Ammonium-based Fertilizers Research Articles

An Overview of the Soil Acidity Causes in Ethiopia, Consequences, and Mitigation Strategies

Soil acidity is a serious land degradation problem and worldwide danger, impacting approximately 50% of the world's arable soils and limiting agricultural yield. Soil acidification is a complicated series of events that lead to the production of acidic soil. In its widest sense, it can be defined as the total of natural and human processes that reduce the pH of soil solutions. Soil acidity affects around 43% of agricultural land in Ethiopia's humid and sub humid highlands. The main objective of this seminar is to highlight different literatures on the concepts of soil acidity and to give a wealth of knowledge on the causes of soil acidity, the effects it has on agricultural production, and management strategies for reducing soil acidity and raising crop yield. Acid soils in western Ethiopia are mostly caused by topsoil erosion caused by heavy rains and high temperatures. This results in the loss of organic matter and the leaching of exchangeable basic cations (Ca<sup>2+</sup>, Mg<sup>2+</sup>, Na<sup>+</sup>, and K<sup>+</sup>). Because ammonium-based fertilizers are easily converted to nitrate and hydrogen ions in the soil, they play a significant role in acidification. One of the reasons of soil acidity is inefficient nitrogen usage, which is followed by alkalinity exports in crops. Soil acidity in Ethiopian highlands is mostly caused by the clearance of crop residues, continuous crop harvest without sufficient fertilization, cation removal, and usage of acid-forming inorganic fertilizers. Acid soil reduces nutrient availability and produces Al and Mn toxicity. In addition to these effects, soil acidity may rapidly degrade soil physicochemical qualities such as organic carbon (OC), cation exchange capacity (CEC), soil structure, porosity, and texture. Liming, the use of organic materials as ISFM, and the adoption of crop types that are resistant to Al toxicity are all alternatives for correcting acid soils. Liming can minimize toxicity by lowering concentrations, improving the availability of plant nutrients like P, Ca, Mg, and K in the soil, and reducing heavy metal solubility and leaching. Application of organic matter has a liming impact because of its abundance in alkaline cations (such Ca, Mg, and K) that were released from OM during mineralization. The pH of the soil is raised by soil organic matter, which helps with soil acidity supplements.

Evaluation of nanoparticle-enhanced silane and vinyl ester coatings for protecting concrete from ammonium sulfate

Inferior quality of concrete surface layers can lead to significant deterioration of concrete infrastructure due to the infiltration of fluids and deleterious substances from the surrounding environment. Concrete structures such as foundations, abutments, flatwork, and underground tanks in agricultural and mining zones, as well as slabs in factories producing ammonium-based fertilizers, are highly susceptible to ammonium sulfate attack, which is known as the most aggressive sulfate deterioration driven by acid-sulfate reactions. Coatings are an effective strategy for protecting such concrete structures to restore its performance and prolong its service life. Therefore, this study aimed at investigating the performance of nano-based coatings as superficial treatments for concrete elements exposed to aggravated exposures of ammonium sulfate. Silane (hydrophobic agent) and vinyl ester (membrane-forming polymer) were used as base resins, in which nano-clay and nano-calcium carbonate particulates were dispersed at different dosages (0, 2.5, and 5 %). In addition, a colloidal silica solution was used as a surface treatment. The durability of coated concrete specimens was evaluated under two ammonium sulfate exposures: full immersion and combined with cyclic environmental conditions (freezing-thawing and wetting-drying cycles). Degradation of concrete specimens was monitored by visual assessment and quantified in terms of mass and length changes over time. In addition, the deterioration mechanisms and coatings’ performance were studied by thermal, mineralogical, and microstructural tests. The results showed that colloidal silica could not adequately protect concrete specimens from these exposures. Conversely, silane nanocomposites improved the durability of concrete under both exposures and superior performance was generally observed for concrete specimens coated with vinyl ester nanocomposites.

A comprehensive network meta-analysis to assess the benefit of starter fertilization on yield, nutrient uptake and nutrient use efficiency

