Soil NH4 Research Articles

Improving nitrogen cycling in a land surface model (CLM5) to quantify soil N2O, NO, and NH3 emissions from enhanced rock weathering with croplands

Abstract. Surficial enhanced rock weathering (ERW) is a land-based carbon dioxide removal (CDR) strategy that involves applying crushed silicate rock (e.g., basalt) to agricultural soils. However, unintended biogeochemical interactions with the nitrogen cycle may arise through ERW increasing soil pH as basalt grains undergo dissolution that may reinforce, counteract, or even offset the climate benefits from carbon sequestration. Increases in soil pH could drive changes in the soil emissions of key non-CO2 greenhouse gases, e.g., nitrous oxide (N2O), and trace gases, e.g., nitric oxide (NO) and ammonia (NH3), that affect air quality and crop and human health. We present the development and implementation of a new improved nitrogen cycling scheme for the Community Land Model v5 (CLM5), the land component of the Community Earth System Model, allowing evaluation of ERW effects on soil gas emissions. We base the new parameterizations on datasets derived from soil pH responses of N2O, NO, and NH3 in ERW field trial and mesocosm experiments with crushed basalt. These new capabilities involve the direct implementation of routines within the CLM5 N cycle framework, along with asynchronous coupling of soil pH changes estimated through an ERW model. We successfully validated simulated “control” (i.e., no ERW) seasonal cycles of soil N2O, NO, and NH3 emissions against a wide range of global emission inventories. We benchmark simulated mitigation of soil N2O fluxes in response to ERW against a subset of data from ERW field trials in the US Corn Belt. Using the new scheme, we provide a specific example of the effect of large-scale ERW deployment with croplands on soil nitrogen fluxes across five key regions with high potential for CDR with ERW (North America, Brazil, Europe, India, and China). Across these regions, ERW implementation led to marked reductions in N2O and NO (both 18 %), with moderate increases in NH3 (2 %). While further developments are still required in our implementations when additional ERW data become available, our improved N cycle scheme within CLM5 has utility for investigating the potential of ERW point-source and regional effects of soil N2O, NO, and NH3 fluxes in response to current and future climates. This framework also provides the basis for assessing the implications of ERW for air quality given the role of NO in tropospheric ozone formation, as well as both NO and NH3 in inorganic aerosol formation.

Effects of experimental warming on soil enzyme activities in an alpine swamp meadow on the Qinghai-Tibetan Plateau

Information about the response of soil enzymes to field warming in permafrost regions is scarce, and the potential mechanisms by which warming combined with biotic and abiotic factors affect soil enzyme activities in alpine grasslands remain unclear. A 3-year in situ experiment with two warming levels (2.7 °C and 5.3 °C) was conducted in an alpine swamp meadow to investigate the effects of experimental warming on 5 soil enzyme activities involved in soil carbon and nitrogen cycling, and the relationships between soil enzyme activities and soil variables related to physicochemical properties and nutrient levels were examined. Results showed that warming had obvious positive effects on soil moisture (SM), soil organic carbon, total nitrogen, and NH4+-N contents, especially in the surface soil layer. Soil NO3--N tended to decrease under moderate warming, while it significantly increased under high warming. Meanwhile, during the entire growing season, warming strongly enhanced invertase and amylase activities by 39.2–49.0% and 109.9–191.0%, respectively. In contrast, urease activities were significantly decreased by 36.8–55.7% in warming plots and there were no significant differences in catalase or cellulase activities among treatments during the whole growing season, while catalase activities in warming plots were significantly decreased by 2.6–4.0% in June. These inconsistent responses of soil enzyme activities to experimental warming could be partially explained by warming-induced changes in soil variables. Redundancy analysis showed that soil NO3--N and SM were the most important factors, which explained 29.8% and 19.7% of the variations in soil enzyme activities, respectively, suggesting that the warming-induced increase in SM could weaken the soil aeration status and enhance enzyme and substrate diffusion, strongly affecting soil nitrification and microbial enzyme production.

Partial substitution of chemical fertilizer by Trichoderma biofertilizer improved nitrogen use efficiency in wolfberry (Lycium chinense) in coastal saline land.

