NH3 Volatilization Research Articles

Biochar decreased N loss from paddy ecosystem under alternate wetting and drying in the Lower Liaohe River Plain, China

Biochar addition to soil is widely utilized to enhance carbon sequestration and reduce fertilizer N losses. However, little research has been studied on the effect of biochar on reactive gaseous N losses, N leaching and grain yield in paddy ecosystems under water stress, especially in the Lower Liaohe River Plain with a higher water percolation. Our experiment was carried out in 2020 and 2021 utilizing a split-plot design with continuously flooding irrigation and alternate wetting and drying irrigation as main plots and without biochar addition and with 20 t·ha−1 rice husk-derived biochar addition as sub-plots. The results showed that alternate wetting and drying irrigation respectively, decreased N leaching and reactive N losses by 15.9 % and 11.3 % but also respectively, increased seasonal cumulative NH3 volatilization and N2O emissions by 5.0 % and 210 % on average. Rice husk-derived biochar addition significantly mitigated seasonal cumulative NH3 volatilization and N2O emissions by 8.8 % and 19.7 % in 2020, 20.7 % and 19.2 % in 2021, respectively, and decreased inorganic N leaching and reactive N losses by 8.3 % and 14.1 % in 2021. Biochar addition coupling with alternate wetting and drying respectively, mitigated cumulative NH3 volatilization and N2O emissions by 7.3 % and 19.3 % in 2020, and, 22.7 % and 22.0 % in 2021 as compared to that without biochar. Biochar did not differ from without biochar in inorganic N leaching under alternate wetting and drying irrigation in both years but significantly reduced reactive N losses by 17.8 % in 2021, which efficiently inhibited the alternate wetting and drying induced negative effects on the increase in reactive N losses. Therefore, biochar addition to paddy ecosystems under alternate wetting and drying could realize sustainable utilization of water resources, increase soil N fixation, and mitigate N losses.

Impact of a forage legume or nitrogen fertilizer application on ammonia volatilization and nitrous oxide emissions in Brachiaria pastures

ABSTRACT The largest proportion of greenhouse gas (GHG) emissions in the Agriculture sector of the Brazilian national GHG inventory is derived from the large (>200 million head) herd of cattle. The greatest contribution to these emissions comes from the enteric methane from cattle, but the direct and indirect emissions of nitrous oxide (N 2 O) from cattle excreta and N fertilizer are responsible for approximately 9 % of all national anthropogenic GHG emissions. Ammonia (NH 3 ) can be volatilized from N fertilizer and cattle excreta and deposited in sites remote from the source, constituting an indirect source of N 2 O. This study aimed to determine whether direct N 2 O emissions and NH 3 volatilization from N-fertilized pastures were greater than those derived from a mixed grass-legume pasture without N fertilizer addition. Emissions of N 2 O and NH 3 from excreta and N fertilizer from a Palisade grass (Urochloa brizantha cv. Marandu) monoculture fertilized with 2 × 60 kg N ha -1 yr -1 urea were compared to those from a mixed Palisade grass-forage peanut (Arachis pintoi) pasture. Dung and urine were collected from these cattle, and NH 3 losses and N 2 O emissions from the excreta and from N fertilizer were monitored using static chamber techniques. Volatilization of NH 3 and N 2 O emissions were found to be greater from urine than from dung. Ammonia losses from excreta and urea fertilizer were low, not exceeding 6.8, 1.1, and 4.7 % of the N applied as urine, dung, and fertilizer, respectively. The N 2 O emissions showed a tendency to be greater for the urine from the N-fertilized compared to the mixed grass-legume pasture, and the N 2 O emissions from the urine of the N-fertilized pasture ranged from 0.08 to 0.94 % of applied urine N. The N 2 O emission from the N fertilizer was at maximum 0.46 % of the applied N. The direct N 2 O emissions and the loss of NH 3 by volatilization (indirect N 2 O emission) from the excreta of cattle grazing the mixed grass-legume pasture were similar to, or lower than, the grazed grass monoculture fertilized with 120 kg N ha -1 yr -1 . As the mixed pasture received no N fertilizer and hence no GHG emission from its manufacture or application, introducing forage peanut to the Urochloa brizantha pastures shows potential to be responsible for lower GHG emissions than the N fertilized grass pasture.

