Effectiveness of the Sustainable Manure Pile Model for Ammonia Emission and Soil

Abstract

In order to reduce odor emissions and surface water pollution while storing manure in field heaps near a barn, there is a challenge in properly designing manure-storage areas. Therefore, it is important to assess what solutions and conditions, considering environmental requirements, should be considered when storing manure in field heaps. The goal of the research is to determine the impact of various factors on the risk of nutrient leaching, soil, and gas emissions from solid manure heaps, considering climatic factors in the environment. Through various scientific studies, a manure pile model has been developed and evaluated for its impact on the risk of potential leaching and odor emissions (using hyperspectral gas emission analysis mass flow method) from manure and the dynamics of the 0–80 cm soil layer properties (nitrate (N-NO₃) and nitrite (N-NO₂), ammonia (NH₃), mineral, and total N). Based on the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania. An optimal new manure heap model has been identified—a layer of not less than 20 cm of compacted straw (density 150–200 kg m⁻³) or a 10 cm layer of peat for absorbing manure slurries is formed on the soil surface, the manure heap is surrounded by an earth embankment not less than 30 cm high, the manure heap is covered with a layer of finely chopped straw not less than 10 cm thick, or 5 cm of sawdust, or 5 cm of peat. The manure is stored in the heap for 6–12 months. Following the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania, applicable to the northern part of the temperate climate zone and applying similar requirements to the relevant countries.

1. Introduction

Solid manure (i.e., containing more than 20% dry matter) is a valuable organic material rich in nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), and other elements. Approximately 70–80% of N, 60–85% of P, and 80–90% of K found in animal feed end up in manure [1,2]. Manure promotes plant growth, provides nutrients to soil organisms, supplements carbon stores, enhances genetic and functional soil diversity, and improves its physical and chemical properties. More than 75% of the manure generated annually in European Union (EU) countries comes from cattle, while swine and poultry contribute about 12% [3]. In the long term, manure has the potential to replace some mineral fertilizers and reduce farmers’ expenses. However, the significant quantities of manure generated in agriculture necessitate finding appropriate ways to manage it. Improper manure management can lead to public dissatisfaction due to foul odors and other environmental issues, including the accumulation of heavy metals in soil, the spread of antibiotics and pathogens, nitrate pollution of groundwater, eutrophication of surface waters, and increased emissions of NH₃ and other greenhouse gases into the atmosphere.

In livestock urine, urea is the main N component. When urea and uric acid in urine undergo hydrolysis, all the N is produced [4]. Factors like temperature, pH, and moisture content affect the breakdown of uric acid and unprocessed [5]. In livestock yards, manure is another source of NH₃ [6]. N from manure can transform into various forms such as N₂, NH₄⁺, NO₂, NO₃, and N, contributing to amino acids, proteins, and other complex compounds [7]. NH₃ is the primary form in which N₂ enters the environment, along with N₂ and N₂O gases. The transfer of NH₃ from manure to the surface occurs through diffusion, and its release into the air happens through convective mass exchanges [8,9]. The diffusion and evaporation of NH₃ in manure are influenced by chemical and physical factors [7,10]. Urease activity is influenced by temperature, showing lower activity at temperatures below 5–10 °C and above 60 °C [11].

Manure management is one of the priority areas for agricultural development and environmental protection in the EU [12]. Currently, it is not regulated by a single EU regulation or directive. Instead, various directives, regulations, and national laws of member states are applied. Requirements for manure management vary among individual member states. The EU only sets general environmental standards, and individual countries implement and ensure compliance with these standards through their regulatory systems. For example, the Nitrate Directive of the EU (Council Directive 91/676/EEC) requires member states to implement national legislation regulating manure storage, application timing, and quantity. The EU Fertilizing Products Regulation (2019/1009) indirectly establishes guidelines for the management of manure that affects the quality of organic products. The Industrial Emissions Directive aims to allow member states to choose the best methods for managing swine and poultry manure from various available options (2010/75/ES). While the introduction of codes of good agricultural practice and legislative acts by member states (e.g., in Lithuania—Order of 14 July 2005, on the approval of the description of environmental requirements for the management of manure and litter No. D1-367/3D-342 and subsequent amendments) has improved manure-management practices, the European Commission, in its European Green Deal policy and Biodiversity Strategy for 2030 [13], envisions achieving climate neutrality by 2050. The plan urges a 50% reduction in nutrient losses in agriculture and calls for manure-storage facilities to be designed and managed to reduce emissions to the air and pollution of surface and groundwater.

