NH3 Volatilization Research Articles

Effect of Eminex® on Greenhouse Gas and Ammonia Emissions from Dairy Slurry and Lagoon Wastewater

Manure management emits large quantities of greenhouse gases (GHG) in California. Eminex®, a manure additive, previously demonstrated significant GHG reductions in slurry. However, it has not been tested in lagoon wastewater. The aim of the present study was to investigate the effects of Eminex® on GHG, ammonia (NH3), and ethanol (EtOH) emissions from fresh dairy slurry and dairy lagoon wastewater. Both manures received the following treatments: high (1.0 kg Eminex®/m3 manure), low (0.5 kg Eminex®/m3 manure). Experiments were conducted in four replicates with an untreated manure control. The physical characteristics of the manure were determined during the monitoring periods of emissions: 7 days for slurry and 28 days for lagoon wastewater. All slurry emissions, except for N2O, declined over time (p < 0.05). Lagoon wastewater total N increased with treatment (p < 0.05) possibly due to the urea provided by Eminex®. Most lagoon wastewater emissions also decreased over time (p < 0.05). However, Eminex®, compared to control, increased lagoon wastewater NH3 volatilization (p < 0.05). With improvements to manure composition through increasing N content, as well as reductions in emissions, Eminex® is a promising tool to mitigate the negative environmental impacts of manure management.

Interactive effects of soil salinity and nitrogen fertilizer types on nitrous oxide and ammonia fluxes

Soil salinization, impaired by climate change and poor management practices, poses a global threat, particularly in arid and semi-arid regions, leading to significant land degradation. This study aims to investigate the effects of different nitrogen (N) fertilizer sources (urea, ammonium-sulfate, and biogas waste) on CO2, N2O, and NH3 emissions and soil enzyme activities in two soil types varying in salinity level (non-saline: EC = 1.15 dS m−1, and saline: EC = 35.80 dS m−1) in a robotized continuous-flow soil incubation system. Our results showed a sharp increase in N2O and CO2 emissions (up to 0.51 ± 0.02 g N2O-N ha−1 day−1, 28.1 ± 3.9 kg CO2-C ha−1 day−1) in non-saline soils following soil rewetting, attributed to bacterial denitrification. However, this pattern was not observed in saline soils, suggesting that salinity causes partial inhibition to the regeneration of soil organic matter mineralization and denitrification processes after rewetting. Although salinity did not alter the overall cumulative N2O losses in any fertilizer treatment, it significantly delayed the evolution of N2O peak during the incubation period. On the other hand, NH3 volatilization was significantly higher in N-fertilized saline soils compared to non-saline soils (241% and 157% in ammonium-sulfate and biogas waste treatments, respectively), except for urea treatment, likely due to the decrease in nitrification rates. Furthermore, the study clearly showed lower soil enzyme activity levels for both nitrate reductase and urease activity. Interestingly, the lowest NH3 emissions were measured in urea treatment in both soils. Overall, our findings highlight the complex interplay between soil salinity, nitrogen fertilizer sources, and microbial processes, significantly influencing gaseous nitrogen emissions and N cycling in agricultural soils. Identifying the specific fertilizer treatments that minimize or maximize gaseous nitrogen losses in varying soil salinity, may guide the selection of appropriate fertilization strategies for farmers and policymakers to mitigate environmental impacts of fertilizer use during agricultural production.

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

Nitrous Oxide Emissions and Ammonia Volatilization from Pasture after Cattle Dung and Urine Applications in the Dry and Rainy Seasons of the Brazilian Cerrado