Nitrogen source regulates soil nitrification and nitrogen losses more than nitrification inhibitor and herbicide: A laboratory evaluation

AbstractIncreased environmental nitrogen (N) losses have prompted the use of enhanced efficiency nitrogen fertilizers, including nitrification inhibitors. However, the comparative effects of nitrification inhibitors with conventional nitrogen fertilizers and herbicides on soil nitrification and nitrogen losses remain poorly understood. This study evaluated the impact of a nitrification inhibitor (Instinct NXTGEN), two nitrogen sources (broadcast urea vs. injected aqueous ammonia), and a preemergence herbicide (Acuron) on (1) soil nitrification through a 25‐day soil incubation experiment and (2) NH3 volatilization, NO3‐N leaching, and N2O‐N emissions through a 31‐day soil column study in loamy sand soil. In both experiments, treatments included combinations of nitrification inhibitor versus no inhibitor, two nitrogen sources, and preemergence herbicide versus no herbicide. Results revealed that nitrogen source significantly influenced nitrification, with injected aqueous ammonia reducing nitrification by 33% compared to surface broadcast urea. Nitrification inhibitors and herbicide had no effect on soil nitrification. Injected aqueous ammonia reduced NH3 volatilization by 87% compared to surface broadcast urea, but the effect of the nitrification inhibitor on NH3 volatilization was inconsistent across both nitrogen sources. Injected aqueous ammonia led to 39% higher cumulative nitrogen (NO3‐N + NH4‐N) leaching than urea, while the nitrification inhibitor had an inconsistent effect on NO3‐N leaching across both nitrogen sources. No significant differences in N2O‐N emissions were observed among treatments, and the herbicide had no effect on any measured parameters. These findings suggest that nitrogen source plays a more critical role in regulating soil nitrogen losses than nitrification inhibitors or herbicides.

Soil ammonia volatilization after fertilization using antibiotic-contaminated swine wastewater

The application of wastewater from pig farming is an alternative to fertilize crops using the effluent produced in the activity. However, in addition to nutrients capable of meeting the needs of crops, this effluent also has residues of antibiotics for livestock use in its composition, which can interfere with the activity of soil microorganisms and reduce the enzymatic activity, leading to nitrogen losses into the atmosphere. Hence, this study evaluated ammonia volatilization behavior after adding swine wastewater with tetracycline-class antibiotics. Pots containing soil received doses of raw and digested wastewater (0.06 and 0.09 L), combined or not with doses of tetracycline (35 µg L-1), chlortetracycline (40.9 µg L-1), and doxycycline (14.9 µg L-1 volatilized NH3 was collected by foam absorbers containing phosphoric acid solution on the soil, which were changed every 48 h, totaling 11 collections at a time. The NH3 volatilization significantly increased when the swine wastewater (raw or digested) was added. The presence of antibiotics reduced NH3 losses, showing that they can inhibit urease activity. Our findings showed that tetracycline-class antibiotics can inhibit urease activity, contributing to the continuity of nitrogen in the soil.

Earth-abundant catalyst for modification of wheat straw to enhance ammonia mitigation from fertilized alkaline soil

In this study, inexpensive earth-abundant catalyst of Co/TiO2 is coupled with a low-temperature modification approach to enhance NH3 adsorption capacity on wheat straw (WS). The highest NH3 uptake achieved is 111.9 mg/g, with 80.8 % retention even after 3 h of desorption. Mechanistic investigation indicates that the enhanced adsorption capacity stems from Co/TiO2, which facilitates generation of reactive oxygen species, leading improved ultra-micropore structure that enhances the interaction between NH3 and oxygen-containing functional groups through a trapping effect. The robust stability of adsorbed NH3 is attributed to the formation of amides or amines. Incorporation of only 1 wt% WS-Co to urea-fertilized alkaline soil reduced NH3 volatilization by 83.1 %. The significant effect is primarily attributed to the excellent adsorption capacity of WS-Co, rather than alterations in the relative abundance of the microbial community. These findings present a novel approach for development of effective fertiliser additive to mitigate NH3 volatilization from alkaline soil.

