Nitrogen, Volume 5, Issue 4 (December 2024) – 16 articles

High nitrogen (N) losses and low nitrogen utilisation efficiency (NUE) of conventional-nitrogen fertilisers (CNFs) are due to a mismatch between N-delivery and plant demand; thus, slow-release N fertilisers (SRNFs) are designed to improve the match. A quantitative synthesis is lacking to provide the overall assessment of SRNFs on pasture. This meta-analysis analyses application rate and type of SRNFs on N losses and agronomic performances with 65 data points from 14 studies in seven countries. Standardized mean difference of SRNFs for nitrate leaching losses and N₂O emission were −0.87 and −0.69, respectively, indicating their effectiveness in controlling losses. Undesirably, SRNFs had a more negative impact on dry matter (DM) yield and NUE than CNFs. Subgroup analysis showed that SRNF type and application rate had an impact on all tested parameters. The biodegradable coating-type of SRNF outperformed other types in controlling N losses and improving agronomic performances. High application rates (>100 kg N ha⁻¹) of SRNFs are more effective in controlling N losses. In conclusion, SRNFs are more conducive to controlling N losses, but they showed a negative impact on yield and NUE in pasture. Further studies are recommended to assess the efficacy of SRNFs developed using advanced technologies to understand their impact on pastoral agriculture. Full article

Fertigation practices in soilless crop cultivation often rely on predetermined recipes, which may lead to suboptimal nutrient concentrations due to inherent human error or environmental fluctuations. To address this challenge, the integration of in situ real-time nutrient analyzers becomes imperative for ensuring the delivery of high-quality supply solutions. This study assesses the effectiveness of a real-time nitrate (NO₃⁻) analyzer in optimizing the mineral composition of the nutrient solution for fertigating a decoupled aquaponic cucumber crop. The analyzer was integrated into the programmable logic controller of the greenhouse’s hydroponic system. The NO₃⁻ analyzer was activated during solution preparation, dynamically adjusting the NO₃⁻ concentration based on real-time measurements from either the aquaculture or drainage solution by adding the necessary water or/and nutrients in order to prepare a solution to meet the needs of the crop. Four treatments were evaluated: hydroponics (HP), coupled aquaponics (CAP), decoupled aquaponics (DCAP) with EC adjustment, and decoupled aquaponics with NO₃⁻ adjustment (DCAP_N). Results indicated that the DCAP_N treatment, with NO₃⁻ adjustment, yielded the highest crop productivity, outperforming DCAP, HP, and CAP treatments by 7.4%, 21.2%, and 56.1%, respectively. Additionally, DCAP_N demonstrated superior water use efficiency (WUE) and fertilizer use efficiency (FUE), exhibiting a 21.5% and 52.5% increase over the HP treatment, respectively. These findings align with the European Green Deal’s objectives by enhancing nutrient management practices, which are crucial for minimizing nutrient loss and ensuring the sustainable and efficient use of fertilizers. Full article

Nitrogen is essential for plants’ growth, yield, and crop quality, and its deficiency limits food production worldwide. In addition, excessive fertilization and inefficient use of N can increase production costs and cause environmental problems. A possible solution to this problem is the application of biofertilizers, which improve N assimilation and increase biomass and yield. Therefore, the objective of this research was to evaluate the impact of the application of a combination of green and red algae (Ulva lactuca and Solieria spp.), Rhizobium sp., Trichoderma asperellum, and the combination of the above three biofertilizers on N assimilation. A completely randomized design was performed, with 10 plants per treatment and five treatments: T1 = control; T2 = algal extracts; T3 = Rhizobium sp.; T4 = T. asperellum; T5 = T2 + T3 + T4. Our analyses showed that the biofertilizers’ application was better than the control. The application of Rhizobium sp. had the best performance amongst all of the biofertilizers, with the highest nitrate reductase activity in maize leaves, which enhanced photosynthesis, increasing biomass and yield. The use of Rhizobium sp. showed increases in biomass (13.4%) and yield (11.82%) compared to the control. This research shows that biofertilizers can be a key component for sustainable agricultural practices. Full article

