NH3 Loss Research Articles

Evaluation of Tomato-Based Packing Material for Retention of Ammonia, Nitrous Oxide, Carbon Dioxide and Methane in Gas Phase Biofilters: A Laboratory Study

Biofilters are an effective air pollution control technology to break down gaseous contaminants and produce innocuous end products. This laboratory study aimed to evaluate a biofilter media, mainly composed by tomato waste, as packing material to reduce NH3, N2O, CO2 and CH4 losses from stored pig slurry. Three mixtures of packing materials, with and without oxalic acid, were arranged in treatments, namely: mixture of tomato waste, pine bark and agricultural compost; mixture of tomato waste and rice husk; tomato waste only. A control treatment (no biofilter) was also included. The experiments were conducted using a system of laboratory scale biofilters connected to jars filled with pig slurry and under a constant airflow rate. The gas concentrations were measured for 14 days and the physicochemical of the packing materials were assessed. Results showed that biofilter media mixtures had a potential for NH3 retention ranging from 51 to 77% and the addition of oxalic acid to these biofilters increased NH3 retention to 72–79%. Additionally, the biofilter media mixtures with and without oxalic acid showed a potential retention for CH4 (29–69%) but not for N2O, yet with no impact on the global warming potential. It can be concluded that tomato based biofilters had the potential to reduce gaseous emissions from slurry.

Comparing NH3 emissions under different cattle housing conditions in cold regions in China with an inverse dispersion technique

Accurately assessing ammonia (NH3) emissions from animal farms is necessary for determining the effectiveness of various mitigation practices to minimize related environmental risks and maximize the potential of recycling nitrogen from manure. This study attempted to validate a hypothesis formulated using a mass-flow inventory model, which suggested that "Barn only" housing facilities without open lots might have a lower NH3 loss potential than "Barn+Lot" facilities with both dairy barns and open lots. NH3 emissions from two "Barn+Lot" dairy farms and one "Barn only" dairy farm were measured using a combination of an inverse dispersion modeling technique and an open-path laser in summer and winter. It was found that the uncertainty of emission estimates owing to the spatial variation of animal densities in the three dairy farms was 8–12%, and the total uncertainty of the NH3 emission estimates owing to spatial variation in animal densities, distortion of wind flow by animal buildings, and the inverse dispersion calculation was estimated to be less than 30%. The NH3 emission rates obtained from the "Barn only" farm (28–43 g head−1d − 1) were lower than the rates from the conventional "Barn+Lot" farms (93–184 g head−1d − 1), indicating emission mitigation of 71–76%. In comparison with the conventional dairy farms, the "Barn only" dairy farm had a lower NH3 loss potential, most likely due to the greater animal density, frequent manure removal, and lower crude protein feed. However, more field measurements of such comparisons are necessary to provide robust suggestions for mitigating environmental risks.

Rice Husk Compost Production and Use in Mitigating Ammonia Volatilization from Urea

Using value-added products such as compost in farming systems could enable optimization of nitrogen (N) fertilizers whose world-wide demand is on the increase. The objectives of this study were to: (i) produce compost through co-composting rice husk (RH) with chicken dung slurry (CDS), chicken feed, and molasses, (ii) determine the effects of optimum rate of urea and RH compost on minimizing ammonia (NH3) volatilization, and (iii) determine total N, exchangeable ammonium (NH4+), and available nitrate (NO3−) retained in soil following co-application of urea and RH compost. Compost was produced for 60 days by mixing RH, CDS, chicken feed, and molasses at a ratio of 20:1:1:1. The color of RH compost was dark brown and had significant amounts of major nutrients such as N (1.15%), phosphorus (3101 mg kg−1), potassium (2038 mg kg−1), calcium (863 mg kg−1), magnesium (276 mg kg−1), organic matter (OM) (60.67%), organic carbon (35.17%), and humic acids (5.87%). The C/N ratio of the RH compost was 30. The electrical conductivity and pH of the RH compost were 2.79 µS cm−1 and 6.55, respectively, and they were not phytotoxic because paddy seeds were successfully germinated in all of the RH compost extractants. The high cation exchange capacity (CEC) of the RH compost (100.67 cmolc kg−1) at the end of composting was one of the determinant factors that controlled NH3 loss from urea. The effectiveness of the RH compost in minimizing urea-N loss was determined using a close-dynamic air flow system. The RH compost significantly minimized NH3 volatilization because of the high affinity of the RH compost for NH4+. An attestation of this reaction was that the high negative charges due to high CEC and OM of the RH compost temporarily protected NH4+ from being transformed into NH3 gas. Further evidence is the higher soil total N and exchangeable NH4+ for the treatments with RH compost than with urea alone. High quality compost can be produced from RH to reduce urea-N from being lost from urea. For the optimum rate, co-application of 60 g RH compost and 2.9 g urea per trough is recommended to mitigate NH3 volatilization instead of the existing practice (7.3 g urea alone per trough).