A two-year field trial was conducted to investigate the effects of partial substitution of chemical fertilizer (CF) by Trichoderma biofertilizer (TF) on nitrogen (N) use efficiency and associated mechanisms in wolfberry (Lycium chinense) in coastal saline land. As with plant biomass and fruit yield, apparent N use efficiency and plant N accumulation were also higher with TF plus 75% CF than 100% CF, indicating that TF substitution promoted plant growth and N uptake. As a reason, TF substitution stabilized soil N supply by mitigating steep deceases in soil NH4 +-N and NO3 -N concentrations in the second half of growing seasons. TF substitution also increased carbon (C) fixation according to higher photosynthetic rate (Pn) and stable 13C abundance with TF plus 75% CF than 100% CF. Importantly, leaf N accumulation significantly and positively related with Pn, biomass, and fruit yield, and structural equation modeling also confirmed the importance of the causal relation of N accumulation coupled with C fixation for biomass and yield formation. Consequently, physiological and agronomical N use efficiencies were significantly higher with TF plus 75% CF than 100% CF. Overall, partial substitution of CF by TF improved N use efficiency in wolfberry in coastal saline land by stabilizing soil N supply and coupling N accumulation with C fixation.

Hydrothermal carbonization of biogas slurry and cattle manure into soil conditioner mitigates ammonia volatilization from paddy soil

Hydrothermal carbonization of biogas slurry and animal manure into hydrochar could enhance waste recycling waste and minimize ammonia (NH3) volatilization from paddy fields. In this study, cattle manure-derived hydrochar prepared in the presence of Milli-Q water (CMWH) and biogas slurry (CMBSH), and biogas slurry-based hydrochar embedded with zeolite (ZHC) were applied to rice-paddy soil. The results demonstrated that CMBSH and ZHC treatments could significantly mitigate the cumulative NH3 volatilization and yield-scale NH3 volatilization by 27.9–45.2% and 28.5−45.4%, respectively, compared to the control group (without hydrochar addition), and significantly correlated with pH and ammonium–nitrogen (NH4+–N) concentration in floodwater. Nitrogen (N) loss via NH3 volatilization in the control group accounted for 24.9% of the applied N fertilizer, whereas CMBSH- and ZHC-amended treatments accounted for 13.6−17.9% of N in applied fertilizer. The reduced N loss improved soil N retention and availability for rice; consequently, grain N content significantly increased by 6.5–14.9% and N-use efficiency increased by 6.4–16.0% (P < 0.05), respectively. Based on linear fitting results, NH3 volatilization mitigation resulted from lower pH and NH4+–N concentration in floodwater that resulted from the acidic property and specific surface area of hydrochar treatments. Moreover, NH3-oxidizing archaea abundance in hydrochar-treated soil decreased by 40.9–46.9% in response to CMBSH and ZHC treatments, potentially suppressing NH4+–N transformation into nitrate and improving soil NH4+–N retention capacity. To date, this study applied biogas slurry-based hydrochar into paddy soil for the first time and demonstrated that ZHC significantly mitigated NH3 and increased N content. Overall, this study proposes an environmental-friendly strategy to recycle the wastes, biogas slurry, to the paddy fields to mitigate NH3 volatilization and increase grain yield of rice.

One-time application of controlled-release bulk blending fertilizer enhances yield, quality and photosynthetic efficiency in late japonica rice

