Cumulative NH3 Losses Research Articles

Ammonia volatilisation losses from urea applied to acidic cropping soils is regulated by pH buffering capacity

Context Ammonia (NH3) volatilisation can be a significant nitrogen (N) loss pathway in the grains industry following the surface broadcast application of urea. However, the extent of urea volatilisation from acidic soils and the soil properties that regulate this N loss pathway have not been investigated widely. Aims We conducted a laboratory incubation experiment to measure NH3 volatilisation loss potential following the broadcast application of urea prills (1–2 mm diameter; 50 kg N ha−1) onto moistened acidic and neutral cropping soils, sampled from four long-term cropping research sites. Methods The selected soils varied in pH, clay content, organic carbon, pH buffering capacity (pHBC) and cation exchange capacity. Volatilised NH3 was captured in a phosphoric acid trap after 7, 14 and 21 days and then measured using colorimetric analysis. We compared the measured NH3 losses with predicted NH3 losses derived from an existing empirical NH3 volatilisation prediction model. Key results Of the applied urea-N, 0.9–25% was volatilised. Cumulative NH3 losses were strongly related (R2 = 0.77) with soil pHBC derived from a pedotransfer function. The existing NH3 loss model generally had poor predictive capacity (RMSE = 34%). Conclusions Using clay content as a surrogate variable for pHBC in the predictive model for sandy kaolinitic soils where it is largely a function of organic carbon content can cause poor estimates of NH3 volatilisation loss potential. Implications Grain production on sandy, acidic soils with low pHBC could lead to substantial NH3 volatilisation losses if urea is broadcast.

Environmental risk of microplastics after field aging: Reduced rice yield without mitigating yield-scale ammonia volatilization from paddy soils

Microplastics (MPs, <5 mm) are enriched in paddy ecosystems as emerging environmental pollutants. Biochar (BC) is a controversial recalcitrant carbon product that poses potential environmental risks. The presence of these two exogenous organic substances has been demonstrated to have impacts on soil nitrogen cycling and crop production. However, the after-effects of MPs and BC on soil ammonia (NH3) volatilization and rice yield after field aging remain unexplored. In this study, two common MPs, including polyethylene (PE) and polyacrylonitrile (PAN), and BC were selected for rice growing season observations to study the impacts on soil NH3 volatilization and rice yield after field aging. The results showed that the reduction of cumulative soil NH3 losses by MPs was around 45% after one-year field aging, which was within the range of 40–57% in the previous rice season. Abatement of NH3 volatilization by MPs mainly occurred in basal fertilization and was related to floodwater pH. Besides, the reduction rate of NH3 volatilization by BC and MPs + BC was enhanced after field aging (63% and 50–57%) compared to that in the previous rice season (5% and 11–19%), with the abatement process occurring in the first supplementary fertilization. There was a significant positive correlation between cumulative NH3 volatilization and soil urease activity. Notably, field aging removed the positive effect of MPs and MPs + BC in reducing yield-scale NH3 losses in the previous rice season (∼62%). Furthermore, despite BC affecting rice yield insignificantly after field aging, the presence of MPs led to a significant 17–19% reduction in rice yield. Our findings reveal that differences in the after-effects of BC and MPs in field aging emerge, where the negative impacts of MPs on soil NH3 abatement and crop yield are progressively becoming apparent and should be taken into serious consideration.

Delaying tillering nitrogen topdressing until the midtillering phase improves nitrogen use efficiency and reduces ammonia emission via rice canopy recapture

