Nitrification inhibitor (NI) is often claimed to be efficient in mitigating nitrogen (N) losses from agricultural production systems by slowing down nitrification. Increasing evidence suggests that ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) have the genetic potential to produce nitrous oxide (N₂O) and perform the first step of nitrification, but their contribution to N₂O and nitrification remains unclear. Furthermore, both AOA and AOB are probably targets for NIs, but a quantitative synthesis is lacking to identify the “indicator microbe” as the best predictor of NI efficiency under different environmental conditions. In this present study, a meta-analysis to assess the response characteristics of AOB and AOA to NI application was conducted and the relationship between NI efficiency and the AOA and AOB amoA genes response under different conditions was evaluated. The dataset consisted of 48 papers (214 observations). This study showed that NIs on average reduced 58.1% of N₂O emissions and increased 71.4% of soil NH4+ concentrations, respectively. When 3, 4-dimethylpyrazole phosphate (DMPP) was applied with both organic and inorganic fertilizers in alkaline medium soils, it had higher efficacy of decreasing N₂O emissions than in acidic soils. The abundance of AOB amoA genes was dramatically reduced by about 50% with NI application in most soil types. Decrease in N₂O emissions with NI addition was significantly correlated with AOB changes (R² = 0.135, n = 110, P < 0.01) rather than changes in AOA, and there was an obvious correlation between the changes in NH4+ concentration and AOB amoA gene abundance after NI application (R² = 0.037, n = 136, P = 0.014). The results indicated the principal role of AOB in nitrification, furthermore, AOB would be the best predictor of NI efficiency.

Cadmium (Cd) contamination in agricultural soils is a common issue, posing health risks as it enters the human body through the food chain. Commonly used phosphate fertilizers (PFs) not only provide essential phosphorus (P) nutrients to crops but also serve as P-containing materials for immobilizing heavy metals (HMs) like Cd in soils. Therefore, understanding the passivation effects of PFs on soil Cd and their potential influencing factors is crucial for mitigating soil Cd pollution. In this study, the impact of multi-crop applications (75 mg P kg⁻¹, 150 mg P kg⁻¹) of four kinds of PFs on reducing soil Cd toxicity and decreasing Cd accumulation in spinach was investigated. The results indicated that under the low application rate (75.0 mg P kg⁻¹), all PFs could passivate Cd, and CMP demonstrated the most effective passivation of Cd. However, under the high application rate (150 mg P kg⁻¹), the immobilization effect diminished or even activated Cd. Among the different types of PFs, CMP application alleviated soil acidification and significantly reduced soil-available Cd, showing the best performance in promoting spinach growth and Cd inhibition. These results suggest that PF application in Cd-contaminated soils affects spinach growth and Cd accumulation, with soil pH, available phosphorus (AP), and Cd dynamics being crucial; moreover, low-P, micronutrient-rich, alkaline PFs like CMP optimize spinach yields and minimize Cd uptake, and excessive application of soluble PFs decreases pH, increases Cd mobility, and poses health risks, suggesting a need for balanced fertilizer use.

As global efforts to combat climate change intensify, agricultural emissions are increasingly scrutinized. Biogas slurry (BS), a by-product of agricultural waste, not only provides essential nutrients for crops but can also elevate soil nitrous oxide (N₂O) emissions. This study investigates the immediate and long-term impacts of BS application on N₂O emissions, taking into account the frequency of application and evaluating the effectiveness of nitrification inhibitor 3,4-dimethylpyrazole-phosphate (DMPP) in reducing emissions. Through a microcosm incubation experiment with a 108 h robotized incubation-monitoring system, it was found that N₂O emissions spiked immediately following a single BS application, with emissions decreasing within 30 days. Repeated BS applications yielded lower cumulative emissions. Elevated N₂O emissions were linked to higher soil pH and ammonium (NH₄⁺) levels, along with reduced nitrate (NO₃⁻) concentrations after a single BS application. The combined application of BS and DMPP proved most effective in inhibiting nitrification and cumulative N₂O emissions, achieving reductions of 63.0% and 94.6%, respectively. High soil pH, NH₄⁺, and low NO₃⁻ were identified as pivotal factors in this effect. These findings highlight the need for mitigation strategies such as dilution or splitting applications to reduce emissions. Integrating BS with DMPP offers a sustainable approach to achieving both agricultural and environmental goals.