BackgroundPlaced starter fertilization, a well-established fertilization practice in agriculture, aims to increase fertilizer use efficiency and yield. So far, numerous studies have proven positive effect on yields. However, the impact on nutrient use efficiency and nutrient uptake was not investigated profoundly. Additionally, diverse unidentified edaphic and environmental factors, and fertilization strategies cause a high uncertainty for the outcome under field conditions. ObjectivesThe aim of this study was to quantify the impact of a placed starter fertilization on yield, N and P uptake as well as N and P use efficiency. Thereby, the importance of influencing environmental factors and management strategies and the magnitude of their impact should be clarified. MethodsWe performed a network meta-analysis including 1158 observations from 57 peer-reviewed studies and provided a holistic investigation on the effect of placed starter fertilization on yield, nutrient use efficiencies, and aboveground nutrient contents compared to fertilizing without starter fertilization. ResultsThis study revealed that placed starter fertilization significantly increased yield by 9.4 %. Especially in warm, arid climates as well as in warm, hyper-humid climates the fertilizer use efficiency gain was most pronounced. While N uptake and N use efficiency could not benefit significantly from a placed starter fertilization, P uptake and P use efficiency were both enhanced. In the future, combining N and P and using ammonium-based fertilizers can guarantee the effectiveness of a placed starter fertilization. ConclusionsIn summary, placed starter fertilization is a potent strategy to increase yield and improve P use efficiency and P uptake. When applied in the right climate, with the right dosage and N compound, additional advantages of a placed starter fertilization can be exploited. ImplicationsThe current study not only deepens our understanding of the connection of fertilization methods and agronomic performance, but also provides a guideline for improving the efficiency of placed starter fertilization.

Soil Acidity Causes in Ethiopia, Consequences and Mitigation Strategies-A Review

Soil acidity is a serious land degradation problem and worldwide danger, impacting approximately 50% of the world's arable soils and limiting agricultural yield. Soil acidification is a complicated series of events that lead to the production of acidic soil. In its widest sense, it can be defined as the total of natural and human processes that reduce the pH of soil solutions. Soil acidity affects around 43% of agricultural land in Ethiopia's humid and sub humid highlands. Acid soils in western Ethiopia are mostly caused by topsoil erosion caused by heavy rains and high temperatures. This results in the loss of organic matter and the leaching of exchangeable basic cations (Ca2+, Mg2+, Na+, and K+). Because ammonium-based fertilizers are easily converted to nitrate and hydrogen ions in the soil, they play a significant role in acidification. One of the reasons of soil acidity is inefficient nitrogen usage, which is followed by alkalinity exports in crops. Soil acidity in Ethiopian highlands is mostly caused by the clearance of crop residues, continuous crop harvest without sufficient fertilization, cation removal, and usage of acid-forming inorganic fertilizers. Acid soil reduces nutrient availability and produces Al and Mn toxicity. In addition to these effects, soil acidity may rapidly degrade soil physicochemical qualities such as organic carbon (OC), cation exchange capacity (CEC), soil structure, porosity, and texture. Liming, the use of organic materials as ISFM, and the adoption of crop types that are resistant to Al toxicity are all alternatives for correcting acid soils. Liming can minimize toxicity by lowering concentrations, improving the availability of plant nutrients like P, Ca, Mg, and K in the soil, and reducing heavy metal solubility and leaching. Application of organic matter has a liming impact because of its abundance in alkaline cations (such Ca, Mg, and K) that were released from OM during mineralization. The pH of the soil is raised by soil organic matter, which helps with soil acidity supplements.

Nitrogen Supply from Soil Organic Matter: Predictors and Implications for Recommended Nitrogen Application Rates in Northern Highbush Blueberry

Nitrogen (N) management is a key component to maintaining high productivity of northern highbush blueberry (Vaccinium corymbosum L.) and nitrogen is often supplied by applying ammonium-based fertilizers. It can also be supplied through mineralization of soil organic matter (SOM), although the amount released by SOM is difficult to predict and not always considered in the development and implementation of N fertility programs. Laboratory and field experiments were conducted to estimate the timing and magnitude of net N mineralization from SOM throughout the growing season, identify soil properties that can be measured commercially and used to predict net N mineralization across a range of SOM, and determine whether N requirements for maximizing yield and fruit quality of blueberry vary across soils with different amounts of SOM. The laboratory experiment was conducted for 6 months using soil samples collected from 10 representative commercial blueberry fields in northwest Washington. The soils contained 2% to 42% soil organic carbon (SOC). The mean net N mineralization rates were fastest during the first 3 to 4 months of incubation, corresponding to the period during which N uptake reaches its maximum in blueberry. Results indicated that the soil total N may be a useful predictor of the N supply from SOM (6.34 ± 1.13 kg⋅ha−1 increase in net N mineralization with each 0.1% increase in total N), but there was substantial variability in the N supply that could not by explained by the total N (P < 0.001; r2 = 0.433). The field experiment was conducted from 2019 to 2021 and included four mature, regionally representative, commercial fields of ‘Duke’ blueberry. The fields contained 3% to 28% SOC and were each fertilized with low, medium (control), or high N rates, corresponding to 33 to 50, 67 to 84, or 102 to 118 kg⋅ha−1 N per year, respectively. Although soil inorganic N levels suggested that N mineralization was substantial at sites with higher SOM, sites with lower SOM did not require more fertilizer N than those with higher SOM. Under the conditions of this experiment, even the lowest N rates were sufficient to sustain production for at least 3 years at each site. The findings of this study indicate that SOM may be an important contributor to N fertility in managed blueberry systems, and that yield and fruit quality can be maintained across various N fertilizer rates, including at rates <50 kg⋅ha−1 N. However, the long-term impacts of reducing N application rates remain unclear, and future research should monitor long-term changes in plant health and soil fertility associated with reduced N applications across diverse soils and production systems.

