Excess Nitrogen Research Articles

Using the R Package, nsink, to assess landscape N removal in coastal catchments

Background Excess nitrogen (N) loading to coastal ecosystems impairs estuarine water quality. Land management decisions made within estuarine watersheds have a direct impact on downstream N delivery. Natural features within watersheds can act as landscape sinks for N, such as wetlands, streams and ponds that transform dissolved N into gaseous N, effectively removing it from the aquatic system. Identifying and evaluating these landscape sinks and their spatial relationship to N sources can help managers understand the effects of alternative decisions on downstream resources. Methods The N-Sink approach uses widely available GIS data to identify landscape sinks within HUC-12 (or larger) catchments, estimate their N removal potential and map the effect of those sinks on N movement through the catchment. Static maps are produced to visualize N removal efficiency, transport and delivery, the latter in the form of an index. The R package nsink was developed to facilitate data acquisition, processing and visualization. Results nsink creates static maps for a specific HUC-12, or users can visit the University of Connecticut website to explore previously mapped areas. Users can investigate specific flowpaths interactively by clicking on any location within the catchment. A flowpath is generated with a table describing N removal along each segment. We describe the motivation behind developing nsink, discuss implementation in R, and present two use case examples. nsink is available from https://github.com/USEPA/nsink. Conclusions N-Sink is a decision support tool created for local decision-makers and NGOs to facilitate better understanding of the relationship between land use and downstream N delivery. Local decision-makers that have prioritized N mitigation in their long-term planning can use nsink to better understand the potential impact of proposed development projects, zoning variances, and land acquisition or restoration. nsink also allows resource economists to investigate the tradeoffs among different, often costly, N reduction strategies.

Assessing temporal dynamics of nitrogen surplus in Indian agriculture: district scale data from 1966 to 2017

Nitrogen (N) is essential for agricultural productivity, yet its surplus poses significant environmental risks. Currently, over half of applied nitrogen is lost, resulting in resource wastage, contributing to increased greenhouse gas emissions and biodiversity loss. Excess nitrogen persists in the environment, contaminating soil and water bodies for decades. Quantifying detailed historical N-surplus estimation in India remains limited, despite national and global-scaled assessments. Our study develops a district-level dataset of annual agricultural N-surplus from 1966-2017, integrating 12 different estimates to address uncertainties arising from multiple data sources and methodological choices across major elements of the N surplus. This dataset supports flexible spatial aggregation, aiding policymakers in implementing effective nitrogen management strategies in India. In addition, we verified our estimates by comparing them with previous studies. This work underscores the importance of setting realistic nitrogen management targets that account for inherent uncertainties, paving the way for sustainable agricultural practices in India, reducing environmental impacts, and boosting productivity.

Microbial Ecology of Denitrification Process and Its Application in Wastewater: Treatment, Challenges and Opportunities

Denitrification is a crucial microbial process in the nitrogen cycle, transforming nitrate (NO₃⁻) into nitrogen gas (N₂), thereby mitigating nitrogen pollution in aquatic ecosystems. This microbial activity plays a vital role in wastewater treatment by removing excess nitrogen, which contributes to eutrophication and water contamination. The denitrification process involves various microbial communities, including bacteria such as Pseudomonas, Paracoccus, and Bacillus, which operate under anoxic conditions to achieve nitrogen reduction, an optimizing denitrification in wastewater treatment presents several challenges, such as maintaining ideal environmental conditions (e.g., carbon availability, oxygen levels, pH) and overcoming issues related to incomplete denitrification, which can lead to the production of harmful intermediates like nitrous oxide (N₂O). Despite these hurdles, recent advancements in microbial ecology, such as the use of biofilms, bioreactors, and genetic engineering, offer promising opportunities to enhance denitrification efficiency. This review explores the microbial ecology of the denitrification process, its application in wastewater treatment, and the challenges and opportunities associated with its practical implementation in reducing nitrogen pollution.

Bulk milk urea as an indicator of herd dietary nitrogen surplus and nitrogen use efficiency on Canterbury dairy farms.

Bulk milk urea as an indicator of herd dietary nitrogen surplus and nitrogen use efficiency on Canterbury dairy farms.

Nitrogen induced soil carbon gains are resistant to loss after the cessation of excess nitrogen inputs

Nitrogen (N) deposition has increased soil carbon (C) storage across eastern US temperate forests by reducing microbial decomposition. However, the fate of these N-induced soil C gains are uncertain given strong declines in N-deposition rates and rising soil temperatures. As N deposition has reduced soil pH and plant C investments into the rhizosphere, we compared the extent to which removing limitations to microbial decomposition by increasing soil pH, adding artificial root exudates, or elevating soil temperature would increase microbial decomposition in soils that have and have not received excess N inputs. We hypothesized that alleviating these microbial decomposition limitations would prime soil C losses from soils that have received excess N inputs. To test this hypothesis, we conducted a soil microcosm experiment where we compared microbial respiration, microbial biomass, and soil enzyme activity in soils from an unfertilized watershed and a previously N-fertilized watershed 4 years after the end of a 30-year N deposition experiment at the Fernow Experimental Forest in West Virginia. In both watersheds, we found that removing pH, plant carbon, or temperature limitations to decomposition stimulated microbial respiration. However, microbial decomposition and soil C losses were consistently lower in the previously N-fertilized watershed across all treatments. This response, coupled with a lack of differences in microbial biomass between watersheds and treatments, suggests that long-term N fertilization has fundamentally altered soil microbial communities and has led to a sustained impairment of the ability of the microbial community to decompose soil organic matter. Collectively, our results indicate that the legacy effect of N deposition on microbial communities may influence the persistence of soil C stocks in the face of global change.