Modeling ammonia volatilization from urea application to agricultural soils in the DayCent model

Nitrogen (N) loss through ammonia $$({\mathrm{NH}}_{3})$$ volatilization in agricultural soils is a significant source of atmospheric $${\mathrm{NH}}_{3}$$ , contributing to low N use efficiency in crops, risk to human health, environmental pollution, and is an indirect source of nitrous oxide $$({\mathrm{N}}_{2}\mathrm{O})$$ emissions. Our objective was to develop an ammonia volatilization method within the DayCent ecosystem model that incorporates key 4R N management practices (right type, right rate, right placement, and right timing) that influence $${\mathrm{NH}}_{3}$$ volatilization associated with application of urea-based nitrogen fertilizers to agricultural soils. The $${\mathrm{NH}}_{3}$$ volatilization method was developed with Bayesian calibration using sampling importance resampling methods and Bayes factors to select the level of complexity in the model that best represents $${\mathrm{NH}}_{3}$$ volatilization given the observed data. The final model included urea hydrolysis and the influence of urease inhibitors; short-term soil pH changes following fertilization; fertilizer incorporation into the soil (mechanically and through irrigation/precipitation); and specification of the fertilizer placement method (i.e. broadcast vs. banding and surface vs incorporated). DayCent predicts $${\mathrm{NH}}_{3}$$ volatilization with a root-mean-squared error of 158 (95% interval ranging from 133 to 192), bias of 7 (95% interval ranging from − 106 to 102) g NH3-N ha−1 day−1, and with a Bayesian R2 value of 0.39 (95% interval ranging from 0.17 to 0.62). Furthermore, the model incorporates key management options influencing $${\mathrm{NH}}_{3}$$ volatilization related to placement method and fertilizer type with and without urease inhibitors that can be used to evaluate management and policy options for reducing losses of NH3 from urea fertilization.

Nitrous oxide emissions, ammonia volatilization, and grain-heavy metal levels during the wheat season: Effect of partial organic substitution for chemical fertilizer

Wheat is one of the most important staple foods worldwide, and the organic substitution for chemical fertilizer has been increasingly receiving attention in wheat planting. However, its impact on nitrous oxide (N2O) emissions and ammonia (NH3) volatilization from the wheat fields, as well as on the heavy metal [Nickel (Ni), Copper (Cu), Zinc (Zn), Cadmium (Cd), and Lead (Pb)] contents in the wheat grain is poorly known. A two-year field experiment was performed with two organic manures (sewage sludge compost and pig manure compost) and two substitution ratios (25 % and 50 %) for chemical nitrogen (N) fertilizer during the wheat season. An increasing trend in wheat yield (0.33∼5.9 %) was observed and total N2O emission was significantly decreased by 33∼77 % with partial organic substitution (POS). Therefore, the fertilizer-induced N2O emission factor was highly decreased (0.12∼0.47 % VS. 0.77∼0.92 %). The POS relatively increased NH3 volatilization by 7.9∼17 % (p > 0.05) and as a whole, it played little role in the cumulative N losses of N2O and NH3. The concentrations of Ni, Cu, Zn, Cd, and Pb in wheat grain were 97.4∼335 μg kg−1, 4.51∼5.88 mg kg−1, 28.5∼47.5 mg kg−1, 24.7∼79.6 μg kg−1, and 16.6∼33.4 μg kg−1, respectively. Although POS relatively increased the contents of Cu and Zn, they were all lower than those of the food standard limit for wheat in China. Moreover, the values of metal pollution index (0.39∼0.71) in all treatments were less than one. Our health risk assessment further demonstrated that POS did not pose any health risks. The findings suggest that partial replacement of chemical fertilizer with sewage sludge compost and pig manure compost in the wheat season can significantly decrease N2O emissions while not increasing N losses or compromising yield and its quality.