Manure-storage facilities of various durations must meet certain requirements. In many EU countries and others (Norway, USA, Canada), it is allowed to temporarily store solid manure in specially designed manure heaps in agricultural fields. Recommendations and technical parameters for manure heap construction vary among different countries, but their application is based on similar principles.

Summarizing the analyzed requirements and practical recommendations in various countries, the following describes the differences in site selection, surface slopes, manure pile-storage time, water conductivity, groundwater level, soil compaction, pile base, and coatings when evaluating the various applicable requirements in identifying the permissible limits. Solid manure heaps must be located at a distance of 30–100 m (varies among countries) from water bodies (rivers, lakes, and ponds); 200–300 m from household water supply wells; 100 m from farmers’ water wells; 20–30 m from drainage ditches and karst sinkholes; 60 m from surface water drainage ditch drains; 150–300 m from public and residential buildings; and 50 m from regional roads. Heaps cannot be formed in flooded areas and possible surface water accumulation areas [14,15,16,17,18,19,20,21,22,23]. Accumulated solid manure should not be stored in piles for more than 120–180 days (in many European and North American countries, the 6-month “standard” is applied, but in the Czech Republic, Spain, Italy, and other regions of Southern Europe, the period is 4 months). The location of the pile should be chosen where there are slight surface slopes. The recommended slope varies from 3 to 8% in different countries and varies from country to country, but usually no more than 3%. The pile is formed in low water conductivity or specially compacted soils, when the water conductivity is up to 1.20 m/d. The soil-selection condition does not apply if the pile is covered with a waterproof coating.

It is prohibited to form a solid manure heap above underground drainage lines. The prevailing groundwater level (varies among countries) must be below 90–120 cm from the soil surface. If this condition is maintained or the base of the heap is made of water-impermeable material, the heap can be constructed above drainage lines. In all cases, the impermeable soil layer must be deeper than 150 cm.

The base (pad) of the heap must be made of water-impermeable material or a layer of materials (such as straw, peat, wood shavings, and sawdust separately or together) that can absorb manure filtrate and water, not less than 30 cm thick.

Solid manure heaps must be covered with a water-impermeable coating (varies among countries) or a 10–20 cm layer of straw, peat, and/or soil (reducing odors) immediately or within 3 weeks from the day the heap is formed in the field. Heaps should be covered with a water-impermeable coating if the manure is stored for more than 120 days in them.

In the same location, a manure heap can only be formed once every 3–4 years. A grass strip, 2–10 m wide (varies among countries), must be formed around the heap. Manure residues and materials absorbing filtrate under the heap pad must be removed and spread in the surrounding agricultural fields. The former heap site should be planted with plants that quickly absorb nutrients accumulated in the soil. Temporary heaps containing only poultry manure are not allowed.

It is recommended to shape solid manure heaps in the form of a sphere or elongated oval. The manure should be sufficiently dry. The recommended height of the heap is 1.5–2.2 m; the distance between adjacent heaps is 30–40 m. The amount of manure in one heap should correspond to the amount that can be spread in the adjacent fields, but not exceeding 130 ha. A mound is recommended/required around the heap.

Various country regulations state that the start and location of solid manure accumulation in the field, the volume of stored manure, and the removal time must be specified in fertilizer plans and assessed in soil nutrient balance calculations.

The aspects of international experience in setting conditions for the construction of solid manure heaps outlined here define the conditions for the temporary construction of heaps. The goal is to retain precipitation water and runoff in the heap, prevent it from entering the environment, and ensure the protection of surface and groundwater. The critical factor here is a 30 cm high mound around the heap and a layer of not less than 20 cm of peat or straw, or compressed wood shavings on the soil surface to absorb liquids from the manure. The mentioned materials, as well as wood shavings, absorb water and manure filtrate, although not uniformly.

The goal of the research is to determine the impact of various factors on water pollution, the risk of nutrient leaching, soil, and gas emissions from solid manure heaps, considering climatic factors in the environment.

