General Overview of the Slurry Issue
Slurry is a buzzword in the public eye when it comes to agriculture and economics, and it has ultimately found its way into European legislation.
Farmyard manure such as slurry or manure was the most important source of nitrogen for fertilizing fields until the commercial implementation of the Haber-Bosch process for the synthetic production of nitrogen (early 20th century). Slurry was viewed positively. Due to the advancing industrialization of agriculture in the areas of animal husbandry and crop cultivation, a change has occurred:
Ø Due to the change in feed composition towards more concentrated protein feed, the proportion of NH³ in the slurry has increased (undigested protein breaks down into nitrogen components).
Ø Intensive livestock farming produces ever larger quantities of slurry in ever smaller spaces, which are then spread over limited areas. The result in connection with over-fertilization from synthetically produced and natural nitrogen is nitrate contamination of the soil and groundwater. Slurry has been declared the factor primarily responsible and has thus become negatively associated with it.
Ø Because slurry from animals with poor rumen fermentation is rich in nitrogen, relatively low in carbon, and high in emissions, it tends to form a floating layer, foam layer, or gas layer on the surface. The part of the slurry beneath this layer then rots and produces many toxins. The greatly increased administration of medications, disinfectants from foot baths, or flush water from milking machines also makes slurry a partially toxic product. Untreated, it is not good food for soil life.
Today, the picture is beginning to change. Slurry is increasingly seen as an affordable, environmentally friendly alternative to fertilization with synthetic nitrogen. Its use meets the requirements of sustainable agriculture.
In addition, new technologies have been developed that combine high-tech with agriculture adapted to nature and support it. And thus slurry becomes a highly effective product that can bind nitrogen. Together with other substances and added products such as silicon and other trace elements, slurry becomes a complex fertilizer or additive at low manufacturing costs. Furthermore, the various components required by the soil can be applied together in this way, and the price increase of the nitrogen components due to higher energy prices can be at least partially offset.
It is gradually becoming clear even to the experts that a virtue can be made of necessity here:
The production of high-quality fertilizer in which NH³ emissions can be greatly reduced.
Processed slurry closes the nutrient cycle with its high content of naturally processed and bound nutrients, the lower NH³ content, and the microorganisms involved, with the highest soil-ecological effectiveness.
Slurry treatment also improves the flowability of the slurry, which is advantageous for all slurry applications and in slurry channels. Last but not least, the reduction in odor to be achieved during application. A big plus for the population, for the farmers, and for the environment.
Generally, the nutrient cycle in slurry production must be observed. The "pre- and post-care" by:
- Animal care with naturally sourced prebiotics and probiotic microorganisms to ensure animal health
- Barn hygiene with suitable means (e.g., fogging of ferments, conditioning of bedding)
- Slurry treatment with natural products under suitable storage conditions for a high-performance organic fertilizer
This results in healthy soil as well as healthy plants, bringing us back to the starting point of the cycle.
Current Slurry Situation in Detail
Around 95% of ammonia emissions (NH³ emissions) in Germany come from agriculture (German Environment Agency-UBA 2020). According to the NEC Directive (Directive on national emission ceilings for certain air pollutants), these emissions must be reduced in Germany by at least 29% compared to 2005 by 2030 (UBA 2020).
Especially in the handling of organic fertilizers, such as slurry, the Fertilizer Ordinance (DüV) prescribes stricter requirements to reduce ammonia emissions. Here, agricultural businesses are obliged to apply liquid farmyard manure with a substantial content of available nitrogen or ammonium nitrogen only in strips on the soil or directly into the soil in the event of cultivated arable land (DüV, as of 28.04.2020). Due to bad experiences with feed contamination and the high financial burden on the agricultural business, farmers have great concerns about implementing the soil-close and strip-shaped application obligation (IG gesunde Gülle 2019).
