NH3 Volatilization Research Articles

Potential ammonia volatilization from 39 different novel biobased fertilizers on the European market – A laboratory study using 5 European soils

Current political focus on promoting circular economy in the European Union drives great interest in developing and using more biobased fertilizers (BBFs, most often waste or residue-derived). Many studies have been published on environmental emissions, including ammonia (NH3) volatilization from manures, but there have only been a few such studies on BBFs. Ammonia volatilization from agriculture poses a risk to the environment and human health, causing pollution in natural ecosystems when deposited and formation of fine particulate matter (PMx). Furthermore, NH3 volatilization results in removal of plant-available N from agricultural systems, constituting an economic loss for farmers.The aim of this laboratory study was to determine the potential NH3 volatilization from 39 different BBFs commercially available on the European market. In addition, this study aimed to investigate the effect of incorporation, application rate, soil type, and soil moisture content on potential NH3 volatilization in order to derive suggestions for the optimal field application conditions. Results showed a great variation between BBFs in potential NH3 volatilization, both in terms of their temporal pattern of volatilization and amount of NH3 volatilized. The potential NH3 volatilization varied from 0% of applied total N (olive oil compost) to 64% of applied total N (manure and crop digestate) during a 27- or 44-day incubation period. Characteristics of BBFs (pH, NH4+-N, NO3−-N, DM, C:N) and their interaction with time could explain 89% of the variation in accumulated potential NH3 volatilization. Incorporation of BBFs into an acidic sandy soil effectively reduced potential NH3 volatilization by 37%–96% compared to surface application of BBFs. Potential NH3 volatilization was not significantly affected by differences in application rate or soil moisture content, but varied between five different soils (with different clay and organic matter content), with the highest NH3 volatilization potential from the acidic sandy soil.

Combing mechanical side-deep fertilization and controlled-release nitrogen fertilizer to increase nitrogen use efficiency by reducing ammonia volatilization in a double rice cropping system

Ammonia (NH3) volatilization losses result in low nitrogen use efficiency (NUE) and various environmental impacts in agroecosystems. Machine-transplanted rice with side-deep fertilization (MRSF) has been recommended as an effective alternative to traditional transplantation with manual broadcasting of fertilizer. Controlled-release nitrogen fertilizer (CRF) can enhance rice yield and NUE in paddy fields. However, there is scarce information about combined effects of MRSF and CRF on NH3 volatilization loss and rice grain yield, NUE, net economic benefit (NEB) in a double rice cropping system. In this study, a field experiment was conducted to evaluate the impact of MRSF with CRF on grain yields, NUE and economic returns of early rice and late rice from 2019 to 2021, as well as NH3 emissions in two rice seasons (2019 and 2021). Six treatments were designed as no N fertilizer (N0), compound fertilizer broadcasting (CFB), compound fertilizer side-deep placement (CFD), CRF broadcasting (CRFB), CRF side-deep placement (CRFD1), and single side-deep placement of CRF (CRFD2). The results showed that the CFD and CRFB treatments decreased NH3 volatilization while enhancing or maintaining rice yield and NUE compared to the CFB treatment. MRSF with CRF (CRFD1 and CRFD2) significantly reduced NH3 emissions of early and late rice by 57.6–67.9% and 62.2–80.9% by decreasing the NH4+–N concentrations in the surface water compared to the CFB treatment, respectively. Rice grain yields in the MRSF with CRF treatments increased by 3.9–17.3% in early rice and 5.4–21.6% in late rice relative to the CFB treatment. In addition, MRSF with CRF treatments improved NUE for early and late rice from 32.1 to 36.2% and 21.3–28.4% in the CFB treatment to 48.4–61.2% and 39.7–62.3%, respectively. The yield-scale NH3 volatilization losses were reduced under the MRSF with CRF treatments by 61.2–71.5% in early rice and 67.4–84.3% in late rice. Furthermore, MRSF with single basal application of CRF reduced time-consuming and labor-intensive while increasing rice yields and net economic benefits. Overall, co-application of MRSF and CRF can reduce NH3 emissions, and improve rice yield, NUE and profitability in double rice cropping systems.

Changes in swine ammonia emissions associated with improved production management.

Swine manure management and storage have been implicated as major sources of increasing agricultural ammonia (NH3 ) emissions resulting in increased ammonium deposition in North Carolina. This study was conducted to establish how improvements in manure and animal management have affected lagoon nutrient loading and subsequent NH3 emissions determined from measured lagoon chemistry and climate data. Archived lagoon chemistry analyses from 182 farm lagoons (106,000 sample analyses) were used to evaluate trends in lagoon chemical properties. Process and empirical (statistical) NH3 volatilization models were used with the data to calculate changes in NH3 emissions from 2001 through 2018. Lagoon nutrient trends for finisher and sow farms showed that annual averages of nutrients had decreases ranging from 18 to 93%, except for a 41% increase in copper for finisher primary lagoons. Because of reduced nitrogen and pH in the lagoons, a process model of NH3 emissions suggested decreases from primary lagoons of 49 and 25% from finisher and sow farm lagoons, respectively. Empirical (statistical) models predicted even larger relative NH3 decreases (up to 54%).