2. Materials and Methods

2.1. Assessment of Manure Pile Model Impact

To assess the risk of reducing air pollution, experiments are conducted under production conditions by storing manure in pits in the fields. In a cattle farm, two manure pits of the same size are installed—the first manure pit is a new optimal model that meets all the requirements for manure pit construction, and the second manure pit (control) is constructed without a straw layer and ground mound. The new manure pile model is capped with a 10 cm layer of finely chopped wheat straw. The initial manure pit, constructed according to the scheme illustrated in Figure 1, measures 8.2 m in length, 4.2 m in width, and 1.83 m in height. The total volume of stored manure is approximately 48 m³ or 35 t, equivalent to the amount required to fertilize one hectare. The compressed layer of wheat straw designed for runoff absorption has dimensions of 0.20 m in height, 4.60 m in width, and 8.6 m in length, with a total volume of around 8.0 m³. The manure is then overlaid with a 0.10 m layer of wheat straw, constituting a volume of approximately 4.5 m³. The manure pit is enclosed by a 0.30 m high soil embankment.

The diagram of the installation of the second manure stack-pile is presented in Figure 2. The length of the manure stack is 8.1 m, the width is 4.3 m, the height is 1.85 m, and the total amount of manure is about 48 m³ or 35 t. This is the amount of manure required to fertilize 1 ha. Under the pile of manure, there is no layer of compressed straw to absorb the slurry, the manure is not covered with a layer of straw, and the pile of manure is not surrounded by a poured soil embankment.

The manure stacks were installed on 24 October 2022, the distance between the stacks is 32.4 m. The study area is dominated by flat relief (<1%) and sandy loam soil (up to 100 cm deep) and heavy loam layer (deeper than 100 cm). The manure was stored in the stacks until 17 April 2023, and spread on the soil.

The acidity, moisture content, and composition of manure piled up in stacks do not differ significantly.

The soil in which the manure storage tests were carried out had a close neutral reaction (pH 6.85–6.95), high P content (221.0–226.0 mg kg⁻¹), medium hardness (139.50–141, 50 mg kg⁻¹), and high humic content in soil (2.36–3.44%); the organic matter was 4.50–4.58%. 6.08–6.33 mg kg⁻¹ of NO₃ and NO₂, 3.02–3.25 mg kg⁻¹ of NH₃, 9.33–9.35 mg kg⁻¹ of mineral, and 0.218–0.268% of total N.

2.2. Analysis of the Impact of Dynamics of Meteorological Conditions on Manure Storage

The assessment of the dynamics of meteorological conditions was carried out based on the main observations at a constant semi-automatic meteorological station at a fixed time. According to the World Meteorological Organization, observations are recorded at 00, 03, 06, 09, 12, 15, 18, and 21 h Greenwich Mean Time. Knowing the area where the station is located (Kaunas Meteorological Station, Lithuanian Hydrometeorological Service under the Ministry of Environment Rapsu str. 5, Noreikiškių k., 53367 Kaunas district), the time zone and the time difference from Greenwich Mean Time can be determined by observation deadlines in local time (in Lithuania, taking into account the extremely frequent time lane change, this was done often). The results of observations at the meteorological station are automatically recorded continuously (not only during observation periods) and stored on computer disks. Fixed essential parameters were precipitation and temperature. Precipitation is water that falls from clouds and air onto the surface of the earth and other terrestrial objects. According to the phase condition, they are divided into solid, liquid, and mixed composition. Depending on the conditions, the precipitation of each phase condition can be of several types. Hard precipitation includes snow, hail, snow or ice flakes, snow grains, ice needles, etc.; for liquid—rain and fog; for mixed—wet snow, rain with snow, etc. At the meteorological station, the amount of precipitation was measured by the thickness (mm) of the water layer that would form on a horizontal surface if the precipitation did not absorb, flow, or evaporate anywhere. This layer is evaluated with an accuracy of 0.1 mm every 6 h. Rainfall intensity (amount per time unit) was also measured. The amount of precipitation in the semi-automatic station was measured by sensors with a swing mechanism. Sensors on one side of the bucket accumulate the amount of precipitation corresponding to a layer of 0.2 or 0.25 mm. Information is permanently stored in the automatic station’s memory block (computer disks). Sensors used to measure air temperature are resistance thermometers. Temperature sensors can act as recording devices (in this case, they turn on periodically every few minutes), so they can not only measure the instantaneous temperature of the measured medium, but also find out its extreme values over a certain period of time and their observation time.

After making boreholes at a depth of 120 cm and monitoring the weekly (every 7 days) dynamics of the underground water level in 8 wells (4 around the perimeter of each of the stacks), no cases of water rise above this limit were detected during the entire period. Cases of surface water formation in relief depressions around the stacks were also not recorded. The study area is dominated by flat terrain (<1%) and sandy loam soil (up to 100 cm deep) with a layer of heavy loam (deeper than 100 cm) with deep drainage. All this resulted in good conditions for rainfall infiltration and low groundwater level subsidence.