Controlled-release urea (CRU) releases nitrogen (N) at the same pace that rice takes it up, which can effectively improve N use efficiency, increase rice yield and improve rice quality. However, few studies have described the effects of CRU application on the photosynthetic rate and endogenous enzyme activities of rice. Accordingly, a two-year field trial was conducted with a total of seven treatments: CK, no N fertilizer; BBF, regular blended fertilizer; RBBF, 20% N-reduced regular blended fertilizer; CRF1, 70% CRU+30% regular urea one-time base application; CRF2, 60% CRU+40% regular urea one-time base application; RCRF1, CRF1 treatment with 20% N reduction; and RCRF2, CRF2 treatment with 20% N reduction. Each treatment was conducted in triplicate. The results showed that the N recovery efficiency (NRE) of the controlled-release bulk blending fertilizer (CRBBF) treatments was significantly greater over the two years. There were significant yield increases of 4.1–5.9% under the CRF1 treatment and 5.6–7.6% under the CRF2 treatment compared to the BBF treatment, but the differences between the reduced-N treatments RBBF and RCRF2 were not significant. Photosynthetic rates under the CRF1 and CRF2 treatments were significantly higher than under the other treatments, and they had significantly greater RuBPCase, RuBisCO, glutamate synthase (GOGAT) and glutamine synthetase (GS) enzyme activities. Additionally, the soil NH4+-N and NO3−-N contents under the CRBBF treatments were significantly higher at the late growth stage of rice, which was more in-line with the fertilizer requirements of rice throughout the reproductive period. CRBBF also led to some improvement in rice quality. Compared with the BBF and RBBF treatments, the protein contents under the CRBBF treatments were reduced but the milling, appearance, eating and cooking qualities of the rice were improved. These results showed that the application of CRBBF can improve the NRE, photosynthetic rate and endogenous enzyme activities of rice, ensuring sufficient N nutrition and photosynthetic material production during rice growth and thereby achieving improved rice yield and quality.

Metagenomic insight into antagonistic effects of a nitrification inhibitor and phosphate‐solubilizing bacteria on soil protease activity

AbstractSoil protease plays a fundamental role in soil nitrogen (N) transformations. Soil N and phosphorus (P) management significantly influence soil protease activity. However, the impacts of N and P combined modification on soil protease remain unclear. A better understanding of the activity and dynamic of soil protease could provide new insights into soil N cycling and available N supply. This study aimed to quantify the influences of combined effects of N and P managements on soil protease activities and decipher the potential mechanism from the perspectives of soil chemical properties, functional microbes, and functional genes. The nitrification inhibitor 3, 4‐dimethylpyrazole phosphate (DMPP) application or phosphate‐solubilizing bacteria (PSB) Klebsiella inoculation significantly increased soil protease activity (23.39% and 70.99%, respectively) and ammonium N (NH4+–N) contents, relative to the blank control. However, compared with the DMPP or PSB alone application, the combined applications of DMPP and PSB significantly decreased protease activity, implying that an antagonistic effect on soil protease activity was generated. The abundances of genus Klebsiella were stimulated by the DMPP or PSB but significantly inhibited by the combined additions of DMPP and PSB. The DMPP and PSB applications also significantly changed soil microbial communities and led to more complicated soil microbial co‐occurrence networks. Soil protease activity had a significantly positive correlation with the normalized abundances of tri and clpX genes. Our findings suggested that the combined additions of DMPP and PSB generated an antagonistic effect on soil protease activity and that the antagonistic effect was directly associated with soil NH4+–N and NO3−–N contents, P fractions, and functional gene abundances.

Single-Time Mechanical Deep Placement Fertilization Using Bulk Blending Fertilizer on Machine-Transplanted Rice: Balanced Yield, Nitrogen Utilization Efficiency, and Economic Benefits

Despite growing interest in controlled-release N fertilizers (CRNFs) because of their potential for enhancing nitrogen use efficiency (NUE) and economic returns, their comprehensive impact on machine-transplanted rice remains to be understudied. To address this gap, here, we present a two-year field experiment that assessed the impact of CRNF using mechanical deep placement fertilization (DPF) on rice cultivation. The study involved three CRNF types (bulk blending fertilizer (BBF), polymer-coated urea (PCU), and sulfur-coated urea (SCU)) and two fertilization methods (DPF and broadcast application), with a high-yield split fertilization of urea as a control (CK). The results showed that DPF, especially with SCU, greatly enhanced soil NH4+-N concentrations, NUE, rice yield, and economic benefits compared to broadcast application. BBF consistently exhibited superior NUE and notable economic benefits, regardless of the application method used. Conversely, single-time application of PCU was less favorable for rice growth. In conclusion, for optimal economic benefits and NUE, DPF combined with single-time application of SCU is recommended. However, if deep application is not feasible and only broadcasting is possible in rice cultivation, BBF emerges as the ideal choice for both high NUE and significant economic returns. This research offers insights for improved nitrogen management in machine-transplanted rice, effectively optimizing yield, NUE, and profitability.

