Nitrogen, Volume 5, Issue 4 (December 2024) – 24 articles

Drought and low nitrogen stress are the leading cause of low crop production and productivity worldwide. Developing drought-tolerant wheat germplasm resilient to low nitrogen conditions is essential through genetic enhancement and selection for novel traits. The objective of the research was to investigate genetic diversity, parameters, and trait relationships within a wheat genotype panel to inform drought- and low-N-tolerant variety selection. This study evaluated 50 wheat genotypes under drought-stressed and non-stressed conditions, with varying nitrogen (50 kg ha⁻¹, 100 kg ha⁻¹, and 200 kg ha⁻¹) levels across four testing sites during the 2019/2020 growing season. Statistical analysis (combined ANOVA) revealed substantial genetic variation (p < 0.05) for the majority of tested traits. High heritability and substantial genetic gain for KPS (97.49%, 28.10% GAM) and SE (96.48%, 14.28% GAM) were determined under drought and low nitrogen stress. Under drought-stressed and non-stressed (at 200 kg N ha⁻¹), grain yield expressed high heritability estimates of 80.43% and 75.68% and genetic advance at 21.90% and 21.56%, respectively. Positive and significant correlations (r > 0.5; p < 0.001) were measured between grain yield and yield components, implicating simultaneous direct and indirect selection of desired traits. The positive relationship between grain yield and yield components suggests that further quantitative trait loci analysis and progeny testing are crucial to guide genotype selection and breeding for drought and low-N stress-tolerant wheat genotypes. Full article

Wildfires in the western U.S. have increased in severity and duration in recent decades. Severe wildfires can enhance the rates of nutrient mineralization, causing large exports of inorganic nitrogen and other ions from forests to streams. Measuring the degree to which streams respond to severe, stand-replacing wildfires is critical to estimate in ecosystems prone to disturbance. In 2003, two severe crown wildfires burned in Yellowstone National Park, WY, USA. We studied the extent to which these fires increased nitrogen (ammonium, nitrate and nitrite), sulfate, chloride, and total dissolved phosphorus concentrations and export in three watersheds prior to and during the first four years post-fire. We measured higher concentrations of most ions after wildfire, and nitrate and chloride concentrations increased the most, increasing > 1000 µg/L. Concentrations of nitrate (≤146 times pre-fire concentrations), total dissolved nitrogen (≤11 times), chloride (≤9 times), and total dissolved phosphorus (≤7 times) were higher four years post-fire than before the wildfires burned. Exports of nitrate (≤1392 times), sulfate (≤14 times), and chloride (≤37 times) were also higher after wildfire, while nitrite (≤2.9 times) and ammonium (≤6.4 times) increased to a lesser degree. Stream concentrations of most ions were higher in watersheds that had a larger percent of the area burned. Comparing ion concentrations in streams before and after severe wildfires provides critical information to managers as the climate warms and the frequency of fire-conductive weather increases. Full article

Abiotic factors, such as drought, can significantly impact the vegetative growth and productivity of maize. To investigate the effects of the combined foliar application of zinc (Zn) and iron (Fe) nanoparticles with the recommended nitrogen dose (RND) on maize production and grain chemical composition under different water regimes, two field experiments were conducted in El-Ayyat city, Giza, Egypt, during the summer seasons of 2022 and 2023. This study utilized a split-split-plot experimental design with three replications. The main plots were designated to different water regimes (100, 80, 60, and 40% of estimated evapotranspiration), while the sub-plots were randomly distributed with Zn and Fe nanoparticle concentrations (0, 100, and 200 mg/L). The sub-sub-plots were randomly allocated to three maize cultivars (SC-P3062, SC-32D99, and SC-P3433). The results revealed that exposure to drought conditions resulted in a significant decline in the yield and yield-related attributes across all maize cultivars examined. Grain yield decreased by 10–50% under drought conditions. However, the foliar application of Zn and Fe nanoparticles was found to significantly improve grain yield, protein content, oil content, starch content, crude fiber, ash, and macro- and micronutrient concentrations in the maize cultivars under control and drought stress conditions. The foliar application of Zn and Fe nanoparticles at a concentration of 200 mg/L to the SC-P3433 maize cultivar led to the greatest grain yield per hectare, reaching 11,749 and 11,657 kg under the irrigation regimes with 100 and 80% total evapotranspiration, respectively. According to the assessment using the relative drought index, the SC-P3062 maize cultivar demonstrated tolerance (T) to water stress conditions. In conclusion, the foliar application of Zn and Fe nanoparticles (100–200 mg/L) effectively mitigated the negative effects of drought stress on maize plants. This approach can be recommended for farmers in arid and semi-arid regions to maintain and improve maize yield and grain quality under water-deficit conditions. Full article