An important source of greenhouse gases in Brazil is the nitrous oxide (N2O) emission from pasture, and microorganisms play an important role in nitrogen transformations in the soil. This study aimed to evaluate N2O emission and NH3 volatilization from bovine excreta in pasture in an integrated crop–livestock system (ICL) in the Brazilian Cerrado. Three treatments (urine, dung and control) were performed in two pastures (Area 1—three-year pasture of Urochloa ruziziensis and Area 2—one-year pasture of Urochloa brizantha cv. Piatã), with two application times of the excreta (dry and rainy season), during two successive years of application. Compared to the control, the excreta deposition on ICL increased soil N2O and NH3 fluxes. In the dry season, N2O fluxes were associated with higher ammonium (NH4+) availability. In the rainy season, these fluxes were related to NO3− availability and water-filled pore space (WFPS). In both areas, NH3 volatilization was higher after urine than dung application, especially in the dry season. The highest N2O emission factors were obtained for urine (0.32%), the rainy season (0.36%), and older pasture (Area 1: 0.24%). All these values were below the mean IPCC default values (0.77%). These results indicate that N2O emissions in pasture should be evaluated in regional conditions.

Biochar-Poultry Manure Compost Alters Temperature and Nitrogen Dynamics during Composting and Improves Potato Growth Following Field Application

Composting is an aerobic process that transforms organic wastes into valuable agricultural product, but the composting process frequently results in losses of nitrogen (N) through NH3 volatilization. We evaluated the potential for high-temperature, wood-based biochar to reduce N loss when included as a compost feedstock. Biochar was composted with wood shavings and poultry manure (4:1 v/v) at rates of 0, 20 and 40% (v/v) in replicated, actively aerated 1.43 m3 in-vessel compost piles. Biochar addition caused more rapid temperature increase and truncated thermophilic phase. N loss from the entire compost mass was reduced with 40% and 20% biochar addition compared to the control (29.9, 32.3, and 35.6% N loss, respectively; P value = 0.027). However, assuming no N was lost from the added biochar, difference in N loss was less significant (P value = 0.100). With 40% biochar addition, finished compost had greater NO3 --N concentration, lower electrical conductivity, greater carbon to nitrogen ratio, and greater total carbon content. Compost products were amended to soil at rates of 7 or 15 Mg C ha−1 in potato production. Relative to an unamended control, the high application rates tended to decrease bulk density and increase total N in soil, but no differences were detected between the compost or composted biochar treatments. Tuber weights were increased 40% with application of composted biochar (biochar 40% v/v). Biochar is a promising bulking agent for composting which may reduce N loss and increase nitrification. Future studies should examine how specific biochar products affect the compost process, nutrient retention, and crop production.

Dual inhibitors for mitigating greenhouse gas emissions and ammonia volatilization in rice for enhancing environmental sustainability

The use of inhibitors retain nitrogen as ammonium in soil, giving plants ample time for its uptake. This can reduce nitrous oxide (N2O) emissions, but extended retention may increase ammonia (NH3) volatilization. This study assessed the efficacy of coated urea fertilizers in reducing greenhouse gas (GHG) emissions and NH3 volatilization in rice fields. A field experiment with Pusa 44 rice in the kharif seasons of 2019 and 2020 compared unfertilized control (No N), prilled urea (PU), nitrification inhibitors (NIs): neem oil-coated urea (NCU), karanj oil-coated urea, and dual inhibitor (DI: Limus + NCU). The coated urea fertilizers were analysed with scanning electron microscopy, fourier transform infrared spectrometry, and energy-dispersive spectroscopy. Compared to PU, DI reduced N2O emissions by 23.7%, methane by 11.9%, and NH3 by 29.8%. DI also reduced NH3 emissions by 36–39% compared to other NIs. Overall, DI can lower the global warming potential of rice cultivation in trans Indo-Gangetic plains region by 17.1% for both direct and indirect emissions, suggesting its significant potential to reduce India's contribution to total agricultural GHG emissions.