Soil biota associated with soil N cycling under multiple anthropogenic stressors in grasslands

Soil nitrogen (N) processes and statuses are two essential components for soil N cycling in terrestrial ecosystems. Although studies have estimated the effects of multiple anthropogenic stressors (e.g., nutrient enrichment and soil acidification) on soil N cycling, how multiple trophic levels of soil biota regulate the responses of soil N processes and statuses under multiple anthropogenic stressors has not yet been studied. We established an N and phosphorus (P) enrichment and acid addition experiment in a semi-arid grassland on the Mongolian Plateau. After five years, our results showed that soil acidification strongly inhibited soil N processes (via decreasing N mineralization rate, potential nitrification rate, and potential denitrification rate) and soil N statuses (via decreasing dissolved organic N, NO3−-N, and microbial biomass N). Acid addition-induced declines in soil N processes or N statuses were mainly associated with the inhibition of the abundance/richness of soil N-related bacteria and nematodes. Compared with soil acidification, N or P enrichment had relatively minor effects on soil N processes or N statuses, except for the N enrichment-induced decline in the potential nitrification rate and increase in soil NH4+-N and P enrichment-induced decline in soil NO3−-N. Furthermore, we found that the responses of soil N processes or statuses to nutrient enrichment were different between non-acidified soils and acidified soils. Overall, our results evidenced that soil biota strongly mediated the responses of soil N processes and statuses to nutrient enrichment and acid addition in semi-arid grasslands, and soil acidification weakened the associations between soil biota and soil N cycling. These findings indicate that we should concentrate more on the importance of soil biota in maintaining ecosystem N functions and services against a background of global change.

Electrical signal of pepper during cropping period affected by different amount of fertilizer

Precision agriculture requires supply of adequate amount of fertilizer application to increase crop yield and prevent environmental contamination. Objective of the study was to evaluate response of pepper under different fertigation method and amount using plant induced electrical signal (PIES) for precision agriculture. Pepper was fertigated 10 times with recommended additional nitrogen fertilizer and set as a control. Low fertilizer treatment did not receive additional urea and high fertilizer received three times higher amount of nitrogen fertilizer. Conventional treatment was fertigated as basal fertilizer and once with additional fertilizer. The PIES decreased during vegetative stage and remained constant at reproductive stage because of reduced nutrient and water uptake. The PIES showed positive relationship with soil NH4+, NO3−, stem NO3− and leaf N, which resulted in highest PIES value during reproductive stage in high fertilizer treated pepper. Plant growth parameters were also related with the PIES although yield was not affected by different fertilizer treatment.

Metagenomics reveals the effects of glyphosate on soil microbial communities and functional profiles of C and P cycling in the competitive vegetation control process of Chinese fir plantation

Although considerable efforts have been devoted to investigate the behavior of glyphosate on microbiome in various environment, knowledge about the soil microbial community and functional profile in weeds control process of the Chinese fir plantation are limited. In this study, shotgun metagenomic sequencing was used to determine the abundance and diversity of microbial communities and functional genes after foliar application of glyphosate for 1, 2, 3 and 4 months in a Chinese fir plantation. The results showed that glyphosate increased the copy numbers (qPCR) of 16S rRNA gene for 16.9%, improved the bacterial diversity (Shannon index) and complexity of bacterial co-occurrence network, and changed the abundances of some bacterial and fungal taxa, but had no effects on ITS gene copy numbers, fungal Shannon index, and bacterial and fungal communities (PCoA). Glyphosate application significantly decreased the amount of microbial function potentials involved in organic P mineralization for 10.7%, chitin degradation for 13.1%, and CAZy gene families with an exception of PL for 11.5% at the first month, while did not affect the profile of microbial genes response to P and C cycling in longer term. In addition, glyphosate reduced the contents of soil TOC, DOC and NH4+-H for 17.6%, 52.3% and 44.6% respectively, and decreased the starch, soluble sugar, Zn and Fe of Chinese fir leaves for 20.6%, 19.8%, 32.8% and 48.4% respectively. Mantle test, Spearman's correlation, and PLS-PM model revealed the connections among soil properties, tree nutrients, bacterial and fungal communities, and microbial function potentials were influenced by glyphosate. While our findings need to be validated in other filed and mechanistic studies, they may indicate that the foliar application of glyphosate has a potential effect on Chinese fir seedlings, and this effect may contribute to the changes of the bacterial community and soil properties including AN, DON and NH4+-H.