Excessive nitrate loading from agricultural runoff leads to substantial environmental and economic harm, and although hydrological models are used to mitigate these effects, the influence of various satellite precipitation products (SPPs) on nitrate load simulations is often overlooked. This study addresses this research gap by evaluating the impacts of using different satellite precipitation products—ERA5, IMERG, and gridMET—on flow and nitrate load simulations with the Soil and Water Assessment Tool Plus (SWAT+), using the Tar-Pamlico watershed as a case study. Although agricultural activities are higher in the summer, this study found the lowest nitrate load during this season due to reduced runoff. In contrast, the nitrate load was higher in the winter because of increased runoff, highlighting the dominance of water flow in driving riverine nitrate load. This study found that although IMERG predicts the highest annual average flow (120 m³/s in Pamlico Sound), it unexpectedly results in the lowest annual average nitrate load (1750 metric tons/year). In contrast, gridMET estimates significantly higher annual average nitrate loads (3850 metric tons/year). This discrepancy underscores the crucial impact of rainfall datasets on nitrate transport predictions and highlights how the choice of dataset can significantly influence nitrate load simulations. Full article

Oilseed rape is one of many crops with high nutritional requirements, particularly for nitrogen (N) and sulphur (S). Both macronutrients affect important physiological plant functions and are essential for the proper growth and development of oilseed rape. The objective of the experiment was to investigate the impact of nitrogen and sulphur fertilization on the yield of the winter oilseed rape cultivar LG Absolut. The experiment was conducted during the 2019/2020, 2020/2021, and 2022/2023 growing seasons on Haplic Cambisol soil formed from loess, with medium levels of mineral nitrogen and sulphur. In the experiment, two nitrogen fertilization treatments (150 and 200 kg ha⁻¹) were compared in combination with three additional sulphur fertilization rates (20, 40, and 60 kg ha⁻¹). The results demonstrated that the effectiveness of N and S fertilization varied between individual years. On average, the highest seed yields were obtained with the application of 200 kg N ha⁻¹ combined with sulphur, regardless of the rate. This was attributed to a significant increase in soil–plant analysis development (SPAD) values, the number of pods per plant, and the thousand-seed weight. The increase in seed yield with the higher nitrogen rate without sulphur ranged from 0.36 to 0.57 t ha⁻¹ compared to the lower rate (control 150 N kg ha⁻¹). Supplementary sulphur fertilization increased seed yield ranging from 0.22 to 0.76 t ha⁻¹. The protein content in the seeds increased, while the fat content decreased, following the application of the higher nitrogen rate. The decrease in fat content was mitigated by higher rates of sulphur. The application of 60 kg S ha⁻¹ yielded similar results of the tested parameters to the lower rates. Therefore, for soils with moderate levels of mineral nitrogen and sulphur, it is recommended to fertilize winter oilseed rape with 200 kg N ha⁻¹ combined with 20 or 40 kg S ha⁻¹. Full article

Drought is the primary limiting factor affecting soybean productivity, and is exacerbated by climate change. In legumes like soybeans, biological nitrogen fixation (BNF) is the main form of nitrogen acquisition, with nitrogen being converted into ureides. A greenhouse experiment was conducted using the soybean cultivar BMX Zeus IPRO, with two water treatments applied during the vegetative phase: control (C) and water deficit (D). The relative water content and number of nodules were reduced in the D plants. Ureide concentrations (allantoin and allantoic acid) were higher in nodules under D conditions. However, no differences were observed in allantoin, total ureide, and soluble sugar concentrations in leaves. Our results suggest that reducing the number of nodules may be a key strategy for maintaining BNF under drought conditions and that ureide accumulation could be the primary metabolic response in this soybean cultivar. These findings indicate that the effects of water restriction on BNF are likely associated with local metabolic responses rather than a systemic ureide feedback mechanism inhibiting BNF. Full article

Global food security is at risk due to climate change. Soil fertility loss is among the impacts of climate change which reduces the productivity of rice–wheat cropping systems. This study investigated the effects of varying nitrogen levels and transplanting/sowing dates on the grain yield (GY) and biological yield (BY) of rice and wheat cultivars over two growing seasons (2017–2019). Additionally, the impact of climate change on the productivity of both crops was tested under a 1.5 °C temperature increase and 510 ppm CO₂ concentration while nitrogen fertilization and sowing window adjustments were evaluated as adaptation options using the DSSAT and APSIM models. Results indicated that the application of 120 kg N ha⁻¹ significantly enhanced both GY and BY in all rice cultivars. The highest wheat yields were obtained with 140 kg N ha⁻¹ for all cultivars. Rice transplanting on the 1st of July and wheat sowing on the 15th of November showed the best yields. The statistical indices of the model’s forecast results were satisfactory for rice (R² = 0.83–0.85, root mean square error (RMSE) = 341–441, model efficiency (EF) = 0.82–0.89) and wheat (R² = 0.84–0.89, RMSE = 213–303, EF = 0.88–0.91). Both models predicted yield loss in wheat (20–25%) and rice (28–30%) under a climate change scenario. The models also predicted that increased nitrogen application and earlier planting would be necessary to reduce the impacts of climate change on the productivity of both crops. Full article

