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Effects of temperature, wind speed and air humidity on ammonia volatilization from surface applied cattle slurry
Abstract
Ammonia losses from surface-applied cattle slurry were measured under field conditions using a wind tunnel system that allows variables affecting ammonia loss to be examined under controlled conditions. The experiments were carried out on a sandy soil with seven different surface covers. This report considers the effect of wind speed, temperature and water vapour deficit on the ammonia loss over a series of 6-day periods. During October 1986 to November 1989 42 treatments were examined, using slurries taken from the same slurry tank to provide slurries of similar chemical composition.
When temperatures were near zero, the rate of ammonia loss was generally low. The accumulated loss over 6 days was high, however, because the rate of loss was constant throughout the period. In these experiments the soil was saturated with water and partly frozen, and the infiltration of slurry into the soil reduced. At 19 °C initial loss rates were high but, after 12 h, almost no further loss occurred. Apart from these extremes, the ammonia loss rates within the initial 24 h were significantly affected by temperature and wind speed.
Ammonia volatilization after 6 h was exponentially related to temperature ( r ² = 0·841) but the correlation weakened with time after slurry application. An increase in ammonia volatilization with increasing water vapour pressure deficit was considered to be an effect of temperature.
The ammonia loss rate increased when wind speeds increased up to 2·5 m/s. No consistent increase in ammonia volatilization was found when the wind speed increased from 2·5 to 4 m/s. Ammonia loss after 24 h increased with increasing initial pH of the slurry.
A two-stage pattern for ammonia volatilization from slurry is proposed. During the first stage (the initial 24 h) ammonia loss rate is high due to an elevated pH at the slurry surface followingv application, and temperature significantly affects the loss rate. In the next stage, pH declines and the rate of ammonia volatilization decreases. During this stage other factors, including the dry matter content of the slurry, control the rate of ammonia loss.
... In topdressing application, without incorporation into the soil, emissions were higher as DM increased from 84 up to 101 kg m −3 (Table 2, Figure 3b). It is known that slurries with a low DM content are generally associated with lower ammonia emissions due to better infiltration into the soil, thereby reducing the contact area between the slurry and the air [19,41,42] as it has also been reported in other Mediterranean experiments [14]. However, in the present experiment slurry DM was high. ...
... Several authors observed that, during the first 24 h after application, the volatilization rate was the highest [43]. Furthermore, it is well documented that most NH 3 -N emissions in agricultural soils occur within a few days after fertilizer application [17,41]. The present study agrees with such findings, as the main NH 3 -N emissions occurred during the first 72 h after application. ...
Slurries are one of the main NH3 emission sources. Nitrogen losses impact air quality, and
they constrain the sustainability of farming activities. In a rainfed Mediterranean agricultural system,
the aim was to quantify NH3 emissions at a time when plants do not yet cover the soil surface and
according to fertilization practices. One treatment was slurry from fattening pigs (PSF) applied before
cereal sowing and incorporated into the soil; two treatments were PSF or from sows (PSS) applied
at the cereal tillering stage (topdressing); and two more treatments received slurries twice, before
sowing and as topdressing. Ammonia emissions were quantified with semi-static chambers during
145 h (before sowing) and 576 h (at cereal tillering) after slurry application. Before sowing, tillage
after slurry application controlled NH3-N emissions, but they accounted for 14% of the total NH4-N
applied. At tillering, average NH3-N emissions also accounted for ca. 14% of total NH4-N applied as
PSF or PSS, respectively. Slurry dry matter from 84 kg m−3 (PSS) up to 127 kg m−3 (PSF), combined
with low soil moisture content (below 30% of water holding capacity) at application time, helped in
NH3 emission control. Slurry applications before sowing did not enhance later NH3-N emissions
at topdressing.
... Temperature increases the rate of urea hydrolysis and the transfer of NH 3 from the soil solution to the atmosphere (Sommer et al., 2004). Therefore, a positive effect of temperature on NH 3 losses frequently has been observed (Sommer et al., 1991;Ni et al., 2014). Due to regional climatic trends, Skjøth and Geels (2013), expected that the variability of NH 3 emissions in larger European countries such as Germany, covering different climatic regions, is considerable, suggesting that regionalizing EFs based on climatic regions might be more accurate for NH 3 reporting than static EFs. ...
