Nitrogen, Volume 6, Issue 1 (March 2025) – 19 articles

The development of critical levels for sap nitrate and chlorophyll meter reading (SPAD test) in the case of various crops is of great importance for growers in characterizing a plant’s N status. A field experiment with spring oat (Avena sativa L.) was carried out on loamy soil in Debrecen, Hungary, using a small-plot design. Ammonium nitrate was broadcast at rates of 0, 30, 60, and 90 kg N/ha in three replicates. The total N content of the plant, sap nitrate content, and SPAD values were measured at jointing when the first node appeared above the soil surface (Feekes 6) and at boot stage (Feekes 10). Regression analysis between total N content and sap nitrate showed cubic and linear relationships with r² = 0.7982 (Feekes 6, whole plant) and 0.9625 (Feekes 10, upper developed leaves), respectively. Optimal grain yield was obtained when sap nitrate exceeded 650 mg/L and 540 mg/L at Feekes 6 and Feekes 10, respectively. There were linear and logarithmic relationships between total N content and SPAD values with r² = 0.8058 and 0.6258 at Feekes 6 and 10. Optimal grain yield occurred over SPAD values of 43 and 48 at Feekes 6 and 10, respectively. Optimal N rate was 60 kg N/ha on the experimental site. Full article

Excessive irrigation in protected vegetable production often results in soil nutrient loss and groundwater contamination. Cucumber (Cucumis sativus L.) is a widely cultivated and important vegetable in the world and a sensitive plant to irrigation water supply. In order to obtain higher water use efficiency (WUE) and to assess the leaching loss of mineral elements under the current strategies of irrigation and fertilization in the production of protected crops, we conducted experiments with three irrigation levels, namely, normal (NI), optimized (OI), and deficit irrigation (DI), on cucumber in a solar greenhouse. The results indicated that the contents of nitrate–nitrogen (NO₃⁻–N) in the top soil layer increased significantly under the reduced irrigation condition (OI and DI) after two cultivation seasons compared with normal irrigation (NI). However, there were no significant differences in the contents of available phosphorus (A–P) and available potassium (A–K) between the three treatments in each soil layer during a single irrigation cycle and for the whole growth cycle. In addition, compared to the NI condition, reducing the amount of irrigation (OI and DI) decreased the amount of leaching of the soil mineral elements by more than half without jeopardizing the fruit yield of cucumber, particularly for DI. Under the three irrigation treatments, the economic yield of cucumber varied from 64,513 to 72,604 kg·ha⁻¹ in the autumn–winter season and from 89,699 to 106,367 kg·ha⁻¹ in the winter–spring season, but the differences among the treatments were not significant. Moreover, the reduced irrigation treatments (OI and DI) substantially improved WUE by 43.9% and 135.3% in the autumn–winter season, and by 82.2% and 173.7%, respectively, in the winter–spring season, compared to the NI condition. Therefore, deficit or optimized irrigation was a potential and suitable irrigation strategy in the solar greenhouse for increasing the water use efficiency, reducing the amount of leached soil mineral elements, and maintaining the economic yield of cucumber crop. Overall, our results provided some insight into the future applications of water-saving irrigation techniques in sustainable greenhouse vegetable production. Full article

An experiment was conducted in spring 2024 to investigate the effects of biochar, biogas slurry, and dicyandiamide (DCD) on N₂O emissions from soil in protected tomato cultivation. Five treatments were applied: conventional fertilization (CK1), biogas slurry alone (CK2), biochar combined with biogas slurry (T1), DCD combined with biogas slurry (T2), and the combination of biochar, biogas slurry, and DCD (T3). The study aimed to assess the response of the soil physicochemical properties and nitrifying ammonia-oxidizing microorganisms in the tomato root zone to these treatments and to determine their impact on soil N₂O emissions. The results showed that adding biochar and biogas slurry increased the soil pH, organic matter content, and levels of nitrate-N and ammonium-N, without affecting ammonia-oxidizing archaea (AOA) but inhibiting ammonia-oxidizing bacteria (AOB). The inclusion of DCD raised the soil pH and ammonium-N levels, enhanced AOA growth, did not alter organic matter content, and significantly reduced nitrate-N levels and AOB activity. Compared to CK1, treatments CK2, T1, T2, and T3 decreased the average N₂O emission flux by 5.83%, 8.24%, 15.27%, and 16.16%, respectively. The application of biochar, biogas slurry, and DCD enhanced the physicochemical properties of the root zone soil and notably reduced N₂O emissions in protected tomato cultivation, with T3 showing the most effective results. The biochar and biogas slurry used in this study, both derived from agricultural waste, promote sustainable agricultural development and enhance economic benefits. However, this study only considered the short-term effects of biochar, biogas slurry, and DCD, necessitating further research to explore their long-term impacts and mechanisms. Full article