Green manuring alters reactive N losses and N pools in arable soils: A meta-regression study

Green manuring is a conservation agricultural practice that improves soil quality and crop yield. However, increasing the active nitrogen (N) and carbon (C) pools during green manure (GM) amendment may accelerate soil N transformation and stimulate N loss. Previous studies have reported the effects of cover crop incorporation on N2O emission; however, the driving mechanisms and other N losses remain unclear. Therefore, we conducted a comprehensive meta-analysis of 109 published articles (517 paired observations) to clarify the effects of GM amendment on soil reactive N (Nr) losses (N2O emissions, NH3 volatilization, and N leaching and runoff), N pools, and N cycling functional gene abundance. The results showed that green manuring increased soil microbial biomass N (MBN) and NO3−-N concentrations and stimulated N2O emission but significantly lowered N leaching and yield-scaled NH3 volatilization. Practices of green manuring made a dominant contribution to the variation in N2O emissions and NH3 volatilization after GM application. Furthermore, applying legume-based GM, using N derived from GM (GMN) as an additional input, and short-term GM amendment each stimulated N2O emissions. In contrast, adopting non-legume GM, using GMN to partially substitute mineral N, and applying GM to the soil surface or paddy field mitigated NH3 loss during GM amendment. Additionally, the variation in NH3 volatilization was positively related to soil pH and N application rate (NAR) but had a negative relationship with mean annual precipitation (MAP). This study highlighted the marked effects of green manuring on soil N retention and loss. Agricultural operations that adopt GM amendment should select suitable GM species and optimize mineral N inputs to minimize N loss.

Microplastic Has No Effect on Rice Yield and Gaseous N Emission from an Infertile Soil with High Inorganic N Inputs.

Microplastic might affect the crop yield, nitrogen (N) use efficiency and reactive N losses from agricultural soil systems. However, evaluation of these effects in infertile soil planted with different rice cultivars is lacking. We conducted a soil column experiment to determine the influence of a typical microplastic polyethylene (PE) input into an infertile soil with 270 kg N ha-1 and planted with two rice cultivars, i.e., a common rice Nangeng 5055 (NG) and a hybrid rice Jiafengyou 6 (JFY). The results showed that JFY produced a significantly (p < 0.05) greater grain yield than NG (61.6-66.2 vs. 48.2-52.5 g pot-1) but was not influenced by PE. Overall, PE hardly changed the N use efficiency of NG and JFY. Unexpectedly, PE significantly (p < 0.05) increased the total amino acid content of NG. Compared with JFY, NG volatilized significantly (p < 0.05) more ammonia (NH3) (0.84-0.92 vs. 0.64-0.67 g N pot-1) but emitted equal nitrous oxide (N2O). PE exerted no effect on either NH3 volatilization or the N2O emission flux pattern and cumulative losses of the rice growth cycle, whether with NG or JFY. Some properties of tested soils changed after planting with different rice cultivars and incorporating with microplastic. In conclusion, the rice production, N use efficiency, NH3 volatilization and N2O emission from the N-fertilized infertile soil were pronouncedly influenced by the rice cultivar, but not the PE. However, PE influenced the grain quality of common rice and some properties of tested soils with both rice cultivars.

Stacking nitrogen management practices: Combining double‐slot fertilizer injection with urease and nitrification inhibitors improves yields and reduces ammonia and nitrous oxide emissions

AbstractAmmonia loss following nitrogen fertilization can degrade air quality and impact human health, whereas nitrous oxide (N2O) can contribute to global warming and climate change. Mitigation practices that target only one N‐loss pathway can lead to pollution swamping; hence, practices targeting both N‐losses are required. A 3‐year field study examined fertilizer N‐placement (broadcast urea, single‐slot injection of urea ammonium nitrate [UAN], double‐slot UAN injection) and N‐metabolization inhibitors (with/without urease and nitrification inhibitors) impacts on NH3 and N2O losses and corn yields. Ammonia volatilization was reduced (p &lt; 0.05) by 26% with single‐slot UAN injection (10.6 kg N ha−1) and by 63% with double‐slot UAN injection (5.32 kg N ha−1) compared to broadcast urea (14.3 kg N ha−1). Dual urease and nitrification inhibitors reduced NH3 volatilization (0.84–3.86 kg N ha−1) by 57%–92% compared to no inhibitors (5.32–14.3 kg N ha−1). When no inhibitors were applied, N2O emissions from slot injection (6.43–7.62 kg N ha−1) were 2.6–3.1 times greater than from broadcast urea (2.43 kg N ha−1). Dual inhibitors reduced N2O emissions by 43% from 6.43 to 3.66 kg N ha−1 with double‐slot injection. Double‐slot UAN injection increased corn grain yields (9.73 t ha−1) by 12%–13% compared to single‐slot UAN injection (8.71 t ha−1) and broadcast urea (8.6 t ha−1). Double‐slot UAN injection effectively decreased NH3 losses and increased corn grain yields, but dual N inhibitors were required to also reduce N2O. Hence, combined productivity and environmental benefits were accrued only when fertilizer containing urease and nitrification inhibitors was combined with double‐slot injection.