Nitrogen: from discovery, plant assimilation, sustainable usage to current enhanced efficiency fertilizers technologies – A review

ABSTRACT From 1913 onwards, the global situation changed from a scenario of nitrogen (N) scarcity to an abundance of ammonia (NH 3 ) produced synthetically via the Haber-Bosch process. Several N compounds have been synthesized since then, with urea becoming the main source of N, accounting for 55 % of current N consumption. However, N efficiency in agroecosystems is low and, normally, N recovery in cultivated plants is less than 50 %. This occurs because a large amount of reactive N is lost to the environment, inducing various forms of pollution, threatening human and environmental health, in addition to causing a negative economic impact on the farmer. The main processes responsible for low N efficiency are NH 3 volatilization, leaching, and N denitrification. Considering global NH 3 volatilization losses of 14 %, it can be assumed that up to 8.6 million Mg of urea are lost every year in the form of NH 3 . For each ton of NH 3 produced, 1.9 to 3.8 Mg of CO 2 is emitted into the atmosphere. Therefore, increasing N use efficiency (NUE) without compromising yield is a necessity and a challenge for crop improvement programs and current management systems, in addition to reducing greenhouse gas emissions. In this context, enhanced efficiency fertilizers (EEFs), which contain technologies that minimize the potential for nutrient losses compared to conventional sources, are an alternative to increasing the efficiency of nitrogen fertilization. Currently, EEFs are classified into three categories: stabilized, slow-release, and controlled-release. This study aims to understand the technologies used to produce EEFs and the factors that govern their availability to plants. This review covers the following topics: the discovery of N, N dynamics in the soil-atmosphere system, N assimilation in plants, strategies to increase NUE in agrosystems, NH 3 synthesis, NH 3 volatilization losses, N fertilizer technologies, the importance of characterization of EEFs, conventional nitrate or ammonium-based fertilizers to reduce gaseous losses of NH 3 and future prospects for the use of N fertilizers in agriculture.

Nitrification-induced acidity controls CO2 emission from soil carbonates

Nitrification acidifies soil, and the produced H+ are neutralized by inorganic carbon (C) in soil leading to irreversible CO2 emissions. CO2 released by nitrogen (N) fertilizer-induced acidification is partitioned between solid (CaCO3 re-precipitation), liquid (dissolved HCO3− and CO32−) and gaseous (CO2) phases. Therefore, quantifying the effects of N fertilization on CO2 emissions from soil inorganic C is an enormous challenge. 14C-labeled CaCO3 was used as a model inorganic C to trace the released CO2 caused by acidification by five fertilizers: chicken manure, urea, KNO3, NH4NO3, and (NH4)2SO4 added at three N rates. Cropland soil was homogenously mixed with Ca14CO3 powder and fertilizers, and the emitted CO2 was trapped in NaOH solution to determine total CO2 and 14CO2 efflux originated from inorganic C. Fertilization, particularly ammonium-based fertilizers ((NH4)2SO4, NH4NO3), strongly decreased soil pH by 0.35 units over 40 days. All fertilizers except KNO3 increased total CO2 emissions by 21%–490% compared to the unfertilized control soil. The fertilization effects on cumulative 14CO2 emission induced by CaCO3 neutralization, corresponded to acidification and decreased in the order (NH4)2SO4 > NH4NO3 > urea > KNO3 > chicken manure. Ammonium-based fertilizers induced the strongest CO2 emissions originated from inorganic C, emitting 1.6–4.5 times more 14CO2 than non-fertilized soils during the first nine days. The total CO2 emissions from SIC were proportional to the fertilizer dose applied. Therefore, we conclude that both the choice of N fertilizers and their application rates need to be considered to control CO2 emissions originated from inorganic C. The soil inorganic C losses should be prevented not only because of their irreversible contribution to atmospheric CO2, but also to safeguard ecosystem services of CaCO3, such as organic matter preservation, soil structure stabilization, and C sequestration.