Among the synthetic fertilizers used in crop production, the application of conventional urea is one of the major sources of ammonia (NH 3) emissions. However, NH 3 emission estimates based on existing emission factors (EFs) are subject to significant uncertainties due to limited underlying data, obtained under various conditions and applied methods. To assess the accuracy of current EFs for different regions within Germany, NH₃ emissions were measured using the integrated horizontal flux (IHF) method employing ALPHA passive samplers following urea application in 2021, 2022, and 2023 across six agroecological regions of Germany. Measurements were conducted under winter wheat cropping, with total nitrogen (N) rates of 145-230 kg N ha⁻¹ , split into two or three applications, resulting in 51 measurement campaigns. Measured N input related NH 3 emission (NH3 Ninput) ranged from 1.1 % to 20.7 % (median 4.8 %, mean 8.5 %), significantly lower than the 2019 IPCC (14.2 %) and 2023 EMEP (16.1 % for pH<7) estimates for urea. No consistent trend in NH 3Ninput was observed between fertilizer applications and regions, though NH 3Ninput tended to be higher at sites with higher sand contents than sites with higher clay contents. Rainfall was negatively correlated with NH 3Ninput , while N application rates had no effect. The current EFs overestimate the NH 3 emissions from urea applied to winter wheat under the conditions tested in Germany. The observed emissions may deviate from long-term regional trends due to inter-annual variability and complex environmental interactions. Nevertheless, establishing a national EF for Ger-many could enhance the accuracy of NH₃ emission estimates and improve assessments of mitigation measures' potential to reduce emissions.
... Fischer et al. (2016) reported NH 3 EFs in Ireland between 2.8% and 5.3% TN and between 8.7% and 14.9% TN for dung and urine, respectively, depending on the season of application (spring, summer, autumn). Surprisingly, the largest emissions were observed in spring despite lower air temperatures compared to summer, which is typically associated with higher emissions (Clay et al., 1990;Lockyer & Whitehead, 1990;Sommer et al., 1991). This clearly highlights the importance of other factors such as rainfall aiding infiltration of the excreted material. ...
Ammonia (NH 3 ) 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 NH 3 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 NH 3 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 NH 3 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.
... The sunshine duration was only about 1 h/d, the light intensity was small, and the temperature was low, while the sunshine duration was about 7 h/d when the ammonia volatilization rate increased. It aggravated the evaporation of field water and promoted ammonia volatilization under the action of high temperature and intense light [31]. The ammonia volatilization rate continued to rise in 1~3 days after applying base fertilizer and tillering fertilizer, and was large about 5~7 days after applying panicle fertilizer in 2019 and 2020. ...
A experiment was conducted at the Jiangxi Province Center Station of Irrigation Experiment from 2019 to 2021 to study the water and nitrogen balance under water and fertilizer regulation modes. The study aimed to propose a recommended mode for paddy fields that could save water, control pollution, reduce gas emission, and improve fertilizer use efficiency. This study examined the impact of different irrigation methods and nitrogen application levels on water saving and emission reduction in paddy fields. The experiment included six treatments, which involved two irrigation methods (intermittent irrigation and flooding irrigation, referred to as W1 and W0, respectively) and three application rates of nitrogen fertilizer (0 kg/ha, 135 kg/ha, 180 kg/ha, referred to as N0, N1 and N2, respectively). The study found that irrigation methods had a significant effect on the amount of irrigation, drainage, leakage, nitrogen load from drainage, soil nitrification potential, and ammonia volatilization. The results showed that compared to flooding irrigation, intermittent irrigation reduced the amount of irrigation, drainage, leakage and nitrogen load from drainage by an average of 25.98%, 16.03%, 8.43% and 10.86%, respectively. However, the study also found that the nitrification potential and ammonia volatilization increased by an average of 6.45% and 4.32%, respectively. Fertilization levels had a significant effect on drainage nitrogen load, early soil nitrification potential and ammonia volatilization. Compared with the treatment of N2 (180 kg N/ha), the drainage nitrogen load under the treatment of N1 (135 kg N/ha) decreased by 10.86% on average, while nitrification potential and ammonia volatilization increased by 38.74% and 3.33%, respectively. In terms of nitrogen output, the amount of nitrogen absorbed by crops was the largest, followed by the nitrogen load from field drainage, then ammonia volatilization, and then denitrification. Considering the goals of water saving, emission reduction, and the efficient utilization of water and fertilizer in paddy fields, the optimal water and fertilizer regulation mode was the W1N1 mode (intermittent irrigation combined with reduced nitrogen fertilizer application rate, 135 kg N/ha).