2.3. Evaluation of the Impact of Manure Storage on Soil

Soil samples for the study of agrochemical properties will be collected before the installation of litter piles in the fall of 2022. After the end of the survey on 20 October 2023, two soil samples were taken on April 17 from the site where manure stacks were stored. Two samples were taken from areas where the stacks were kept without straw, and two from areas where they were kept with straw. In the spring, two soil samples were also taken from areas more than 15 m away from the manure piles. The samples were collected using a soil drill from the 0–20 cm soil layer. Each soil sample was composed of material collected from 12 different locations.

To evaluate nutrient leaching during manure storage, soil samples were collected from different soil layers: 0–20 cm, 20–40 cm, 40–60 cm, and 60–80 cm. Samples were taken from sites where manure was stored in piles without straw, with straw after the piles were pushed, and from a site that had been free of experimental litter piles for over 15 years. Soil samples were collected using a soil drill, with two replicates from three different locations. The indicators of agrochemical properties of the soil were studied in the Agrochemical Research Laboratory of the Institute of Agriculture at the Lithuanian Agricultural Forest Science Center.

2.4. NH₃ Emission Studies from a Manure Pile

A static chamber method was used to determine NH₃ emissions from manure piles, which can be used to compare the intensity of gas emissions from various surfaces, i.e., from two installed manure piles. A sealed chamber is installed on the surface of the manure and the gas concentration gradient is measured in the chamber with respect to time and the relative NH₃ emission intensity (mg m⁻² h⁻¹).

In the manure stack, a sealed chamber with a capacity of 30 L is placed on the surface of the manure, under which the concentration of NH₃ gas is measured for 3–5 min (Figure 3). Measurements are made 2–3 times a month in each stack from 5 manure surfaces. NH₃ concentration is measured with the analyzer “Aeroqual Series 500”, the measurement limits of which are 0–100 ppm and accuracy < ±0.5 ppm.

During the NH₃ emission tests, the temperature of the manure is also measured at a depth of up to 1.0 m. The temperature is measured on a thermocouple attached to the end of a 1.0 m long rod connected to an Almemo 2590-9.

2.5. Statistical Analysis

In the characterization of alternatives, the description of the mean values of the indicators was useful, as was the comparison and assessment of the nature of their changes. To determine whether the differences were statistically significant, ANOVA one-factor analysis and graphical analysis were applied (using the Honest Significant Difference Method between the averages of the data evaluation (HSD₀₅) (probability level 95%). Arithmetic averages, standard deviation, and their intervals of confidence were determined with probability level (p < 0.05), respectively. After the evaluation of the accuracy of the experimental data, the calculated numerical values of the test accuracy revealed that the calculated data were very precise. The accuracy specified did not exceed 5% (with a numeric accuracy value of p < 0.05).

3. Results

3.1. Assessment of the Impact of Meteorological Conditions on Manure Storage

To assess the water quality, wells were drilled around the control stack and around the newly modeled stack, but since the areas were properly located according to all requirements and there was a well-functioning drainage system in the field, water did not accumulate in the test wells. Therefore, a detailed analysis of the absorptions of the soil (target elements), manure, and manure coatings and the substrate (in the case of the new model) was carried out, determining and proving the essential criteria, assessing the interdependencies of long-term environmental meteorological conditions, why the water did not accumulate. Further, considering long-term data and changes in the dynamics of elements absorbed by the soil, the underlying calculations were carried out and forecasting was provided based on meteorological parameters and soil dynamics.

During the experiment period from 24 October 2022, to 15 March 2023, 189.3 mm of precipitation fell. This was 69.8% of the multi-year average rainfall for the same period.

The highest amount of precipitation was recorded on 5 January 2023, with 17.5 mm of rainfall. The average daily air temperature during the entire experiment was +0.9 °C and ranged from −10.3 to +12.7 °C. It was 0.1 °C (10%) higher than the multi-year value for the same period.