Environmental factors militating against the activities of ammonia oxidizing archaea and ammonia oxidizing bacteria in soil

This review aims to scrutinize the effect of ammonia concentration, temperature, pH, drought and inhibitors on activity of AOA and AOB in soil. Ammonia concentration in soil increases during drought due to the reduced soil water content and, with desiccation stress or a combination of both factors result in greater inhibition of AOA than AOB during drought. AOA were more susceptible to increased desiccation stress than AOB, irrespective of initial soil ammonium concentration and AOA cultures were more sensitive than AOB to osmotic stress which represent an additional niche differentiating factor between AOA and AOB in soil. Activity and growth of AOA and AOB observed in soil amended with high ammonium concentration at different temperature, suggesting that AOA can contribute to nitrification in highly fertilized soil. The selective inhibition of AOA by simvastatin in culture and in soil provides evidence for oxidation of ammonia by AOB at low ammonium concentration. The findings advance our understanding of the influence of ammonium supply, temperature and osmotic stress on soil nitrification and its role in controlling the availability of ammonium-based fertilizers for plant uptake.

Juglone, a plant-derived 1,4-naphthoquinone, binds to hydroxylamine oxidoreductase and inhibits the electron transfer to cytochrome c554.

Nitrification, the microbial conversion of ammonia to nitrate via nitrite, plays a pivotal role in the global nitrogen cycle. However, the excessive use of ammonium-based fertilizers in agriculture has disrupted this cycle, leading to groundwater pollution and greenhouse gas emissions. In this study, we have demonstrated the inhibitory effects of plant-derived juglone and related 1,4-naphthoquinones on the nitrification process in Nitrosomonas europaea. Notably, the inhibition mechanism is elucidated in which 1,4-naphthoquinones interact with hydroxylamine oxidoreductase, disrupting the electron transfer to cytochrome c554, a physiological electron acceptor. These findings support the notion that phytochemicals can impede nitrification by interfering with the essential electron transfer process in ammonia oxidation. The findings presented in this article offer valuable insights for the development of strategies aimed at the management of nitrification, reduction of fertilizer utilization, and mitigation of greenhouse gas emissions.

Short Term Effects of Chemical Fertilizer, Compost and Zeolite on Yield of Lettuce, Nutrient Composition and Soil Properties

The proper management of treated agricultural wastes (e.g., composts) contributes to the protection of water and soil quality by reducing the use of chemical fertilizers, lowering leachate, and protecting renewable and nonrenewable resources. Natural zeolites, particularly clinoptilolite, can be used in agriculture to improve soil quality and increase yields due to their unique properties. The objective of the study was to test the effects of the co-addition of compost, zeolite and ammonium-based fertilizer on the Above-ground Fresh Weight (AFW) of lettuce (Lactuca sativa L.), leaf nutrients and soil fertility. To this aim, a soil pot experiment was carried out at the Department of Soil Science of Athens, which is located in the region of Attica, in the area of central Greece. Two levels of olive compost originated from olive leaves (0% and 10% v/v), three levels of zeolite (0%, 2%, and 5% w/w) and two levels of chemical fertilization (no fertilization and NPK fertilization) were combined. Furthermore, two different soils were introduced, one moderately acidic (pH = 5.6) and sandy loam in texture (Ac-LT), and the other slightly alkaline (pH = 7.7) and sandy clay in texture (Al-HT). Results showed that the response of lettuce yield to chemical fertilization and zeolite application is soil type-dependent, whereas compost application significantly improved AFW in both soil types. The availability of macronutrients (P, K, and Na) in the soil, as well as their concentration in leaves, were significantly increased by NPK fertilization in most cases. Conversely, the impact of inorganic fertilization on DTPA extractable micronutrients and leaf micronutrient contents was found to be associated with the type of soil. The study recorded a significant reduction in available Fe, Cu, and Mn in AL-HT soil, whereas DTPA-Mn and -Zn were significantly enhanced in Ac-LT soil. Comparable patterns were also documented for the micronutrient concentration in leaves. In most cases, compost application had significant and beneficial effects on plant nutrients. On the contrary, different responses of soil properties to compost addition were registered. The main effect of compost treatment on soil pH, EC, SOM, total N, and available P was significant and positive in both soil types, except for pH and EC in Al-HT soil. On the other hand, exchangeable K and Na were significantly reduced by compost. Zeolite substantially increased the availability of P, K, and Na in soil and plants, whereas the concentrations of DTPA-extractable micronutrients and leaf macronutrients were largely unaffected. In addition, the results of our study indicated that co-additions of organic and inorganic amendments did not yield any significant impact on the lettuce yield, leaf nutrient content and soil fertility. It is suggested that the degree of changes in main soil properties (e.g., pH, EC, SOM) as a result of amendment application as well as the interaction of the amendments with nutrient availability are strongly related to soil type.