Nitrogen, an essential element for plant growth and food production, presents significant challenges in agriculture due to the environmental consequences of synthetic nitrogen fertilizers. This review explores the potential of nitrogen-fixing cyanobacteria as a sustainable alternative for agricultural nitrogen fertilization. The molecular mechanisms underlying nitrogen fixation in cyanobacteria, including key genes such as nif and related biochemical pathways, are examined in detail. Biotechnological approaches for utilizing nitrogen-fixing cyanobacteria as biofertilizers are discussed, alongside strategies for genetic engineering to improve nitrogen fixation efficiency. The review further evaluates the impact of cyanobacteria on soil health and environmental sustainability, emphasizing their role in mitigating the detrimental effects of synthetic fertilizers. While promising, challenges such as oxygen sensitivity during nitrogen fixation and competition with native microorganisms are critically analyzed. Finally, future directions are proposed, including advancements in synthetic biology, integration with conventional agricultural practices, and scalable implementation strategies. This review underscores the transformative potential of nitrogen-fixing cyanobacteria in promoting sustainable agriculture and enhancing global food security. Full article

The use of nitrification inhibitors (NIs) with nitrogen fertilizers represents an effective strategy to reduce nitrogen loss. In addition, nitrification inhibitors are widely applied to improve agricultural yield. However, it is necessary to continue investigating the crop-specific agricultural practice. In this study, a nitrapyrin-based nitrification inhibitor was used to assess its effects on Brassica oleracea L. var. botrytis growth and on the environment. In a pot experiment, cauliflower plants were grown in fertilized soils based on calcium nitrate (SF) and SF + nitrapyrin. At the end of the experiment, the content of nitrogen compounds in soil and percolation water and the cauliflower yield were determined, and the plant tissues were characterized by Fourier-transform infrared spectroscopy. The application of the NI significantly reduced nitrogen losses, increasing nutrient availability in the soil and the element’s absorption in the plant. Co-application of fertilizers and NIs reduced ${NO}_3^{-}$ leaching from 925 to 294 mg/L. Plant tissue characterization by FTIR spectroscopy highlighted variations in the functional groups in response to the application of NIs. These results suggest that applying nitrogen fertilizer in combination with nitrapyrin can mitigate nitrate pollution and improve element absorption and plant growth. Our research has shown that application methods and cropping systems need to be studied to maximize the effectiveness of nitrapyrin-based NIs. Full article

Nitrous oxide (N₂O) is a potent greenhouse gas, and agriculture represents more than fifty percent of total anthropogenic emissions. The production of N₂O in soil is biogenic through nitrification, denitrification, chemonitrification, nitrifier denitrification, etc., which are processes influenced by the soil pH, temperature, moisture, oxygen concentration, organic carbon, and soil nitrogen. Higher N₂O emissions from the soil result in lower nitrogen use efficiency and higher environmental pollution in terms of global warming. Therefore, an understanding of different pathways for N₂O production in soil and the affecting factors is essential to mitigate N₂O emissions from soil to the atmosphere. Nitrification inhibitor application has been reported in many studies, but the impact of nitrification inhibitors in different perennials (orchards) and biennials (rice, wheat, maize, etc.) is not lacking. In this study, we develop an understanding of different N₂O production pathways and different influencing factors. The role of the different nitrification inhibitors was also developed to achieve low N₂O emissions from soils to the atmosphere. Full article

Bark beetle-associated bacteria from the sub-boreal and boreal forests of northern Canada represent a largely unexplored source of bioactive natural products. This study aims to investigate the chemical potential of bacteria isolated from Dendroctonus ponderosae, Dendroctonus rufipennis, Dendroctonus pseudotsugae, and Ips perturbatus by focusing on nitrogen-containing secondary metabolites. Genomic analyses of the bacterial isolates identified diverse biosynthetic gene clusters (BGCs), including nonribosomal peptides (NRPs), NRPS-PKS hybrids, and ribosomally synthesized and post-translationally modified peptides (RiPPs), many of which exhibit low sequence homology, suggesting potential for novel bioactive compounds. Nitrogen-15 NMR spectroscopy was employed to detect nitrogen-containing functional groups in crude extracts, revealing distinct signals for amides, amines, and nitrogen heterocycles. The combination of BGC predictions and NMR data highlighted the genetic and chemical diversity of these bacteria and underscored the potential for discovering novel nitrogen-rich metabolites. These findings provide a foundation for further exploration of bioactive natural products with pharmaceutical and agrochemical applications and potential to contribute to the understanding of the chemical ecology of bark beetle–microbe interactions in northern ecosystems. Full article

