Effects of a nitrification inhibitor on nitrogen species in the soil and the yield and phosphorus uptake of maize

Factors regulating interaction among inorganic nitrogen and phosphorus species, plant uptake, and relevant cycling genes in a weakly alkaline soil treated with biochar and inorganic fertilizer

To highlight how biochar affects the interaction between inorganic nitrogen species (ammonium nitrogen, nitrate nitrogen, and nitrite nitrogen: NH4+-N, NO3¯-N, and NO2¯-N) and phosphorus species (calcium phosphate, iron phosphate, and aluminum phosphate: CaP, FeP and AlP) in soil and plant uptake of these nutrients, walnut shell (WS)- and corn cob (CC)-derived biochars (0.5 %, 1 %, 2 %, and 4 %, w/w) were added to a weakly alkaline soil, and then Chinese cabbages were planted. The results showed that the changes in soil inorganic nitrogen were related to biochar feedstock, pyrolysis temperature, and application rate. For soil under the active nitrification condition (dominant NO3¯-N), a significant decrease in the NH4+-N/NO3¯-N ratio after biochar addition indicates enhanced nitrification (excluding WS-derived biochars at 2 % and 4 %), which can be explained by the most positive response of ammonia-oxidizing archaeal amoA to biochar addition. The CC-derived biochar more effectively enhanced soil nitrification than WS-derived biochar did. The addition of 4 % of biochars significantly increased soil inorganic phosphorus, and the addition of CC-derived biochars more effectively increased Ca2P than WS-derived biochars. Biochars significantly decreased plant uptake of phosphorus, while generally had little influence on plant uptake of nitrogen. Interestingly, NO2¯-N in soil significantly positively correlated with total phosphorus in both soil and plant, and significantly negatively correlated with phoC, indicating that a certain degree of NO2¯-N accumulation in soil slightly facilitated plant uptake of phosphorus but inhibited phoC-harboring bacteria. The NO3¯-N in soil significantly positively correlated with Ca2P and Ca8P, while the NH4+-N/NO3¯-N ratio significantly negatively correlated with Ca10P and FeP, indicating that the enhanced nitrification seemed to facilitate the change in phosphorus to readly available ones. This study will help determine how to scientifically and rationally use biochar to regulate inorganic nitrogen and phosphorus species in soil and plant uptake of these nutrients.

Integrative knowledge-based nitrogen management practices can provide positive effects on ecosystem nitrogen retention

Knowledge-based nitrogen (N) management provides better synchronization of crop N demand with N supply to enhance crop production while reducing N losses. Yet, how these N management practices contribute to reducing N losses globally is unclear. Here we compiled 5,448 paired observations from 336 publications representing 286 sites to assess the impacts of four common knowledge-based N management practices, including balanced fertilization, organic fertilization, co-application of synthetic and organic fertilizers, and nitrification inhibitors, on global ecosystem N cycling. We found that organic and balanced fertilization rather than N-only fertilization stimulated soil nitrate retention by enhancing microbial biomass, but also stimulated soil N leaching and emissions relative to no fertilizer addition. Nitrification inhibitors, however, stimulated soil ammonium retention and plant N uptake while reducing N leaching and emissions. Therefore, integrative application of knowledge-based N management practices is imperative to stimulate ecosystem N retention and minimize the risk of N loss globally.

Enhancing Phosphorus and Nitrogen Uptake in Maize Crops with Food Industry Biosolids and Azotobacter nigricans

The problem of phosphorus and nitrogen deficiency in agricultural soils has been solved by adding chemical fertilizers. However, their excessive use and their accumulation have only contributed to environmental contamination. Given the high content of nutrients in biosolids collected from a food industry waste treatment plant, their use as fertilizers was investigated in Zea mays plants grown in sandy loam soil collected from a semi-desert area. These biosolids contained insoluble phosphorus sources; therefore, given the ability of Azotobacter nigricans to solubilize phosphates, this strain was incorporated into the study. In vitro, the suitable conditions for the growth of Z. mays plants were determined by using biosolids as a fertilizer and A. nigricans as a plant-growth-promoting microorganism; in vitro, the ability of A. nigricans to solubilize phosphates, fix nitrogen, and produce indole acetic acid, a phytohormone that promotes root formation, was also evaluated. At the greenhouse stage, the Z. mays plants fertilized with biosolids at concentrations of 15 and 20% (v/w) and inoculated with A. nigricans favored the development of bending strength plants, which was observed on the increased stem diameter (>13.5% compared with the negative control and >7.4% compared with the positive control), as well as a better absorption of phosphorus and nitrogen, the concentration of which increased up to 62.8% when compared with that in the control treatments. The interactions between plants and A. nigricans were observed via scanning electron microscopy. The application of biosolids and A. nigricans in Z. mays plants grown in greenhouses presented better development than when Z. mays plants were treated with a chemical fertilizer. The enhanced plant growth was attributed to the increase in root surface area.