Corn cobs efficiently reduced ammonia volatilization and improved nutrient value of stored dairy effluents

Dairy farms produce considerable quantities of nutrient-rich effluent, which is generally stored before use as a soil amendment. Unfortunately, a portion of the dairy effluent N can be lost through volatilization during open pond storage to the atmosphere. Adding of covering materials to effluent during storage could increase contact with NH4+ and modify effluent pH, thereby reducing NH3 volatilization and retaining the effluent N as fertilizer for crop application. Here the mitigation effect of cover materials on ammonia (NH3) volatilization from open stored effluents was measured. A pilot-scale study was conducted using effluent collected at the Youran Dairy Farm Company Limited, Luhe County, Jiangsu, China, from 15 June to 15 August 2019. The study included seven treatments: control without amendment (Control), 30-mm × 25-mm corn cob pieces (CC), light expanded clay aggregate - LECA (CP), lactic acid (LA) and lactic acid plus CC (CCL), CP (CPL) or 20-mm plastic balls (PBL). The NH3 emission from the Control treatment was 120.1 g N m−2, which was increased by 38.1% in the CP treatment, possibly due to increased effluent pH. The application of CC reduced NH3 loss by 69.2%, compared with the Control, possibly due to high physical resistance, adsorption of NH4+ and effluent pH reduction. The lactic acid amendment alone and in combination with other materials also reduced NH3 volatilization by 27.4% and 31.0–46.7%, respectively. After 62 days of storage, effluent N conserved in the CC and CCL treatments were 21.0% and 22.0% higher than that in the Control (P < 0.05). Our results suggest that application of corn cob pieces, alone or in combination with lactic acid, as effluent cover could effectively mitigate NH3 volatilization and retain N, thereby enhancing the fertilizer value of the stored dairy effluent and co-applied as a soil amendment after two months open storage.

Effects of different types of humic acid isolated from coal on soil NH3 volatilization and CO2 emissions

Humic acid can improve soil nutrients and promote plant growth. Weathered coal and lignite can be used as agricultural resources due to high humic acid content, but their impact on soil NH3 volatilization and CO2 emissions are yet to be determined. In this study, a field experiment was carried out to compare the effects of four types of humic acid isolated from coal (pulverized weathered coal (HC), pulverized lignite (HL), alkalized weathered coal (AC) and alkalized lignite (AL)) on NH3 volatilization, CO2 emissions, pH, the C/N ratio and enzyme activities in soil cultivated with maize. The effect of biotechnology humic acids (BHA) was also examined for comparison. HL, AC, AL and BHA all increased cumulative NH3 losses by 147.7, 278.5, 113.9, and 355.3%, respectively, compared with the control (chemical fertilizer only), and notably, BHA caused an increase of 90.71% compared with the humic acids isolated from coal. A significant increase in cumulative CO2 losses was observed only under AL treatment, by 14.44–24.90% compared with all other treatments. Soil urease activity was positively correlated with cumulative NH3 losses (P < 0.001), while the soil C/N ratio (P < 0.001) and soil sucrase activity (P < 0.05) were positively correlated with cumulative CO2 losses. Since humic acid from pulverized weathered coal caused no increase in NH3 volatilization or CO2 emissions, it is therefore thought to be the most suitable humic acid for field application.