Nitrogen (N) deficiency in soil limits the development of forage grasses, while its application can significantly increase productivity. This study aimed to evaluate the effects of increasing N doses and cutting intervals on structural and productive traits, biomass allocation, leaf chlorophyll index, and specific leaf area in Megathyrsus maximus cv. MG12 Paredão. The experiment was conducted with a randomized block design in the field, using a 5 × 2 factorial scheme, with five N fertilization levels (0, 100, 200, 300, and 400 kg N ha⁻¹ year⁻¹) and two cutting intervals (either 28 or 56 days). Our measurements included plant height, number of tillers, dry mass production, fresh shoot weight, root dry mass, leaf and stem biomass, SPAD readings, and specific leaf area. The results indicated a significant increase in SPAD values associated with higher N fertilization levels, so that the 300 kg N ha⁻¹ year⁻¹ dose resulted in the most significant changes compared to the control, with SPAD values increasing from 38.2 in the control group to 54.7. Dry mass production (DMP) was higher at the 28-day cutting interval compared to 56 days, particularly with 400 kg N ha⁻¹. The 400 kg N ha⁻¹ year⁻¹ dose resulted in a 68% increase in DMP compared to the control at 28-day intervals. Additionally, fertilization enhanced the number of tillers, leading to greater biomass accumulation. Significant differences in plant height were observed between cutting intervals, with taller plants recorded at 56 days. N fertilization promoted increased plant height, particularly at doses of 200, 300, and 400 kg ha⁻¹year⁻¹. Therefore, our study suggests the use of 400 kg N ha⁻¹ year⁻¹ dose at 28-day intervals. Thus, cutting frequency directly influenced plant growth. Full article

The hybrid progeny (1-1) resulting from the cross between Caucasian clover and white clover initially demonstrated an inability to fix nitrogen naturally via spontaneous nodulation. However, following inoculation with specific rhizobia strains derived from the Trifolium genus, successful nodulation and nitrogen fixation were observed in the 1-1 progeny, resulting in enhanced biomass production and adaptability. To explore in greater depth the mechanisms driving nitrogen fixation in these hybrid progeny, the inoculation was carried out using the dominant rhizobia strain (No. 5), isolated from Mengnong Clover No. 1. Root samples were collected at 3, 6, and 9 days post inoculation for RNA sequencing. A total of 1755 differentially expressed unigenes were identified between the control and treatment groups. KEGG pathway analysis highlighted key pathways associated with nodule nitrogen fixation. In combination with Weighted Gene Co-expression Network Analysis (WGCNA) and Gene Set Enrichment Analysis (GSEA), several differentially expressed genes were identified, suggesting their potential contribution to nitrogen fixation. Noteworthy among these, the gene TRINITY_DN7551_c0_g1 in the Phenylpropanoid biosynthesis pathway (MAP00940) emerged as a key candidate. This study offers valuable RNA-seq data, contributing significantly to the understanding of the molecular regulatory mechanisms underpinning nodule nitrogen fixation in legumes, thereby laying a solid foundation for future investigations into the hybrid progeny of Caucasian and white clover crosses. Full article

Nitrogen fertilization greatly affects the development of sugar beet leaf and photosynthetic activity. This study aimed to evaluate the dynamics of leaf SPAD index, chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (Caro), and the macronutrient status (N, P, K, Na, Mg) in different N fertilization rates in sugar beet production. This study set up a two-year field experiment in Eastern Croatia. The N fertilization rate was applied as: N0—control, N1—only presowing fertilization (45 kg/ha), and N2—presowing with topdressing (99 kg/ha in 2014 and 85.5 kg/ha in 2015). In general, N fertilization has a significant (p ≤ 0.05) influence on leaf pigments, except for Chl b. With the highest N dose (N2), the Chl content in the leaves increased by 12% compared to the control treatment (0.75 mg/g FW). The Caro dynamics in the leaves of vegetative growth were significantly different (p ≤ 0.05); leaves in the younger growth stage at the end of May had the highest Caro content (0.011 mg/g FW). In general, the SPAD index was significantly different (p ≤ 0.05), among N fertilization, whereas the lowest SPAD was found at the control treatment (38.7) and the highest at the N2 treatment (40.8). In general, regarding nitrogen fertilization, the lowest SPAD readings had sugar beet leaves at the control treatment (38.7), whereas the highest was determined at the N2 treatment (40.8). A strong positive relationship (p ≤ 0.01) was determined for Chl a, Chl b, Chl a + b, and Chl a + b/Caro with the SPAD index, whereas an inverse relationship with the SPAD index was determined for Caro and Chl a/b. The results demonstrate that nitrogen application, particularly at higher rates, positively influences chlorophyll and carotenoid content, as well as overall plant health, which can inform agricultural practices for more sustainable and efficient sugar beet cultivation. Full article