Tillering nitrogen (N) topdressing is commonly employed to enhance primary-tiller number and achieve a high grain yield for wetland rice. Unfortunately, farmers typically apply N fertiliser shortly at tillering initiation following basal fertilisation, and substantial soil ammonia (NH3) volatilisation occurs due to the low N demand of small plants. Herein, we hypothesised that delaying topdressing N until the midtillering phase could increase canopy recapture of soil NH3 emission and better synchronise N supply with crop N demand, leading to reduced NH3 losses and increased fertiliser N use efficiency. A field experiment was conducted to investigate the effect of conventional tillering N topdressing (CT) at the early tillering stage (2 weeks after basal N application) and delayed tillering N topdressing (DT) until the midtillering phase (∼4 weeks after basal N application) on NH3 emission from soil and the soil-plant system, as well as N uptake, N use efficiency and yield. The 2-year field results showed that DT did not hinder effective tiller production or above-ground dry biomass compared with CT, but improved plant N uptake and total N accumulation after midtillering, leading to 18–27 % higher agronomic efficiency. Correspondingly, 8.9–15 % increases in grain yield were observed for DT compared with CT, mainly attributable to increased panicle number per area and filled grain number per panicle. Following tillering N application, NH3 loss from the soil-plant system under CT accounted for 22 % of top-dressed N, showing only a slight decline compared with that of soil emission. For DT, NH3 loss from the soil-plant system was reduced to 6 %, even though 15 % soil NH3 emission was observed, indicating a more than two-fold increase for in-canopy NH3 recapture. Correspondingly, cumulative net NH3 losses for the entire rice season were decreased by 31% under DT relative to CT. These results provide evidence that delaying tillering N topdressing until the midtillering phase when rice canopy formation is enhanced, can better synchronise fertiliser N supply with crop demand and increase in-canopy NH3 recapture. A large discrepancy remains between NH3 emission from soil and the soil-plant system at midtillering and panicle initiation stages, highlighting the overestimation by the soil dynamic chamber method when quantifying NH3 losses due to overlooking the contribution of canopy recapture of soil-emitted NH3.

Slurry acidification outperformed injection as an ammonia emission-reducing technique in boreal grass cultivation

Ammonia (NH3) constitutes the single largest loss of manure nitrogen (N), making measures targeted at reducing its emissions meaningful for the environment and the overall efficiency of manure N use. In this study, the performance of two emission-reducing techniques, acidification and injection, were studied in a field experiment with grass ley over two growing seasons. Emissions of NH3, crop growth, and N use efficiency were determined from plots fertilized with cattle slurry either band spread, injected or band spread after acidification. The approximate cumulative NH3 losses from the plots with band-spread untreated slurry amounted to about 22 kg NH3-N ha−1 over the observation periods in 2017 and 10 kg NH3-N ha−1 in 2018. The injection and acidification reduced the estimated cumulative NH3 emissions by 43 and 95% respectively in 2018, and both by 97% in 2017. In 2017, the emission-reducing techniques had no impacts on crop growth, but in 2018, acidification increased dry matter yield by 29% and apparent N recovery by 65% compared with band-spread untreated slurry. According to the current results, acidification consistently produced the lowest NH3 emissions and a discernible positive yield effect. It can therefore be recommended instead of injection for reducing NH3 emissions in boreal grass cultivation.

Cover crops can increase ammonia volatilization and reduce the efficacy of urease inhibitors

AbstractSurface application of urea can result in high nitrogen (N) losses through ammonia (NH3) volatilization. While management practices aim to increase the efficiency of nutrient cycling and prevent N loss, it is unknown whether the combination of multiple practices will have a synergistic or antagonistic effect. Therefore, laboratory volatilization studies were conducted to determine the effect of five cover crop treatments (surface clover [Trifolium incarnatum L.] and rye [Secale cereale L.], incorporated clover and rye, and bare soil), three N application timings (2, 4, and 8 wk after cover crop addition), and two N sources (untreated and treated urea) on the effectiveness of a urease inhibitor. Soils were incubated according to N application timing treatment, amended with the appropriate N source, and placed in chambers which captured NH3 over 7 d. There were significant interactions between cover crop treatment and N source and N source and N application timing on cumulative NH3 loss, ranging from 29 to 174 kg N ha−1. Losses were highest from treated urea when applied 2 wk after residue addition (75.9 kg N ha−1) or on top of surface residues (85.8 kg N ha−1). There was no significant effect of application timing on cumulative NH3 loss from untreated urea. However, inhibitor effectiveness did increase when residue was applied eight weeks after residue addition (77%) as compared with 2 wk after residue addition (45%). Future research should focus on alternate dosing or application timing to overcome high residue scenarios in these systems.

The effect of an acidified-gypsum mixture on broiler litter urease-producing bacteria and nitrogen mineralization.