Poly-γ-glutamic acid affects NH3 volatilization, soil nitrogen content, and soybean seedling growth

Abstract Poly-γ-glutamic acid (γ-PGA) is a soil amendment that has been shown to enhance soil water retention capacity. However, the effects of γ-PGA on soil NH3 volatilization, soil nitrogen pool, and crop growth have been rarely studied. This study aimed to investigate the effect of γ-PGA on NH3 volatilization, soil mineral nitrogen content, and soybean seed productivity. We conducted an incubation experiment and a pot experiment using two different textured soils (sandy soil and sandy loam soil) with four γ-PGA application rates (0, 0.1, 0.3, and 0.5%, w/w). The results showed that the application of γ-PGA decreased the peak value of NH3 volatilization and cumulative NH3 emission through the incubation experiment. Cumulative NH3 volatilization decreased with increasing γ-PGA application amount. The addition of γ-PGA to sandy soil and sandy loam soil increased soil N content by 17–63% and 7–33%, respectively. Based on pot experimental results and principal component analysis, we recommend the optimal rates of γ-PGA application were 0.3% (w/w) in sandy soil and 0.1% (w/w) in sandy loam soil. This study provides a theoretical basis for the addition of γ-PGA as a promising strategy to reduce NH3 volatilization and increase soil nitrogen content.

Effects of microplastics exposure on soil inorganic nitrogen: A comprehensive synthesis

Microplastics, a growing environmental concern, impact soil inorganic nitrogen (N) transformation, specifically affecting water-extractable nitrate N (NO3−−N) and ammonium N (NH4+−N). However, inconsistencies among relevant findings necessitate a systematic analysis. Accordingly, the present meta-analysis addresses these discrepancies by evaluating the effects of microplastics on soil inorganic N and identifying key influencing factors. Our meta-analysis of 216 paired observations from 47 studies demonstrates microplastics exposure causes an overall significant reduction of 7.89% in soil NO3−−N concentration, but has no significant impact on NH4+−N concentration. Subgroup analysis further revealed effects of microplastics on soil inorganic N were modulated by microplastics characteristics, experimental conditions (exposure time, experimental temperature, plant effects), and soil properties (soil texture, initial soil pH, initial soil organic carbon, soil total N concentration). We found that microplastics exposure above 27 ℃ enhances soil NO3−−N concentration, a finding linked to specific soil properties and conditions, underscoring the impacts of global warming. Importantly, the microplastics polymer type was the most influential predictor of effects on soil NO3−−N concentration, while soil NH4+−N concentration was primarily affected by soil texture and microplastics type. These findings illuminate the complex effects of microplastics on soil inorganic N, informing soil management amid increasing microplastics pollution.

Effects of rainfall amount and frequencies on soil net nitrogen mineralization in Gahai wet meadow in the Qinghai-Tibetan Plateau

Global climate change has led to a significant increase in the frequency of extreme rainfall events in the Qinghai-Tibetan Plateau (QTP), thus potentially increasing the annual rainfall amounts and, consequently, affecting the net soil nitrogen (N) mineralization process. However, few studies on the responses of the soil net N mineralization rates to the increases in rainfall amounts and frequencies in alpine wet meadows have been carried out. Therefore, the present study aims to assess the effects of rainfall frequency and amount changes on the N fixation capacity of wet meadow soils by varying the rainfall frequency and amount in the Gahai wet meadow in the northeastern margin of the QTP during the plant-growing season in 2019. The treatment scenarios consisted of ambient rain (CK) and supplementary irrigation at a rate of 25 mm, with different irrigation frequencies, namely weekly (DF1), biweekly (DF2), every three weeks (DF3), and every four weeks (DF4). According to the obtained results, the increased rainfall frequency and amount decreased the soil mineral N stock and increased the aboveground vegetation biomass (AB) amounts and soil water contents in the wet meadows of the QTP. Ammonium (NH4+-N) and nitrate N (NO3–-N) contributed similarly to the mineral N contents. However, the ammonification process played a major role in the soil mineralization process. The effects of increasing rainfall amount and frequency on N mineralization showed seasonal variations. The N mineralization rate showed a single-peaked curve with increasing soil temperature during the rapid vegetation growth phase, reaching the highest value in August. In addition, the N mineralization rates showed significant positive correlations with soil temperatures and NH4+-N contents and a significant negative correlation with AB (P < 0.05). The results of this study demonstrated the key role of low extreme rainfall event frequencies in increasing the net soil N mineralization rates in the vegetation growing season, which is detrimental to soil N accumulation, thereby affecting the effectiveness of soil N contents.