... Neither the measured nor calculated average values provide insight into the variations of air velocity that are known to occur within the chamber (Jiang et al., 1995;Scotto di Perta et al., 2016) or the mass transfer coefficient near the soil surface, which depends on the velocity profile and turbulence intensity . Flux has been found to increase with air velocity and turbulence intensity (Sommer et al., 1991;Mannheim et al., 1995), and decrease with wind tunnel size, probably due to differences in velocity profiles and turbulence (Saha et al., 2011). ...
Volatilization of ammonia from field-applied animal slurry is a significant problem. Accurate emission measurements are needed for inventories and research, but are not provided by all measurement methods. Wind tunnels may give emission values substantially above or below micrometeorological results, which have been shown to be accurate. This limitation reduces the utility of wind tunnel results, which make up a large fraction of available measurements. The present work focused on understanding wind tunnel measurement error by comparing micrometeorological and wind tunnel measurements with the aid of a semi-empirical model. Ammonia loss from digestate after field application was measured in high time resolution in three field trials using wind tunnels and the backward Lagrangian stochastic (bLS) dispersion technique simultaneously. Differences in measured emission were interpreted using the ALFAM2 model, and measurements were used to evaluate the model. Results showed that wind tunnel and bLS methods provided different cumulative emission estimates, although there were similarities in measured emission dynamics. The ALFAM2 model was generally able to reproduce emission dynamics for both measurement methods, but only when differences in mass transfer between the two methods were incorporated in an experimental parameter set. This important result suggests that: 1) the simple structure of the ALFAM2 model captures the essential physical and chemical processes controlling emission and 2) the two measurement methods differ only (or mainly) through mass transfer above the slurry/ soil surface and rain. Therefore, with careful selection of wind tunnel air flow it should be possible to approximately match emission that occurs under open-air conditions. But without temporal variation in air flow, actual emission dynamics cannot be captured. This work provides a template for integrating and comparing measurements from different methods, and suggests it is possible to use wind tunnel measurements for model evaluation and even parameter estimation.
The global dependency on synthetic fertilizers has significantly revolutionized the agroecosystem. Excessive use of synthetic N fertilizers (SNF) for rapid agricultural expansion has become the next global threat to the natural ecosystem. A few of the prominent impacts of SNF on climate change is due to its emission of powerful greenhouse gases (GHG), ammonium volatilization, soil acidification, and coastal eutrophication. The release of these GHG gases and agricultural ammonia volatilization has been reported to be the crucial driver in the alteration of carbon sequestration and fine particulate matter pollution. Globally, the production of nitrogen contributed to approximately 0.41 GtCO2e, which is equivalent to 0.7% of total global GHG emissions. Additionally, the redeposition of nitrous oxides (NO2) by ammonia volatilization has largely disrupted the soil equilibrium causing an enormous rise in the problem of soil acidification. The devastating environmental changes have immensely reformed the soil microbial diversity and natural biochemical processes. Likewise, the release of SNF into water bodies and groundwater reservoirs has significantly impacted aquatic lives by reducing the abundance and biodiversity of bottom fauna leading to coastal eutrophication. The current chapter discusses the pressing issue of SNF pollution highlighting the following key objectives: (i) to provide an insight into the GHG emissions and ammonia volatilization, (ii) to illustrate the concerns of soil acidification and coastal eutrophication, (iii) to address the strategies to mitigate the environmental damage and uplift the sustainable nutrient management practices. Overall, this chapter provides an analysis of the prevailing scenario on the agro-environmental consequences of SNF pollution, strategies, and sustainable approaches for effective abatement of agrochemical pollution.
Ammonia (NH3) volatilization is a main pathway of nitrogen (N) loss from rice (Oryza sativa L.) paddies, which results in lower N use efficiency (NUE) and greater risk of environmental pollution. Excessive N fertilization has a negative effect on yield sustainability and NUE to varying degrees. NH3 emissions are affected by many factors, and the climatic conditions and planting patterns of rice fields in Northeast China are different from those in other regions, resulting in the specificity of NH3 emissions in this region. The current two-year field experiment studied the effects of different N application levels, 0, 75, 105, 135 and 165 kg N ha-1, on NH3 emissions and the related factors affecting NH3 volatilization loss and their relationships. The results demonstrated that the loss of NH3 from volatilization and the ratio of NH3 volatilization to N application increased with increasing N fertilizer application. The NH3 losses resulting from basal N fertilizer, first N topdressing and second N topdressing accounted for 35.29-59.59%, 29.32-59.66% and 3.08-26.49%, respectively, of the seasonal cumulative NH3 volatilization. The seasonal cumulative NH3 volatilization from the N application treatments accounted for 0.32–0.64% and 1.84–2.40%,
respectively, of the applied N fertilizer. The main factor influencing NH3 volatilization was the surface water ammonium-N (NH4+-N) concentration (p<0.01); precipitation inhibited the volatilization of NH3, and surface water pH fluctuated the least. There was a linear plateau between yield and N application, and a quadratic relationship between NUE and N application. Compared with the N135 and N165 treatments, lower N application increased NUE and significantly reduced NH3 volatilization losses while maintaining yield. Our research revealed that an appropriate decrease in N fertilizer application in Northeast China paddy fields could meet agronomic and environmental goals, and the appropriate N fertilizer application rate for our experiment was approximately 125 kg N ha-1.