Modelling of Water and Nitrogen Flow in a Rain-Fed Ridge-Furrow Maize System with Plastic Mulch

Soil water and nitrogen are two important factors in the agro-ecosystem of the Loess Plateau, China. The ridge-furrow maize system with plastic mulch (RFPM) is a widely used measure to increase crop yield in the Loess Plateau area. The purpose of this study was to investigate the effect of the RFPM on soil water and inorganic nitrogen (N) distribution, especially with regard to the risk and dynamic of nitrogen losses, by using Hydrus-2D. The study was conducted over two consecutive years and consisted of two treatments: (i) the RFPM with the split application of nitrogen in 2013 (160 + 60 kg N ha−1, sowing and jointing stage) and (ii) the RFPM with a one-time fertilizer in 2014 (220 kg N ha−1, sowing stage). The results showed that the dynamic of soil water and nitrogen was clearly illustrated by Hydrus-2D, especially with regard to the nitrogen losses and utilization. The RFPM improved soil water consumption in both the ridge and the furrow; the soil water content was obviously fluctuating during the maize growing season, and the degree of fluctuation decreased as the depth increased. The soil NH4+-N concentration was mainly accumulated in the surface soil layer +15–10 cm; the highest NH4+-N concentrations were 69.12 and 104.62 mg·kg−1 in 2013 and 2014, respectively. The highest NO3−-N concentrations were 130.86 and 198.20 mg·kg−1 in 2013 and 2014, respectively. There was an exchange of NO3−-N between the ridge and the furrow when urea was applied in the furrow. The one-time fertilizer caused a high risk of NH3 volatilization; they were 20.40 and 27.41 kg N ha−1 in 2013 and 2014, respectively, which accounted for 9.27% and 12.46% of the N fertilizer inputs in 2013 and 2014, respectively. The rate of nitrite leaching was higher in the furrow than the ridge. However, a proper ratio of the split application of nitrogen would contribute to the NO3−-N leaching reduction; the NO3−-N leaching amounts were 18.13 and 31.26 kg N ha−1, which accounted for 8.24% and 14.21% of the N fertilizer inputs in 2013 and 2014, respectively. Our study indicates, therefore, that the RFPM with a split application of nitrogen would be more effective for the nitrogen losses; the RFPM is a suitable system for agriculture in the rain-fed area of the Loess Plateau, with the benefits of water-use efficiency and non-point source pollution reduction.

Effects of biological nitrification inhibitor in regulating NH3 volatilization and fertilizer nitrogen recovery efficiency in soils under rice cropping.

Biological nitrification inhibitors are exudates from plant roots that can inhibit nitrification, and have advantages over traditional synthetic nitrification inhibitors. However, our understanding of the effects of biological nitrification inhibitors on nitrogen (N) loss and fertilizer N recovery efficiency in staple food crops is limited. In this study, acidic and calcareous soils were selected, and rice growth pot experiments were conducted to investigate the effects of the biological nitrification inhibitor, methyl 3-(4-hydroxyphenyl) propionate (MHPP) and/or a urease inhibitor (N-[n-butyl], thiophosphoric triamide [NBPT]) on NH3 volatilization, N leaching, fertilizer N recovery efficiency under a 20% reduction of the conventional N application rate. Our results show that rice yield and fertilizer N recovery efficiency were more sensitive to reduced N application in the calcareous soil than in the acidic soil. MHPP stimulated NH3 volatilization by 13.2% in acidic soil and 9.06% in calcareous soil but these results were not significant. In the calcareous soil, fertilizer N recovery efficiency significantly increased by 19.3% and 44.4% in the MHPP and NBPT+MHPP groups, respectively, relative to the reduced N treatment, and the rice yield increased by 16.7% in the NBPT+MHPP treatment (P < 0.05). However, such effects were not significant in the acidic soil. MHPP exerted a significant effect on soil ammonia oxidizers, and the response of abundance and community structure of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and total bacteria to MHPP depended on the soil type. MHPP+NBPT reduced NH3 volatilization, N leaching, and maintaining rice yield for a 20% reduction in conventional N fertilizer application rate. This could represent a viable strategy for more sustainable rice production, despite the inevitable increase in cost for famers.