Considering precipitation and air temperature conditions, the risk of groundwater and surface water pollution under and near the stacks always remains. It was determined during the experiment that 189.3 L (190 L can be accepted) of water fell on a 1 m² stack. It is estimated that during the period of experimental research, water evaporated on average 90–100 L m⁻². However, considering the higher than ambient manure temperature, which was recorded during the research, the evaporation from the stack was recalculated and accepted as an average of 110–125 L m⁻². Then the final result was obtained in the control stack, which does not comply with the manure storage requirements—70–80 L m⁻² of precipitation water filters into or drains from the stack. After evaluating the new stack model installed according to the target requirements, and after covering the stack with a 10 cm thick layer of whole wheat straw, whose estimated absorbency was 2.1 kg kg⁻¹, it is estimated that 10–12 L m⁻² of water can be additionally retained and gradually evaporated. Calculate the remaining 60–70 L m⁻² of precipitation and the amount of water contained in the thick manure itself (about 40% of the volume) is transformed in the stack in both cases. It can only be removed as manure leachate or surface runoff (Figure 4).

The risk of surface water pollution when stacks are installed under the recommended conditions of low (<3%) ground surface and distances from other objects (water bodies, buildings, etc.) is minimal. Our study showed that around the stack, when there is not even a 30 cm high protective embankment, infiltration of water coming off the stack takes place. Surface runoff does not form behind the stack. Contaminated water coming from the stack and pollution of surface water is likely only in heavy rain conditions. In the new stack model, there is no risk because of surface runoff from the stack and water pollution when 30 cm high dikes are installed around the stack. It was recorded that the dykes adequately retain rainwater in the stack. Therefore, the stack installed in accordance with the requirements of the new model with environmental bio protections is significantly more effective in reducing water pollution, because the bio-coating, the layer of compressed straw under the manure, absorbs the water polluted by the manure; this is proven by the absence of accumulated water and soil composition studies, which are analyzed in detail later in this article.

The greatest risk remains the formation of manure filtrate under the pile. Installing a layer of compressed straw of at least 20 cm reduces this risk but does not eliminate it. Assuming that the average density of compressed whole wheat straw is 150 kg m⁻³, a 20 cm layer of it can “absorb” more than 60 L m⁻² of filtrate and to a certain extent compensate (according to the conditions of 2022–2023) the “excess” of the amount of precipitation. Unfortunately, the amount of precipitation falls in different years during the storage period of the stacks and is unevenly distributed in time, air temperature, wind speed, and evaporation change. In addition, the possibilities of forming the base of the stack (the thickness of the layer of materials used and its compaction) and the quality of the work are very important. The amount of water in the manure brought to the piles and the soil moisture conditions are different. Knowing that the solid manure contains at least 40% water, under each of the 48 m³ manure stacks installed in the 32–40 m² research area, more than 400 L⁻¹m² (estimated evaporation) of leachate is potentially formed. Due to these circumstances, the weighting of manure filtrate under the pile (at least 400 L⁻¹m², and in wet years and more) is inevitable, even with the application of the provisions of point 14.3 of the description of requirements (No. D1-755/3D-844, 2020 version). The complete absence of filtrate under the stack is possible only by installing an impermeable layer.

3.2. Assessment of the Manure Piles’ Impact on the Soil

Research conducted during the experiment showed that the amounts of mineral N (NO₃-N + NO₂-N + NH₄-N), mobile P (P₂O₅), and K (K₂O) compounds significantly increase under the stacks. Compared to the field of perennial grasses, in the 0–20 cm soil layer, the amount of mineral N under the pile, where there was no straw layer, was 8 times higher, and with the straw layer it was 3.9 times higher and reached 158.7 mg kg⁻¹ and 76.0 mg kg ⁻¹, respectively (in the grass field—19.79 mg kg⁻¹). The effect of manure leachate under the stacks is well reflected by the abundance of incompletely mineralized ammonium N (NH₄-N) compounds of organic origin. In the stack without straw base, its amount reached 155.4 mg kg⁻¹, and with straw—53.7 mg kg⁻¹, while its amount in field soil was only 10.92 mg kg⁻¹ at that time. Fertilizer filtrate adds mobile potash to the soil especially abundantly. Under the pile, K (K₂O) was almost 8 times higher without straw, and more than 4 times higher with straw than in the field soil. An increase in mobile P was found only under the stack without straw when it reached 335.5 mg kg⁻¹ compared to 237.5 mg kg⁻¹ in the field soil. The lower amount of mobile P (147.0 mg kg⁻¹) under the straw pile than in the field soil indicates that the straw layer can be a suitable medium for adsorbing P. The retention of mobile P under straw is determined by the conditions of a more acidic soil solution (pH = 6.5, and pH = 7.6 without straw). At low pH, insoluble aluminum and iron compounds form in the soil, forming very strong bonds with phosphate (Figure 5 and Figure 6).