Soft X-ray Fluorescence and Near-Edge Absorption Microscopy for Investigating Metabolic Features in Biological Systems: A Review

Scanning transmission X-ray microscopy (STXM) provides the imaging of biological specimens allowing the parallel collection of localized spectroscopic information by X-ray fluorescence (XRF) and/or X-ray Absorption Near Edge Spectroscopy (XANES). The complex metabolic mechanisms which can take place in biological systems can be explored by these techniques by tracing even small quantities of the chemical elements involved in the metabolic pathways. Here, we present a review of the most recent publications in the synchrotrons' scenario where soft X-ray spectro-microscopy has been employed in life science as well as in environmental research.

Investigation of the effect of nitrification inhibition on the performance and effluent quality of aerobic sequential batch reactors

The use of nitrification inhibition as a concentrating step for ammonium (NH₄⁺), for the purpose of increasing the potential for simultaneous recovery of phosphate (PO₄^3-) and NH₄⁺ from effluent streams of an aerobic sequencing batch reactor (SBR) system, has never been investigated in the literature. Therefore, the present study aimed to determine the effect of the inhibition of nitrification on both the reactor performance and effluent quality in a laboratory scale aerobic SBR system. In order to compare the observed results, a separate reactor, where the inhibition was not applied, was operated as a control reactor (CR) under the identical operational conditions used for the inhibitory reactor (IR). Experimental results for the reactor performance showed that effluents with low total suspended solids (< 50 mg/L) and chemical oxygen demand concentrations (> 90% of removal efficiency based on the influent concentration of 500 mg/L) were achieved for both SBRs by obtaining an activated sludge with a sludge volume index < 60 mL/g after the acclimation period. In the same period, the effluent PO₄^3-, NH₄⁺, and nitrate (NO₃^-) concentrations were found to be 17.0 ± 4.0, 1.26 ± 0.84, and 21.5 ± 39 mg/L for the CR and 10.0 ± 4.4, 3.9 ± 2.4, and 9.2 ± 1.5 mg/L for the IR, respectively. During this period, 94% of the removed NH₄⁺ (NH₄⁺_rem.) was converted to NO₃^- in the CR, indicating almost complete nitrification occurred in the reactor. However, only 47% of the NH₄⁺_rem. was converted to NO₃^- in the IR as a result of the inhibition of nitrification, meaning a partial inhibition (53%) occurred due to the inhibition treatment. These results clearly demonstrated that the inhibition of nitrification allowed the effluent NH₄⁺ concentrations to increase by suppressing the formation of NO₃^- ions. Based on the results, it can be concluded that inhibition of nitrification in an aerobic SBR system creates a potential for conserving the effluent NH₄⁺ concentration and increasing consecutive recovery of PO₄^3- together with NH₄⁺ from the effluent discharges.

Mitigation of nitrous oxide emission through fertigation and 'N' inhibitors - A sustainable climatic crop cultivation in tomato

The impact of nitrous oxide (N₂O) released from the fertilized agro-ecosystems are of increasing concern. Governing fertilizer requirements and utilizing nitrification inhibitors (NI) are effective methodologies to increase nitrogen retention and reduce N₂O emissions from soil. Therefore, the effect of potassium thiosulfate (KTS) and neem-coated urea (NCU) on N₂O efflux under irrigated tomato cultivation was assessed. Soil Test Crop Response (STCR) based recommendation of NPK with normal Urea and KTS at 1% of applied N (183:160:125 kg ha^-1) (STCR-U + KTS) recorded the least N₂O emission and high efficiency in suppressing the nitrate reductase activity. STCR-NCU was on par with STCR-U + KTS, reporting a higher reduction of N₂O (21.1, 31.2, and 34.4% during the basal application, 1^st and 2^nd top dressing, respectively) compared to the blanket recommendation of nutrients. Similarly, STCR-U + KTS recorded the highest reduction (26.2, 25.6, and 30.9% during the basal application, 1^st and 2^nd top dressing, respectively) after fertilizer application. Besides, the yield of tomatoes is increased in the STCR-NCU (14.08%) and STCR-U + KTS (12.48%) with good quality fruit along (AA, Lycopene, and TSS contents) with low N₂O emissions. The DeNitrification-DeComposition (DNDC) model further revealed that the simulated data and assessed findings were in good accord, proving the model's reliability and use as a tool for predicting the efficiency of fertilizer application.