Optimizing nitrogen management to mitigate gaseous losses and improve net benefits of an open-field Chinese cabbage system.

The excessive and inappropriate application of nitrogen (N) fertilizer in open vegetable fields is a major anthropogenic source of gaseous N losses including nitrous oxide (N2O) and ammonia (NH3) emissions in China. A 2-yr Chinese cabbage (Brassica pekinensis L.) experiment was carried out to explore the impacts of optimized N management (reduced N application rate, controlled-release urea [CRF] and nitrification inhibitor [NI]) on cabbage yield, soil inorganic N, and N2O and NH3 emissions, and to assess their economic benefits by a cost-benefit analysis. Six treatments including i) no N fertilizer (CK), ii) conventional urea fertilizer at 400kgN ha-1 based on farmers' practices (CN), iii) conventional urea at 320kgN ha-1 (RN), iv) conventional urea (320kgN ha-1) with the addition of NI (RN+NI), v) CRF at 320kgN ha-1 (CR) and vi) CRF (320kgN ha-1) with the addition of NI (CR+NI) were implemented in an open Chinese cabbage field. No significant differences were found in the cabbage yields and soil NH4+-N contents under different N fertilization treatments. Only CR+NI treatment had significantly lower soil NO3--N contents than CN by 17.6%-34.6% at the early growing stages of cabbage in both years. Compared with CN, the N2O emissions were significantly decreased by 8.61%, 34.4%, 37.8% and 46.6% under RN, RN+NI, CR and CR+NI, respectively, indicating that CR+NI favors N2O abatement especially when NH3 has been suppressed by other 4R practices. Meanwhile, the NH3 volatilization was 20.6% higher under RN+NI and 30.8% and 17.3% lower under CR and CR+NI compared to CN, respectively, which implied that CR was the most effective treatment in reducing the NH3 volatilization and total gaseous N loss in high NH3-N loss scenarios. Moreover, the net benefit of RN decreased by $945 USD ha-1 and those of RN+NI, CR and CR+NI treatments increased by $855, $930 and $1004 USD ha-1 compared to CN, respectively. This study recommends CR+NI as the optimal N fertilizer management for the sustainable production of vegetables with the lowest environmental risks and the greatest economic benefits.

Citric acid modified biochar application at a low dosage can synchronically mitigate the nitrogenous gas pollutants emission from rice paddy soils

Raw biochar with high pH possibly stimulated ammonia (NH3) volatilization in the agricultural soil. We hypothesized that the modified biochar (MBC) with low pH can synchronically decrease the NH3 and nitrous oxide (N2O) losses. We performed a two-year experiment to clarify how citric acid MBC influence the NH3 volatilization and N2O emission as well as the underlying mechanisms. Two typical paddy soils, i.e., Hydragric Anthrosol and Haplic Acrisol, receiving equal urea N with 240 kg ha−1 but varied rates of MBC with 0, 5, 10, and 20 t ha−1 (named Urea, Urea + MBC5, Urea + MBC10, and Urea + MBC20, respectively) were studied. The results showed that MBC-amended treatments effectively mitigated the NH3 volatilization from Hydragric Anthrosol and Haplic Acrisol by 29.6%–57.9% and 30.5%–62.4% in 2017, and by 16.5%–21.0% and 24.5%–35.0% in 2018, respectively, compared to Urea treatment. In addition, significantly lower N2O emissions with averaged 38.3% and 43.1% in 2017, and 51.7% and 26.7% were recorded under Hydragric Anthrosol and Haplic Acrisol, respectively, following the MBC application (P < 0.05). Increased MBC addition performed higher efficacy on mitigating NH3 volatilization, particularly in the first rice season, while this “dosage effect” was not found for N2O reduction. Lowered pH in overlying water, enhanced adsorption of NH4+-N and its nitrification rate likely contributed to the lower NH3 volatilization as result of MBC addition. The nirS and nosZ gene copies were not changed by MBC, while the nirK gene copies were decreased as result of MBC amendment by 8.3%–25.2% under Hydragric Anthrosol and by 21.8%–24.9% under Haplic Acrisol. Consequent lower ratio of nirK/(nirS + nosZ) explained the mitigation effect of MBC on N2O emission. In conclusion, the present two-year study recommends that MBC applied at a low dosage can perform positive effect on controlling the nitrogenous gas pollutants from paddy soil.

Influences of split application and nitrification inhibitor on nitrogen losses, grain yield, and net income for summer maize production.