Polyamine-producing bacteria inhibit the absorption of Cd by spinach and alter the bacterial community composition of rhizosphere soil

Polyamines (PAs) are small aliphatic nitrogenous bases with strong biological activity that participate in plant stress response signaling and the alleviation of damage from stress. Herein, the effects of the PA-producing bacterium Bacillus megaterium N3 and PAs on the immobilization of Cd and inhibition of Cd absorption by spinach and the underlying mechanisms were studied. A solution test showed that strain N3 secreted spermine and spermidine in the presence of Cd. Both strain N3 and the PAs (spermine+spermidine) immobilized Cd and increased the pH of the solution. Untargeted metabolomics results showed that strain N3 secreted PAs, N1-acetylspermidine, 3-indolepropionic acid, indole-3-acetaldehyde, cysteinyl-gamma-glutamate, and choline, which correlated with plant growth promotion and Cd immobilization. A pot experiment showed that rhizosphere soil inoculation with strain N3 and PAs improved spinach dry weight and reduced spinach Cd absorption compared with the control. These positive effects were likely due to the increase in rhizosphere soil pH and NH4+-N and PA contents, which can be attributed primarily to Cd immobilization. Moreover, inoculation with strain N3 more effectively inhibited the absorption of Cd by spinach than spraying PAs, mainly because strain N3 enabled a better relative abundance of bacteria (Microvirga, Pedobacter, Bacillus, Brevundimonas, Pseudomonas, Serratia, Devosid, and Aminobacter), that have been reported to have the ability to resist heavy metals and produce PAs. Strain N3 regulated the structure of rhizosphere functional bacterial communities and inhibited Cd uptake by spinach. These results provide a theoretical basis for the prevention of heavy metal absorption by vegetables using PA-producing bacteria.

The effect of afforestation type on soil nitrogen dynamics in the riparian zone of the upper Yangtze River of China

Afforestation is increasingly important in nutrient cycling in riparian ecotones given that ecosystems in riparian zones are susceptible to anthropogenic activities induced by land use change. However, how land use change (e.g., afforestation) with different planting types influences nitrogen (N) dynamics in riparian zones remains unclear. Here, we examined soil N dynamics following afforestation with three types of plantations of pure willow (Salix babylonica), pure mulberry (Morus alba), and the mixed two species paired with adjacent maize croplands in the upper Yangtze River of China. Our results showed afforestation with the two pure species significantly reduced soil total N (TN) concentration. Soil NO3−-N concentration was significantly reduced by the willow and mixed-species afforestation, but soil NH4+-N concentration was significantly higher in the willow and mixed woodlands compared to the paired croplands. Soil N concentrations were tightly associated with the potential N transformation rates, which showed a roughly decreasing trend in N mineralization following afforestation. Soil properties, microbial biomass, and extracellular enzymes jointly explained a large proportion of the total variation in soil N concentrations, with soil enzymes largely contributing to N variation in the topsoil and soil properties primarily contributing to N variation in the subsoil. Overall, our results demonstrate that afforestation with different planting types had contrasting effects on soil N content in the riparian zone. These findings provide new insights into the management of afforestation types to retain soil N by mediating soil properties and microbial activities in the riparian zones under future land use change.