Rising CO₂ levels, as predicted by global climate models, are altering environmental factors such as the water cycle, leading to soil waterlogging and reduced oxygen availability for plant roots. These conditions result in decreased energy production, increased fermentative metabolism, impaired nutrient uptake, reduced nitrogen fixation, and altered leaf gas exchanges, ultimately reducing crop productivity. Co-inoculation techniques involving multiple plant growth-promoting bacteria or arbuscular mycorrhizal fungi have shown promise in enhancing plant resilience to stress by improving nutrient uptake, biomass production, and nitrogen fixation. This study aimed to investigate carbon and nitrogen metabolism adaptations in soybean plants co-inoculated with Bradyrhizobium elkanii, Azospirillum brasilense, and Rhizophagus intraradices under waterlogged conditions in CO₂-enriched environments. Plants were grown in pots in open-top chambers at ambient CO₂ concentration (a[CO₂]) and elevated CO₂ concentration (e[CO₂]). After reaching the V5 growth stage, the plants were subjected to waterlogging for seven days, followed by a four-day reoxygenation period. The results showed that plants’ co-inoculation under e[CO₂] mitigated the adverse effects of waterlogging. Notably, plants inoculated solely with B. elkanii under e[CO₂] displayed results similar to co-inoculated plants under a[CO₂], suggesting that co-inoculation effectively mitigates the waterlogging stress, with plant physiological traits comparable to those observed under elevated CO₂ conditions. Full article

The extensive application of nitrogen (N) fertilizers in agriculture has resulted in a considerable accumulation of N in the soil, particularly nitrate (NO₃⁻), which can be easily lost to the surrounding environments through leaching and denitrification. Improving the immobilization of NO₃⁻ by soil microorganisms in agriculture is crucial to improve soil N retention capacity and reduce the risk of NO₃⁻ loss. In this paper, we reviewed the significance of microbial immobilization of soil NO₃⁻ in soil N retention, the techniques to quantify soil gross microbial NO₃⁻ immobilization rate, and its influencing factors. Specifically, we discussed the respective contribution of fungi and bacteria in soil NO₃⁻ retention, and we clarified that the incorporation of organic materials is of vital importance in enhancing soil microbial NO₃⁻ immobilization capacities in agricultural soils. However, there is still a lack of research on the utilization of NO₃⁻ by microorganisms of different functional groups in soil due to the limited techniques. In the future, attention should be paid to how to regulate the microbial NO₃⁻ immobilization to make soil NO₃⁻ supply capacity match better with the crop N demand, thereby improving N use efficiency and reducing NO₃⁻ losses. Full article

Tropical trees that remain evergreen and exhibit leaf litterfall that is gradual over time coexist with trees that are seasonally deciduous and exhibit pulsed litterfall. The manner in which these trees acquire, store, and contribute nutrients to the biogeochemical cycle may differ. Green and senesced leaves from deciduous Ficus prolixa trees were compared with those from Ficus tinctoria on the island of Guam. The results enabled stoichiometry and resorption calculations. F. prolixa’s young green leaf nitrogen (N) and potassium (K) concentrations were double, and the phosphorus (P) concentration was triple, those of F. tinctoria. Concentrations converged as the leaves aged such that no differences in concentration occurred for senesced leaves, indicating that nutrient resorption proficiency did not differ between the two species. In contrast, the resorption efficiency was greater for F. prolixa than F. tinctoria for all three nutrients. The N:P values of 6–11 and K:P values of 5–7 were greater for young F. tinctoria leaves than young F. prolixa leaves. The N:K values were 1.1–1.6 and did not differ between the two species. No differences in pairwise stoichiometry occurred for senesced leaves for any of the nutrients. These Guam results conformed to global trends indicating that seasonally deciduous plants are more acquisitive and exhibit greater nutrient resorption efficiency. The differences in how these two native trees influence the community food web and nutrient cycling lies mostly in the volume and synchronicity of pulsed F. prolixa litter inputs, and not in differences in litter quality. These novel findings inform strategic foresight about sustaining ecosystem health in Guam’s heavily threatened forests. Full article