The application of nitrogen (N) fertilizer combined with nitrification inhibitor is considered to be one of the effective strategies to improve N efficiency and reduce N loss. While the chemical and physical properties of nitrapyrin (CP) in fertilizers have been evaluated to increase N efficiency, a lack of comprehensive evaluation of the effects of adding CP on summer maize yield, environmental benefits and economic income under different fertilization methods. In this study, two fertilization methods were used: split-N application and one-time basal N fertilizer before sowing. The comprehensive effects of N fertilizer with CP on N loss (NH3 volatilization, NO3– leaching, and N2O emissions), N efficiency, yield and profit under two N application methods were explored. Results showed that under the two N application methods, N fertilizer with CP treatment increased the N efficiency and yield (+3.4%∼+5.7%), significantly reduced the soil NO3–-N content and N2O emissions, while increased NH3 volatilization. Especially, the increase amplitude of NH3 was much less than the decrease amplitude of N2O induced by adding CP. Although split-N application could achieve higher yield and N efficiency, N2O emissions and NH3 volatilization also increased. However, the T1 + N (one-time basal N fertilizer before sowing mixed with CP) achieved the same yield level as T2 treatment (split-N application). Taking agronomic, economic and environmental benefits into consideration, one-time basal N fertilizer before sowing mixed with CP could ensure the target yield, increase economic benefits, maintain soil N content, and reduce N losses. Therefore, optimizing N management is essential to the sustainable development of agriculture.

Effect of Deep Placement of Large Granular Fertilizer on Ammonia Volatilization, Soil Nitrogen Distribution and Rice Growth

Excessive fertilization is often applied to produce rice. To reduce nitrogen loss and improve nitrogen use efficiency (NUE), we studied the effects of application depth (surface application, 5 and 10 cm) and shape of nitrogen fertilizers (row application and deep application of large granular fertilizer) on rice growth, soil N distribution and ammonia volatilization. The results showed that grain yield, shoot biomass and total dry biomass of the treatment with N in large granular fertilizer applied at 10 cm depth were significantly higher than those of all other treatments. Moreover, compared with the surface application, the N recovery efficiency and the N agronomic efficiency of deep application treatments were enhanced by 18.1–52.3% and 35.6–95.6%, respectively. Deep application significantly increased NH4+-N concentration at their fertilization points. During the growth season, N in large granular fertilizer treatments (mixed with clay to form an unusually large pellet of 1.0–1.5 cm in diameter) distributed closer to the roots, while N in other treatments, including row application treatments, was more widely distributed. Compared with the surface application, deep application significantly reduced NH3 volatilization and NH4+-N concentration in surface water by 58.7–64.8% and 26.0–72.5%, respectively. Furthermore, the NH3 volatilization from large granular treatment was 7.6–11.0% lower than that in the row application. In conclusion, applying N in large granular fertilizer at 10 cm depth reduces ammonia volatilization, and improves rice growth and grain yield, indicating improved NUE and lowered environmental risks.

Large differences in ammonia emission factors between greenhouse and open-field systems under different practices across Chinese vegetable cultivation

Estimating ammonia (NH3) emission factors (EFs) for vegetable production can support assessment of potential atmospheric pollution risk and provide information for mitigating NH3 volatilization. The EFs in greenhouse and open-field systems under different fertilization, irrigation regimes, vegetable types and soil properties in both greenhouse and open-field vegetable production systems in China are poorly understood. An integrated analysis was performed, including 282 field measurements of NH3 volatilization from 54 field studies, to quantify ammonia EFs under different management practices and soil properties. The results showed that the mean ammonia EF across all measurements was 4.2 % (3.6 %–4.8 %). The EFs of greenhouse and open-field systems were 2.0 % (1.5 %–2.5 %) and 6.3 % (5.4 %–7.2 %), respectively. There was a power function relationship between nitrogen application rate and ammonia EF in greenhouses. No relationship was identified between nitrogen application rate and ammonia EF in the open-field system. The EFs of organic fertilizers were lower than those of both chemical fertilizers and the combination of chemical and organic fertilizers. EFs of leafy vegetables, cabbages, solanaceous vegetables and melons were 2.7 %, 2.9 %, 1.4 % and 1.4 % in the greenhouse system, and 5.2 %, 5.7 %, 7.6 % and 9.7 % in the open-field system, respectively. The EFs of the greenhouse production system increased with increasing soil organic matter. Boosted regression tree analysis showed that N application rate, pH and soil organic matter were the main driving factors of EFs in the greenhouse system. Vegetable type, pH and soil organic matter were the main driving factors in the open-field system. In this study, the EFs were evaluated and distinguished across greenhouse and open-field systems, and the results provided accurate EFs under different management practices and soil properties for vegetable production in both greenhouse and open-field systems.