Interaction of the Coupled Effects of Irrigation Mode and Nitrogen Fertilizer Format on Tomato Production

The production efficiency and quality of tomatoes is affected by the mode of irrigation and the nitrogen forms. This study explored the impacts of different irrigation regimes, nitrogen forms, and their coupled effects on tomato production. The various irrigation regimes were set at 50%FC~90%FC (W1), 60%FC~90%FC (W2), 70%FC~90%FC (W3), and 80%FC~90%FC (W4) Furthermore, the control (CK) group followed a conventional drip irrigation regime in the local area. Nitrogen forms in this study comprised urea-based fertilizer (urea N 32%, F1), nitrate-based fertilizer (calcium ammonium nitrate N 15%, F2), and ammonium-based fertilizer (ammonium sulfate N 21%, F3). Combining these two factors yielded 15 treatment groups. The experiment was conducted in a solar greenhouse, and the soil type was sandy loam soil. The research focused on observing the yield, quality, and water–fertilizer use efficiency of tomatoes under these 15 treatment groups. The results demonstrate that irrigation had a more significant impact on the yield and nutrient accumulation rate compared to the nitrogen forms. To comprehensively evaluate the yield, quality, and water–fertilizer use efficiency of tomatoes, a combination evaluation method was employed. W3F2 produced the highest yield, CKF2 achieved the highest comprehensive quality score, and W2F2 had the highest comprehensive water and fertilizer use efficiency score. Using the fuzzy Borda model, the evaluation information of the three dimensions was combined. W3F2 ranked first, suggesting the adoption of an irrigation control regime of 70%FC to 90%FC, along with the application of nitrate-based nitrogen fertilizer during the fruit set to the harvest stage. It presented the best performance of tomato yield, quality, and water–fertilizer use efficiency across multiple dimensions.

Spatio-Temporal Variations in Soil pH and Aluminum Toxicity in Sub-Saharan African Croplands (1980–2050)

Soil acidity threatens food production in the tropics. The effect of increasing ammonium-based fertilizer (INF) on soil pH was assessed in sub-Saharan Africa (SSA). A total of 9043 soil data from Africa soil information services, past INF use, and two future scenarios of INF use (business as usual (BAU) and equitable diet (EqD)) were used to determine soil pH variations from 1980 to 2022 and to predict soil PH variations from 2022 to 2050. Random forest and extreme gradient boosting algorithms and soil-forming factor covariates were used for the spatio-temporal soil pH predictions. Topsoil acidification was shown to be significant, with mean annual decrements of 0.014, 0.024, and 0.048 from 1980 to 2022, 2022 to 2050 (BAU), and 2022 to 2050 (EqD), respectively. Over the past 42 years, croplands with soil pH < 6.5 have declined significantly, and soil acidification is predicted to become severe by 2050 in the BAU and EqD scenarios. This was indicated by a predicted 3% increase in croplands at risk of aluminum toxicity (soil pH < 5.5) from 66 × 106 ha in 2022 to 78.5 × 106 ha in 2050. The drivers of the spatial variations in the soil pH between 1980 and 2050 were the MAP, basic cation, clay content, SOC, and nitrogen fertilizers. The evaluation metrics of the 10-fold cross-validation showed that the root mean squared errors (RMSEs) of the soil pH from 1980 to 2022, as well as the predicted soil PH from 2022 to 2050 (BAU) and 2022 to 2050 (EqD), were 0.53 pH units, 0.54 pH units, and 0.56 pH units, respectively, with coefficients of determination (R2) of 0.63, 0.64, and 0.66. The findings of this study can be used for the establishment of management strategies for increasing INF use in acidic soils.