Field efficacy of urease inhibitors for mitigation of ammonia emissions in agricultural field settings: a systematic review

Globally, ammonia (NH3) is one of the key air pollutants and reducing NH3 emissions and the associated indirect emission of the greenhouse gas nitrous oxide remains challenging for the agricultural sector. During the past three decades, a number of urease inhibitors have been placed on the market with the goal of reducing NH3 loss from urea containing fertilisers. N–(n-butyl) thiophosphoric triamide (NBPT), N–(2-nitrophenyl) phosphoric triamide (2-NPT), a 3:1 ratio of NBPT + N-(n-propyl) thiophosphoric triamide (NPPT) and the maleic and itaconic acid co-polymer (MIP) are registered urease inhibitors under the European Commission Fertilising Products Regulation (FPR). However, the availability of several inhibitor options has raised questions from farmers, policymakers and emissions inventory compiling authorities regarding the field efficacy of the different options available for reducing NH3 loss. Despite many disparate NH3 field studies existing for NBPT, 2-NPT, NBPT + NPPT and MIP there is presently no review that brings these results together, a significant and important knowledge gap. This review addresses the gap by summarising the published field trial literature on NH3 volatilisation mitigation offered by NBPT, 2-NPT, NBPT + NPPT and MIP. Our review identified 48 peer reviewed studies where NH3 loss mitigation was measured in a field setting, giving 256 replicated comparisons. The synthesised literature results revealed that NBPT + NPPT reduced NH3 loss by 75% (95% CI = 58–82% n = 32), 2-NPT reduced NH3 loss by 70% (95% CI = 63–76% n = 19) and NBPT reduced NH3 loss by 61% (95% CI = 57–64% n = 165), giving on average a 69% reduction by these three urease inhibitors. In contrast, MIP increased NH3 loss by 0.3% on average (95% CI = −8–9% n = 40). The results presented in this review broaden the understanding of urease inhibitor efficacy in field conditions and demonstrate that not all products behave the same in terms of field NH3 reduction efficacy. This review is important for farmers, policymakers, emission inventory compilers and other stakeholders.

Optimal Application of Biogas Slurry in Paddy Fields under the Dual Constraints of Agronomy and Environment in the Yangtze River Delta Region

The production of huge amounts of biogas slurry during livestock breeding has resulted in pressing environmental issues. Although paddy fields can be potential sinks for the disposal of biogas slurry, the impacts of biogas slurry on rice production, grain quality, and relevant environmental risks in the Yangtze Delta region remain unclear. Herein, we conducted a field trial from 2021 to 2023 which involved different gradients of biogas slurry utilization, including CK (no fertilizer), CN (100% chemical nitrogen (N) of 240 kg ha−1), NBS (biogas slurry replacing 50% chemical N), BS1 (replacing 100% chemical N), BS1.5 (replacing 150% chemical N), and BS2 (replacing 200% chemical N). The results showed that there were no significant differences in average rice yields between CN, NBS, BS1.5, and BS2 over the three-year study period, with an average yield of 8283 kg ha−1, and the average yields of BS1 and CK were 7815 kg ha−1 and 6236 kg ha−1, respectively. However, heavy utilization of biogas slurry (BS1.5 and BS2) not only significantly reduced the rice seed-setting rate, the 1000-grain weight, and the processing quality, but also significantly increased the protein, amylose, Cu, and Zn content in rice grains; additionally, higher N losses occurred via surface water and increased NH3 volatilization was observed, finally resulting in lower nitrogen-use efficiency. Meanwhile, moderate utilization of biogas slurry (NBS and BS1) led to better rice quality and nitrogen-use efficiency, lower potential food safety risk, and N loss. Further, compared to BS1, NBS showed higher yield, harvest index, processing quality, gel consistency, palatability scores, and nitrogen-use efficiency, but lower N losses were present. Overall, the NBS treatment balanced the agronomic benefits and environmental risks in the Yangtze River Delta region. In the future, more attention should be paid to food safety and environmental risks when using biogas slurry.