Impact of nitrogen and phosphorus additions on soil gross nitrogen transformations in a temperate desert steppe

AbstractNutrient addition has a significant impact on plant growth and nutrient cycling. Yet, the understanding of how the addition of nitrogen (N) or phosphorus (P) significantly affects soil gross N transformations and N availability in temperate desert steppes is still limited. Therefore, a 15N tracing experiment was conducted to study these processes and their underlying mechanism in a desert steppe soil that had been supplemented with N and P for 4 years in northwestern China. Soil N mineralization was increased significantly by P addition, and N and P additions significantly promoted soil autotrophic nitrification, rather than NH4+‐N immobilization. The addition of N promoted dissimilatory NO3− reduction to NH4+, while that of P inhibited it. Soil NO3−‐N production was greatly increased by N added alone and by that of N and P combined, while net NH4+‐N production was decreased by these treatments. Soil N mineralization was primarily mediated by pH, P content or organic carbon, while soil NH4+‐N content regulated autotrophic nitrification mainly, and this process was mainly controlled by ammonia‐oxidizing bacteria rather than archaea and comammox. NH4+‐N immobilization was mainly affected by functional microorganisms, the abundance of narG gene and comammox Ntsp‐amoA. In conclusion, gross N transformations in the temperate desert steppe largely depended on soil inorganic N, P contents and related functional microorganisms. Soil acidification plays a more key role in N mineralization than other environmental factors or functional microorganisms.

N-loaded clinoptilolite under water-saving irrigation mitigates ammonia volatilization while increasing grain yield and water-nitrogen use efficiency

Minimizing ammonia volatilization (AV) in paddy fields can not only reduce nitrogen (N) loss but also prevent environmental pollution. While clinoptilolite has been shown to effectively decrease AV, it is important to note that natural clinoptilolite contains non-desorption active sites that can hinder soil N effectiveness, ultimately leading to decreased N utilization. Therefore, we proposed modifying clinoptilolite with a weakly acidic NH4Cl solution (N-loaded clinoptilolite, NZ) to replenish exogenous N while continuously reducing AV. A lysimeter experiment was conducted under two irrigation regimes (ICF: continuous flooding irrigation; IAWD: alternate wet-dry irrigation) to examine the effect of N-loaded clinoptilolite on soil N, water-N use, AV loss and grain yield over two rice-growing seasons in Northeast China. The results show that AWD significantly reduced AV during the basal fertilization period and the first top-dressing period in 2020 and 2021. Compared with the control (without N-loaded clinoptilolite), N-loaded clinoptilolite at 10 t·ha−1 (NZ10) significantly reduced the total AV by 29% and 33% in the two years, respectively, with the most significant reduction impact (30% and 36%) occurring in the first top-dressing period. NZ10 coupled with AWD regime reduced AV more significantly and compared with conventional management (ICFNZ0), IAWDNZ10 decreased the total amount of AV by 36% and 42% in two years, respectively. N-loaded clinoptilolite also increased the soil NH4+-N and NO3--N content during the tillering and grain-filling stages of rice, which in turn increased the rate of maximum N accumulation, shortened the duration, promoted N accumulation and translocation in rice plants, and finally reduced AV. Additionally, when compared to the control, the utilization of NZ10 under the AWD irrigation regime resulted in an average 29% reduction in irrigation water usage and a yield increase of 5% over two years. Thus, IAWDNZ10 was not only highly productive and water-efficient but also significantly reduced AV, making it an environmentally friendly and effective management model for on-farm practices.

Tree-Structured Parzan Estimator–Machine Learning–Ordinary Kriging: An Integration Method for Soil Ammonia Spatial Prediction in the Typical Cropland of Chinese Yellow River Delta with Sentinel-2 Remote Sensing Image and Air Quality Data