In addition, according to the UBA (2020), the measures of soil-close application technology are not sufficient to fall below the limit values. Thus, according to the NEC Directive, an upper limit of 431 kilotonnes of ammonia emissions (from 2030) must be observed (Thünen Institute). The so far only approach recognized in the DüV to reduce NH³ emissions at the end of the process chain through soil-close application limits the possibilities of reduction. From previous studies, it can be concluded that the use of the cascade effect through, for example, the housing system, adapted feeding, or treatment with additives can lead to a significantly more effective reduction compared to the sole measure of soil-close application.
These reduction possibilities, which act at the beginning of the process chain, are expressly mentioned in Paragraph 6, Section 3 of the DüV, but are not accepted as an alternative to soil-close application due to the lack of scientifically sound evidence regarding their effectiveness in reducing NH³ emissions (Müller and Aures 2020).
This state of knowledge led to the development of the measurement and testing procedure used here.
The implementation took place from January 2019 with and by the IG gesunde Gülle. In cooperation with the State Laboratory in Kassel under the leadership of Dr. Harald Schaaf, the foundation for this measurement and testing procedure was laid. The further development of the method took place in a specially set up laboratory in Hebertsfelden, which Ingrid Bauer from Hebertsfelden made available and advanced the development. The project was financed from private contributions from farmers and other committed people, companies, and organizations. Jens Keim and Ingrid Bauer use a lot of technical and professional support in the background, which led the whole project to success.
A professional testing and measurement method was developed, consisting of the NH³ emission test vessel, a calibration fluid, and a protocol. The development of the calibration fluid was carried out based on many individual trials using the "trial-and-error" method.
The functionality and suitability of this testing and measurement method was confirmed by the DLG with the test report 2012-0032 on behalf of the IG gesunde Gülle.
The company Extox provided a specially developed "Red Suitcase" for this purpose, with which the measurement results can be recorded. The measurement of ammonia emissions from organic farmyard manure from sample vessels under defined framework and laboratory conditions can serve as a basis for investigating the effectiveness of various reduction measures at the individual farm level and lead to a results-oriented and verifiable reduction of ammonia emissions in agriculture. Furthermore, the development of a reference value makes comparison between the measurement results possible. The recognition as a scientific method is given by the development of a standardizable measurement and testing procedure.
The primary goal is the establishment of a measurement-technology-independent, or compatible with almost any measurement technology, scientifically recognized method for the verifiable, repeatable, and comparable determination of ammonia emissions (e.g., slurry) in vessels under definable laboratory conditions. The methodology of ammonia emission measurement is complex. The LfL and TU (Technical University) of Munich offered the IG gesunde Gülle, upon submission of a detailed method description in the sense of the VERA protocol, to organize an international review of the methodology." (Müller and Aures 2020)
Overview of the simple and recognized measurement and testing procedure "Red Suitcase":
- calibratable measurement technology with defined tolerances
- reproducible emission test vessel for verifiable emission sampling
- defined air velocity
- repeatable and standardizable methodology with defined framework conditions,
- factors and their parameters as well as a precisely described procedure
2. Investigation of the effect of mineral slurry additives (tribomechanically activated) on the reduction of NH³ emissions
2.1 Hypothesis of the investigation
By "mixing in" slurry additives based on a product mix of various clay minerals that have been tribomechanically activated*, the NH³ emission is significantly reduced.
*Tribomechanical activation (pulverization process):
Tribomechanical activation is a special micronization process in which the raw materials are not crushed, but ground. The particles are accelerated very strongly by centrifugal forces. Through a technical redirection of the direction of motion, they collide with each other and thus break themselves down. This means there is no abrasion (as with ball mills), the material gets a high basic energy and retains its purity. That is, this process has no effect on the chemical composition of the raw material, on the contrary - the crystal lattices remain intact and are not broken. The electrostatic charge, the particle surface, and the ion exchange capacity experience an optimization. The entire surface of the particles is greatly enlarged and thus increases the reaction speed or ability of the physical and electrolytic processes.