Inhibitory effect of ammonium conversion by deep nitrogen application effectively reduces gaseous nitrogen losses

Increasing the depth of nitrogen (N) fertilizer application is an effective agronomic management measure for mitigating NH3 volatilization and N2O emissions. However, the information about reasons for the reduction of gaseous N loss and the responses of soil N transformation processes to deep N fertilization is limited. This field experiment monitored NH3 volatilization, N2O emission, and soil NH4+/NO3- dynamics under three N application depths (8, 16, and 24 cm) in the typical soil of Loess Plateau (Cumulic Anthrosol) during 2021–2022 and 2022–2023. The N transformation rate under different soil depths was determined by laboratory 15N tracing experiments, and driving contributions of soil physicochemical properties and biological characteristics to gaseous N emissions were considered comprehensively. Our field results verified that increasing N fertilization depth effectively reduces NH3 volatilization and N2O emission by 20.7–55.6% and 17.9–45.8%; Simultaneously, deep N fertilization delayed the peak time of NH3 or N2O and retained a higher concentration of NH4+ in deep soil (37.3–46.4 mg kg−1). The 15N tracing experiments revealed that the lower soil enzymatic activity and microbial abundance in deep soil significantly decreased N mineralization, NH4+ consumption, and nitrification rates by 30.6–44.1%, 37.1–44.9%, and 22.5–31.1% (P < 0.05), compared with the shallow soil. Random forest analysis explored that the predictive factors of NH3 volatilization were soil urease activity, NH4+ consumption rate, soil NH4+, and TOC (P < 0.01). Interestingly, N2O emission was also mainly affected by soil urease activity, hydroxylamine oxidoreductase (HAO) activity, soil NH4+, and NO3- (P < 0.01); Through partial least squares path models (PLS-PMs), deep N fertilization mainly reduced risk of gaseous N loss by changing the environmental conditions required for N transformation and affecting the N mineralization and nitrification processes to limit NH4+ generation and consumption. This study provides a theoretical foundation for the demonstration and promotion of deep fertilization in the Loess Plateau.

Polymer-coated urea applied at one-time mechanical topdressing increases nitrogen use efficiency and rice yield in the cold area

Context The application of slow and controlled release fertilisers can reduce nitrogen loss, but the research is still scarce in the cold rice region of China. Aims The study was conducted to screen slow-release or controlled-release fertilisers which can meet the nitrogen demand of rice and reduce NH3 volatilisation in different pH soils. Methods This experiment includes four fertilisation treatments: no fertiliser (control), urea, urea with N-(n-butyl) thiophosphorictriamide (NBPT), and polymer-coated urea (PCU). The amounts of urea-N, pH, ammonium-N (NH4+-N) in the surface water, and NH3 volatilisation were determined. Thereafter, to evaluate the effects of one-time mechanical topdressing of PCU mixed with compound fertilisers along with farmers’ fertilisation practice (FFP), field experiments carried out in wide soil pH differences were conducted. Key results Cumulative NH3 volatilisation was reduced in the NBPT treatment compared with the urea treatment. There was no significant difference between urea-N, NH4+-N, and pH in the surface water under PCU and control. NH3 volatilisation of PCU is negligible and significantly prolongs the soil nitrogen storage time. In the subsequent experiment, PCU blend increased yield, dry matter, nitrogen uptake, and the partial factor productivity of applied nitrogen (PFPN) compared to FFP. Conclusions PCU treatment slows down urea release and reduces ammonia volatilisation from paddy fields. In turn, it reduces ammonia-nitrogen levels and pH in surface water and further slows down the rate of ammonia volatilisation. Implications Application of PCU as a one-time mechanical topdressing fertiliser in rice fields in cold regions saves nitrogen fertiliser, increases crop yields, and reduces labour.

