Nitrogen, Volume 6, Issue 1 (March 2025) – 7 articles

The imbalanced use of fertilizers, particularly the inefficient application of nitrogen (N), has led to reduced nitrogen use efficiency (NUE), lowered crop yields and increased N losses in Nepal. This study aimed to enhance yields, NUE and farm profitability by optimizing N fertilizer rates, application timing and methods through multilocation trials and demonstrations. In 2017, 57 field trials were conducted in two mid-hill districts using a completely randomized block design. The treatments included control (CK), NPK omission (N0, P0 and K0), variable N rates (60, 120, 180 and 210 kg N ha⁻¹) and top-dressing timings (120 kg N ha⁻¹ applied at knee height and shoulder height, V6, V10 and V8 stages). A full dose of recommended P (60 kg ha⁻¹) and K (40 kg ha⁻¹) were applied at planting, while N was top-dressed in two equal splits at knee-height and shoulder-height growth stages for P and K omission treatments, as well as for treatment with variable N rates. Grain yields responded quadratically, with optimum N rates ranging from 120 to 180 kg ha⁻¹ across the districts. N applied at 120 kg ha⁻¹ and top-dressed at V6 and V10 increased maize yield by 20–25%, partial factor productivity of nitrogen (PFPN) by 12%, agronomic efficiency of nitrogen (AEN) by 21% and gross margin by 10% compared to conventional knee and shoulder height application. In 2018 and 2019, fertilizer BMPs, including V6 and V10 top-dressing and the urea briquette deep placement (UDP) were demonstrated on 102 farmers’ fields across five mid-hill districts to compare their agronomic and economic significance over traditional farmers’ practice (FP). UDP, validated in 2018 field trials, increased yields by 34% (8.8 t ha⁻¹) and urea top-dressing at V6 and V10 increased yield by 33% (8.7 t ha⁻¹) compared to FP (5.8 t ha⁻¹), reducing the average yield gap by 3.0 t ha⁻¹. Moreover, the gross margin was increased by 39% (V6 and V10) and 40% (UDP) over FP. The findings highlight the need for widespread adoption of fertilizer BMPs to close the yield gap and maximize profitability with minimal nitrogen footprint. Full article

The objective of this study was to treat groundwaters with a high initial nitrate (NO₃⁻) content (125 mg/L, and 177 mg/L) by adsorption onto a local bentonite in its raw state (RB), treated with a ratio of H₂SO₄/bentonite = 0.2 (B0.2), and another treated with a ratio of H₂SO₄/bentonite = 0.6 (B0.6). Non-linear modelling of the nitrate adsorption kinetics of two water samples showed the pseudo-first-order model was the best fit, confirming that nitrate retention on each adsorbent was due to chemisorption. The intra-particle diffusion curves were multi-linear, indicating that there are other mechanisms influencing nitrate ion adsorption on bentonite than intra-particle diffusion. The effectiveness of the adsorbents tested was in the following order: B0.6 > B0.2 > RB. This finding demonstrates that acid activation of the clay improves its characteristics. The optimal adsorbent dose was found to be 1 g/L after changing the bentonite dose from 0.1 to 4 g/L. The pH of the treatment affects nitrate removal rates. The greatest results are achieved at pH levels close to 6. It also appears that the treatment was more effective for water with low initial nitrate levels. Full article

Understanding how transport and storage conditions affect enzymatic activity is essential for accurate biomonitoring of nitrogen metabolism in plants. This study evaluated the effects of transport conditions and low-temperature storage on the enzymatic activities of nitrate reductase (NR), glutamine synthetase (GS), and phosphomonoesterase (PME) for Chloris gayana, Fraxinus uhdei, and Trifolium repens. Enzymatic activities were measured for leaf samples immediately after collection, after 18 h at room temperature, or after 18 h on ice. Additionally, samples were stored at −16 °C or −45 °C for up to 28 days. NR activity decreased to near-zero levels under all storage conditions, indicating that this enzyme is unsuitable for delayed analysis. In contrast, GS and PME activities showed species-dependent responses to storage, with increased activity observed for T. repens and C. gayana, potentially reflecting tissue degradation processes. F. uhdei exhibited greater stability in enzyme activities, suggesting a higher resilience to storage. These findings highlight the importance of minimizing storage time to preserve enzymatic integrity, particularly for NR, while providing insight into the potential for delayed analysis of GS and PME in specific species. This work offers practical recommendations for future biomonitoring efforts in nitrogen deposition studies. Full article

Climate change and anthropogenic nitrogen addition alter the soil physicochemical properties and microbial activity in oligotrophic forest soil. Unbalanced and non-selective nitrogen fertilizer application is lost as gas emissions (N₂O, NO) and also contributed to eutrophication through NO₃⁻ leachate. Similarly, NO₃⁻ infiltrates and contaminated drinking water sources lead to human thyroid dysfunction. In order to protect depleting timber growth due to nitrogen deficiency and increasing ecological concerns from nitrogen misapplication, we reviewed the effects of different synthetic nitrogen forms and levels on the biogeochemical process. In this review, we focused on the most recent findings from research articles, review articles, and meta-analyses on forest soil and also followed the complementary insights from agricultural soil so that we may be able to highlight how these observations contribute to the understanding of the forest soil nitrogen cycle. Firstly, we elaborated the role of nitrification and denitrification in the nitrogen transformation process. Secondly, we discussed the effect of different nitrogen forms and levels on nitrification and denitrification functional gene abundances. Thirdly, we analyzed the possible effect of gene abundances on the nitrogen conversion process. Finally, we revealed that different forms and levels of synthetic nitrogen not only alter the nitrogen conversion pathways by increasing the gene abundances through substrate availability but also shift the gene dominance, thereby modifying soil physicochemical properties, such as pH. This collectively changes the conditions, which are critical for gene expression potential involved in the nitrogen conversion process. These findings may create a direction for sustainable and eco-friendly fertilizer application in nitrogen-deficient soil. Full article