Mitigating nitrogen loss in paddy field microcosms through indigenous arbuscular mycorrhizal fungi assemblage

AbstractWhether farmers should consider the role of arbuscular mycorrhizal fungi (AMF) in agriculture is a hotly debated topic. We aimed to investigate the role of indigenous AMF in reducing nitrogen (N) loss from paddy fields via runoff, leaching, NH3 volatilization, and N2O emission. We conducted a pot experiment employing a mycorrhiza‐defective rice mutant (non‐mycorrhizal) as the control, grown in soil containing indigenous AMF. The corresponding AMF treatment used the progenitor of this mutant with the same soil. The plants were fertilized with nitrogen, phosphorus and potassium 6 weeks after sowing. The root colonization was 23% in mycorrhizal rice, and no typical AMF structures were observed in the roots of non‐mycorrhizal rice. Our findings indicated that the mycorrhizal system exhibited lower N concentrations of runoff and leachate further compounded by reduced fluxes of N2O and NH3. This led to 14% decrease (mycorrhizal rice 111 kg N ha−1; the non‐mycorrhizal rice: 129 kg N ha−1) in cumulative N loss within 3 days post‐fertilization. While this AMF effect was consistent across the four tested N loss pathways, differences were observed between NH4+‐N and NO3−‐N in the runoff pathway. Notably, our results revealed no evidence of trade‐offs in AMF effect on N loss among the tested pathways. Additionally, mycorrhizal rice had larger shoots and roots than their non‐mycorrhizal counterparts. Our study underscores the potential benefits of indigenous AMF in paddy fields for mitigating water pollution and reducing greenhouse gas emission.

Large loss of reactive nitrogen and the associated environmental damages from tea production in China

Tea (Camellia sinensis L.), the most popular beverage worldwide and an important cash crop in China, plays a crucial role in the socio-economic landscape. Reactive nitrogen (Nr) loss from tea cultivation in China has become a major environmental problem due to the high input of N fertilizers. However, the scale of the Nr loss and its environmental impact on tea production in China remains unknown. Hence, we conducted a comprehensive meta-analysis of ammonia volatilization (NH3), nitrogen oxide (NOx), nitrous oxide (N2O) emissions, N leaching (total nitrogen, TN), and N runoff (TN) losses in tea plantations in China. The total Nr loss in Chinese tea plantations was 376 Gg yr−1 (149 kg N ha−1 yr−1) in 2014, with N leaching, NH3 volatilization, N2O emissions, NOx emissions, and N runoff losses accounting for 52.2 %, 33.2 %, 7.5 %, 5.4 %, and 1.7 %, respectively. The total Nr loss-related environmental damage cost of tea cultivation reached 9.53 billion CNY yr−1 in 2014, which was 7.7 % of the total tea production output value. The bulk of the environmental damage cost was attributed to NH3 volatilization (49.1 %), N2O emissions (24.9 %), and N leaching (19.2 %). Large Nr losses occurred during tea production in Sichuan, Hubei, Guizhou, Yunnan, Zhejiang, and Hunan provinces, accounting for 17.7 %, 17.0 %, 13.4 %, 10.7 %, 7.6 %, and 7.0 % of the total Nr losses in China, respectively. Our analysis showed that the adoption of integrated nutrient management reduced N fertilizer inputs to 300 kg N ha−1, lowered Nr loss from 376 Gg to 172 Gg yr−1, and reduced the environmental damage cost of N loss by 45.4 %. These findings, along with detailed data on the N balance of tea cultivation, provides critical information needed to develop effective region-specific N nutrient management practices and policies for sustainable and profitable tea crop production in China, and possibly in other similar geographies.

Ameliorating the response of slow-releasing nitrogen fertilizer on sustainable maize growth

The extensive utilization of nitrogen (N) fertilizers within maize cultivation systems has resulted in diminished nitrogen use efficiency (NUE) and contributed to nitrogen pollution on a global scale. To assess the ecological repercussions of excessive fertilization, it is imperative to elucidate both the nitrogen use efficiency and the fate of nitrogenous fertilizers upon application. The current research evaluated the potential of a newly developed slow-release nitrogen fertilizer on maize growth and its behavior in soil under controlled conditions. Six different levels of urea fertilizer (UF) and slow-release nitrogen fertilizer (SRNF) were administered within the field, representing 100%, 85%, and 70% of the recommended application rates. The slow-release nitrogen fertilizer (SRNF) exhibited superior performance regarding growth, yield and nutrient retention in comparison to urea fertilizer (UF). Moreover, minimal ammonia emissions were detected with the employment of the slow-release nitrogen fertilizer (SRNF), while other urea-based fertilizers proved inefficient in mitigating ammonia emissions, despite enhancing various growth and yield parameters. The efficiency in nutrient recovery followed a distinct pattern, with polymer-coated fertilizers demonstrating superiority. The plots treated with SRNF displayed significantly higher growth and yield characteristics compared to those treated with urea fertilizer. In terms of NH3 volatilization, the urea fertilizer (UF) treatment at 100% application rate showed higher emissions (1.99 mg g-1) after a 27-day incubation period, as opposed to the slow-release nitrogen fertilizer (SRNF) treatment (1.68 mg g-1). Leaching data indicated that urea fertilizer treatments led to greater losses of NO3-N (2.01 mg L-1) compared to SRNF treatments (0.88 mg L-1).