Context
Manure deposition during livestock export voyages contributes to air ammonia levels, potentially affecting human and animal health if not managed. Mitigation strategies may include increased air change rates and application of bedding.
Aim
This study examined the effect of bedding application rate (BAR) and air change rate (ACH) on air ammonia (NH3) concentrations and pad properties, including pad surface condition, pH, moisture, and pad ammonium (NH4⁺) concentrations, for intensively housed beef cattle.
Methods
Six 7-day runs were conducted with 72 Bos indicus cross steers (mean liveweight ± s.d. = 338 ± 32 kg) housed in respiration chambers by using a 3 × 3 factorial design. The BARs were set to 0%, 50%, and 100% of the Australian Standards for the Export of Livestock (ASEL), and ACH were varied at 20, 35, and 52. Air NH3 was measured twice daily at three heights. Pad surface condition was collected with the first air NH3 measurement. Video footage captured standing and lying behaviours for each steer. Pad samples were collected on the final day for pad chemical analysis.
Key results
The ACH of 20 changes per hour resulted in higher air NH3 concentration than ACH of 35 and 52. Higher BAR led to lower pad pH and moisture, with slightly lower pad NH4⁺ concentration in 100% and 50% BAR than 0% BAR. Although air NH3 concentration on Day 7 was positively correlated with pad NH4⁺ concentration, BAR had no marked effect on air NH3 concentration (within the temperature range of this experiment). Drier and firmer pad surfaces were associated with each high BAR and high ACH. Moreover, high BAR increased the frequency of lying behaviour in steers.
Conclusions
These findings indicated that NH3 can be mitigated by optimising air changes to minimise air NH3 concentration and utilising bedding to minimise pad NH4⁺. This offers practical solutions for intensively housed beef cattle, such as livestock export voyages to improve human and animal welfare onboard.
Implications
The study results emphasised the importance of optimising ACH to maintain low air NH3 concentrations in livestock export conditions. Although there was no evidence that BAR affects air NH3 directly, it reduced pad NH4⁺ and improved pad conditions for overall animal comfort and environmental quality in confined housing with sufficient air changes.
A forced‐air polyvinyl chloride (PVC) cylinder manifold chamber was used to collect ammonia (NH 3 ) volatilized from sewage sludges applied to soil in the laboratory. A series of experiments were conducted in which the effect on NH 3 volatilization of a single variable was studied. The reference control conditions were: Columbus, Ohio anaerobically digested liquid sewage sludge applied at 5 Mg ha ⁻¹ (dry wt) to a Crosby silt loam soil (pH 6.7) at 0.01 MPa initial moisture tension. The soil was bare and the sludge was unincorporated during the 24‐h study period. Air temperature was 26 ± 2°C. The variable conditions were: (i) initial soil moisture (0, 0.01, 1.5 MPa and air‐dry); (ii) time of incorporation (0.25, 1, 3, 6, 12, and 24 h after sludge application); (iii) soil pH (5.1, 6.7, 7.5); (iv) sludge type (anaerobically digested Columbus liquid sludge, partially dewatered Columbus anaerobic sludge, aerobically digested Medina liquid sludge, lime stabilized primary Ashland sludge, and composted primary Columbus sludge); (v) temperature (12.8, 18.3, 26.7°C); and (vi) vegetative cover [bare, grass sod ( Poa pratensis ), wheat straw ( Triticum aestivum )].