The lower amount of organic matter (respectively, 3.41%, 6.09%, and 4.33%) and humus (respectively, 1.84%, 3.70%, and 2.55%) under the pile with straw than without it and in the surrounding field reveals a more active activity of aerobic microorganisms in the straw medium and a greater decomposition of organic matter. This is well supported by the higher amounts of mineralized forms of N (NO₃ and NO₂) (22.2 mg kg⁻¹ compared to 8.86 and 3.27 mg kg⁻¹) measured in the soil under the straw than elsewhere (i.e., in the field and in the soil under the stack without straw) (

Table 1. The influence of manure-storage methods on the amount of organic matter and humus in the soil in the spring after manure storage in stacks in the 0–20 cm soil layer.

Variants	Organic Materials, %	Hummus, %
Perennial grasses field without a manure pile	4.33	3.38
Storage of litter in a stack without straw	6.10	3.58
New model—storage of litter manure in a stack with straw	5.41	3.46
R05	1.661	0.32

).

The distribution of the mentioned substances in deeper soil layers (from 20 to 80 cm) shows that the filtrate saturates the 20–40 cm layer the most. The highest amounts of ammonium N, total N, mobile P, and K were determined there. In a soil layer deeper than 60 cm, the amounts of all substances decrease significantly and become like the values measured in the outdoor environment. Moreover, the distribution of total N and P compounds under the straw stack is even lower than measured in the field.

All these facts show that the straw layer under the stack reduces the risk of groundwater pollution. Studies have also revealed that the risk of water pollution under the stacks is greatly reduced if the groundwater level is lower than the recommended international practice of 90 cm from the ground surface. Only in such places can the installation of manure piles be justified from the point of view of the compatibility of environmental protection and economic activity. If the water level under the stacks fluctuates and rises higher, water pollution is inevitable and the installation of stacks there is not allowed.

3.3. Assessment of NH₃ Emissions from Manure Piles

3.3.1. Changes in Manure Properties after Manure Pile Storage

Thick, fresh cattle manure is piled in stacks. Manure piled in the first stack: pH 9.2 ± 0.15; dry matter 24.76 ± 2.61% in total mass; organic matter 22.52 ± 1.4%; N 0.67 ± 0.09%; NH₄ 865 ± 87 mg kg⁻¹; P₂O₅ 0.14 ± 0.04%; K₂O 1.06 ± 0.09%; C 8.69 ± 0.13%.

Manure piled in the second stack: pH 8.9 ± 0.11; dry matter 22.96 ± 2.33% in total mass; organic matter 23.49 ± 1.7%; N 0.64 ± 0.07%; NH₄ 974 ± 74 mg kg⁻¹; P₂O₅ 0.11 ± 0.04%; K₂O 1.09 ± 0.07%; C 7.89 ± 0.89%.

3.3.2. Temporal Dynamics of Ammonia Emission during Manure Storage

The acidity, moisture content, and composition of manure piled up in stacks do not differ significantly. NH₃ emission from manure in both stacks is also similar (Figure 7). The moisture content of the manure is low, which leads to low NH₃ emissions: only 50–54 mg m⁻²h⁻¹. The low acidity, moisture, and favorable C-N ratio of the manure create good conditions for the composting process, which took place intensively in both manure stacks. The temperature of the manure (at a depth of 40 cm in the pile) rose to 49.1 °C in 7 days and reached 73.2 °C in 16 days (Figure 8). The increase in temperature also influenced the intensive NH₃ emission from the solid manure: the emission increased from 54 mg m⁻²h⁻¹ to 545 mg m⁻²h⁻¹ in 16 days and remained that high for 14 days (Figure 7). The manure in the piles was not mixed and the height of the pile decreased by 21–26 cm within 30 days. Also, the porosity of the manure layer decreased, and less air (oxygen) entered the inner layers of the manure. In the absence of oxygen, the activity of microorganisms slows down, less heat is released, the temperature of the manure drops, and the NH₃ evaporation from the manure also slows down. NH₃ volatilization intensity decreased significantly after 39 days (to 289 mg m⁻²h⁻¹) and continued to decrease intensively until it was only 19 mg m⁻²h⁻¹ on day 73. During the entire research period, NH₃ evaporated from the manure piles, very intensively for the first 39 days, then moderately until day 73, and weakly during the last 78 days of the research (on average 6–9 mg m⁻²h⁻¹).