Sustainable agricultural practices are pivotal for environmental preservation and enhancing crop quality. Understanding soil nutrient levels is crucial in determining appropriate fertilizer application in agriculture production systems. In the 2022/23 agricultural season, an experiment that aimed to investigate the spatial distribution of nitrogen (N₂) fixation or absorption in fields cultivated with diverse crops was carried out in Mozambique. Three experimental fields were established, and the following crops were used—maize (local variety), soybean (SAN-BEIB variety), and cotton (ALBAR SZ9314 variety)—each measuring 83.35 m × 30 m. A sampling grid of 13.9 m × 10 m facilitated the collection of 24 composite soil samples per field, consisting of 5 sub-samples within 12 cells, taken at a depth of 0.0–0.20 m before planting and after harvesting, totaling 12 samples per period per field. Laboratory analysis employed the Kjeldahl method to determine total soil nitrogen levels. The Inverse Distance Weighted (IDW) method was used for mapping the spatial total soil nitrogen distribution. The results revealed distinct total soil nitrogen credit and debit patterns. Variations were notable between pre-planting and post-harvest analyses in maize and cotton, showcasing high absorption and minimal fixation. Contrary to expectations, soybeans exhibited high absorption and low fixation, challenging the determination of optimal crop rotation intervals. Quantitative results identified specific total soil nitrogen debit efficiencies of approximately 1692.29 kg ha⁻¹ in cotton and 1081.5 kg ha⁻¹ in maize, respectively, and a credit of 459.215 kg ha⁻¹ in soybeans. Despite discrepancies, this study serves as a foundational platform for future research. As the findings of this study advocate for continued crop rotation practices to bolster soil health and enhance nutrient utilization, it provides the first novel insights into nitrogen dynamics of global key crops in Mozambique, revealing significant variations in nitrogen fixation and absorption across different crop types and fields, which is crucial for informing tailored agricultural practices and soil fertility management strategies. Full article

Commercial mango growers commonly spray potassium nitrate (KNO₃) solution to enhance flowering and fruit quality, yet there is limited information on the uptake efficiency of nitrogen (N) by mango cultivars through leaf cuticles. The study aimed to assess N uptake efficiency (NUpE) from foliar application of KNO₃ solution and compare NUpE among mango varieties. Mango cultivars were ‘Kensington Pride’ (‘KP’), ‘B74’ (‘Calypso^®’), and ‘NMBP 1201’ (‘AhHa!^®’), ‘NMBP 1243’ (‘Yess!^®’), and ‘NMBP 4069’ (‘Now^®’) grafted onto ‘KP’ seedlings. Leaves of six-month-old seedlings were dipped in ¹⁵N-enriched KNO₃ solution and analyzed for total N and ¹⁵N contents. A significant correlation was observed between the leaf area and the amount of solution retained after dipping the leaves in the KNO₃ solution. Moreover, leaves treated with the KNO₃ solution had higher ¹⁵N levels than the natural ¹⁵N abundance, indicating successful N uptake from the KNO₃ solution. The NUpE ranged from 27% to 44% and varied with variety. Cultivar ‘NMBP 4069’ had the highest NUE (44%) which was comparable with that of ‘B74’ (40%). ‘NMBP 1201’ showed the lowest (27%) NUpE which was comparable with that of ‘NMBP 1243’ (30%) and ‘KP’ (33%). These data on ¹⁵N uptake through the mango leaf cuticle demonstrates the effectiveness of foliar application as a method of supplying N to mango trees, highlighting important varietal differences in foliar ¹⁵N uptake efficiency. Considering these differences in NUpE among mango varieties will help in making informed decisions about cultivar selection and N management strategies for sustainable mango production. Full article