This study aimed to explore the impact of various ornamental plants (Heliconia psittacorum, Etlingera elatior, Spatyphilum walisii) grown in different filter media (porous river rock (PR) and tepezyl (TZ)) on the removal of pollutants in vertical-subsurface-microcosm treatment wetlands (TWs). This study also sought to assess the adaptability of these plant species to TW conditions. Twenty-four microcosm systems were utilized, with twelve containing PR and twelve containing TZ as the filter media. Each porous media type had three units planted with each species, and three were left unplanted. Rural community wastewater was treated in the TWs. The results showed no significant differences in the effects of the porous media on pollutant removal performance (p > 0.05). However, it was noted that while both porous media were efficient, TZ, a residue of construction materials, is recommended for sites facing economic constraints. Additionally, the removal efficiency was found to be independent of the type of ornamental plant used (p > 0.05); however, the measured parameters varied with plant spp. The adaptation of the plants varied depending on the species. H. psittacorum grew faster and produced a larger number of flowers compared to the other species (20–22 cm). S. wallisii typically produced 7–8 flowers. E. elatior did not produce flowers, and some plants showed signs of slight disease and pests, with the leaves turning yellow. In terms of plant biomass, the type of porous media used did not have a significant effect on the production of above (p = 0.111) or below-ground biomass (p = 0.092). The removal percentages for COD in the presence and absence of plants were in the ranges of 64–77% and 27–27.7%, respectively. For TN, the numbers were 52–65% and 30–31.8%, and for N-NO₃, they were 54–60% and 12–18%. N-NH₄ saw removal rates of 67–71% and 28–33%, while P-PO₄ saw removal rates of 60–72% and 22–25%. The difference in removal percentages between microcosms with and without plants ranged from 30 to 50%, underscoring the importance of plants in the bio-removal processes (phytoremediation). These results reveal that incorporating ornamental plants in TWs with TZ for wastewater in rural areas holds great promise for enhancing the visual appeal of these systems and ultimately gaining public approval. Our findings also enable us to offer recommendations for selecting suitable plants and substrates, as well as designing combinations for TWs. Full article

Urea is the primary source of nitrogen (N) used in agriculture. However, it has a high N loss potential through volatilization. Various mechanisms can be employed to reduce N volatilization losses by inhibiting urease. When added to urea, iodine (I) has high potential for this purpose. Thus, this study aimed to determine whether adding I to urea reduces volatilization losses and increases N uptake in maize plants. Maize plants were cultivated in greenhouse conditions for 36 days. Urea treatments were applied at 15 days of testing, including iodine-enriched urea, conventional urea, and no urea application. Additionally, a study concerning N volatilization from urea was conducted using the same treatments under the same environmental conditions. Iodine was incorporated and adhered to urea, at an I concentration of 0.2%, using potassium iodate (KIO₃). Under controlled conditions and over a short period of time, it was observed that the application of iodine-enriched urea increased the chlorophyll b content, root N accumulation, and total N accumulation in maize plants compared with conventional urea. Moreover, iodine-enriched urea reduced N losses from volatilization by 11% compared with conventional urea. The reduction in N volatilization correlated positively with the increased chlorophyll b, total chlorophyll, root N accumulation, and total N accumulation favored by the iodine-enriched urea treatment. Our findings demonstrated that adding I to urea is an efficient and promising strategy to reduce N losses and increase N uptake in plants. Full article

Cover crops protecting soil erosion during the summer fallow in the monsoon weather may enhance dryland winter wheat yield and N relations. We examined the effects of four summer cover crops (soybean (Glycine max L., SB), sudangrass (Sorghum sudanense {Piper} Stapf, SG), soybean and sudangrass mixture (SS), and no cover crop (CK)) and three N fertilization rates (0, 60, and 120 kg N ha⁻¹) on winter wheat yield, quality, and N relations from 2017–2018 to 2020–2021 in the Loess Plateau of China. Cover crop biomass and N accumulation, soil mineral N, and winter wheat yield, protein concentration, and N uptake were greater for SB and SS than other cover crops at most N fertilization rates and years. The N fertilization rate had variable effects on these parameters. Winter wheat aboveground biomass and grain N productivities were greater for CK than other cover crops at all N fertilization rates and years. Nitrogen balance was greater for SS than other cover crops at 60 and 120 kg N ha⁻¹ in all years. The SS with 120 kg N ha⁻¹ can enhance soil mineral N, winter wheat yield and quality, and N balance compared to CK and SG with or without N fertilization rates. Full article