Vermicompost and flue gas desulfurization gypsum addition to saline-alkali soil decreases nitrogen losses and enhances nitrogen storage capacity by lowering sodium concentration and alkalinity

Saline-alkali soils have poor N storage capacity, high N loss and inadequate nutrient supply potential, which are the main limiting factors for crop yields. Vermicompost can increase organic nutrient content, improve soil structure, and enhance microbial activity and function, and the Ca2+ in flue gas desulfurization (FGD) gypsum can replace Na+ and neutralize alkalinity in saline-alkali soils though chemical improvement. This study aimed to determine if vermicompost and FGD gypsum addition could improve the N storage capacity through decreasing NH3 volatilization and 15N/NO3− leaching from saline-alkali soils. The results indicate that the combined application of vermicompost and FGD gypsum led to the displacement and leaching Na+ in the upper soil layer (0–10 cm), as well as the neutralization of HCO3− by the reaction with Ca2+. This treatment also improved soil organic matter content and macroaggregate structure. Also, these amendments significantly increased the abundance of nifH and amoA genes, while concurrently decreasing the abundance of nirK gene. The structural improvements and the lowering of Na + concentration in and alkalinity decreased cumulative NH3 volatilization, and leaching of 15N and NO3− to the deep soil layer (20–30 cm). FGD gypsum increased the 15N stocks and inorganic N stocks of saline-alkali soil, whereas vermicompost not only increased the 15N and inorganic N stocks, but also increased the total N stocks, the combination of vermicompost and FGD gypsum can not only increase the available N storage capacity, but also enhance the potential for N supply. Therefore, vermicompost and FGD gypsum decrease N loss and increase N storage capacity through structural improvement, and lowering of Na+ concentration and alkalinity, which is crucial for improving the productivity of saline-alkali soil.

12-year continuous biochar application: Mitigating reactive nitrogen loss in paddy fields but without rice yield enhancement

Numerous studies have documented the beneficial effects of short-term biochar application on soil carbon sequestration, greenhouse gas emissions reduction, and ecological functions enhancement. However, concerns persist regarding the impacts on soil reactive nitrogen (N) loss and crop yields under long-term biochar application (more than ten years), due to the irreversibility once biochar is incorporated into soils. This study presents the results of a 12-year field experiment in a rice-wheat rotation system with treatments including a control (CK, no corn straw or biochar), annual corn straw returning (CS, 6 Mg·ha−1·yr−1), and annual application of corn straw biochar pyrolyzed at 400°C at rates of 2.4, 6, and 12 Mg·ha−1·yr−1 (BC1, BC2, and BC3), investigating rice yields (2011–2022) and reactive N loss (2021–2022). The results showed that after 11 years of continuous biochar application until the 2021 rice season, alkaline hydrolysis N (AN, equivalent to an average of 347 kg N ha−1) within the 0–15 cm soil layer in biochar treatments was significantly higher than that of the CK (200 kg N ha−1), attributable to the biochar-induced enhancement of cation exchange capacity (CEC). The application of biochar reduced inorganic N leaching and NH3 volatilization losses by an average of 42.21 % and 30.85 %, respectively. However, N2O emission in the BC3 treatment was over 2 times as high as in the CK. Continuous biochar applications did not increase rice yield over the 12 rice seasons, as excessive soil AN level under biochar application reduced the rice harvest index. The results indicated that continuous biochar application was effective in reducing reactive N losses and increasing plant-available N supply, suggesting a potential to sustain rice production with lower fertilizer N inputs.