Prolonged inoculation of soya bean (Glycine max L.) farms with exotic strains of Bradyrhizobium species starting in the 1960s resulted in the establishment of populations of Bradyrhizobium strains in the soils of several soya bean farms in South Africa. With the increasing number of new soya bean genotypes in the country, it is challenging to determine which genotypes are highly compatible with a given rhizobium strain. In this study, we investigated the symbiotic compatibility of native rhizobial isolates and the strains from the South African Rhizobium Culture Collection (SARCC) on ten selected locally available soya bean genotypes. A glasshouse soil trap experiment using soil samples collected from Lothair, Bothaville, and Standerton was performed on five cultivars. The trapped rhizobial strains were further screened in the glasshouse to authenticate their nodulation compatibility with the different soya bean cultivars. The rhizobial strains showed significant nodulation compatibility with the selected cultivars. These strains were also tested for beneficial traits in vitro and characterized using DNA sequencing methods to elucidate their taxonomic identity. Some of the most nodulation-compatible strains characterized as Bradyrhizobium and Sinorhizobium species exhibited significant symbiotic performance in terms of plant biomass, nodule number, and nodule dry weight. The study generated valuable data that provide information on the extent of symbiotic compatibility of some of the existing cultivars used in South Africa with native rhizobia and whether inoculation of soya bean with commercial products is vital on some soya bean farms. Full article

Substituting soybean meal (SM) with other protein sources can be advantageous in reducing production costs without increasing nitrogen losses in the environment. Peanut cake (PC) might be a strategy in ruminant herds to result in a performance similar to that observed in animals fed SM. This study assessed the PC inclusion at rates of 0, 250, 500, 750, and 1000 g/kg on intake and digestibility, performance, nitrogen balance, microbial protein synthesis, and carcass traits of lambs. Forty-five entire, crossbreed Dorper × Santa Inês lambs (average age = five months and 24.49 ± 5.27 kg of BW) were distributed in a completely randomized design. Only the ether extract intake was not affected by the PC inclusion, and only the crude protein digestibility was affected by the diets. The total weight and average daily gains decreased, and the feed conversion increased. Hot carcass yield was influenced quadratically, the leg depth increased and the loin-eye area decreased. The total replacement of soybean meal with peanut cake in diets for lambs did not compromise nutrient digestibility, microbial protein synthesis, and carcass characteristics. Nevertheless, peanut cake as a protein source in the diet had adverse effects on nutrient intake and growth performance of feedlot lambs. Full article

Nitrogen fertilizers have a significant impact on the growth of rice. The overuse and inappropriate application of nitrogen fertilizers have resulted in environmental pollution, in addition to subjecting both humans and livestock to negative health hazards. Finding a viable substitute for traditional nitrogen fertilizers is crucial and essential to help improve crop yield and minimize environmental damage. Nano-nitrogen fertilizers offer a possible alternative to traditional fertilizers due to a slow/controlled release of nitrogen. The present work aimed to study the effect of a slow-release urea nanofertilizer on soil ammonical (NH₄-N) and nitrate-N (NO₃-N) content, culturable soil microflora, and soil enzyme activities in three different soil samples procured from Ludhiana and Patiala districts through a soil column study. Seven treatments, including 0, 50 (75 kg/ha N), 75 (112.5 kg/ha N), and 100% (150 kg/ha N) of the recommended dose (RD) of conventional urea and nano-urea fertilizer were applied. The leachate samples collected from nano-urea treatment exhibited NH₄-N for the first two weeks, followed by NO₃-N appearance. The higher NH₄-N and NO₃-N contents in the leachate were recorded for light-textured soil as compared to medium- and heavy-textured soil samples. The soil microbial counts and enzyme activities were recorded to be maximum in light-textured soils. Therefore, this slow-release formulation could be more useful for light-textured soils to decrease applied N-fertilizer losses, as well as for improving the soil microbial viable cell counts and soil enzyme activities. The effect of urea nanofertilizer on the growth and yield of direct-seeded rice (Oryza sativa L.) was also evaluated under field conditions. Both studies were performed independently. Numerically, the highest shoot height, fresh and dry shoot weight, and significantly maximum total chlorophyll, carotenoid, and anthocyanins were recorded in the T2 (100% RDF through nano-urea) treatment. The yield-attributing traits, including the number of filled grains and thousand-grain weight, were also recorded to have increased in T2 treatment. A numerical increase in NPK for plant and grain of rice at 100% RDN through nano-urea was recorded. The soil application of the product exhibited no negative effect on the soil microbial viable cell count on different doses of nano-urea fertilizer. The soil nitrogen fixer viable counts were rather improved in nano-urea treatments. The results reflect that nano-urea fertilizer could be considered as a possible alternative to conventional fertilizer. Full article

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