Adsorption and leaching characteristics of ammonium and nitrate from paddy soil as affected by biochar amendment

Biochar plays a key role in nitrogen cycling, potentially affecting nitrogen adsorption and leaching when applied to soils. The laboratory experiments were conducted to investigate the adsorption characteristics of rice straw biochar (RSBC) to ammonium (NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;) and nitrate (NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;) and the influence of RSBC on leaching characteristics of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt; at different soil depths using multi-layered soil columns. The results showed that the adsorption characteristics were significantly fitted with Freundlich and Langmuir adsorption isothermal curve models. The Freundlich isotherm model indicated that RSBC has relatively higher adsorption capacity and adsorption intensity to NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; than NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;. Moreover, the Langmuir isotherm model showed that the maximum adsorption capacity of RSBC to NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt; were 31.25 and 10.00 mg/g, respectively. The leaching experiments showed that the contents of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; in the leachates from the soil columns showed significant differences at different depths depending on the application amount of RSBC. Compared with CK (0% RSBC amendment), the overall cumulative losses of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; via leaching were decreased by 23.3, 35.1 and 13.7% after adding 2, 4 and 6% RSBC, respectively. Correspondingly, the contents of residual soil NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; in the soil column were increased significantly with the RSBC amendment at different depths. However, the losses of NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt; via leaching from the soil columns could not be retarded obviously by RSBC. Therefore, the application of an appropriate biochar rate is beneficial to retard the losses of soil NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; from paddy soil.

A simple and easy method to measure ammonia volatilization: Accuracy under field conditions

Field studies on soil ammonia (NH3) volatilization are restricted in many countries owing to the high costs commonly demanded for accurate quantification. We assessed the accuracy of a simple, open chamber design to capture NH3 under field conditions, as affected by different chamber placement schemes. Urea-15N was surface applied to lysimeters installed in the spaces between maize rows. Open chambers made from plastic bottles were installed on each lysimeter with variations in i) N rates (3, 8, 13, and 18 g m–2), ii) the height of the chamber above the soil surface (0, 5, and 10 mm), and iii) chamber relocation (static vs. dynamic). Reference lysimeters without chambers were used to measure NH3 losses by 15N-balance. Losses of NH3 -N accounted for more than 50% of the applied N. Relocation of the chambers had no impact on their NH3-trapping efficiencies, proving to be an unnecessary procedure. Variation in the height of the chambers above the soil surface affected the capture of NH3, but the results still maintained high linearity with the NH3 losses quantified by the reference method (R2 > 0.98). When the same placement scheme used in the introductory study describing the chamber was utilized (static and touching the soil surface), we found a trapping efficiency of 60%, which was very similar to that (57%) obtained in the previous study. Our results show that this simple, open chamber design can be used with satisfactory accuracy under field conditions, provided that simple, standardized procedures are warranted.

Nitrogen dynamics under corn fields in the Red River Valley of North Dakota

AbstractExcessive applications of fertilizer N in corn (Zea mays L.) has profound environmental and economic consequences. Corn grain yield, N losses, N2O denitrification, NH3 volatilization, and soil water NO3 concentration at 60‐cm depth were collected for eight corn fields in the Red River Valley of North Dakota. Relationships of soil and management factors with cumulative N2O and NH3 losses were studied. Grain yield varied from 3.58 to 5.66 Mg ha–1. Cumulative NH3 and N2O losses were ranged between 1.0–2.4 kg ha–1 and 24.7–150 g N2O‐N ha–1, respectively. Soil organic matter (SOM; r = .94, p = .001), clay (r = .94, p = .001), and initial inorganic N (0–60 cm) content (r = .83, p = .01) had a positive relationship with cumulative N2O losses. Cumulative NH3 had a negative relationship with soil pH (r2 = .63, p = .01). Results indicate that soil properties such as, SOM, clay concentration, and initial profile N had a control over N losses.