2.2 Measurement method: "Ammonia Emission Potential with the Red Suitcase" according to the method of the IG-Gesunde Gülle
The measurement technology used, "Red Suitcase", is a sample-sucking system using an electrochemical NH³ sensor. The ammonia concentration can be measured in real time with this technology. The control and visualization are carried out via the PC. Automatic documentation of the measurement as well as the creation of the protocol is carried out in the PDF format, among others. The determined NH³ measurement value (ppm) is based on the average of the 60 individual measurements of the last measurement minute. In addition to the sensors for NH³ measurement, the temperature of the test material and the supply air (°C), as well as the volume flow (l/h), the air pressure (hPa), the relative humidity (%) can be captured simultaneously every second and documented electronically.
See the scientific work by Anna-Maria Bissinger, Chapter 5.2.-5.3.
"Measurement method for determining current ammonia emissions of various substrates with scientifically sound and verifiable NH³ emission determination with permanent system calibration" II./3 Literature search and problem statement
At the end of the investigations, you get a so-called NH³ emission protocol. The NH³ emission protocol represents the basis of this measurement and testing procedure. It describes the exact standardized procedure and includes all defined parameters and components. The factors such as room and framework conditions, which have been mentioned to a large extent already, are specified and defined there. When using NH³-Stable-Mobile, the underlined parameters are captured and documented independently. If other measurement techniques are used, the values must be captured by tested devices. The following excerpt of the parameters must be documented and observed:
- Room temperature
- Room humidity
- Air pressure
- Measured volume flow
- pH value of the substance
- Type and designation of the measurement technology
- Blank measurement
- Initial calibration or calibration measurement before each measurement series
This documentation is an important component to prove compliance with the defined parameters, to trace it, and to ensure the comparability of the measurement results. The NH³ emission protocol must be attached to every sample measurement result.
2.3 Experimental setup and execution of barrel tests with slurry additives
Basic requirement: Use of the "suitable slurry":
- Homogenization by stirring before sampling
- untreated
- pH value greater than 7
- Initial value in ppm between 40 and 80 AEP (Ammonia Emission Potential)
- Temperature: constant at max. 12°C during the entire experiment
- no sunlight on the barrels, it distorts the results
- Simultaneous measurement of other parameters such as ammonium, total nitrogen, C/N ratio, etc.
2.3.1 Different formulations
Formulations of slurry additives on a purely mineral basis and tribomechanically activated of the brands KALKMEISTER and STEINKRAFT were tested. The mixing ratios were different in each formulation.
Formulation No. 1
Formulation No. 2
Formulation No. 3
Formulation No. 4
The slurry was filled into 60-liter barrels. Each barrel was filled with 50 liters of slurry.
2.3.2 Experimental Setup
Ø 1 control barrel of untreated slurry and 1 slurry barrel with the respective slurry additive
Ø The mixing ratio corresponded to 15 kg of slurry additive per m³ of slurry. On this basis, the respective slurry additive was stirred into the barrels.
Ø The slurry barrels were kept in a place where the temperature remained constant (max. 12 degrees Celsius) and they were not exposed to any sunlight.
0-measurement: All available untreated homogenized barrels were measured through before treatment to confirm the uniformity of the available slurry.
1st measurement: after 30 hours
2nd measurement: after 10 days
3rd measurement: after 14 days
All barrels were briefly stirred before each measurement and before taking the slurry. Each measurement was carried out twice to confirm the accuracy of the results. If a measurement deviated, another repeat measurement was carried out.
The mean value was used for statistical evaluation.
The temperature of the slurry during measurement was always 20 (+/-0.5) degrees Celsius (heated in a microwave or water bath). The untreated barrel was also measured as a control measurement at each measurement.
3. Results
3.1. Tabular presentation of the results
3.2. Graphical presentation of the results
3.3 Verbal description of the results
The current study has shown that all tested slurry additives achieve high NH³ binding. Two of the four studied formulations perform particularly well in the long-term study (after 14 days) with an NH³ binding of 33.63% to 36.91%. Reductions of >30% can generally be described as exceptional. It is worth noting that a reduction in AEP was observed at the same pH value. In addition, the slurry was very homogeneous throughout the entire study period and had high flowability. It should also be positively mentioned that the additives bind the organic nutrients of the slurry.