Mostly, phosphorus (P) fertilizers are fixed in the interlayer of soil and become unavailable to crop plants. Combined inorganic fertilizers with organic manures could be a suitable solution to release these nutrients from the soil. P deficiency in soil adversely affected crop growth and development to a larger extent. To check out this problem, present research was conducted over a two-year period to evaluate the efficiency of a combined mixture of inorganic P and organic manure as a better farming strategy, in relation to their sole treatments, for enhancing P availability, plant growth, yield and quality, and soil properties. The inorganic source of P was SSP in the form of P₂O₅, while the organic source was cattle manure mixed with crop residues called farmyard manure (FYM). The experiment consisted of the same six treatments over each year: (i) control (0F+0P), (ii) 45 kg P₂O₅ ha⁻¹ (45P), (iii) 90 kg P₂O₅ ha⁻¹ (90P), (iv) 45 kg P₂O₅ ha⁻¹ + 1000 kg FYM ha⁻¹ (45P+1000F), (v) 1000 kg FYM ha⁻¹ (1000F), and (vi) 2000 kg FYM ha⁻¹ (2000F), using randomized complete block design (RCBD), to five replications. Results demonstrated that the combination of SSP with FYM increased the plant height (27.9%), grain yield (23.4%), and plant P uptake efficiency (43.7%) of maize as compared to sole SSP at 90 kg P₂O₅ ha⁻¹, which occurred due to improved P availability in soil. By comparing sole amendments of P fertilizer sources, FYM-treated plots have performed better in increasing maize growth and yield components such as plant height, dry matter, crop growth rate (CGR), net photosynthetic rate, grain yield, and crude protein (e.g., nitrogen contents); this happened due to enhanced soil chemical properties that might be related to improvement in P level and decreased bulk density of soil. Further, significant positive correlations were exhibited among studied crop and soil data. The plant available P and grain protein contents (N concentration) also showed a significant positive correlation and exhibited higher nitrogen contents under organic amendments of P fertilizer, as compared to inorganic treatments. The study concluded that combined SSP at 45 kg P₂O₅ ha⁻¹ with organic cattle manure at 1000 kg ha⁻¹ has a great potential for enhancing maize productivity under water deficit conditions. Results of this research may further be improved by including rigorous soil samples and field heterogeneity data between the plots and the years, which will provide more clear findings from a combined mixture of organic and inorganic fertilization. Full article

Nitrogen (N) fertilisers should be utilised as efficiently as possible. In addition to N fertiliser doses, nitrogen use efficiency (NUE) is influenced by other factors. The effects of four different N, phosphorus (P), and potassium (K) supply levels (0–3) and rainfall periods (dry, normal, wet) were investigated on NUE indices in six selected years of a field experiment. Generally, rainfall and N had the strongest effects. N × rainfall supply interaction increased biomass production from 0.915 t ha⁻¹ (N0, dry) to 10.4 t ha⁻¹ (N3, wet). The N balance varied between −47.3 kg ha⁻¹ (N0, wet) and 218 kg ha⁻¹ (N3, dry). The N uptake per unit N of fertiliser (FNRE) was mainly determined by the P × rainfall interaction, varying between 26.13% (P0, dry) and 83.73% (P3, wet). Both the biomass increment per unit N of fertiliser (agronomic efficiency—AE) and the biomass production per unit N uptake (internal efficiency—IE) were mainly influenced by the N × rainfall interaction, with AE decreasing from 43.7 kg kg⁻¹ (N1, wet) to 10.6 kg kg⁻¹ (N3, dry) and IE from 114 kg kg⁻¹ (N0, normal) to 45.9 kg kg⁻¹ (N3, wet). Both P and, to a lesser extent, K had a significant positive effect on these indices. The N dose of 200 kg ha⁻¹ year⁻¹, the P₂O₅ supply of 153 mg kg⁻¹, and the K₂O supply of 279 mg kg⁻¹ proved to be optimal in terms of NUE indices. Full article

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