Responses of crop productivity and reactive nitrogen losses to the application of animal manure to China's main crops: A meta-analysis

The effective utilization of manure in cropland systems is essential to sustain yields and reduce reactive nitrogen (Nr) losses. However, there are still uncertainties regarding the substitution of mineral nitrogen (N) fertilizer with manure in terms of its effects on crop yield and Nr losses. We conducted a comprehensive meta-analysis of wheat, maize, and rice applications in China and discovered that substituting mineral N fertilizer with manure increased wheat and maize yields by 4.9 and 5.5 %, respectively, but decreased rice yield by 1.7 %. The increase of yield is larger at low N application and low mineral N substitution rates ((SR) ≤30 %) for silt soils, warm regions, and acidic soils. High SR (>70 %) decreased rice yield as well as the N use efficiency of wheat and maize. Substitution of mineral N fertilizer with manure resulted in lower NH3 volatilization for wheat (48.7 %), lower N2O and NH3 emissions, and N runoff for maize (12.8, 49.6, and 66.7 %, respectively), and lower total Nr losses for rice (11.3–26.5 %). The loss of Nr was significantly and negatively correlated with soil organic carbon content. The rate of N application, soil properties, and climate were critical factors influencing N2O and NH3 emissions and N leaching, whereas climate or soil properties were the dominant factors influencing response in N runoff. We concluded that in silt soils, warm regions, and neutral soils, a ≤ 50 % substitution of mineral N fertilizer with manure can sustain crop yields while mitigating Nr losses.

WHCNS-Veg Modelling of N2O, NH3 and NO3− Dynamics in a Vegetable Production System under Different Fertilization and Irrigation Regimes

Greenhouse vegetable production in China not only increases farmers’ income, but also increases the risk of nitrogen losses due to excessive water and fertilizer input. Nitrogen losses, including the potent greenhouse gas nitrous oxide (N2O), are driven by water content, soil temperature and pH; regulated by available organic carbon and inorganic nitrogen (N); and affected by management. Therefore, a process-based model was applied to explain the complex interaction of the factors affecting N losses in the form of N2O, NH3 and NO3− from a greenhouse vegetable production system in a northeast suburb of Beijing, China. We designed four treatments: two equal N input treatments with one flooding (FP) and the other drip irrigation (FPD) and two equal water input treatments (drip irrigation) with one 100% chemical N input (FPD) and the other 50% N input (OPTD). The last one was CK treatment (flooding without chemical N). We calibrated the WHCNS-veg model using year-round measurements of soil temperature, N2O emission, NH3volatilization, NO3− distribution and yields for greenhouse cucumber–tomato cultivation under farmers’ practice (flooding + 100% chemical N, FP). Then, we validated the model using the data sets under drip irrigation (70% of flooding amount + 100% chemical N, FPD), reduced chemical N by 50% (drip + 50% chemical N, OPTD) and CK treatment. The WHCNS-veg model was able to capture the above processes under different treatments. Annual N2O emissions were 5.47 and 3.76kg N ha−1 for the cucumber and tomato seasons under FP, respectively. Compared to FP, drip irrigation (FPD) decreased N2O emissions by 19.0% and 45.5% in the two seasons, respectively. Compared to FPD, applying a lower rate of N (OPTD) further reduced N2O emissions by 13.7% and 40.5%, respectively. According to the model simulation, N2O emission was mainly controlled by nitrification/denitrification in the cucumber/tomato seasons, respectively. Compared to FP, drip irrigation (FPD) increased NH3 volatilization by 54.2% in the cucumber season, while in the tomato season, there were no significant differences inNH3 volatilization under the three fertilizer treatments. The nitrate leaching levels were 48.5 and 81.0 kg N ha−1 for the two seasons under FP treatment. Drip irrigation (FPD) decreased NO3− leaching by 20.6% in the cucumber season. Drip irrigation (FPD) and/or reducing chemical N (OPTD) did not compromise vegetable yields. In all, WHCNS-veg performed well in simulating N2O, NH3 and NO3− dynamics from the greenhouse vegetable field, which means that the model can be used to manage water and nitrogen precisely in greenhouse vegetable production systems by scenario analysis, and drip irrigation and/or lower N input can be applied in this area to secure yield and reduce N losses.