Subsurface Drainage and Nitrogen Fertilizer Management Affect Fertilizer Fate in Claypan Soils

Sustainable nitrogen (N) fertilizer management practices in the Midwest U.S. strive to optimize crop production while minimizing N gas emission losses and nitrate-N (NO3-N) losses in subsurface drainage water. A replicated site in upstate Missouri from 2018 to 2020 investigated the influence of different N fertilizer management practices on nutrient concentrations in drainage water, nitrous oxide (N2O) emissions, and ammonia (NH3) volatilization losses in a corn (Zea mays, 2018, 2020)–soybean (Glyince max, 2019) rotation. Four N treatments applied to corn included fall anhydrous ammonia with nitrapyrin (fall AA + NI), spring anhydrous ammonia (spring AA), top dressed SuperU and ESN as a 25:75% granular blend (TD urea), and non-treated control (NTC). All treatments were applied to subsurface-drained (SD) and non-drained (ND) replicated plots, except TD urea, which was only applied with SD. Across the years, NO3-N concentration in subsurface drainage water was similar for fall AA + NI and spring AA treatments. The NO3-N concentration in subsurface drainage water was statistically (p < 0.0001) lower with TD urea (9.1 mg L−1) and NTC (8.9 mg L−1) compared to fall AA + NI (14.6 mg L−1) and spring AA (13.8 mg L−1) in corn growing years. During corn years (2018 and 2020), cumulative N2O emissions were significantly (p < 0.05) higher with spring AA compared to other fertilizer treatments with SD and ND. Reduced corn growth and plant N uptake in 2018 caused greater N2O loss with TD urea and spring AA compared to the NTC and fall AA + NI in 2019. Cumulative NH3 volatilization was ranked as TD urea > spring AA > fall AA + NI. Due to seasonal variability in soil moisture and temperature, gas losses were higher in 2018 compared to 2020. There were no environmental benefits to applying AA in the spring compared to AA + NI in the fall on claypan soils. Fall AA with a nitrification inhibitor is a viable alternative to spring AA, which maintains flexible N application timings for farmers.

The effects of fertilizer pretreatment on nitrogen cycling in an intensively managed temperate grassland

Effective nitrogen (N) management is essential for minimizing fertilizer nutrient losses and maximizing N use efficiency. This study, conducted over two years on permanent grassland sites in Schleswig-Holstein, Germany, explored the effects of urea treatment with a urease inhibitor and digestate acidification on N-cycling and yield performance in a temperate maritime grassland context. Micro plots within these grasslands received varying N rates via acidified (with sulphuric acid) or non-acidified digestate (biogas residues), urea treated with- or without urease inhibitor (N-(n-butyl) thiophosphoric triamide) or calcium ammonium nitrate. Parameters measured included dry and N matter accumulations, NH3 volatilization, N2O emissions, NO3--N leaching, methane (CH4), and total greenhouse gas (GHG) emissions from soils. The findings demonstrated that the acidified digestate consistently enhanced metabolizable energy (ME), N yields (up to 47 %) and the apparent N recovery (ANR). While the acidified digestate and treated urea concurrently reduced NH3 emissions, the treated urea did not significantly affect (p> 0.05) dry matter (DM) and N yields, ANR, or total GHG emissions. Thus, digestate acidification or urea N stabilization could effectively mitigate the environmental impact of forage grass production while maintaining higher or comparable yields. However, higher risks of pollution swapping to groundwater bodies may result from higher N input rates. Applying acidified digestate or stabilized urea N to grasslands at a 120 kg mineral N ha−1 rate offers a practical approach, yielding appreciable N and ME while minimizing N losses.