Initial soil moisture contents ≤1.5 MPa tension increased NH 3 volatilization compared with air‐dry soil. Volatilization increased linearly with time elapsed before sludge incorporation. Ammonia loss was greater from soil at pH 7.5 than at pH 6.7 or 5.1. There was significantly greater loss of NH 3 from the lime‐stabilized sludge (pH 12) than from the anaerobic and aerobic sludges. No detectable NH 3 was lost from the compost. Volatilization decreased with decreasing temperature. When the sludge contained large sludge particles, NH 3 loss increased with vegetative cover. However, cover had no effect when the sludge was well homogenized. For all experiments, 24‐h volatilization losses ranged from 0 to 32% of the NH 3 ‐N applied.
The volatilization of ammonia from applied liquid dairy cattle manure was measured in the field during 6- to 7- day periods in early May of 4 yr. An "open" system involving an aerodynamic diffusion method was employed for these measurements. Ammonia flux followed a diurnal pattern with maxima occurring shortly after midday and minima occurring during the early morning hours. The magnitude of daily flux values tended to decrease with time. However, both temperature and rainfall influenced the magnitude of ammonia flux. Generally, ammonia flux values increased with temperature but were suppressed by rainfall. Over periods of 6 or 7 days following the time of manure application, between 24 and 33% of the ammoniacal N applied in the manure was lost by volatilization. Samples of manure taken immediately following application and 5 days later showed a decrease in ammoniacal N concentration during this period. Although some ammonium moved into the 0- to 2- cm soil layer, immediately following application, most a...
Laboratory studies were conducted to explain the wide variation in reported estimates of ammonia volatilization losses from N‐fertilized paddy fields. The ammonia volatilization capacity of a system was found to be equivalent to its alkalinity [NH 3 (aq), HCO 3 2‐ ]. In solutions lacking alkalinity, loss of (NH 4 ) 2 SO 4 was limited, whereas loss of (NH 4 ) 2 CO 3 was essentially complete.
Ammonia loss from solution is best described as a consecutive reaction with opposing step. Ammonia volatilization per se followed first‐order reaction kinetics. The rate of ammonia volatilization is thus directly related to the concentration of aqueous ammonia and therefore to the concentration of ammoniacal N and pH. The rate of ammonia volatilization was severely restricted by limiting the movement of air above the water, as is often the case in the laboratory and field studies reported to date. Ammonia volatilization was enhanced by water turbulence and increased exponentially with temperature from almost nil at 0°C to approximately 20 mg N/100 cm ² /5 hours at 46°C.
Volatilization of ammoniacal nitrogen from newly applied anaerobically digested sewage sludge was measured in the field using an aerodynamic method in May and Oct. for 5‐ and 7‐day periods, respectively. Sludge was applied in a circular area of 0.405 ha at rates of 116,480 kg/ha (150 kg NH 4 ⁺ ‐N/ha) and 134,400 kg/ha (89 kg NH 4 ⁺ ‐N/ha) in the May and Oct. experiments, respectively. Windspeed and atmospheric ammoniacal N was measured at 10, 50, 100, and 150 cm above the soil surface providing time averaged vertical profiles at the center of the area from which ammoniacal N flux was estimated. Flux was determined on the premise that NH 3 molecules leaving a horizontal surface must be carried through a vertical plane by horizontal air flow.
Fluxes generally followed a diurnal pattern with maximums occurring at about midday. Flux generally decreased with time in an exponential manner. Thus, the “half life” of ammoniacal N applied in the sludge was 3.6 and 5.0 days for the May and Oct. experimental periods, respectively. Of several meteorological variables measured, air temperature appeared to be most closely related to flux rate especially in the two or three days following application. It was estimated that, during the 5‐day experimental period in May, 60% of the 150 kg ammoniacal N/ha applied in sludge was volatilized. During the 7‐day experimental period in Oct. 56% of the 89 kg ammoniacal N/ha applied was volatilized.
Sampling the sludge layer and soil beneath it during and after the Oct. experimental period resulted in considerable variability in ammoniacal N estimates and, hence, in volatilization estimates.
Volatilization of ammonia from manure spread in the field was measured in five experiments carried out over a period of 2 years in spring, summer, and winter. The rates of manure application were 34 and 200 metric tons/ha (15 and 90 tons/acre). Ammonia volatilization was determined after spreading by periodically measuring the total ammoniacal N (TAN) content of manure samples collected from the soil surface. Corrections were made for increase in ammoniacal N in the soil. Time spans of the experiments ranged from 5 to 25 days with total losses of NH3 ranging from 61 to 99% of the TAN content. Quantities of N volatilized as NH3 ranged from 17 to 316 kg N/ha depending on the application rate and TAN content of the manure. In the winter trial NH3 volatilization was precluded by subfreezing temperatures, snow cover, and a rapid thaw which leached the ammoniacal N into the soil. In the other experiments, for a period of 5 to 7 days after spreading, rates of NH3 loss are represented by mean half lives of 1.86 to 3.36 days, respectively, for the low and high rates of manure application. After the initial period of loss, the rate of NH3 volatilization slowed in most cases. The 34 metric tons/ha manure application dried more rapidly because of its thinner ground cover, which increased the rate of NH3 loss from the manure. Volatilization of NH3 was optimum under sustained drying conditions. Effects of drying on the manure in relation to the chemistry of NH3 in aqueous solution in the manure aided in understanding the process of NH3 volatilization from the manure.