Improving Soil Nitrogen Availability and Rice Growth Performance on a Tropical Acid Soil via Mixture of Rice Husk and Rice Straw Biochars

Nitrogen deficiency frequently occurs at agricultural soil because of NH3 volatilization to the environment which results in low urea-N use efficiency by rice plants. A pot experiment was conducted to assess the synergistic effects of a mixture of rice straw and rice husk biochars (RSRH) on (1) total N, soil exchangeable NH4+, and available NO3−, and (2) uptake of N, P, and K in rice plant. RSRH biochar at 5 and 10 t ha−1 had significantly minimized ammonia volatilization by 33.5% and 40.7%. Further, RSRH biochars also had significantly increased available NH4+, NO3−, available P, and available K in the soil over T1. In line to increase in soil nutrient availability, the rice plant height, tiller number, greenness, and panicle number were increased. This resulted in an increase of nutrient uptake, use efficiency, and dry matter production of the rice plant. RSRH biochar altered the soil environment by minimizing NH3 loss and increasing soil nutrients for efficient plant uptake.

Lignite Improved the Quality of Composted Manure and Mitigated Emissions of Ammonia and Greenhouse Gases during Forced Aeration Composting

Lignite amendment of livestock manure is considered a viable ammonia (NH3) emission mitigation technique. However, its impact on the subsequent composting of the manure has not been well studied. This work compared changes in biochemical parameters (e.g., organic matter loss and nitrogen (N) transformation) and also the emissions of NH3 and greenhouse gases (GHGs) between lignite-amended and unamended cattle manure during forced aeration composting. Amending manure with lignite did not alter the time to compost stability despite delaying the onset of the thermophilic temperatures. Lignite treatments retained N in the manure by suppressing NH3 loss by 35–54%, resulting in lignite-amended manure composts having 10–19% more total N than the unamended compost. Relative to manure only, lignites reduced GHG emissions over the composting period: nitrous oxide (N2O) (58–72%), carbon dioxide (CO2) (12–23%) and methane (CH4) (52–59%). Low levels of CH4 and N2O emissions were observed and this was attributed to the continuous forced aeration system used in the composting. Lignite addition also improved the germination index of the final compost: 90–113% compared to 71% for manure only. These findings suggest that lignite amendment of manure has the potential to improve the quality of the final compost whilst mitigating the environmental release of NH3 and GHGs.

Film mulching, residue retention and N fertilization affect ammonia volatilization through soil labile N and C pools

Ammonia (NH3) volatilization was a vital process of the nitrogen cycle in agricultural ecosystems and closely related to the atmospheric environment quality. To investigate the tillage practice and N fertilization impact on the soil labile C, N pools and their effects on ammonia volatilization from wheat fields. A two-year consecutive field experiment was conducted at 2017 and 2018. The split-plot design of three tillage systems (conventional tillage (CT), film mulching (FM), straw residue incorporated into soil (SM)) and three nitrogen rates (the control rate (N0), 144 kg N ha−1 (N144), 180 kg N ha−1 (N180)) was applied. The results showed that the NH3 volatilization occurred during 40 days and peaked in 2 weeks post N fertilization. FM could significantly cut down ammonia volatilization peaks, cumulative NH3 loss and ammonia loss rate during both seasons (p < 0.05). The average fertilizer ammonia loss rates (AFR) in two growth seasons were 3.70% – 3.95%, 1.90% – 2.10% and 3.47% – 3.87% for CT, FM and SM separately. The topsoil water content (SWC) and soil temperature (ST), mineral nitrogen (NH4+-N and NO3−-N) were enhanced by FM during the wheat cultivation. The microbial biomass nitrogen (MBN) and dissolved organic carbon (DOC) contents of SM were higher than others. Water extraction organic nitrogen (WEON) and NO3−-N could be augmented by straw addition during heading stage growth. The ammonia volatilization was closely related with soil NH4+-N content, which was originated from the organic N mineralization in no fertilization condition and significantly affected by ST and SWC. N fertilization increased soil NH4+-N content and ammonia volatilization, and the higher N rate was, the more NH3 volatilization. When film mulching, WEON, MBN and soil mineral nitrogen have been augmented by higher SWC and ST, which increased NH4+-N content and NH3 volatilization potential, nevertheless film barriers mitigated the ammonia volatilization ultimately. Under straw incorporation, DOC, MBN and ST, which significantly affected the immobilization, mineralization and nitrification through microorganism proliferation, were the key factors affecting soil NH4+-N contents and NH3 emission. Overall, N fertilization promoted the ammonia volatilization; FM could mitigate ammonia volatilization through physical barrier or blocking, while the crop residue incorporated into soil had no pronounced impact on the soil ammonia volatilization.