Urea hydrolysis in different farmland soils as affected by long-term biochar application

Urea is a commonly used nitrogen (N) fertilizer that contributes to world food production, and there have been increasing concerns about relatively low urea-N use efficiency. Biochar has shown the potential to mitigate N loss, but how biochar influences urea hydrolysis and the underlying mechanisms are still unclear. In this study, long-term biochar-amended upland, paddy and greenhouse soils were sampled at depths of 0–20 and 20–40 cm in Haicheng City, Northeast China. Soil N contents, urea hydrolysis rates (UHRs), and total, intracellular and extracellular urease activities were determined, as well as the total bacterial and ureolytic microbial gene abundance were quantified. The results showed that biochar increased total urease activity by 32.64–66.39% in upland soil and by 2.90–2.13-fold in paddy soil. Both intracellular and extracellular ureases contributed to the increase in total urease activity. However, in greenhouse soil, extracellular (+35.07–74.22%) and intracellular (−40.14–77.68%) urease activities responded inconsistently to biochar incorporation. Increases in ureC gene copy numbers (2.15- to 4.47-fold) in upland and greenhouse (20.93%) soil implied that biochar stimulated microorganisms capable of producing urease, and the biochar liming effect increased the soil pH (0.11–0.60 units), which optimized the ureolytic reaction, together explained the increases in urease activity. We found that the decreased soil N content was accompanied by a higher UHR in upland and greenhouse soils, suggesting that the accelerated UHR exerted a negative effect on the soil N content, possibly caused by excessive NH3 volatilization. In paddy soil, where the UHR was not increased, biochar was an effective amendment for simultaneously improving soil urease activity and N content.

Optimized fertigation mitigates N2O and NO emissions and enhances NH3 volatilizations in an intensified greenhouse vegetable system

Gaseous reactive nitrogen (GNr) losses (N2O, NO emissions and NH3 volatilization, etc.) in greenhouse vegetable fields (GVF) have received considerable critical attention. Much uncertainty still exists about GNr losses reduction under increasing vegetables demand and environmental policies in China. An experiment spanning four greenhouse vegetable growing seasons (cucumber and tomato) was conducted in North China Plain (NCP). It included four treatments, i.e., flood irrigation with no urea-N application (FU0), flood irrigation with conventional urea-N application (FUN), drip fertigation with conventional urea-N application (DUN), and drip fertigation with 50% reduction of urea-N application (DRUN). Obvious emission peaks of N2O, NO and NH3 flux were captured in the GVF after each fertilization and irrigation event. For FUN treatment, the mean annual area-scaled emissions of N2O, NO, and NH3 were 11.48, 1.66, and 44.90 kg N ha−1 yr−1, respectively; and the mean annual yield-scaled emissions of N2O, NO, and NH3 were 181.86, 23.04, and 800.07 g N t−1 yr−1, respectively. On the mean annual area-scaled and yield-scaled, the N2O emissions were significantly (P < 0.05) lower by 40.1 % and 32.3 %, and the NO emissions were lower by 23.5 % and 28.5 %, but the NH3 volatilization were significantly (P < 0.05) higher by 31.7 % and 49.0 %, respectively, for the DUN treatment than FUN. Also compared with FUN, in DRUN treatment, the mean annual area-scaled N2O emissions, NO emissions and NH3 volatilization were significantly reduced by 46.7 %, 52.4 % and 22.0 %, respectively; and the mean annual yield-scaled N2O emissions, NO emissions and NH3 volatilization were significantly reduced by 40.7 %, 57.1 % and 24.5 %, respectively. Moreover, compared with FUN treatment, DUN and DRUN treatment both alleviated the global temperature potential (GTP) at 20- and 100-year timescales. Overall, compared with conventional water and fertilizer regimes, only changing irrigation mode reduced N2O and NO emissions but increased NH3 volatilization losses in greenhouse cucumber-tomato cultivation system; reducing N application while changing irrigation methods had significant emission reduction effects on N2O, NO and NH3 at both the area-scaled and yield-scaled, and which is an effective water and fertilizer managements for greenhouse cucumber-tomato cultivation system.

Substituting urea with biogas slurry and hydrothermal carbonization aqueous product could decrease NH3 volatilization and increase soil DOM in wheat growth cycle

Biogas slurry (BS) and hydrothermal carbonization aqueous products (HAP), which are rich in nitrogen (N) and dissolved organic matter (DOM), can be used as organic fertilizer to substitute inorganic N fertilizer. To evaluate the effects of co-application of BS and HAP on the ammonia (NH3) volatilization and soil DOM content in wheat growth season, we compared six treatments that substituting 50%, 75%, and 100% of urea-N with BS plus HAP at low (L) or high (H) ratio, named BCL50, BCL75, BCL100, BCH50, BCH75, BCH100, respectively. Meanwhile, urea alone treatment was set as the control (CKU). The results showed that both BCL and BCH treatments significantly mitigate the NH3 volatilizations by 9.1%–45.6% in comparison with CKU (P < 0.05), whose effects were correlated with soil NH4+-N content. In addition, the decrease in soil urease activity contributed to the lower NH3 volatilization following application of BS plus HAP. Notably, BS plus HAP applications increased the microbial byproduct- and humic acid-like substances in soil by 9.9%–74.5% and 100.7%–451.9%, respectively. Consequently, BS and HAP amended treatments significantly increased soil humification index and DOM content by 13.7%–41.2% and 38.4%–158.7%, respectively (P < 0.05). This study suggested that BS and HAP could be co-applied into agricultural soil as a potential alternative of inorganic fertilizer N, which can decrease NH3 loss but increase soil fertility.