3.3.3. Meteorological Factors’ Effect on Ammonia Emission

Meteorological conditions were favorable for the intensive NH₃ emission from manure: there was no low temperature, and the surface of the manure was not frozen and covered with snow. There was only 5 days of continuous snow cover on the manure throughout the research period. Due to sufficiently high temperatures, the snow on the manure pile melted quickly. The main factor affecting the intensity of NH₃ evaporation from the manure in the stack is the temperature of the manure, which depends on the intensity of microbiological processes and changes very intensively.

After analyzing the data, it was found that by the 16th day of experimental research, the ammonia emission increased significantly and reached the maximum values during the entire research period—on average up to 550 mg m⁻²h⁻¹. From day 16, ammonia emissions decreased slightly on average to 470 mg m⁻²h⁻¹. However, by day 40 of the study, it almost doubled, and from day 73, it increased more than 10 times. Therefore, it is further relevant to analyze how this variation was revealed by evaluating the differences between the control and the new model manure stack.

3.3.4. Manure Temperature Effect on Ammonia Emission

The first pile of manure was covered with a 10 cm thick layer of straw, while the second pile was not covered with anything. NH₃ emission differences between piles were found to be small (Figure 8). NH₃ emission from manure in the first pile was higher than manure in the second pile. During the entire research period, NH₃ emission from manure in the first pile was on average only 0.97 ± 0.03 mg m⁻²h⁻¹; i.e., the difference was insignificant. The difference between the control stack and the new model stack was evaluated and it was obtained up to the 20th day of the study and negative from the 83rd day of the study. In the interim period, it was positive, so it was decided to evaluate more deeply dependent relationships and identify the factors that caused such dynamics and data variation. Such results of NH₃ emissions from manure piles were influenced by the highly variable manure temperature and changing meteorological conditions, which is the main factor affecting gas emissions. The straw forms a porous layer on the surface of the manure and when the wind blows, the flow of clean air comes into contact with the manure and a large concentration gradient of NH₃ is formed on the surface of the manure, which is a good condition for intensive gas emission. Therefore, in strong winds, the effect of straw as a cover on the rate of NH₃ volatilization from manure will be small.

During the storage of manure in stacks, meteorological conditions were favorable for composting: the air temperature did not fall below −9.5 °C (Figure 9). The surface of the manure was not frozen and there were favorable conditions for air to enter the inner layers of the manure. The average air temperature during the research period was 1.4 °C. High NH₃ emissions from manure were also caused by high manure temperature: the average manure temperature in the first stack was 36.3 °C; in the second, it was 39.2 °C.

To reduce NH₃ emissions from piled solid manure, the temperature of the manure needs to be controlled. Manure temperature is the most important factor affecting gas emissions. Covering manure with straw has limited opportunities to reduce NH₃ emissions from manure, as rainfall and strong winds reduce the effect of straw on NH₃ emission intensity. After the manure is piled, the most important thing is to reduce the NH₃ emissions from the manure the most during the first 50 days of emission. If the manure is covered with straw, NH₃ emission is significantly reduced during the first days. Later, this effect on gas emissions decreases due to the impact of meteorological conditions on the straw layer (especially wind). Straw can be used as an effective means of reducing NH₃ emissions from manure piles in the short term.

4. Discussion

Experimental studies and calculations evaluated the efficiency of the new optimal manure pile model and other various studies also confirmed our evaluations and proposed recommendations [16,24,25,26,27]. Other scientists have also confirmed the benefits of using manure piles and bio-coating for absorption, as bio-coating can absorb from 4 to 12 kg of water, straw 3.0–4.0 kg, wood shavings 2.5–4.6 kg, and sawdust 1.9–2.5 kg. It has been proven that in manure filtrate (compared to water), the absorption of straw and sawdust almost does not change, but for peat it decreases and can reach 4–5 kg, and for wood chips 2.2–3.5 kg. The importance is also confirmed of the storage time and absorption properties of biomaterials under the same environmental conditions and how long materials saturated with water or manure filtrate can keep them. Scientific studies have summarized that the retention time under the same environmental conditions is determined by the absorption properties of the materials. For example, found that oat and wheat straw, as well as hardwood and softwood shavings and mixed sawdust, after 24 h of storage for 12 h, saturated in water, retained, respectively, oat straw 2.4 kg, wheat straw 2.1 kg, deciduous tree chips 1.2 kg, coniferous chips 1.85 kg, and sawdust 1.6 kg of water, compared to 1 kg of their dry weight. In another similar experiment, after 24 h it was found [28,29] that whole barley straw retained 2.85 kg, wheat straw 2.20 kg, oat 2.28 kg, and mixed sawdust 4.35 kg of water. Discovered a water uptake of 2.4 kg after 2 h after saturating whole barley straw [30]. Research by other scientists confirmed the efficiency of our new stack model with bio-coatings and bio-bed in terms of manure filtrate retention and emission reduction because the results of study showed that unshredded and shredded oat straw retained 1.76 and 1.96 kg of manure filtrate, rye straw 1.64 and 1.58 kg, and wheat 1.72 and 1.36 kg [31]. Other scientific studies also find that whether the structure of the bio-coating will be finer or not does not make a significant difference to the retention of the manure filtrate; therefore, our recommendations do not include the chopping of bio-coatings, because it is not appropriate to chop the straw when forming the base of the stack. It was also established that thick manure, by itself, can hold part of the water and forms the tightness of the surface on which it is spread, and adding bio-coating materials additionally increases NH₃ absorption [32].