Current knowledge on urease and nitrification inhibitors technology and their safety.

Urea is one of the most widely used commercial fertilisers worldwide due to its high N density and cost effectiveness. However, it can be lost in the form of gaseous ammonia and other greenhouse gas (GHG) emissions which can potentially lead to environmental pollution. Farmers are compelled to apply more urea to account for those losses, thereby increasing their expenditure on fertilization. The objective of this paper is to present a literature review on current knowledge regarding inhibitor technologies such as urease inhibitor; n-(N-butyl) thiophosphoric triamide (NBPT), and nitrification inhibitor; dicyandiamide (DCD). A thorough review of all the scientific literature was carried out and a proposed risk assessment framework developed. The study showed that the urease inhibitor NBPT significantly reduced NH3 loss from urea. However, concerns about NBPT safety to human health had been raised when the nitrification inhibitor DCD appeared as a residue in milk. This article presents a risk assessment framework for evaluating human exposure to chemicals like NBPT or DCD, following the consumption of foods of animal origin (e.g. milk) from cows grazing on inhibitor-treated pasture. The EU's target of a 40% reduction of greenhouse gas emissions by 2030 can be aided by using NBPT as part of an overall suite of solutions. A comprehensive risk assessment is advised for effective evaluation of potential risks from exposure to these inhibitors.

Reducing ammonia volatilization and increasing nitrogen use efficiency in machine-transplanted rice with side-deep fertilization in a double-cropping rice system in Southern China

Ammonia (NH3) volatilization contributes to major nitrogen (N) fertilizer loss in rice fields. Deep fertilization can effectively mitigate NH3 volatilization and increase N use efficiency (NUE) in agroecosystems. However, the effects of machine-transplanted rice with side-deep fertilization (MRSF) on NUE and NH3 volatilization from paddy fields in double-cropping systems are still unknown. In this study, a field experiment was conducted with double-cropping rice fields in two regions in Southern China (Miluo and Yiyang). NH3 volatilization was measured during the rice growing seasons using the continuous airflow enclosed chamber method under different N application rates with MRSF treatments. The results show that NH3 fluxes in rice soil subjected to different N application rates varied. The ratio of total NH3 loss to applied N by conventional fertilization (CF) ranged from 41.2 to 45.3% in the early-season rice (ESR) and from 44.9 to 45.2% in the late-season rice (LSR). Unlike CF treatment, MRSF treatments significantly reduced the cumulative NH3 loss by approximately 24.8–26.9 % in Miluo and 20.1–20.8 % in Yiyang for ESR and by 18.6–23.0 % in Miluo and 20.2–21.8 % in Yiyang for LSR. MRSF treatments increased the content of available N in the soil by 0.2–8.8 % and 0.7–6.6 % in Miluo and Yiyang, respectively. Moreover, this mitigation effect is expected to be more effective with lower N application rates. An NH3 accumulation model described by the Elovich equation was established over the study period; notably, the field observations fitted the calculated values well. MRSF with a 20–30 % reduction in N application rate yielded a higher NUE in terms of N recovery efficiency (NRE), by 11.5–27.9 % and 11.7–23.7 % in Miluo and 8.2–17.0 % and 7.0–25.8 % in Yiyang relative to that of the CF treatment in ESR and LSR, respectively. Overall, MRSF can reduce the N loss through NH3 volatilization while improving content of available N in the soil and NUE; therefore, further maximizing the yield and simplifying fertilization practices for a cleaner rice production in Southern China.