Transient nitrite accumulation explains the variation of N2O emissions to N fertilization in upland agricultural soils

Nitrogen (N) fertilization in agricultural soils is the largest anthropogenic source of nitrous oxide (N2O) emissions, but the underlying mechanism of the varied response of N2O emissions to N fertilizer is unclear. We investigated the response of N2O emissions to ammonium-based fertilizers and nitrification inhibitors in upland agricultural soils across northern China. Large variations in N2O emissions in different upland soils in response to N fertilization were found, whereas the variations were well correlated with soil nitrite (NO2−) dynamics (P < 0.01). A higher pH soil is generally correlated with a higher potential nitrification and denitrification rate, a higher AOB/AOA gene abundance ratio, higher NO2− content, and higher N2O emission. The efficacy of 3,4-dimethylpyrazole phosphate (DMPP) for inhibiting net nitrification increased with increasing soil pH. Further investigation showed that rapid ammonia oxidation drives oxygen (O2) depletion and NO2− accumulation in the soil matrix, which stimulates N2O emission and inhibits N2 emission under anoxic conditions. Collectively, our results showed that alkaline soils tend to have rapid ammonia oxidation potential, leading to transient NO2− accumulation and O2 depletion in the soil matrix after large ammonium addition. This might trigger significant N2O emissions from denitrification and DNRA, which explains the spatial heterogeneity of N2O emissions in response to N fertilization in various upland soils.

Upcycling wastewater nitrate into ammonia fertilizer via concurrent electrocatalysis and membrane extraction

Electrocatalytic upcycling of nitrate (NO3−) in wastewater into the valuable ammonium-based fertilizer has been considered as a green and appealing alternative to biological nitrogen removal or the industrial ammonia (NH3) production processes. This work investigated an innovative and energy-efficient electrolysis flow-through cell consisting of a porous activated iron nickel (FeNi) alloy cathode and a hollow polypropylene fiber membrane extraction unit to realize the electrochemical NO3− reduction and simultaneous upcycling to ammonium sulphate salts ((NH4)2SO4). Cathodic and anodic electrochemical half-reactions were coupled to enable NO3− reduction to ammonia and in-situ acid/base productions to promote the membrane stripping of NH3. Our results show that after electrolysis operation for 14 h for a synthetic wastewater containing 150 mM NO3− under a cathodic current density of 30 mA·cm−2, 99 % of NO3− removal efficiency, 98 % of ammonia selectivity, 93 % of Faradic efficiency and 97 % of total ammonia nitrogen (TAN) recovery were achieved respectively. A NH3 recovery flux and a specific energy consumption reached 2050 g-(NH4)2SO4·m−2·d−1 and 11 kWh·kg−1-(NH4)2SO4, respectively, which outcompetes many reported processes. Direct electron transfer was the main mechanisms of electrochemical NO3− reduction to ammonia. Interfacial reaction thermodynamics and kinetics analysis of key intermediates (e.g., *NO3, *NO2, and *NO) shows that the NiFe2O4 (3 1 1)-Ni site on the thermally activated FeNi alloy surface exhibited higher reactivity and specificity toward electrochemical NO3− reduction to ammonia over nitrogen (N2) or hydrogen (H2) generation. Ultimately, this study aims to promote sustainable nitrogen nutrient recovery and ammonia fertilizer synthesis from wastewater treatment.

Characteristics of N2 and N2O Fluxes from a Cultivated Black Soil: A Case Study through In Situ Measurement Using the 15N Gas Flux Method

The magnitudes and source partitioning of soil dinitrogen (N2) and nitrous oxide (N2O) emissions are not well documented, yet. To address both issues for black soil subject to a typical cool temperate climate, soil N2O and N2 fluxes following the basal application event of an ammonium-based fertilizer (labeled by 15N) for maize were simultaneously measured in situ by using the 15N gas flux (15NFG) method. During the two-month field experiment, the measured N2 and N2O fluxes cumulated to 1.61 ± 0.47 and 0.12 ± 0.01 kg N ha−1, respectively, showing N2O to N2O plus N2 ratios (RN2O) of 0.02–0.31 (0.15 on average). Temperature was identified as a key factor regulating the total soil N2 fluxes (r2 = 0.27, p &lt; 0.01), despite the N2 fluxes originated from nitrate denitrification related to dissolved organic carbon concentrations (r2 = 0.39, p &lt; 0.01). Differently, both temperature and soil moisture jointly accounted for 85% and 74% of the variances in the N2O fluxes and the RN2O values, respectively (p &lt; 0.01). Moreover, the process(es) other than autotrophic nitrification and heterotrophic denitrification could be of substantial importance for the soil N2O emissions. Our findings emphasized the importance of temperature in regulating N2 emissions from black soil and the possible site- and/or time specificity of a soil factors-based parametrization of RN2O. In addition, this study implicates that labeling a nitrogen substrate of nitrification while using the 15N enrichment of N2O is necessary to more accurately quantify total soil N2 fluxes in situ by using the 15NFG approach even though further confirmation in future studies is still needed.