Zinc application promotes nitrogen transformation in rice rhizosphere soil by modifying microbial communities and gene expression levels

Application of Zn fertilizers to agricultural field is a simple and effective way for farmers to manage Zn deficient stress in soils to avoid yield lose. Although a synergistic effect of Zn on N transformation in soil has been reported, the mechanism is not fully understood yet. In this study, we planted rice in soils with different combinations of Zn and N supply, and analyzed the plant growth and N uptake, the N transformation, microbial communities, enzyme activities and gene expression levels in rhizosphere soil to reveal the underlying mechanism. Results showed that Zn application promoted the rice growth and N uptake, increased the soil alkali-hydrolyzed N and NH4+, but decreased NO3− and inhibited NH3 volatilization from the rhizosphere soil under optimal N condition. Zn supply significantly increased the relative abundances of Sphingomonas, Gaiella, subgroup_6, and Gemmatimonas, but decreased nitrosifying bacteria Ellin6067; while increased saprophytic fungi Schizothecium and Mortierella, but decreased pathogenic fungi Gaeumannomyces, Acremonium, Curvularia, and Fusarium in the rhizosphere soil under optimal N condition. Meanwhile, Zn application elevated the activities of protease, cellulase and dehydrogenase, and up-regulated the expression levels of napA, nirS, cnorB, and qnorB genes involved in the denitrification process in rice rhizosphere soil under optimal N condition. These results indicated Zn application could facilitate the soil N transformation and improved its availability by modifying both bacterial and fungal communities, and altering the soil enzyme activities and functional gene expression levels, ultimately promoted the N uptake and biomass of rice plant. However, this synergistic effect of Zn on rice growth, N uptake and soil N transformation strongly depended on the external N conditions, as no significant changes were observed under high N condition. Our results indicated that Zn co-fertilized with appropriate application of N is a useful strategy to improve the N bioavailability in rice rhizosphere soil and enhance the N uptake in rice plant.

Nitrogen budget and critical load determination at a Sahelian grazed grassland site

Based on rare and original in situ measurements together with published data, we estimate a complete nitrogen (N) budget for a semi-arid Sahelian grazed grassland located in Dahra (Senegal) in 2014 and 2017. Nitrogen inputs include biological fixation, dry and wet atmospheric deposition, and input from livestock manure. Nitrogen outputs include nitric oxide (NO) and nitrous oxide (N2O) emissions from soils, NO and ammonia (NH3) emissions from biomass burning, NH3 volatilization from manure, ingestion from livestock grazing, uptake by trees and soil leaching. Nitrogen inputs ranged between 11.7 ± 0.5 and 34.4 ± 0.5 kg N ha−1 yr−1 for low and high estimates respectively, and N outputs ranged between 16.4 ± 1.5 and 45.7 ± 1.5 kg N ha−1 yr−1 for low and high estimates respectively, on average for both years. Nitrogen depletion was estimated between 4.7 ± 2.0 and 11.3 ± 2.0 kg N ha−1 yr−1, which involves N mining from soils. The budget is dominated by the impact of livestock through grazing (63% of the outputs), NH3 volatilization (15% of the outputs), manure (68% of the inputs) and atmospheric deposition (19% of the inputs). The N critical load (Steady State Mass Balance method) ranged from 16.7 ± 0.8 to 47.5 ± 1.7 kg N ha−1 yr−1, showing that the grazed grassland of Dahra was not yet threatened by an excess of N. The assessment of the critical load in Sahelian landscapes depends heavily on livestock participation to the ecosystem equilibrium.

A semi-empirical semi-process model of ammonia volatilization from paddy fields under different irrigation modes and urea application regimes