Identifying N fertilizer management strategies to reduce ammonia volatilization: Towards a site-specific approach

Concerns about ammonia (NH3) losses from nitrogen (N) mineral fertilizers have forced policymakers to set emission reduction commitments across Europe. Although best available techniques (BATs) have been recommended, large uncertainties still exist due to poorly targeted site-specific approaches that might compromise their effectiveness. Here we proposed and tested a conceptual framework designed to identify most effective BATs that reduce NH3 at the site-specific level. The study was conducted in the Veneto region, northeast Italy. After the mapping of NH3 emission potential areas, BATs and business-as-usual N fertilization scenarios were assessed using a modified version of the DNDC agroecosystem model and compared with urea broadcast distribution under different pedo-climatic conditions. The most promising practices were further tested in a field experiment using a wind tunnel combined with a FTIR gas analyzer. Results showed that closed-slot injection reduced NH3 emissions with any type of mineral or organic fertilizers. Injected application, with ammonium nitrate or organic fertilizers, reduced NH3 loss in maize by 75% and 96%, respectively, and in winter wheat by 87% and 98%, compared to surface broadcast. Injection was the most promising technology to support, being already available to farmers. However, some increase in nitrate leaching was observed, mostly in case of winter wheat (+24% for AN injection; +89% for organic fertilizers). By contrast, urea incorporation with hoeing, the most common technique used by farmers in spring crops, did not show satisfactory results, because the partial burial of urea caused strong NH3 emissions that were even higher compared to surface broadcast. Recommended NH3 reduction techniques should be tailored to local pedo-climatic and management conditions, and evaluated, in a holistic approach, considering all N fluxes in the environment.

Impacts of ammonia volatilization from broadcast urea on winter wheat production

AbstractAmmonia (NH3) volatilization from broadcast urea may lead to significant N losses in winter wheat. We aimed to: (a) quantify N losses through NH3 volatilization from fields fertilized with urea and urea amended with a urease inhibitor (NBPT) under cold weather months (February–April), and (b) investigate the impact of N losses through NH3 volatilization on the winter wheat production. We employed the integrated horizontal flux (IHF) method with passive NH3 samplers to quantify NH3 volatilization at five sites in Kansas. Urea and urea + NBPT were broadcast at a rate of 60 kg N ha–1 over circular plots. We assessed the impact of NH3 losses on wheat at three sites employing different rates of urea and urea + NBPT. NH3 losses volatilization varied from 0.3 to 29.6% of total N applied. The largest N losses (&gt;23% of applied N) occurred when urea was broadcasted to moist soils followed by a dry period. Amending urea with NBPT reduced NH3 volatilization losses by more than 20% on the campaigns with the largest N losses (&gt;23%). However, our results showed no significant differences for wheat yield, N‐recovery and agronomic efficiency between urea and urea + NBPT treatments likely due to the reduced NH3 volatilization (&lt;17%) where the impact on winter wheat was measured. Our results suggest that winter wheat farmers should carefully evaluate the soil surface moisture conditions before broadcasting urea to avoid potential NH3 volatilization losses even under cold conditions (average soil temperature ranging from 2.5 to 7.7 °C).

Air warming and CO2 enrichment cause more ammonia volatilization from rice paddies: An OTC field study