Nitrogen dynamics as a function of soil types, compaction, and moisture.

In this study, the complex interactions between soil types, compaction, and moisture on nitrogen (N) transformation processes such as ammonia (NH3) volatilization, ammonification, nitrification, and denitrification were examined over a 30-day period using a simulated column approach. Two soil types: loam, and sandy loam, were subjected to three compaction treatments-control, surface, and sub-surface compaction-and two moisture regimes, dry and wet. Liquid urea ammonium nitrate (32-0-0) was used as the N fertilizer source at a rate of 200 kg N ha-1. Key indicators of N transformations were measured, including residual concentrations of ammonium (NH4-N) and nitrate (NO3-N), NO3-N leaching, NH3 volatilization, and nitrous oxide (N2O) emissions. Findings revealed that compaction significantly increased residual NH4-N concentrations in deeper soil profiles, with the highest 190.80 mg kg-1 recorded in loam soil under sub-surface compaction and dry conditions. Nitrification rates decreased across both soil types due to compaction, evidenced by elevated residual NH4-N levels. Increased NO3-N leaching was observed in loam soil (178.06 mg L-1), greater than sandy loam (81.11 mg L-1), due to initial higher residual NO3- in loam soil. The interaction of compaction and moisture most affected N2O emissions, with the highest emissions in control treatments during dry weather at 2.88 kg ha -1. Additionally, higher NH3 volatilization was noted in moist sandy loam soil under control conditions at 19.64 kg ha -1. These results highlight the necessity of considering soil texture, moisture, and compaction in implementing sustainable N management strategies in agriculture and suggest recommendations such as avoiding broadcast application in moist sandy loam and loam soil to mitigate NH3 volatilization and enhance N use efficiency, as well as advocating for readjustment of fertilizer rate based on organic matter content to reduce potential NO3-N leaching and N2O emissions, particularly in loam soil.

Global impact of enhanced-efficiency fertilizers on vegetable productivity and reactive nitrogen losses

Vegetables are the most consumed non-staple food globally, and their production is crucial for dietary diversity and public health. Use of enhanced-efficiency fertilizers (EEFs) in vegetable production could improve vegetable yield and quality while reducing reactive nitrogen (Nr) losses. However, different management and environmental factors has significantly distinctive impacts on the effectiveness of EEFs. In this study, a worldwide meta-analysis based on the data collected from 144 studies was performed to assess the impacts of EEF (nitrification inhibitor [NI] and polymer-coated urea [PCU]) application on vegetable yield, nitrogen (N) uptake, nitrogen use efficiency (NUE), vegetable quality and Nr losses (nitrous oxide [N2O] emissions, ammonia [NH3] volatilization, and nitrate [NO3−] leaching). The effects of the applied EEFs on vegetable yields and N2O emissions were assessed with different management practices (cultivation system, vegetable type and N application rate) and environmental conditions (climatic conditions and soil properties). Compared to conventional fertilizers, EEFs significantly improved vegetable yield (7.5–8.1 %) and quality (vitamin C increased by 10.7–13.6 %, soluble sugar increased by 9.3–10.9 %, and nitrate content reduced by 17.2–25.1 %). Meanwhile, the application of EEFs demonstrated a great potential for Nr loss reduction (N2O emissions reduced by 40.5 %, NO3− leaching reduced by 45.8 %) without compromising vegetable yield. The NI was most effective in reducing N2O emissions (40.5 %), but it significantly increased NH3 volatilization (32.4 %). While PCU not only significantly reduced N2O emissions (24.4 %) and NO3− leaching (28.7 %), but also significantly reduced NH3 volatilization (74.5 %). And N application rate, soil pH, and soil organic carbon (SOC) were the main factors affecting the yield and environmental effects of EEFs. Moreover, the yield-enhancing effect of NI and PCU were better at low soil N availability and SOC, respectively. Thus, it is important to adopt the appropriate EEF application strategy targeting specific environmental conditions and implement it at the optimal N application rate.