Both empirical models and process-based models of ammonia (NH3) volatilization simulation in paddy field have some disadvantages. This work describes a semi-empirical semi-process model, which combines the simplicity of empirical models with the precision of process-based models, and its combinatorial structure is sufficient for reproducing the characteristic course of NH3 volatilization in paddy fields under different irrigation modes and urea application regimes over time. A dataset consisting of seven rice seasons across three locations was used for model development. Performance indexes showed the model is good (R2 values ranged from 0.67 to 0.94). The influence of air temperature and wind speed on NH3 volatilization was not as great as our conventional understanding, and soil temperature was a more accurate indicator than air temperature for model development. Model performance was better where the less urea splits and the higher urea rate, but there was no significant difference between alternate wetting and drying (AWD) irrigation mode (average values of R2, IA, NSI, and RMSE were 0.82, 0.94, 0.96, and 0.53 kg ha-1 d-1) and flooding irrigation (FI) mode (average values of R2, IA, NSI, and RMSE were 0.86, 0.94, 0.96, and 0.58 kg ha-1 d-1). The ammonium nitrogen (NH4+-N) concentration and pH of surface water and soil water in paddy fields had the greatest impact on NH3 volatilization, and they were mainly related to the amount of urea applied. Splitting the urea application and delaying the first urea application are the fundamental countermeasures to reduce NH3 volatilization. The magnitude of developed model performance varied among rice cropping systems, irrigation modes, urea application regimes, and climatic regions, highlighting the need to understand why measured NH3 volatilization varies among locations. The new model may be a useful tool for predicting fertilizer efficiency of paddy fields applied urea, assessing NH3 volatilization factors, and reducing emission.

Every coin has two sides: Continuous and substantial reduction of ammonia volatilization under the coexistence of microplastics and biochar in an annual observation of rice-wheat rotation system

Microplastics (MPs) are verified to affect the fate of ammonia (NH3) in agricultural soils. However, the impacts and mechanisms of MPs coupled with biochar (BC), a widely used agricultural conditioner, on NH3 losses are mostly untapped. The aim of this study was to investigate the mechanisms of common MPs (i.e., polyethylene, polyester, and polyacrylonitrile) and straw-derived BC on NH3 volatilization in rice-wheat rotation soils. Results showed that BC alone and MPs with BC (MPs + BC) reduced 5.5 % and 11.2–26.6 % cumulative NH3 volatilization than the control (CK), respectively, in the rice season. The increased nitrate concentration and soil cation exchange capacity were dominant contributors to the reduced soil NH3 volatilization in the rice season. BC and MPs + BC persistently reduced 44.5 % and 60.0–62.6 % NH3 losses than CK in the wheat season as influenced by pH and nitrate concentration. Moreover, BC and MPs + BC increased humic acid-like substances in soil dissolved organic matter by an average of 159.1 % and 179.6 % than CK, respectively, in rice and wheat seasons. The increased adsorption of soil NH4+ and the promotion of crop root growth were the main mechanisms of NH3 reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH3 mitigation in rice-wheat rotational ecosystems.

Biochar and organic substitution improved net ecosystem economic benefit in intensive vegetable production

Biochar amendment and substituting chemical fertilizers with organic manure (organic substitution) have been widely reported to increase crop production and decrease reactive nitrogen (Nr) loss including nitrous oxide (N2O), nitric oxide (NO), and ammonia (NH3) emissions, and N runoff and leaching. However, few comprehensive evaluations have been performed on the environmental and economic aspects of biochar amendment or organic substitution. Here, we studied the comprehensive effects of biochar amendment, organic substitution, and biochar amendment combined with organic substitution on crop production, Nr loss, and net ecosystem economic benefit (NEEB) in intensive vegetable production by integrating life-cycle assessment for Nr footprints, empirical models for NH3 volatilization and N runoff and leaching derived from peer-reviewed publications and validated by the current measurements and direct field measurement for N2O and NO emissions during 5 consecutive years of vegetable crop rotations. Five fertilization treatments were applied (SN: synthetic fertilizer application; SNB: SN plus 20 t ha−1 biochar amendment; SNM: substituting 50% of chemical N fertilizer with organic manure; SNMB: SNM plus 20 t ha−1 biochar amendment; and CK: no fertilizer or biochar addition). Compared with the SN, the SNB increased vegetable yield (28.4%, p < 0.05; interannually varying from − 10 to 74.9%) and nitrogen use efficiency (29.2%, interannually varying from − 39.7 to 150.4%), and decreased field Nr loss (45.4%, p < 0.01; interannually varying from − 40.3 to 78.4%), and thus improved NEEB by 7.1%; meanwhile, the SNM increased vegetable yield (11.6%, interannually varying from − 5.4 to 27.1%) and nitrogen use efficiency (45.7%, p < 0.05; interannually varying from 2.3 to 154%), reduced field Nr loss (34.9%, p < 0.01; interannually varying from 8.4–39.0%), and thus improved NEEB by 17.8% (p < 0.05) compared to the SN, being 56.0 × 103 Chinese Yuan (CNY) ha−1 crop−1. Due to the high foreground Nr loss during organic manure production and high input costs of biochar production, the SNMB decreased the NEEB by 8.0% as compared to the SN. Moreover, the SNB and SNM improved vegetable qualities by increasing protein, soluble sugar, and vitamin C contents while decreasing nitrate content (p < 0.05). Therefore, single application of biochar amendment or organic substitution would achieve better NEEB and product quality in vegetable production.Graphical