Ammonia (NH3 ) volatilization from broiler (Gallus gallus domesticus) litter is a microbially mediated process that can decrease bird productivity and serves as an environmental pollutant. The release of NH3 is strongly influenced by the pH of litter. Flue-gas desulfurization gypsum (FGDG) has been suggested as a potential amendment to reduce NH3 volatilization due to the pH buffering capacity of calcium carbonate (CaCO3 ) precipitation. However, its effect on litter pH is not as pronounced as acidifying agents, such as aluminum sulfate (alum). The main objective of our study was to develop an acidified-FGDG amendment that has a more pronounced effect on litter pH and NH3 volatilization than FGDG alone. We conducted a 33-d incubation in which litter pH, NH3 volatilization, nitrogen mineralization, PLUP-ureC gene abundance, and CaCO3 precipitation were measured. Treatments in the study included: broiler litter (BL), broiler litter + 20% FGDG (BL+FGDG), broiler litter + FGDG-alum mixture (BL+FGDG+A6), broiler litter + 6% alum (BL+A6), and broiler litter + 10% alum (BL+A10). Our FGDG+alum amendment decreased litter pH (0.68pH units) and PLUP-ureC gene abundance(>1 log) compared with FGDG alone and the control (p<.05). This led to a 25% decrease in cumulative NH3 loss after 33 d. The addition of FGDG alone did not have an effect on litter pH (p=.36) or cumulative NH3 loss (p=.29) due to a lack of significant CaCO3 precipitation. Treating litter with 6 and 10% alum was the most effective amendment for reducing pH and cumulative NH3 loss.

Nitrogen losses from hard red spring wheat fields in the northern plains

AbstractNitrogen dynamics varies spatially in response to complex interactions among weather, soil, and management practices. Twenty‐six spring wheat (Triticum aestivum L.) fields were studied for N losses, nitrous oxide (N2O) flux and ammonia (NH3) volatilization, grain yield and protein concentration in farmers fields in Minnesota and North Dakota of the Red River Valley during 2018– 2020 growing seasons. Spring wheat grain yield ranged from 2.8 to 9.7 Mg ha–1 with protein concentration ranging between 106 and 180 g kg–1. Average cumulative N2O and NH3 losses were 415 g N2O‐N ha–1 and 1.43 kg NH3 ha–1, respectively (n = 26). Spring wheat grain yield (r = .53, p = .01) had positive association with May rainfall. Grain protein concentration declined with delay in planting (r = –0.55, p = .01). Linear regression indicates a close association of daily N2O flux with soil moisture (r2 = .23, p &lt; .01), soil inorganic N concentration (r2 = .02, p = .04), and days after planting (r2 = .20, p &lt; .01). Soil inorganic N concentration (just after planting) had a positive association with cumulative N2O flux (r = .41, p = .03). This study showed rainfall, soil moisture, and inorganic N concentration play a dominant role in N dynamics across the region.

Ammonia volatilization from urea in alfalfa field with different nitrogen application rates, methods and timing

Ammonia (NH3) volatilization from agricultural activities contributes to climate change and nitrogen (N) loss. Nitrogen management method has an important effect on NH3 volatilization. The purpose of this study was to evaluate the influence of N application rate, method and timing on NH3 loss from alfalfa field. In 2017 and 2018, NH3 volatilization was measured by the calibrated Dräger-Tube method under banding, surface broadcasting and center-pivot fertigation methods with three N application rates (27.6, 48.3, 69.0 kg N ha−1 for each alfalfa cutting). Different application timing (7:00, 12:00, 17:00) was applied for sprinkler fertigation in 2017. The results showed that with irrigation method of center pivot, the two-year averaged cumulative NH3 loss under sprinkler fertigation was 6.80 kg N ha−1, was similar to that under broadcasting and 32.55 % higher than that under banding. With the increase of N application rates, the cumulative NH3 loss increased but NH3 loss rate decreased. For different treatments, NH3 loss rate ranged from 1.76 % to 3.88 %. Cumulative NH3 loss for a growing season was only 5.00 kg N ha−1 for sprinkler fertigation at dusk, which could be significantly reduced by 20.38 % and 23.31 % compared with those in the morning and at noon, and even lower than that under banding. Meanwhile, instantaneous NH3 loss flux had a significantly positive correlation with temperature in the two years. Based on our results, in order to minimize NH3 loss, sprinkler fertigation at dusk was more recommendable to the urea application for alfalfa in the North China.