Nitrogen (N) fertilization promotes morphofunctional attributes that enhance plant performance under stress conditions, but the amount and form supplied modify the magnitude of plant responses. We assessed several morpho-physiological and biochemical responses of Prosopis laevigata seedlings to a high supply of N, provided as either inorganic (NH₄NO₃) or organic (amino acids). Such N treatments were applied on four-month-old seedlings as a supplement of 90 mg N to a regular supply of 274 mg N plant⁻¹. Nitrogen supply modified biomass allocation patterns between leaves and roots regardless of N form. Increased N input decreased photosynthetic capacity, even when plants had high internal N reserves. Organic N fertilization reduced the N use efficiency, but increased leaf and root amino acid concentrations. Proteins accumulated in stems in plants receiving inorganic N, while the organic N increased leaf proteins. High N supply promoted root starch accumulation irrespective of N form. Nitrogen supply did not directly influence plants’ regrowth capacity. Still, resprouting was correlated to initial root-to-shoot ratios and root starch, confirming the importance of roots as storage reserves of starch for recovering biomass after browsing. These findings have practical implications for designing nutritional management strategies in nurseries to improve seedling performance in afforestation efforts. Full article

The efficient management of nitrogen (N) on a site-specific basis is critical for the improvement of crop yield and the reduction of environmental impacts. This review examines the application of three primary technologies—canopy reflectance sensors, chlorophyll meters, and leaf color charts—in the context of site-specific N fertilizer management. It delves into the development and effectiveness of these tools in assessing and managing crop N status. Reflectance sensors, which measure the reflection of light at specific wavelengths, provide valuable data on plant N stress and variability. The advent of innovative sensor technology, exemplified by the GreenSeeker, Crop Circle sensors, and Yara N-Sensor, has facilitated real-time monitoring and precise adjustments in fertilizer N application. Chlorophyll meters, including the SPAD meter and the atLeaf meter, quantify chlorophyll content and thereby estimate leaf N levels. This indirect yet effective method of managing N fertilization is based on the principle that the concentration of chlorophyll in leaves is proportional to the N content. These meters have become an indispensable component of precision agriculture due to their accuracy and ease of use. Leaf color charts, while less sophisticated, offer a cost-effective and straightforward approach to visual N assessment, particularly in developing regions. This review synthesizes research on the implementation of these technologies, emphasizing their benefits, constraints, and practical implications. Additionally, it explores integration strategies for combining these tools to enhance N use efficiency and sustainability in agriculture. The review culminates with recommendations for future research and development to further refine the precision and efficacy of N management practices. Full article

Urban and storm water retention ponds eventually become eutrophic after years of receiving runoff water. In 2020, a novel biological and chemical treatment was initiated to remove accumulated nutrients from an urban retention pond that had severe algae and weed growth. Our approach installed two 6.1 m × 6.1 m floating treatment wetlands (FTWs) and two airlift pumps that contained slow-release lanthanum composites, which facilitated phosphate precipitation. Four years of treatment (2020–2023) resulted in median nitrate-N concentrations decreasing from 23 µg L⁻¹ in 2020 to 1.3 µg L⁻¹ in 2023, while PO₄-P decreased from 42 µg L⁻¹ to 19 µg L⁻¹. The removal of N and P from the water column coincided with less algae, weeds, and pond muck (sediment), and greater dissolved oxygen (DO) concentrations and water clarity. To quantify the sustainability of this bio-chemical approach, we focused on quantifying nitrate removal rates beneath FTWs. By enclosing quarter sections (3.05 × 3.05 m) of the field-scale FTWs inside vinyl pool liners, nitrate removal rates were measured by spiking nitrate into the enclosed root zone. The first field experiment showed that DO concentrations inside the pool liners were well below the ambient values of the pond (<0.5 mg/L) and nitrate was quickly removed. The second field experiment quantified nitrate loss under a greater range of DO values (<0.5–7 mg/L) by including aeration as a treatment. Nitrate removal beneath FTWs was roughly one-third less when aerated versus unaerated. Extrapolating experimental removal rates to two full-sized FTWs installed in the pond, we estimate between 0.64 to 3.73 kg of nitrate-N could be removed over a growing season (May–September). Complementary laboratory mesocosm experiments using similar treatments to field experiments also exhibited varying nitrate removal rates that were dependent on DO concentrations. Using an average annual removal rate of 1.8 kg nitrate-N, we estimate the two full-size FTWs could counter 14 to 56% of the annual incoming nitrate load from the contributing watershed. Full article