Spatial prediction of soil ammonia (NH3) plays an important role in monitoring climate warming and soil ecological health. However, traditional machine learning (ML) models do not consider optimal parameter selection and spatial autocorrelation. Here, we present an integration method (tree-structured Parzen estimator–machine learning–ordinary kriging (TPE–ML–OK)) to predict spatial variability of soil NH3 from Sentinel-2 remote sensing image and air quality data. In TPE–ML–OK, we designed the TPE search algorithm, which encourages gradient boosting decision tree (GBDT), random forest (RF), and extreme gradient boosting (XGB) models to pay more attention to the optimal hyperparameters’ high-possibility range, and then the residual ordinary kriging model is used to further improve the prediction accuracy of soil NH3 flux. We found a weak linear correlation between soil NH3 flux and environmental variables using scatter matrix correlation analysis. The optimal hyperparameters from the TPE search algorithm existed in the densest iteration region, and the TPE–XGB–OK method exhibited the highest predicted accuracy (R2 = 85.97%) for soil NH3 flux in comparison with other models. The spatial mapping results based on TPE–ML–OK methods showed that the high fluxes of soil NH3 were concentrated in the central and northeast areas, which may be influenced by rivers or soil water. The analysis result of the SHapley additive explanation (SHAP) algorithm found that the variables with the highest contribution to soil NH3 were O3, SO2, PM10, CO, and NDWI. The above results demonstrate the powerful linear–nonlinear interpretation ability between soil NH3 and environmental variables using the integration method, which can reduce the impact on agricultural nitrogen deposition and regional air quality.

Towards Improved Grain Yield and Soil Microbial Communities of Super Hybrid Rice through Sustainable Management

Superior yields of super hybrid rice have demonstrably contributed to contemporary food security. Despite this, the extent to which intensive nitrogen fertilizer requirements of such crops have impacted on soil health and microbial communities primarily remains unchartered territory, evoking questions of sustainability. Here, we examine how four management treatments (zero fertilizer, CK; farm practice, FP; high-yield and high-efficiency, HYHE; and super-high-yield management, SHY) influenced the grain yields, soil biodiversity and community strata underpinning soil health of an elite super hybrid rice variety (Y-liangyou 900). We show that SHY treatments increased yields, altered soil physicochemical properties, and fostered greater biodiversity and soil bacteria and fungi abundance, while FP, HYHE and SHY treatments transformed community bacteria and fungi strata. Environmental regulators of bacterial and fungal communities differed widely, with bacterial communities most closely associated with soil organic carbon (SOC) and NH4+-N, and with fungal communities more related to available phosphorus. We show that alpha diversity of bacteria and fungi and community composition of fungi were positively correlated with yield, but bacterial community composition was negatively correlated with yield. Our work clearly exemplifies the nexus between appropriate farm and landscape management in enabling soil health and driving consistently high yields, of which both are required for sustainable food security.

Prolonged flooding followed by drying increase greenhouse gas emissions differently from soils under grassland and arable land uses

Several climate change scenarios have predicted that heavy precipitation could result in prolonged flooding (PF) and flooding–drying (FD) of soils under agriculture. The influence of PF and FD on soil greenhouse gas (GHG) fluxes and ammonium‑nitrogen (NH4+-N) and nitrate‑nitrogen (NO3−-N) dynamics of arable and grassland soils, the dominant land-use types in the UK, remain unclear. A two-month soil incubation experiment was conducted to determine the impact of PF and FD on soil N dynamics and GHG fluxes from arable and grassland soils. Arable soil emitted more N2O-N when soil moisture exceeded 100% water-holding capacity (WHC) compared to grassland soil under PF. Grassland soils exhibited increased N2O-N emissions than arable soils when soil moisture was lower than 100% WHC under FD. When soil moisture exceeded 100% WHC, the available NO3−-N in the soil contributed 58% of N2O-N emissions potentially by denitrification from grassland. When soil moisture was lower than 100% WHC, soil NH4+-N and NO3−-N contributed 71% of N2O-N emissions, which suggests coupling of nitrification-denitrification processes in driving high emissions from grassland soils. The N2O-N and CO2-C emissions increased with the incubation time under FD. Moreover, FD significantly increased N2O-N, CO2-C, and CH4-C emissions in grassland soil by 0.93, 2.15, and 37.29 times more than arable soil, respectively. These findings points to important tipping points in the source strengths of GHG fluxes from the two land use types differently. Future land use changes should consider the contribution of the changing dynamics of GHG fluxes in light of climate extremes and its implications for net zero greenhouse gas emission ambitions.