Reactive nitrogen losses from Canadian agricultural soils over 36 years

Agriculture is a major source of reactive nitrogen (Nr) losses through ammonia (NH3) volatilization, nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. A Canadian Agricultural Nitrogen Budget for Reactive N (CANBNr) model was developed to estimate the nitrogen (N) balance in soils, including N removals by harvested crops and Nr losses for the years 1981–2016 across Canada. Annual N inputs to farmland include commercial fertilizer N, livestock manure N, symbiotic and asymbiotic biological N fixation and atmospheric N deposition of NOx and NH3. The total annual N input for Canadian farmland was 5528 Gg N (103.2 kg N ha−1) in 2016 where N removal by crops and Nr accounted for 72.5 % (74.9 kg N ha−1) and 13.4 % (13.9 kg N ha−1), respectively. The Nr losses from N2O emissions, NH3 volatilization and NO3− leaching accounted for 64 Gg N (1.2 kg N ha−1), 330 Gg N (6.2 kg N ha−1) and 348 Gg N (6.5 kg N ha−1), which represents between1.2–6.3 % of total N input. A total of 777 Gg N (14.5 kg N ha−1) remained in the soil as surplus N (14.1 % of total N input), which could be available to subsequent crops in dryer regions but might be subject to N2O loss through nitrification or denitrification processes or NO3− leaching following heavy rains in humid regions. Nitrous oxide and ammonia emissions increased over a 36-year period due to increased fertilizer N inputs. The percentage of N inputs that was estimated to be lost as Nr increased from 17.9 % in 1981 to the peak level of 19.8 % in 2001 and then declined to 13.4 % in 2016. Total N removal by crops increased at a greater rate than N input during the 2001–2016 period resulting in an increased N uptake by crops over the last 15 years. The improved management of fertilizer N for agricultural systems represents a key opportunity for both farmers and policy makers to further reduce Nr losses from Canadian farmland without negatively impacting productivity.

Recirculating frass from food waste bioconversion using black soldier fly larvae: Impacts on process efficiency and product quality

Biowaste generation is increasing worldwide and inadequate disposal has strong negative impacts on food systems and ecosystems. Biodigestion of biowaste using black soldier fly (Hermetia illucens) larvae (BSFL) generates valuable by-products such as animal feed (larval biomass) and organic fertiliser (frass). However, the latter is typically unstable immediately after waste conversion and is thus unsafe for use as a fertilizer in terms of maturity. This study evaluated recirculation of frass within bioconversion of post-consumer food waste (FW) as a dietary component for BSFL to improve the quality of the subsequent frass obtained. Frass was introduced at increasing inclusion levels replacing food waste (2.5–100% on wet-weight basis) as part of the larvae's feeding substrate. Bioconversion efficiency and material reduction were significantly reduced by frass inclusion, while larval yield per experimental unit remained unchanged. When considering only the waste component in the larval diet, larval yield (dry-weight basis) ranged between 207 (0% frass inclusion) and 403 (40% frass inclusion) kg tonne FW−1, thus increasing by up to 94% at higher frass inclusion. With increasing dietary inclusion rate of frass from 0% to 100%, crude protein content of larval biomass increased by 41%, while fat content was reduced by 32%. The recirculated frass (obtained after including frass in the larval diet) had elevated concentrations of P, K, S, Na and B and around 6% lower organic matter content, demonstrating a higher degree of decomposition. Frass inclusion in the larval diet generated recirculated frass that were more stable and mature, as indicated by self-heating capacity, CO2 and NH3 volatilisation, seed germination bioassays and other parameters. It was concluded that frass recirculation improves waste bioconversion efficiency in relation to food waste unit, as well as larval biomass and frass quality, ensuring safer use as a fertilizer.

Hydrogel Effects on Soil Nitrogen Transformations in pH-Contrasting Soils

ABSTRACT Superabsorbent hydrogels (HGs) are three-dimensional, polymeric networks that have been shown to increase soil water holding capacity, but little is known about their effect on nitrogen (N) transformations in soil. The objective of this study was to determine the effect of two types of HGs (polyacrylate (TS) or cellulose-based (H30)) applied as soil amendment on pH, urea hydrolysis, nitrification, NH3 volatilization, and soil respiration in two soils receiving urea or ammonium sulfate. Separate studies with each HG in each of two soils (four studies) were conducted with an acidic sandy loam collected in Georgia (USA) and a basic sandy loam collected in the Veneto region of Italy. The results showed that the addition of TS increased the pH of the acidic soil, whereas H30 did not have a major effect on soil pH in either soil. In the acidic soil receiving urea, H30 increased nitrification, whereas TS decreased initial nitrification. Neither HG affected urea hydrolysis, N immobilization and NH3 volatilization in either soil, but both HGs increased soil respiration in the basic soil, possibly due to HG degradation by microorganisms. These results show that the use of HGs together with N fertilizers may affect soil pH, nitrification, and respiration.

