the carbon footprint of silage fermentation is negative. Graphical Abstract

Calcium cyanamide (CaCN2) has been used in agriculture for more than a century as a nitrogen fertilizer with nitrification inhibiting and pest-controlling characteristics. However, in this study, a completely new application area was investigated, as CaCN2 was used as a slurry additive to evaluate its effect on the emission of ammonia and greenhouse gases (GHG) consisting of methane, carbon dioxide, and nitrous oxide. Efficiently reducing these emissions is a key challenge facing the agriculture sector, as stored slurry is a major contributor to global GHG and ammonia emissions. Therefore, dairy cattle and fattening pig slurry was treated with either 300 mg kg-1 or 500 mg kg-1 cyanamide formulated in a low-nitrate CaCN2 product (Eminex®). The slurry was stripped with nitrogen gas to remove dissolved gases and then stored for 26 weeks, during which gas volume and concentration were measured. Suppression of methane production by CaCN2 began within 45 min after application and persisted until the storage end in all variants, except in the fattening pig slurry treated with 300 mg kg-1, in which the effect faded after 12 weeks, indicating that the effect is reversible. Furthermore, total GHG emissions decreased by 99% for dairy cattle treated with 300 and 500 mg kg-1 and by 81% and 99% for fattening pig, respectively. The underlying mechanism is related to CaCN2-induced inhibition of microbial degradation of volatile fatty acids (VFA) and its conversion to methane during methanogenesis. This increases the VFA concentration in the slurry, lowering its pH and thereby reducing ammonia emissions.

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.

Silage is an essential global feedstuff. The microbiological ensiling process forms carbon dioxide, methane and nitrous oxide, and silage additives can affect this process. The study’s objective was to measure the climate-relevant emissions during the ensiling process depending on silage additive application. Corn was chopped under practical conditions. Twelve barrels were filled with 10.2 kg fresh mass each (44.9% dry matter concentration). Three variants (n=4) were used: control variant (CON), biological additive variant (BIO; 10 6 colony-forming units Lactobacillus Buchneri (kg FM)-1 and 10^5 colony-forming units Lactobacillus Plantarum (kg FM)-1) and chemical additive variant (CHE; 0.5 g sodium benzoate (kg FM)-1 and 0.3 g potassium sorbate (kg FM)-1). The quantity and quality of gas emissions were measured by gas bags connected to the barrels and gas samples taken from the barrels’ headspaces and subsequently analyzed by gas chromatography. CON silage showed a gas formation of 7.93 L (kg DM)-1 in the first 25 ensiling days, BIO 8.18 L (kg DM)-1 and CHE 6.16 L (kg DM)-1, respectively. Most gases were produced within the first 72 ensiling hours; CHE showed a significantly slower gas formation and CO2 concentration increase (p<0.05). All variants peak up to 7.00–7.65 ppm methane between hours 120–148; in detail, CHE indicated lower concentrations between ensiling hours 36–64 (p<0.05). In contrast, this variant showed the highest nitrous oxide concentrations between ensiling days 2–11 (p<0.05) with values up to 36.15 ppm at the typical peak between ensiling hours 36–44. The total emissions after 25 days were 6.48 g CO2-eq. (kg DM)-1 for CON, 6.55 g CO2-eq. (kg DM)-1 for BIO and 4.36 g CO2-eq. (kg DM)-1 for CHE, respectively. Compared to chemical ensiling additives, biological additives could not influence gas formation or reduce emissions; however, both promise higher aerobic stability.

Acidification of slurry is known to reduce ammonia emissions. In some European countries, for example Denmark, this method is already in use. At present, the system is only integrated in the construction of new barns with flat slurry channels. The aim of this study is to investigate whether acidification technology can also be retrofitted in existing barns with slurry storage under the floor. Furthermore, it is to be investigated whether ammonia and methane emissions are reduced with this method. Therefore, a trial compartment with 32 fattening pigs was retrofitted with the new acidification technology. The pH value of the slurry stored under the floor was reduced to 5.5. For this purpose, part of the slurry was mixed with sulfuric acid in an external process tank and then pumped back into the slurry channels. In the identical reference compartment (partially slatted floor, 4 pens with 8 animals each), the fattening pigs were housed simultaneously. The air volume flow was recorded with measuring fans in the exhaust air ducts. The ammonia and methane concentration in the inlet and outlet air were measured using photoacoustic infrared spectroscopy. In this way, the emission mass flow of ammonia and methane from the respective compartment could be quantified during the entire fattening period. Three fattening periods were carried out. The ammonia and methane emissions rose with increasing animal weight. Compared to the reference compartment without acidification, ammonia emissions were reduced by about 40% through slurry acidification. Furthermore, a reduction of methane emissions by about 67% was observed. The pH value in the slurry channels had to be below pH 5.5 to ensure a considerable reduction in emissions. In-house slurry acidification can thus contribute to environmental and climate protection. In addition, it is possible to still use the slurry channels as storages.