Nutrient management in coupled aquaponic systems presents significant challenges due to competing requirements between fish and plant production within a single-loop framework. These challenges often result in suboptimal nutrient concentrations, compromised system efficiency, and reduced yields. This critical review examines the Decoupled recirculating aquaponics system (DRAPS) as an innovative solution that separates fish and plant nutrient cycles while maintaining water recirculation benefits. This study provides a comprehensive review of DRAPS, emphasizing how its decoupled structure enhances nutrient management and promotes sustainable production. It specifically evaluates the ability of DRAPS to optimize macronutrient and micronutrient levels, control agronomic factors independently, and improve both nutrient and water use efficiency. Additionally, this review highlights the advantages of using urea as a nitrogen source, which can enhance plant productivity without compromising fish health. The findings indicate that the loops of DRAPS facilitate customized nutrient concentrations, fostering optimal growth conditions for both plants and fish. By safely incorporating urea as a nitrogen source, DRAPS increases plant productivity while reducing the risk of ammonia toxicity for fish. Furthermore, independent control over agronomic factors enhances nutrient uptake, nutrient use efficiency, and water use efficiency. This approach minimizes the risks of cross-toxicity and enables higher levels of essential micronutrients, such as iron and nickel, which are beneficial for plant health but can be toxic in coupled systems. DRAPS signifies a significant advancement in sustainable agriculture, particularly in regions with limited water and land resources. By optimizing nutrient management and supporting the high-density production of plants and fish, DRAPS presents a scalable, resource-efficient model that aligns with sustainable development goals. Its capacity for precise nutrient control with minimal environmental impact positions it as a valuable solution for sustainable, high-yield food production in resource-constrained settings. Full article

This study presents the results of two on-farm trials evaluating the efficacy of a nitrogen (N)-fixing inoculant (Methylobacterium symbioticum) applied as a foliar spray to provide N to hazelnut (Corylus avellana L.) and walnut (Juglans regia L.) trees. In the hazelnut trial, a factorial design was employed with soil N application at three levels [0 (N0), 40 (N40), and 80 (N80) kg ha⁻¹] and foliar application of the inoculant (Yes and No). The walnut trial was arranged as a completely randomized design with three treatments: the N-fixing microorganism, a seaweed extract, and a control. Soil N application significantly increased hazelnut yield in 2021 (1.99, 2.49, and 2.65 t ha⁻¹ for N0, N40, and N80, respectively) but not in 2022 (average values ranging from 0.28 to 0.33 t ha⁻¹). The inoculant application did not significantly affect hazelnut yield. In the walnut trial, no significant differences were observed among the treatments in either year. The average yields ranged from 1.72 to 2.38 t ha⁻¹ in 2021 and 0.66 to 0.84 t ha⁻¹ in 2022. Soil N application in hazelnuts tended to increase leaf N concentration and significantly increased kernel N concentration. The inoculant increased leaf N concentration in one of the three sampling dates but did not affect kernel N concentration. In walnuts, the inoculant did not increase leaf N concentration but significantly increased kernel N concentration in one of the two years. The seaweed extract did not influence walnut yield or leaf N concentration. None of the treatments in either trial consistently affected the concentration of other macronutrients and micronutrients in the leaves. Therefore, while the inoculant showed some potential to improve the N nutritional status of the trees, it did not affect the yield. Overall, the results of the inoculant application were not sufficiently compelling, indicating the need for further studies on these species before the commercial product can be confidently recommended to farmers. Full article

The application of nitrogenous fertilizer in reduced (“split”) doses of its total is suggested as a means to increase nitrogen use efficiency and rice productivity whilst reducing its environmental impact. Field trials conducted in 2022 and 2023 aimed to assess the impact of split nitrogen fertilizer applications on the productivity and nitrogen use efficiency of rice. This experiment included three nitrogen treatments (N1: control (no nitrogen); N2: 50% basal + 25% at tillering stage + 25% at panicle initiation stage (conventional method); N3: 33.33% basal + 33.33% at tillering stage + 33.33% at panicle initiation stage (equal split of nitrogen)) and four high-yielding rice varieties (V1: Super Gold 2019; V2: Super Basmati 2019; V3: Noor Basmati 2017; V4: Kissan Basmati 2016). The results indicated that the N3 treatment, with an equal split of nitrogen, combined with the V4 variety (Kissan Basmati 2016) produced the most favorable outcomes. The results indicated that the N3 treatment, particularly when applied to Kissan Basmati (V4), produced, statistically, the highest leaf area index (32.98%, 29.59%), 1000-grain weight (32.84%, 46.97%), grain yield (30.02%, 38.09%), agronomic nitrogen use efficiency (9.21%, 11.63%), and partial factor productivity (29.98%, 38.11%) compared to the control for the study periods of 2022 and 2023, respectively. Moreover, the grain yield demonstrated a strong positive correlation with growth traits and other yield components, except for plant height. The results showed that the application of three equal nitrogen doses significantly increases rice production, and therefore, in this yield context, improves nitrogen use efficiency. Full article