pH titrations of gülle samples disclosed differences of composition related to origin, age, and storage conditions prior to collection. Buffering capacities depended partly on ammonium bicarbonate content, which fluctuated from sample to sample but increased during laboratory storage, at 4C or room temperature. Organic compounds both in solution and solid phases buffered in the lower pH ranges, in some instances having greater influence on total buffering capacity than any other factor. The nature as well as the amount of these compounds differed between samples. Many were modified or decomposed during storage at laboratory temperature. Inorganic components of the solid phase, such as ammonium, magnesium, and calcium phosphates, as well as calcium carbonate, made significant though relatively minor contributions.
Tyrosine was identified in gülle solutions by TLC, while other amino acids, glutamic acid and histidine, were likely constituents. There were no simple carboxylic acid anions of the type that inhibit phosphate uptake by iron oxides.
Pig and cow slurries were applied to bare soil surfaces in the laboratory. Volatilization of NH 3 was measured using ventilated enclosures for 3·25 days after slurry application. Slurries were acidified to pH values between 7 and 4 with 5 M H 2 SO 4 . Lowering cow slurry pH to 5·5 decreased NH 2 volatilization by 95%, while lowering pig slurry pH to 6·0 decreased NH 3 volatilization by 82%. A field experiment, measuring the volatilization of NH 3 for 2 h after application to grassland stubble of slurry acidified to pH values between 7·5 and 5, gave similar results to the laboratory study.
Titration curves were constructed within the pH range of 9 to 4 with cow and pig slurries. There was a significant ( P < 0·05) positive correlation between the NH 4 ⁺ -N content of the slurries and the volume of acid required to attain a target pH of 6·0 for pig slurries and a pH of 5·5 for cow slurries. One litre of slurry containing 2 g of NH 4 ⁺ -N required c . 20 ml of 5 M H 2 SO 4 for acidification.
A new method of calculation of vapor-liquid equilibria for ammonia/hydrogen sulfide/water and ammonia/carbon dioxide/water at 0/sup 0/-100/sup 0/C at the concentrations encountered in refinery sour water strippers and for ammonia/sulfur dioxide/water as found in gas cleaning systems was developed. The model was based on the Edwards et al. thermodynamic approach.
Rates of ammonia (NH3) loss from a ryegrass sward measured using a system of small wind tunnels were compared with concurrent measurements made using a micrometeorological mass balance method. Measurements were made during two experiments within a circular plot (radius 10m) treated with urea at a rate of 200kgNha−1. In the first experiment, air speed through the tunnels was adjusted as necessary to maintain a value of approximately 1ms−1. This value differed on most occasions from the mean ambient wind speed which was measured at a height of 250mm and which ranged from 0.61 to 2.95ms−1. Rates of loss measured using the wind tunnels differed by a factor of between two and five from those measured using the mass balance method; there was no consistent pattern in the differences between the rates of loss. The total losses of NH3 measured during 15 days were equivalent to 49.1 and 30.2kg Nha−1 for the mass balance and wind tunnel methods, respectively. In the second experiment, air speed through the tunnels was adjusted as necessary to maintain a value as close as possible to the mean ambient wind speed measured at a height of 250mm. Rates of NH3 loss measured using the two methods did not differ significantly; total losses of NH3 during 17 days were equivalent to 96.9 and 101kg Nha−1 for the mass balance and wind tunnel methods, respectively. The difference between the findings of the two experiments could be attributed to the direct effect of air speed through the tunnels rather than to differences between ambient temperatures and those inside the tunnels. During and following periods of rain the rates of loss measured using the tunnels were up to six times greater than those observed with the mass balance method. Rates of loss measured by the two methods became similar again when the tunnels were moved following rain. The study demonstrates that enclosures can be designed and operated to provide reliable measurements of the rate of NH3 loss from grassland. Potential applications of the two methods are discussed.