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.

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.

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.

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.

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.

Effect of a New Manure Amendment on Ammonia Emissions from Poultry Litter

Treating manure with aluminum sulfate (alum) is a best management practice (BMP) which reduces ammonia (NH3) emissions and phosphorus (P) runoff from poultry litter. However, the price of alum has increased markedly in recent years, creating a need for less expensive products to control NH3 volatilization. The objective of this study was to evaluate the effects of a new litter amendment made from alum mud, bauxite, and sulfuric acid (alum mud litter amendment or AMLA) on NH3 emissions, litter chemistry, and poultry production in a pen trial. Three separate flocks of 1000 broilers were used for this study. The first flock of birds was used to produce the poultry litter needed for the experiment. The second and third flocks of birds were allocated to 20 pens in a randomized block design with four replicates of five treatments: (1) control, (2) 49 kg AMLA/100 m2 incorporated, (3) 98 kg AMLA/100 m2 incorporated, (4) 98 kg AMLA/100 m2 surface applied, and (5) 98 kg alum/100 m2 incorporated. Ammonia flux measurements and litter samples were collected from each pen at day 0, 7, 14, 21, 28, 35, and 42. The average litter pH for both flocks was higher in untreated litter (7.92) compared to incorporating alum (7.32) or AMLA (7.18). The two flocks’ average NH4-N concentrations at day 42 were 38% and 30% higher for the high rates of incorporated alum and AMLA compared to the untreated litter. Compared with untreated litter, AMLA reduced overall NH3 emissions by 27% to 52% which was not significantly different from reductions in emissions by alum (35%). Alum mud litter amendment reduced cumulative NH3 losses from litter as much as, and in some cases more than, alum applied at the same rate. These data indicate that AMLA, which can be manufactured for lower price than alum, is an effective alternative litter amendment for reducing NH3 emissions from poultry litter.

Effects of enhanced efficiency nitrogen fertilizers on NH3 losses in a calcareous fluvo-aquic soil: a laboratory study

Excessive ammonia (NH3) emission to the atmosphere can cause a series of environmental problems and further cost to human health. Enhanced efficiency nitrogen (N) fertilizers (EENFs) were designed to reduce N losses to the environment and thus to improve fertilizer N use efficiency. The aim of the present study was to test the effectiveness of EENFs on NH3 emissions from surface-broadcast urea (dominant N application method for the studied region) in a fluvo-aquic soil under laboratory conditions. The study consisted of five treatments: (1) UREA: common urea; (2) UREA + NP: urea with incorporated nitrification inhibitor nitrapyrin; (3) UREA + DCD: urea with incorporated nitrification inhibitor dicyandiamide; (4) UREA + NBPT: urea with incorporated urease inhibitor NBPT [N-(n-butyl) thiophosphoric triamide]; (5) PCU, a polymer-coated urea. Urea with or without NP, DCD, and NBPT was dissolved in deionized water and was then carefully broadcast to the soil surface. The polymer-coated urea was surface-broadcast uniformly, and thereafter, deionized water was carefully dripped onto the soil surface. A forced-draft system with a volatilization chamber was employed to measure the NH3 flux. After the main experiment, the upper and lower soil layer was separately homogenized for analysis of soil ammonium N (NH4+-N) and nitrate N (NO3−-N) contents. The NH3 flux peak for UREA + NP, UREA + DCD, and UREA + NBPT treatment occurred on 5–8 days after fertilizer application, which were 1.04, 1.16, and 0.36 μg N cm−2 h−1, respectively, while NH3 flux for PCU treatment was very low (0.02–0.19 μg N cm−2 h−1) and no obvious NH3 flux peak emerged during the whole experiment. Urea with incorporated NP and DCD increased cumulative NH3 losses by 59% and 202% compared to urea only, respectively, while urea incorporated with NBPT and PCU reduced cumulative NH3 losses by 59% and 82% compared to urea only, respectively, Our results suggested that NH3 losses were greatly increased by applying the nitrification inhibitors nitrapyrin and dicyandiamide to urea, and nitrification inhibitors need to be carefully used in the fluvo-aquic soil. As surface-broadcast urea is nowadays still the dominant N application method in the NCP, surface application of NBPT-amended urea or PCU would be good options to reduce NH3 losses without having to change farmers’ fertilizer application method.