As found in previous studies, this study also confirms that the additives react relatively quickly. NH³ bindings of 9.96% to 25.03% are already recorded after 30 hours. However, the maximum NH³ binding is observed after 14 days. .
To better contextualize the presented results, it should be noted that a reduction of the NH³ value by approx.
Ø 20% = can be described as a good result
Ø 30% and more = is an exceptional result
In the studies, all mixtures reacted positively. Two mixtures in particular proved to be particularly reactive and thus effective in terms of NH³ binding in the long-term study:
Ø Formulation No. 1: KALKMEISTER N-Fix / STEINKRAFT Güllekraft N-Fix
Ø Formulation No. 2: STEINKRAFT Güllekraft N-Fix Humin
In both formulations, significant NH³ reductions of up to >30% could be observed in all study periods. The highest value was measured after approx. 14 days.
4. Conclusion
The tested slurry additives all make a very good to exceptional contribution to the reduction of NH³ by fixing the off-gassing from the slurry. This is accompanied by the fact that the generation of NH³ emissions from slurry application could be reduced by up to 30% and beyond. The air pollutant is thus significantly reduced.
Two products were particularly convincing in the study:
- KALKMEISTER N-Fix / STEINKRAFT Güllekraft N-Fix
- STEINKRAFT Güllekraft N-Fix Humin
Mixing in mineral additives before applying the slurry has further advantages for agriculture:
- Slurry is applied with the additional nutrients and trace elements required (= 1 operation).
- The odor burden on the surroundings is greatly reduced
- Processed slurry contains fewer salts and does not have an etching effect on plants, which is particularly valuable when applied to grassland.
- Slurry sausages with a trailing shoe are better incorporated with processed slurry and thus cause less contamination in the feed.
- The improvement of feed for pasture management in terms of grass quantity and quality is significant.
- Processed slurry has fewer decomposing substances. Everything that rots and stinks is not good for humans or soil life.
- The additives are natural minerals that are available in sufficient quantities.
- By applying them in the field, they can even permanently return CO₂ to the soil by increasing biomass (humus formation).
5. Recommendation:
We can only recommend the use of the tested additives in view of their NH³ binding potential, but also due to their positive effect on the soil.
We recommend all end-users/applicators to add the additive approx. 14 days before application and to stir the slurry before application, as otherwise anaerobic processes could re-establish themselves, depending on how strong or advanced the initial decomposition of the slurry is.
From previous studies, we know that the ppm value of the slurry can be reduced beforehand through feeding and barn hygiene (bedding). Because it becomes more stable and decomposition processes can establish themselves less. In general, we also recommend "moving" the slurry to counteract the decomposition pressure in a natural way.
The mineral-based slurry additives tested in this study and tribomechanically activated simultaneously:
§ with the primarily lime-based slurry additive (KALKMEISTER N-Fix / STEINKRAFT Güllekraft N-fix) support the liming of the soils
§ with the slurry additive primarily based on the zeolite and leonardite mixture (STEINKRAFT Güllekraft N-Fix Humin) make a valuable contribution to the urgently needed humus formation
§ the tested additives from the KALKMEISTER and STEINKRAFT brands also ensure activation of the microbiology and humus formation in the soil, thus making a valuable contribution to the revitalization of the soils
The dosage of approx. 15 kg to max. 20 kg per m³ of slurry makes this powerful and natural variant of slurry processing also attractive in terms of price and has the potential to call into question the dogma of low-level application more than ever.
In summary, it should be noted that in this study we have received more than initial indications of the positive effect of mineral additives for NH³ binding in the slurry and that their use is already sensible today.
This has encouraged us to document the slurry additives in other areas of effect, such as in biogas plants.
Ingrid Bauer Measurement Service: www.ingridbauer.de
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