Differential impacts of microplastics on carbon and nitrogen cycling in plant-soil systems: A meta-analysis

Microplastics (MPs) are widely present in terrestrial ecosystems. However, how MPs impact carbon (C) and nitrogen (N) cycling within plant-soil system is still poorly understood. Here, we conducted a meta-analysis utilizing 3338 paired observations from 180 publications to estimate the effects of MPs on plant growth (biomass, nitrogen content, nitrogen uptake and nitrogen use efficiency), change in soil C content (total carbon (TC), soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC)), C losses (carbon dioxide (CO2) and methane), soil N content (total nitrogen, dissolved organic nitrogen, microbial biomass nitrogen, total dissolve nitrogen, ammonium, nitrate (NO3−-N) and nitrite) and nitrogen losses (nitrous oxide, ammonia (NH3) volatilization and N leaching) comprehensively. Results showed that although MPs significantly increased CO2 emissions by 25.7 %, they also increased TC, SOC, MBC, DOC and CO2 by 53.3 %, 25.4 %, 19.6 % and 24.7 %, respectively, and thus increased soil carbon sink capacity. However, MPs significantly decreased NO3−-N and NH3 volatilization by 14.7 % and 43.3 %, respectively. Meanwhile, MPs significantly decreased plant aboveground biomass, whereas no significant changes were detected in plant belowground biomass and plant N content. The impacts of MPs on soil C, N and plant growth varied depending on MP types, sizes, concentrations, and experimental durations, in part influenced by initial soil properties. Overall, although MPs enhanced soil carbon sink capacity, they may pose a significant threat to future agricultural productivity.

Higher rice productivity and lower paddy nitrogen loss with optimized irrigation and fertilization practices in a rice-upland system

Intermittent irrigation and controlled-release fertilizers are considered effective practices for rice growth; however, their combined effects on nitrogen (N) loss from intensified agricultural lands remain unclear. Here, a two-year field experiment was conducted using two irrigation regimens (flooded irrigation, FI; controlled irrigation, CI) and two fertilizer types (conventional urea, CU, split applied; controlled-release blend fertilizer, CRBF, one-time basal applied) to investigate their effects on N turnover in rice upland systems. The results demonstrated that CI not only saved 56.7 % of irrigation water compared to FI but also increased rice yield (5.3 %) and N use efficiency (7.8 %). The significant reduction in water input and soil water content for the CI led to lower N leaching (47.5 %) and N runoff (20.2 %) than for the FI. In contrast, N2O emissions increased by 27.8 % under CI compared with FI. CRBF reduced NH3 volatilization by 18.8 % and improved N use efficiency by 14.0 %, due to decreased N diffusion from the soil to surface water compared to CU. However, the N runoff of the CRBF was 23.8 % greater than that of the CU. The CI-CRBF improved the rice yield by 6.3 % and decreased N loss (22.3 %) by reducing NH3 volatilization (21.4 %) and N leaching (46.9 %). The findings suggest CI-CRBF to be an eco-friendly and lightly simplified pattern in rice upland systems, with higher rice productivity and lower paddy N loss.

Inhibit ammonia volatilization from agriculture and livestock by air plasma-activated water

Ammonia volatilization in agriculture and livestock is a considerable cause of air pollution and a significant way of N loss. In this study, we propose a method of using air plasma-activated water (PAW) to inhibit ammonia volatilization from agriculture and livestock and report the inhibitory effect under different discharge times and concentration gradients. PAW was generated through needle–water discharge, while ammonia waters with different concentrations served as simplified models for ammonia release. The compositions of the gas/liquid products of the PAW and those after mixing with ammonia water were detected and analyzed. It was found that the PAW could effectively inhibit the NH3 volatilization from ammonia water over a large range of conditions, however, NH3 volatilization promotion could also happen in some cases. The inhibition rate (IR) generally increased with the longer discharge time of the PAW and decreased with the higher ammonia water concentration. As the discharge time increased, the PAW became more acidic and had more active N components, converting more volatile NH3 to NH4 + when mixed with ammonia water. Finally, a relationship model was developed between the IR and pH of the mixture. The IR basically decreased with the increase of the mixture pH, and reached ∼100% when a PAW with a discharge time of 7.5 min or 10 min was mixed with ammonia water with a mass fraction of 0.15%, or PAW of 10 min mixed with 0.25% ammonia water in this study, with the mixture pH lower than 8. The basic chemical process and possible reaction mechanisms were discussed. The proposed method not only effectively reduces ammonia volatilization but also adds more N elements in the form of NO3 − and NH4 +, which further improves fertility.