Coal char affects soil pH to reduce ammonia volatilization from sandy loam soil

AbstractAmmonia (NH3) volatilization loss adversely affects N availability in soil‐plant systems, reduces crop yield, and negatively impacts environment. Char (coal combustion residue), which contains up to 293 g kg−1 total C by weight, has been shown to reduce NH3 volatilization due to its considerably high surface area and cation exchange capacity. The NH3 loss can be greatly affected by a shift in soil pH or urea hydrolysis. A 21‐d laboratory study was conducted to evaluate the effects of char on soil pH, N transformations, and subsequent NH3 volatilization in sandy loam soil. Two char rates (0 and 13.4 Mg C ha−1) and two urea rates (0 and 200 kg N ha−1) were mixed in soil in four 2‐way combinations with four replications of each. There were 11 sets of all treatment combinations and each set was analyzed for soil moisture, pH, NH3 volatilization, and residual N (urea, NH4, and NO3) every other day for 3 wk. Char application reduced cumulative NH3 loss in the fertilized treatment. Reduction in NH3 loss due to char addition was evidenced by greater residual NH4–N on certain days in treatments with char compared to treatments without char. Char did not affect urea hydrolysis process but it lowered soil pH in the fertilized treatments in the first week. This study supported our hypothesis that char altered soil pH and thereby reduced NH3 volatilization loss from the fertilized soil.

Ammonia volatilization under different nitrogen and water treatments of tomato-watermelon rotation system in solar greenhouse in Losses Plateau, China

To understand the characteristics of ammonia volatilization in Losses Plateau, an experiment was conducted in a typical solar greenhouse involving four treatments. Intermittent ventilation chamber method was used to measure NH3 volatilization over the period of tomato-watermelon rotation. The results showed that nitrogen transformation was rapid in solar greenhouse system. The peak NH3 volatilization rate appeared one to two days after fertilization with the range from 0.26 to 2.02 kg N·hm-2·d-1. The NH3 volatilization lasted for about one week in all treatments. No significant differences were recorded in terms of cumulative NH3 volatilization among all nitrogen fertilizer input treatments. The cumulative NH3 losses further increased about 46.7% in two seasons under the same nitrogen application rate, however when irrigation application was decreased. The average NH3 vola-tilization rate and cumulative NH3 losses in watermelon season were higher compared to tomato season, which might be attributed to high temperature during watermelon season. Soil NH4+-N content, water filled pore space, soil temperature of 0-5 cm layer and air temperature all had extremely significant effect on NH3 volatilization rate, while a negative correlation was observed between soil pH and NH3 volatilization rate. Between the different cropping seasons, the rate of NH3 volatilization and cumulative NH3 losses were different, and decreased with decreases in nitrogen input, while reduced irrigation volume increased NH3 volatilization under the same nitrogen application rate.

The effect of nitrification inhibitors on NH3 and N2O emissions in highly N fertilized irrigated Mediterranean cropping systems

There is an increasing concern about the negative impacts associated to the release of reactive nitrogen (N) from highly fertilized agro-ecosystems. Ammonia (NH3) and nitrous oxide (N2O) are harmful N pollutants that may contribute both directly and indirectly to global warming. Surface applied manure, urea and ammonium (NH4+) based fertilizers are important anthropogenic sources of these emissions. Nitrification inhibitors (NIs) have been proposed as a useful technological approach to reduce N2O emission although they can lead to large NH3 losses due to increasing NH4+ pool in soils. In this context, a field experiment was carried out in a maize field with aiming to simultaneously quantify NH3 volatilization and N2O emission, assessing the effect of two NIs 3,4‑dimethilpyrazol phosphate (DMPP) and 3,4‑dimethylpyrazole succinic acid (DMPSA). The first treatment was pig slurry (PS) before seeding (50 kg N ha−1) and calcium ammonium nitrate (CAN) at top-dressing (150 kg N ha−1), and the second was DMPP diluted in PS (PS + DMPP) (50 kg N ha−1) and CAN + DMPSA (150 kg N ha−1) also before seeding and at top-dressing, respectively. Ammonia emissions were quantified by a micrometeorological method during 20 days after fertilization and N2O emissions were assessed using manual static chambers during all crop period. The treatment with NIs was effective in reducing c. 30% cumulative N2O losses. However, considering only direct N2O emissions after second fertilization event, a significant reduction was not observed using CAN+DMPSA, probably because high WFPS of soil, driven by irrigation, favored denitrification. Cumulative NH3 losses were not significantly affected by NIs. Indeed, NH3 volatilization accounted 14% and 10% of N applied in PS + DMPP and PS plots, respectively and c. 2% of total N applied in CAN+DMPSA and CAN plots. Since important NH3 losses still exist even although abating strategies are implemented, structural and political initiatives are needed to face this issue.