The Application of Rice Straw with Reduced N Fertilizer Improves the Rice Yield While Decreasing Environmental N Losses in Southern China

To investigate the effects of straw residues with reduced nitrogen (N) fertilizer on greenhouse gas (GHG) and N losses in paddy fields, we conducted a field experiment during two growing seasons in paddy rice systems in southern China to evaluate the impacts of the application of straw residues with reduced N fertilizer on rice yield, GHG emissions, and ammonia (NH3) volatilization. The four treatments included N100 (conventional dose of N fertilizer), SN100 (conventional dose of N fertilizer + straw), N60 (60% of the conventional dose of N fertilizer), and SN60 (60% of the conventional dose of N fertilizer + straw). We found that the yield of the SN60 treatment was slightly reduced, but the partial factor productivity of applied N (PFPN) was significantly increased by 63.9% compared to the N100 treatment. At the same N application rate, the application of straw increased soil organic C (SOC), methane (CH4) emissions, carbon dioxide (CO2) emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), and net ecosystem carbon budget (NECB), but significantly decreased soil N2O emissions and NH3 volatilization. Compared with conventional fertilization (N100), straw residues with reduced N fertilization (SN60) reduced N2O emissions and NH3 volatilization by 42.1% and 23.9%, and increased GHGI and NECB by 11.1% and 18.3%, respectively. The results indicate that straw residues with reduced N fertilizer are a feasible strategy to reduce N losses in paddy fields while increasing carbon sequestration.

Soil aggregate stability helps construct a stable nitrogen fixation system in lignite-based amendment-driven saline-sodic soil remediation

Lignite−based amendments are promising soil conditioners for improving crop yield and nitrogen use efficiency, but there is limited knowledge regarding the potential effects of lignite−based amendment on nitrogen cycling−related microbial communities and their impacts on NH3 volatilization and crop nitrogen uptake in saline−sodic farmland. Here, we investigated the influences of lignite bioorganic fertilizer (LBF) on NH3 volatilization, nitrogen uptake, and microbial communities containing nifH, amoA, and nirS genes through a two−year field experiment. Three treatments were considered in the experiment, i.e., a control treatment with no organic fertilizer application (CK), a farmyard manure treatment (FYM) involving the application of sheep manure at a rate of 21 t ha−1, and a LBF treatment with optimal application rates of 3.0 and 4.5 t ha−1. Results showed that compared with the control treatment (CK), the LBF treatment reduced the total NH3 volatilization by 22.3% and 13.5% in 2019 and 2020, respectively. In addition, the LBF treatment significantly increased sunflower nitrogen uptake by 52.5% and 114.2% in 2019 and 2020, respectively, in comparison with the CK treatment. Moreover, the LBF treatment not only increased the absolute abundance of the nifH gene by 111.5% and altered the core microbes in the nifH−containing community, but it also enhanced the complexity, stability, and cooperation of co−occurrence network of the nifH−containing community, which were positively related to the sunflower nitrogen uptake. The LBF and FYM treatments reduced NH3 volatilization by improving the soil aggregate stability and saturate hydraulic conductivity. These results indicated that LBF may offer a feasible measure to improve the sunflower nitrogen uptake by constructing a complex, stable, and cooperative nitrogen fixation system, without the risk of NH3 volatilization in saline−sodic farmland.