Functional N-cycle genes in soil and N2O emissions in tropical grass-maize intercropping systems

There is evidence that forage grasses such as Megathyrsus and Urochloa can suppress nitrification, with direct or indirect consequences on soil inorganic N dynamics and nitrous oxide (N2O) emissions. However, the influence of soil chemical properties on the dynamics of functional N-genes and losses of N in maize (Zea mays L.) intercropped with forage grasses under N fertilization is poorly understood. In this study, soil samples and N2O emissions were analyzed from a field experiment in which maize (fertilized or not with ammonium-based fertilizer) was intercropped with Guinea grass (M. maximus cv. Tanzânia), palisade grass (U. brizantha cv. Marandu), and ruzigrass (U. ruziziensis cv. Comum). Soil N-cycle microorganisms [16S rRNA of bacteria and archaea, nifH (gene encoding N2-fixing bacteria), ammonia-oxidizing bacteria (AOB) and archaea (AOA), nirS (encoding nitrite reductase), and nosZ (encoding nitrous oxide reductase)] were influenced by forage grass, N fertilization, and sampling time, but no evidence of biological nitrification inhibition was found. Palisade grass was associated with a higher abundance of nifH (7.0 × 105 gene copies g−1 soil, on average) in the absence of N compared with the other grasses (4.3 × 105 gene copies g−1 soil, on average). Nitrogen fertilization increased the abundance of AOB but not AOA. Furthermore, N2O flux was influenced by AOB, water-filled pore space, and N fertilization, whereas the cumulative N2O emission and fertilizer-induced emission factor (0.36%, on average) were not affected by the grasses. In conclusion, this study reveals the strong dominance of AOB under ammonium supply, potentially stimulating N2O emissions in maize-forage grass intercropping systems.

A global synthesis of soil denitrification: Driving factors and mitigation strategies

Dinitrogen (N2) and nitrous oxide (N2O) produced via denitrification may represent major nitrogen (N) loss in terrestrial ecosystems. A global assessment of soil denitrification rate, N2O/(N2O+N2) ratio, and their driving factors and mitigation strategies is lacking. We conducted a global synthesis using 225 studies (3367 observations) to fill this knowledge gap. We found that daily N loss through soil denitrification varied with ecosystems and averaged 0.25 kg N ha−1. The average emission factor of denitrification (EFD) was 4.8%. The average N2O/(N2O+N2) ratio from soil denitrification was 0.33. Soil denitrification rate was positively related to soil water-filled pore space (WFPS) (p < 0.01), nitrate (NO3-) content (p < 0.05) and soil temperature (p < 0.01), and decreased with higher soil oxygen content (p < 0.01). N2 emissions increased with latitude (p < 0.05), WFPS (p < 0.01) and soil mineral N (p < 0.05) but decreased with soil oxygen content (p < 0.05). The N2O/(N2O+N2) ratio increased with soil oxygen content (p < 0.01) but decreased with organic carbon (C) (p < 0.05), C/N ratio (p < 0.01), soil pH (p < 0.05) and WFPS (p < 0.01). We also found that optimizing N application rates, using ammonium-based fertilizers compared to nitrate-based fertilizers, biochar amendment, and application of nitrification inhibitors could effectively reduce soil denitrification rate and associated N2 emissions. These findings highlight that N loss via soil denitrification and N2 emissions cannot be neglected, and that mitigation strategies should be adopted to reduce N loss and improve N use efficiency. Our study presents a comprehensive data synthesis for large-scale estimations of denitrification and the refinement of relevant parameters used in the submodels of denitrification in process-based models.

Effects of long-term (70 years) nitrogen fertilization and liming on carbon storage in water-stable aggregates of a semi-arid grassland soil