Ammonia (NH3) volatilization in rice paddies may be affected by elevated atmospheric CO2 concentration ([CO2]) and temperature due to changes in plant and soil nitrogen (N) metabolism. At present, little is known about the individual and combined effects of CO2 enrichment and warming on NH3 volatilization under field conditions. An experiment was conducted in a rice paddy in Central China, after 4 years of warming and CO2 enrichment using open-top chamber (OTC) devices. Compared with ambient conditions, elevated [CO2] had no significant effects on NH3 volatilization, although increases in soil pH and urease activity were observed. The stimulation on plant N assimilation under CO2 enrichment might offset the possible enhancement on NH3 volatilization, as more soil N was absorbed by plant thus reducing NH3 loss potential. Elevated temperature increased NH3 volatilization significantly, which could be attributed to increased soil ammonium nitrogen (NH4+-N) concentration, pH, and urease activity. Combination of CO2 enrichment and warming caused the highest cumulative NH3 loss, which increased by 26.5% compared with ambient conditions, but the interaction was not significant. Higher plant N uptake, soil NH4+-N concentration, pH and urease activity were also observed with co-elevation of [CO2] and temperature, but the combined effects were variable and not synergistic. Our findings confirm that field warming and CO2 enrichment cause more NH3 volatilization in rice paddies, among which warming effects are dominant, and suggest that improved N management or field practices are required to reduce NH3 losses under future climate change.

Predicting soil pH changes in response to application of urea and sheep urine.

Volatilization of NH3 following urea application or livestock urine deposition can result in significant loss of N to the environment. Urea hydrolysis to NH4 + results in an increase in pH, which in turn promotes transformation of NH4 + to NH3 . Accurately predicting changes in soil pH following urea (or urine) application will allow successful simulation of NH3 volatilization. The magnitude of the pH change depends on the soil's pH buffering capacity (pHBC). However, as actual pHBC values are not generally available, pHBC proxies (e.g., cation exchange capacity) have been used in modeling studies. In a 34-d laboratory incubation study, we measured soil pH and mineral N (NH4 + and NO3 - ) following a large application of urea (800mg N kg-1 soil) to four soils with a range of pHBC values. In a second incubation, pH changes and mineral N dynamics were monitored in soil treated with sheep urine (773mg N kg-1 soil) in the absence and presence of the nitrification inhibitor dicyandiamide. In both incubations, pH changes associated with urea hydrolysis and subsequent nitrification of NH4 + were predicted well using measured pHBC data. Our results confirmed that pHBC is base-type dependent (values greater when measured using KOH than NH4 OH). Soil pHBC is easily measured, and the use of a measured value (determined using NH4 OH) can improve model simulations of pH in the field and, potentially, lead to improved estimates of NH3 loss from animal-deposited urine patches and urea-treated soil.

Direct and Indirect Effects of Urease and Nitrification Inhibitors on N2O-N Losses from Urea Fertilization to Winter Wheat in Southern Germany

Urea (U) is the most important nitrogen (N) fertilizer in agriculture worldwide, and as N fertilizer can result in large gaseous losses of NH3 and N2O. Thus, urease inhibitors (UIs) and nitrification inhibitors (NIs) have been coupled with U fertilizers to mitigate NH3 and N2O emissions. However, it is still unclear whether adding NIs and/or UIs to U stimulates other pollutants, while reducing one pollutant. Furthermore, part of the NH3 deposition to earth is converted to N2O, leading to indirect N2O emission. To estimate direct and indirect effect of UIs and NIs on the N2O-N and NH3-N losses from U; therefore, we analyzed multi-year field experiments from the same site during 2004 to 2005 and 2011 to 2013. The field experiments with U fertilization with or without UI (IPAT, N-isopropoxycarbonyl phosphoric acid triamide) and NI (DCD/TZ, Dicyandiamide/1H-1, 2, 4-Triazol) in winter wheat and with calcium ammonium nitrate (CAN) were conducted in southern Germany. Fluxes of NH3 or N2O emissions were determined following each split N fertilization in separate experiments on the same site. Our results showed that U with NIs considerably reduced N2O emissions, and adding UIs decreased NH3 emissions. However, the effect on N2O emissions exerted by (U + UIs) or (U + UIs + NIs) was inconsistent. In contrast to the treatment of (U + UIs + NIs), the addition of NIs alone to U stimulated NH3 emission compared to treatment with U. When 1% indirect N2O emission from NH3 (IPCC emission factor (EF4)) was considered to estimate the indirect N2O emission, total N2O emissions from (U + NIs) were approximately 29% compared to that from U alone and 36% compared to that from (U + UI), indicating that indirect N2O emission from NH3 induced by NIs may be negligible.