Integrated nutrient recycling: Ammonia recovery from thermophilic composting of shrimp aquaculture sludge via self-heated bench-scale reactor and mango plant growth enhancement by the compost

Due to the rapid growth of the aquaculture industry, large amounts of organic waste are released into nature and polluted the environment. Traditional organic waste treatment such as composting is a time-consuming process that retains the ammonia (NH3) in the compost, and the compost produced has little economic value as organic fertilizer. Illegal direct discharge into the environment is therefore widespread. This study investigates the recovery of NH3 through thermophilic composting of shrimp aquaculture sludge (SAS) and its application as a soil conditioner for the growth of mango plants. A maximum composting temperature of 57.10 °C was achieved through self-heating in a 200 L bench-scale reactor, resulting in NH3 recovery of 224.04 mol/ton-ds after 14 days. The addition of calcium hydroxide and increased aeration have been shown to increase NH3 volatilization. The recovered NH3 up to 3 kg-N can be used as a source of clean nitrogen for high-value microalgae cultivation, with a theoretical yield of up to 34.85 kg-algae of microalgae biomass from 1 ton-ds of SAS composting. Despite the high salinity, SAS compost improved mango plant growth and disease resistance. These results highlight the potential of SAS compost as a sustainable source of clean nitrogen for microalgae cultivation and soil conditioner, contributing to a waste-free circular economy through nutrient recycling and sustainable agriculture.

Biochar and hydrochar application influence soil ammonia volatilization and the dissolved organic matter in salt-affected soils

Biochar, which including pyrochar (PBC) and hydrochar (HBC), has been tested as a soil enhancer to improve saline soils. However, the effects of PBC and HBC application on ammonia (NH3) volatilization and dissolved organic matter (DOM) in saline paddy soils are poorly understood. In this research, marsh moss-derived PBC and HBC biochar types were applied to paddy saline soils at 0.5 % (w/w) and 1.5 % (w/w) rates to assess their impact on soil NH3 volatilization and DOM using a soil column experiment. The results revealed that soil NH3 volatilization significantly increased by 56.1 % in the treatment with 1.5 % (w/w) HBC compared to the control without PBC or HBC. Conversely, PBC and the lower application rate of HBC led to decrease in NH3 volatilization ranging from 2.4 % to 12.1 %. Floodwater EC is a dominant factor in NH3 emission. Furthermore, the fluorescence intensities of the four fractions (all humic substances) were found to be significantly higher in the 1.5 % (w/w) HBC treatment applied compared to the other treatments, as indicated by parallel factor analysis modeling. This study highlights the potential for soil NH3 losses and DOM leaching in saline paddy soils due to the high application rate of HBC. These findings offer valuable insights into the effects of PBC and HBC on rice paddy saline soil ecosystems.

Benefits and trade-offs of replacing inorganic fertilizer by organic substrate in crop production: A global meta-analysis

Replacing inorganic fertilizer with organic substrate contributes to sustainable agricultural production capacity. However, the effects of organic substitution regimes (OSR) on global crop productivity, soil carbon (C) and nitrogen (N) losses and biofertility as function of environmental variables have not been systematically quantified. Here, we have conducted a meta-analysis of these effects using field data (211 papers with 852 observations) collected around the world. Results indicated that OSR increased crop productivity (3.04 %) and soil biofertility (soil qMBC, qMBN, microbial richness, Shannon and functionality by 11.4 %, 21.1 %, 10.2 %, 3.95 %, and 38.5 %, respectively), and reduced soil N losses (N2O emissions, NH3 volatilization and soil N leaching by 26.5 %, 26.1 %, and 33.8 %, respectively), but increased CO2 emissions (19.4 %), and paddy fields CH4 emissions (41.2 %). N rate was an important factor influencing crop productivity and soil biofertility response to OSR, and crop productivity and soil biofertility had a greater positive response at moderate substitution rates in acid soil and long-term trials, but full substitution significantly decreased crop yield. Furthermore, the increase in soil biofertility and crop yield saturated in ~10–14 and ~ 22 years after organic substrate input. The emissions of CO2, CH4, and N2O significantly increased with increasing substitution rates, while the opposite was true for N leaching. The NH3 volatilization response to OSR presented a positive effect in acidic and coarse texture soil. OSR was more beneficial in mitigating soil C and N loss response (except CO2 emissions) in uplands compared to paddy fields. Therefore, implementation of OSR requires site-specific strategies to better achieve a balance between increasing crop production and reducing environmental benefits. Given that the OSR improvement varies depending on environmental variables, we propose a predictive model to initially assess the potential for OSR improvement. This study will provide scientific guidance on the reasonable application of organic substrate in agroecosystems.