Grasslands cover up to 40.5% of the world's landmass and store 30% terrestrial carbon (C). Various practices, including mineral fertilization and liming, are used to manage these ecosystems with potential long-term effects on the size and distribution of soil aggregates and inevitably carbon dynamics. The objective of this study was to examine the long-term effects of nitrogen fertilization and liming on soil carbon storage and its dynamics in water-stable aggregates of a semi-arid grassland. Soil samples (0–10 cm) were collected from Ukulinga long-term grassland trial in Pietermaritzburg, South Africa where nitrogen fertilizers have been applied annually and lime every five years for 70 years. Ten treatments were studied: the control (0 kgN/ha and unlimited), lime at 2250 kg/ha (L), ammonium sulphate at 70 kg/ha (AS70) and 211 kg/ha (AS211); ammonium nitrate at 70 kg/ha (AN70) and 211 kg/ha (AN211); AS70 + lime (AS70L); AS211 + lime (AS211L); AN70 + lime (AN70L) and AN211 + lime (AN211L).Nitrogen fertilizers significantly reduced soil pH and increased total soil N. Liming increased soil pH with no effect on total soil N. Lime and lime + N fertilizer treatments had no effect on mean weight diameter (MWD) while separate N application decreased MWD and large macro-aggregates (LMA). Lime only treatment had no effect on water stable aggregate (WSA) fractions. Nitrogen fertilization and liming (separately or in combination) did not affect total C concentration and stocks. Overall, soils had very high total soil organic carbon ranging from 49.7 – 57.6 g/kg across treatments. Nitrogen fertilization decreased organic carbon in LMA in AS70 (1.52%) and AN211 (1.67%) treatments compared to the control (3.40%) which was in concert with increases in C associated with small macro-aggregates (SMA) and micro-aggregates (MiA and SCA). Organic carbon in SMA was 2.67 % (AS70); AS211 (2.62 %); AN70 (2.02 %); AN211 (2.49 %) compared to 1.26 % in the control. Lime + N fertilizer treatments increased C storage in all aggregate fractions compared to N fertilizer only treatments. The lack of response in total SOC to 70 years of N fertilization and liming suggests possible C saturation given the high soil C concentration. Changes in C associated with WSA fractions suggests their importance as diagnostic indicators of N fertilization and liming induced changes in SOC. Findings also show that ammonium-based N fertilization is associated with soil acidification, dispersion of LMA resulting in an increase of microaggregates and C stored in them. Liming can counteracts acidifying and the dispersive effect on NH4+ associated with ammonium-based fertilizers thus restoring macro-aggregation in N fertilized grasslands. These findings suggests that long-term N addition may result in poor soil physical condition and possible stabilization of C in stable fractions.

Correction to: Effects of N Application Rate and Dicyandiamide on the Fate of 15N Fertilizer and the Abundance of Microbial Genes in a Sandy Soil Amended with Sugarcane Litter

Renewable energy produced from sugarcane (Saccharum spp.) has clear advantages over fossil fuels in mitigating climate change. However, N2O emissions and NO3− leaching from fertilizer nitrogen (N) addition can jeopardize the sustainability of sugarcane production worldwide. One of the possible approaches to mitigating these N-loss pathways is the use of nitrification inhibitors such as dicyandiamide (DCD). However, the effects of DCD on the fate of fertilizer-derived N in soil pools and functional N genes (e.g., nitrifiers and denitrifiers) remain unclear. We performed a laboratory incubation study for 54 days to evaluate the influence of DCD and fertilizer N rate ((15NH4)2SO4 applied at 40, 80, 120, and 160 µg N g−1) on 15N transformation and abundance of total prokaryotes (16S rRNA), nitrifiers (ammonia-oxidizing archaea (AOA) and bacteria (AOB)), and denitrifiers (nirK and nosZ) in a tropical sandy soil amended with sugarcane residues. Especially for high N rates (120 and 160 µg N g−1), DCD not only increased the NH4+-15N recovery by inhibiting nitrification but also stimulated microbial immobilization. However, the nitrification inhibitor decreased N losses (i.e., unrecovered 15N). The abundance of total archaea and bacteria was unaffected by both the fertilizer N rate and DCD. While the abundance of AOB and nirK was suppressed by DCD, AOA and nosZ abundance increased, with the latter gene being the highest at 160 µg g−1. We conclude that DCD mitigates N losses from ammonium-based fertilizer by inhibiting NO3− production and changing nitrifying and denitrifying microorganisms in sandy acidic soil.

Implementing a sustainable photochemical step to produce value-added products in flue gas desulfurization

Coal consumption has led to a worrying surge in flue gas emissions, aggravating health and environmental issues worldwide. Therefore, novel approaches supported by sustainable technologies are needed to exploit flue gas emissions effectively. Here, we evaluate an ammonia-based flue gas desulfurization process based on the photochemical capture of CO2 and SO2 for producing hydrogen and ammonium-based fertilizers. The kinetics and mechanistic pathways for sulfite photooxidation are examined, while process feasibility and environmental relevance are evaluated by process simulation and life cycle assessment. Results show that increasing the initial sulfite concentration results in faster reaction rates, following first-order kinetics with an activation energy of 32.9 kJ/mol. Moreover, kinetics is ascribed to two competing photoinduced radical-mediated reaction pathways. Finally, powering the process by renewable energy leads to positive human health, ecosystems, and resources scores in life cycle assessment, supporting the sustainability of the process. Overall, this approach offers essential insights for large-scale hydrogen production through the photooxidation of captured flue gas emissions.