The accurate measurement of environmentally-relevant gases such as ammonia (NH3) is increasingly important, especially in agricultural science. Accurate and continuous measurement of gases is essential for evaluating NH3 and other gases as resource-based indicators of air quality in forced ventilation barns and for determining emission rates. To better assess measuring devices under different barn conditions (e.g. relative humidity or concentration range) self-conducted tests should be implemented at the laboratory scale before, during and after (experimental) measurements in the barn, independent of the manufacturer's specifications. Therefore, in this study, a gas calibration unit was set up for measurements at the laboratory scale. Moreover, measurement protocols were developed to investigate the accuracy at different gas concentrations and relative humidity levels and the responsiveness to rapid gas concentration changes. Measurements were performed with photoacoustic gas analysers (INNOVA 1412) and transmitters with electrochemical gas sensors (Polytron 8100 and C300). In addition to the presentation of results of the devices used in this case, this study should above all offer suggestions for quality monitoring to test sensors more intensively at the laboratory scale in order to be able to use them in a more targeted manner according to their optimal suitability.

Silage is an essential global feedstuff and an emitter of greenhouse gases. However, few studies have examined the formation of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) during the ensiling process. This study aimed to record the course of gas concentrations in forage during the ensiling process and determine the temporal variation in the (microbiological) formation processes. Grass and lucerne, each with two different dry matter (DM) concentrations (four variants, each n = 3), were ensiled in laboratory-scale barrels (120 L). Gas samples were taken from the headspace of the barrels and analysed using a gas chromatograph. The measurement period included the first 49 days of the ensiling process and the measurement interval was 0.5–48.0 h. For all variants, a rapid increase in CO2 concentration and a one-time N2O concentration peak was observed between ensiling hours 36 and 96. Lower DM concentration led to significantly faster CO2 production (p < 0.05). Lucerne forage and higher DM concentrations led to significantly increased N2O concentrations (p < 0.05). The extensive measurements demonstrated that butyric acid formation by clostridia contributes to CH4 formation; thus, lucerne silage had a significantly higher concentration from ensiling day 13 (p < 0.05). Therefore, malfermentation actively contributes to the formation of greenhouse gases. The method described here provides further insights into greenhouse gas formation during the ensiling process and can thus help to improve ensiling research and management.

For several decades, farmers have been mixing rock powders with livestock slurry to reduce its NH3 emissions and increase its nutrient content. However, mixing rock powders with slurry is controversial, and there is currently no scientific evidence for its effects on NH3 and greenhouse gas (GHG) emissions or on changes in its nutrient content due to element release from rock powders. The major aim of this study was therefore to analyse the effects of mixing two commercially established rock powders with cattle slurry on NH3, CO2, N2O and CH4 emissions, and on nutrient release over a course of 46 days. We found that rock powders did not significantly affect CO2 emission rates. NH3 and N2O emission rates did not differ significantly up until the end of the trial, when the emission rates of the rock powder treatments significantly increased for NH3 and significantly decreased for N2O, respectively, which coincided with a reduction of the slurry crust. Cumulative NH3 emissions did not, however, differ significantly between treatments. Unexpected and significant increases in CH4 emission rates occurred for the rock powder treatments. Rock powders increased the macroand micronutrient content of the slurry. The conflicting results are discussed and future research directions are proposed.

Acidification of slurry is a common practice to reduce ammonia and methane emissions. Sulfuric acid is usually used for this process. However, this has been criticized due to the high sulfur input into soils. Therefore, the objective of this study is to show the effectiveness of a one-time acidification with alternative acids also in combination with other treatment strategies. The amount of acid as well as the change of pH value during storage were investigated. For most variants, a strong pH increase occurred within the first ten days after acidification. Mineral acids (sulfuric or hydrochloric acid) resulted in a lower pH increase compared to organic acids (lactic, acetic, and citric acid). Under anaerobic storage conditions, the pH remained significantly lower. The addition of glucose before acidification resulted in lower pH values during the first week, but in the long term, the conversion of glucose to carbonate led to higher pH values. A previous separation process was able to reduce the amount of acid. Although the pH increase was not that strong in the first days after acidification, it was much faster and stronger afterwards due to the lower buffer capacity in the separated slurry. A long-term pH reduction was achieved by acidification to pH 3.0, but this was associated with an increased amount of acid. On the basis of the results, a combination of organic acids with anaerobic storage can be recommended as an alternative to sulfuric acid.

Slurry acidification is a well-known method for reducing methane and ammonia emissions. Since there are different buffers in the slurry, the acid addition must be adapted to the different buffer capacities. In the acidic range, fatty acid buffer and the carbonate buffer are relevant. The objective of the present study was to investigate slurries with different pretreatments (storage conditions, separation) with regard to their acid consumption for defined pH values. Titration experiments were carried out with samples of fresh dairy cow slurry, fattening pig slurry and sow slurry, which were stored over a period of 12 weeks at 4.7 °C and 23.6 °C. Additionally, the liquid phase was observed immediately after separation and after 8 weeks. The slurries were titrated weekly with HCl to pH value 2.5 by using a titrator. The acid consumption up to pH values 5.5 and 3.0 of the various treatments were compared with each other. Results showed a lower acid consumption for the liquid phase compared to the non-separated slurry when titrating up to pH value 3.0. Furthermore, different storage temperatures affected the acid consumption. Within storage time the acid consumption for achieving the pH value 3.0 from 5.5 changes in all slurries. This effect could be an indicator for changes between the fatty acid buffer and carbonate buffer over the storage period. The slurry pretreatment and the condition and duration of storage have an influence on the buffer capacity and amount of acid for targeted pH value. This influences the current costs of acidification technologies.