Nitrogen (N) availability is generally a limiting factor in highly acidic soil, which could be improved by amending these soils with alkaline materials. Soil extracellular enzyme activity (EEA) plays an important role in N transformation; a current knowledge gap is how this occurs in acidic soils amended with alkaline material. The present 45-day incubation experiment was designed to examine the effects of different amounts of alkaline materials (urea and/or calcium–silicon–magnesium–potassium fertilizer (CSMP)) on N transformation. The results show that soil pH significantly increased after the CSMP amendment (1.2 units) and increased soil net N mineralization (R_min), net nitrification (R_nit) rates, and net ammonification (R_amo) rates. CSMP amendment changed the different soil EEA but with differing or opposing effects, e.g., R_nit was positively correlated with the activities of L-leucine aminopeptidase, β-xylosidase, α-glucosidase, and N-acetyl-β-glucosaminidase but negatively correlated with β-1, 4-glucosidase and β-cellobiosidase. A machine learning analysis indicated that the best predictor for R_min and R_amo was soil pH, and for R_nit, it was nitrate. The results of the present study improve our understanding of N availability in acidic soils amended with materials to control soil pH. Such knowledge could lead to more bespoke nutrient management planning at the field scale, leading to better agronomic and environmental outcomes.

Nitrous oxide (N₂O) is a potent greenhouse gas with intensive emissions from acidic soil. This study explored the impact of the disruption of the microbial balance from microbial inhibitors (streptomycin and cycloheximide) on soil’s N₂O emission and nitrogen (N) dynamics. Under all the conditions examined, biotic processes accounted for 96–98% of total N₂O emissions. High concentrations of streptomycin (6 and 10 mg g⁻¹) reduced N₂O emissions from 2.24 μg kg⁻¹ h⁻¹ to 1.93 μg kg⁻¹ h⁻¹ and 2.12 μg kg⁻¹ h⁻¹, respectively, whereas lower concentrations (2 and 4.5 mg g⁻¹) increased emissions from 2.24 μg kg⁻¹ h⁻¹ to 2.95 μg kg⁻¹ h⁻¹ and 3.27 μg kg⁻¹ h⁻¹, respectively. Lower cycloheximide (2 and 4.5 mg g⁻¹) significantly enhanced N₂O emissions, reaching 9.15 μg kg⁻¹ h⁻¹ and 5.68 μg kg⁻¹ h⁻¹, respectively, whereas higher dosages (6 mg g⁻¹ and 10 mg g⁻¹) inhibited N₂O emissions, reducing them to 5.55 μg kg⁻¹ h⁻¹ and 4.84 μg kg⁻¹ h⁻¹, respectively. Carbon dioxide (CO₂) emissions generally decreased with increasing inhibitor dosages but significantly increased at 2 mg g⁻¹ and 4.5 mg g⁻¹ streptomycin. The inhibitors also altered soil N and carbon (C) dynamics, increasing ammonium (NH₄⁺-N), dissolved organic nitrogen (DON), and dissolved organic carbon (DOC) levels. Pearson correlation analysis indicated that N₂O emission was negatively correlated with cycloheximide dosage (R = −0.68, p < 0.001), NH₄⁺-N (R = −0.31, p < 0.001) and DOC content (R = −0.57, p < 0.05). These findings highlight the consequences of microbial disruption on N₂O emission and the complex microbial interactions in acidic soils. High concentrations of microbial inhibitors effectively reduce N₂O emissions by suppressing key microbial groups in nitrification and denitrification. Conversely, lower concentrations may prompt compensatory responses from surviving microorganisms, resulting in increased N₂O production. Future research should focus on sustainable management strategies to mitigate N₂O emissions while preserving the soil’s microbial community.