In summary, taking into account the research carried out by us and other scientists, in accordance with all environmental requirements to reduce environmental pollution in order to further develop and improve the application of the efficient manure stack model in agricultural practice, it can be said that on farms, if conditions allow, it is recommended to expand availability and applicability criteria—to install the base of the stack from peat, compressed straw, or sawdust. Straw is the most suitable material for holding liquids from manure and rainwater (stack base and cover) in our designed model because of the cost of installation and easier availability to apply in farm practice. Also, when looking holistically and predicting the expected use of manure for field fertilization, straw, once spread out in a stack, has a higher nutritional value than peat, sawdust, or wood shavings; therefore, it is singled out as the most optimal solution considering the spectrum of the area of use. In the future, it is promising to envisage multi-criteria applicability to different climate zones, predictive modeling of soil, water and crops, agricultural practices, and international wide-ranging experimental studies adapting to the conditions of different places.

5. Conclusions

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Evaluating the new stack model—after covering the stack with a 10 cm thick layer of whole wheat straw, the absorbency of which is 2.1 kg kg⁻¹, it is calculated that 10–12 L m⁻² of water can be additionally retained and gradually evaporated; for the remaining 60–70 L m⁻², the amount of precipitation and water in the manure (about 40% of the volume) is transformed in the stack (can be removed as manure filtrate or surface runoff). The values of the indicators of agrochemical properties of the soil depended significantly on the thickness (depth) of the soil layer and the method of storage of litter manure. Storing litter in stacks with straw reduces the leaching depth of individual substances in the soil compared to storing litter without straw. The lower amount of organic matter (respectively, 3.41%, 6.09%, and 4.33%) and humus (respectively, 1.84%, 3.70%, and 2.55%) under the new pile model with straw than without it (control) and in the surrounding field reveals a more active activity of aerobic microorganisms in the straw medium and a greater decomposition of organic matter.

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The low acidity, moisture, and favorable C-N ratio of the manure identified by experiments created good conditions for an intensive composting process. The temperature of the manure (40 cm deep in the pile) rose to 49.1 °C in 7 days and reached 73.2 °C in 16 days. The increase in temperature dependently affected the intensive emission of NH₃ from solid manure—the emission increased from 54 mg m⁻²h⁻¹ to 545 mg m⁻²h⁻¹ in 16 days and remained that high for 14 days. NH₃ evaporated intensively from manure piles for the first 39 days, then on average up to day 73, and weakly during the last 78 days of the study—on average 6–9 mg m⁻²h⁻¹.

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These results for NH₃ emissions from manure piles were affected by the highly variable manure temperature (the average manure temperature in the control stack was 36.3 °C, and in the new model it was 39.2 °C), which is the main factor influencing gas emissions, and changing meteorological conditions. The straw forms a porous layer on the surface of the manure and when the wind blows, the flow of clean air comes into contact with the manure and a large concentration gradient of NH₃ is formed on the surface of the manure, which is in a good condition for intensive outgassing.

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Experimental studies have proved that a new pile model—when manure is covered with a 0.10 m layer of wheat straw (volume 4.5 m³) under the manure, there is a compressed 0.20 m high layer of wheat straw, and the manure pit is enclosed by a 0.30 m high soil berm—is an effective means of reducing NH₃ emissions from manure piles in the short period of the first days after manure stacking, when gas emissions are the most intense. Later, the efficiency of the straw decreases due to the impact of meteorological conditions, so the simulation of the improvement of the bio-coating of the investigated pile prototype is relevant in the future.