Effects of application methods and urea rates on ammonia volatilization, yields and fine root biomass of alfalfa

Minimizing nitrogen (N) losses via ammonia (NH3) volatilization and maximizing yields with effective fertilization technologies in intensive cropping system is an essential part of sustainable agriculture. In 2016 and 2017, a study was conducted at an experimental station of China Agricultural University in Zhuozhou, Hebei Province, China, to quantify NH3 volatilization by banding, surface broadcasting and center-pivot fertigation methods at three different N application rates (69.0, 48.3, 27.6 kg N hm−2) by the calibrated Dräger-Tube method. The results showed that cumulative NH3 volatilization losses were significantly affected (P ≤ 0.05) by N application methods The air temperature and wind speed had positive correlations with NH3 flux. The losses of banding, broadcasting, and fertigation were 1.08%, 1.34%, and 3.80% of total N application rates, respectively. The cumulative NH3 volatilization losses increased, but the proportions of total N application rates decreased with increasing N application rates. The alfalfa yields of the 3rd and 4th cuttings were not significantly influenced (P > 0.05) by N application methods, while the fine root biomass was significantly affected (P ≤ 0.05) by N application methods The season averaged NH3 volatilization losses of each cutting was 1.73 kg N hm−2 under fertigation, which might not bring heavy burden to environment. Comparing to banding and broadcasting methods, fertigation caused a higher cumulative NH3 losses, but led to a much higher yields and fine root biomass, with average values of 2.48 Mg hm−2 and 45.53 kg hm−2,respectively. Therefore, the fertigation method could be economically beneficial and environmentally sound in the North China Plain, where intensive cropping system is widely adopted.

Optimizing urease inhibitor usage to reduce ammonia emission following urea application over crop residues

Abstract Nitrogen loss as ammonia (NH3) is a major problem when urea is topdressed over crop residues. The treatment of urea with N-(n-butyl) thiophosphoric triamide (NBPT) temporarily inhibits urease activity and reduces NH3 volatilization loss under many agro­ecological conditions. However, the amount of straw on the soil in green sugarcane trash blanketing (GCTB) systems affects the success of NBPT in reducing NH3 loss. We hypothesized that an increase in the NBPT concentration in urea above the current level (530 mg NBPT kg−1 urea) in Brazil is necessary to reduce the NH3 volatilization and to improve the efficiency of urea in GCTB systems. We evaluated the NH3 loss from urea treated with NBPT under field conditions in GCTB systems. Six field trials were conducted across the State of Sao Paulo, the main sugarcane-growing region in Brazil. The treatments were urea, ammonium nitrate, urea treated with NBPT at concentrations of 530, 850, 1500, and 2000 mg kg−1, and a control plot without N fertilizer. The amount of volatized NH3 was assessed through a closed semi-static collector containing two acid-trap foam disks, and analyzed by colorimetry using flow injection analysis. NBPT concentrations above 530 mg kg−1 delayed the time of maximum rate of loss and also reduced cumulative NH3 loss. Ammonia emissions were linearly reduced with increasing NBPT concentrations until 1000 mg kg−1. Any further increase in the NBPT concentration did not result in a substantial reduction of NH3 volatilization. Increasing the NBPT concentration in urea is an effective approach to optimize the adoption of urea-based fertilizers in tropical GCTB systems.