How do green manure management practices affect ammonia emissions from maize fields?

The use of “green manure”—crops that are cultivated specifically to be incorporated into the soil to increase its organic matter content—has been proposed as an alternative to chemical fertilizer because of its benefits in terms of crop yield. Nonetheless, the differential impacts of green manure on ammonia volatilization remains underexplored. In this study, the influence of various green manure management strategies on ammonia volatilization in maize cultivation were examined. Field experiments conducted from 2020 to 2022, the field experiment applied common vetch after the spring wheat harvest, with five distinct treatments: conventional tillage without green manures as a control (CT); tillage with total green manure incorporation (TG); no-tillage with total green manure mulching (NTG); tillage with only root incorporation (T); and no-tillage with removal of aboveground green manure (NT). The results showed that under TG and NTG, the maize yields were 12.3%-33.2% higher than under CT, and 6.8%-18.8% higher than under T and NT. Compared with CT, all four green manure management practices also significantly increased NH3 emissions in maize fields, and they increased ammonia volatilization by 12.0%-13.7% in NTG and TG compared to root retention patterns, with NTG exhibiting higher rates than TG. NTG significantly increased soil organic matter, total nitrogen, mineral nitrogen, water-filled pore space (WFPS), microbial biomass carbon and nitrogen, and C: N, and it decreased soil pH compared to TG. Regression analysis showed that these factors were correlated with NH3 volatilization. In addition, soil urease and ammonia-oxidation functional genes (amoA) showed differences under green manure management practices. Structural equation modeling showed that NH4+-N had the greatest positive impact on NH3, and urease activity and total nitrogen had positive effects on NH4+-N. Furthermore, microbial biomass carbon and pH had positive and negative effects on urease activity, respectively, both of which were only related to SOM. At the same time, WFPS had a positive impact on total nitrogen. In summary, no-tillage with total green manure mulching increases maize yield but also increases NH3 emissions. NH4+-N formed by the hydrolysis of urea by soil urease and the conversion of total nitrogen were found to be the main reasons for high NH3 emissions. In addition, SOM can promote urease activity, increase NH4+-N content and NH3 volatilization by increasing MBC and decreasing soil pH.

Soil amendments reduce CH4 and CO2 but increase N2O and NH3 emissions in saline-alkali paddy fields

Limited research has been conducted on ammonia (NH3) volatilization and greenhouse gases (GHGs) emissions in saline-alkali paddy fields, along with complex interaction involving various genes (16sRNA, amoA, narG, nirK, nosZ, and nifH). This study employed mesocosm-scale experiment to investigate NH3 volatilization and GHGs emissions, focusing on bacterial communities and genic abundance, in saline-alkali paddy fields with desulfurized gypsum (DG) and organic fertilizer (OF) amendments. Compared to the control (CK) treatment, DG and OF treatments reduced methane (CH4) and carbon dioxide (CO2) emissions by 78.05 % and 26.18 %, and 65.84 % and 11.62 %, respectively. However, these treatments increased NH3 volatilization by 26.26 % and 45.23 %, and nitrous oxide (N2O) emission by 41.00 % and 12.31 %. Notably, NH3 volatilization primarily stemmed from ammonia nitrogen (NH4+-N), rather than total nitrogen (TN) in soil and water. N2O was mainly produced from nitrate nitrogen (NO3−-N) in soil and water, as well as NH4+-N in water. The increase in NH3 volatilization and N2O emission in DG and OF treatments, was attributed to the reduced competition among bacterial communities, rather than the increased bacterial activity and genic copies. These findings offer valuable insights for managing nutrient loss and gaseous emissions in saline-alkali paddy fields.