The Effect of the Use of a Novel Urease Inhibitor Coated Urea on the Greenhouse Gas Emissions and Ammonia Volatilization Losses from a Maize Field

Nitrogen fertilizers are essential for enhancing agricultural productivity but are also major contributors to greenhouse gas (GHG) emissions and ammonia volatilization, which affect environmental sustainability. This study evaluated the effect of cashew nut shell liquid (CNSL)-coated urea on GHG emissions and ammonia losses from maize fields in the Indo-Gangetic Plains, known for excessive nitrogen fertilizer usage. A randomized block design was employed with four treatments: control (no nitrogen), prilled urea, neem-coated urea (NCU), and CNSL-coated urea (CCU). Gas samples were collected using the closed chamber method, and emissions of CO₂ and N₂O were analyzed via gas chromatography. Ammonia volatilization was measured using the forced air draft method. Results showed that the CCU treatment significantly reduced ammonia volatilization compared to prilled urea (15.84% reduction), with reductions of 9% to those observed with NCU. Moreover, CCU-treated plots exhibited reduced cumulative GHG and lower global warming potential (GWP) without compromising maize yields. Cumulative GHG emissions varied among the treatments in the order urea> CCU> NCU> Control. CCU treated plots exhibited a net GWP decrease of 8.59% compared to urea and an increase of 4.13% compared to NCU. These findings suggest that CNSL-coated urea can serve as an eco-friendly alternative to conventional urea, potentially mitigating environmental impacts associated with nitrogen fertilization. Further studies are recommended to assess the long-term efficacy of CNSL in various soil types and climatic conditions.

Effects of SPAD value variations according to nitrogen application levels on rice yield and its components.

Nitrogen (N) is the most essential element for growth, development, and grain yield determination in crops. However, excessive nitrogen application can result in environmental pollution and greenhouse gas emissions that contribute to climate change. In this study, we used 158 rice genetic resources to evaluate the relationships between the soil and plant analysis development (SPAD) value and grain yield (GY) and its components. The SPAD value ranged between 30.5 and 55.8, with a mean of 41.7 ± 5.3, under normal nitrogen conditions (NN, 9 kg/10a), and between 27.5 and 52.3, with a mean of 38.6 ± 4.8, under low nitrogen conditions (LN, 4.5 kg/10a). Under NN conditions, the SPAD values were in the following order: japonica (43.5 ± 5.8), Tongil-type (41.7 ± 2.5), others (41.7 ± 5.2), and indica (38.3 ± 3.8). By contrast, under LN conditions, the SPAD values were in the following order: Tongil-type (40.4 ± 2.1), others (40.1 ± 4.5), japonica (39.6 ± 5.2), and indica (35.6 ± 3.9). The 158 genetic resources showed no correlation between SPAD and yield. Therefore, the low-decrease rate (LDR) and high-decrease rate (HDR) SPAD groups were selected to reanalyze the relationships between the surveyed traits. The SPAD values were positively correlated with 1000-grain weight (TGW) for both LDR and HDR groups (NN: 0.63, LN: 0.53), However, SPAD and GY were positively correlated only in the LDR group. For TGW, the coefficient of determination (R 2) was 20% and 13% under NN and LN conditions, respectively. For GY, R 2 values of 32% and 52% were observed under NN and LN conditions, respectively. Genetic resources with higher SPAD values in the LDR group exhibited the highest yield (NN: 1.19 kg/m2, LN: 1.04 kg/m2) under both NN and LN conditions. In conclusion, we selected 10 genetic resources that exhibited higher GY under both NN and LN conditions with minimal yield reductions. These genetic resources represent valuable breeding materials for nitrogen deficiency adaptation.

Study of Different Parameters Affecting Production and Productivity of Polyunsaturated Fatty Acids (PUFAs) and γ-Linolenic Acid (GLA) by Cunninghamella elegans Through Glycerol Conversion in Shake Flasks and Bioreactors.

Microbial cultures repurposing organic industrial residues for value-added metabolite production is pivotal for sustainable resource use. Highlighting polyunsaturated fatty acids (PUFAs), particularly gamma-linolenic acid (GLA), renowned for their nutritional and therapeutic value. Notably, Zygomycetes' filamentous fungi harbor abundant GLA-rich lipid content, furthering their relevance in this approach. In this study, the strain C. elegans NRRL Y-1392 was evaluated for its capability to metabolize glycerol and produce lipids rich in GLA under different culture conditions. Various carbon-to-nitrogen ratios (C/N = 11.0, 110.0, and 220.0 mol/mol) were tested in batch-flask cultivations. The highest GLA production of 224.0 mg/L (productivity equal to 2.0 mg/L/h) was observed under nitrogen excess conditions, while low nitrogen content promoted lipid accumulation (0.59 g of lipids per g of dry biomass) without yielding more PUFAs and GLA. After improving the C/N ratio at 18.3 mol/mol, even higher PUFA (600 mg/L) and GLA (243 mg/L) production values were recorded. GLA content increased when the fungus was cultivated at 12 °C (15.5% w/w compared to 12.8% w/w at 28 °C), but productivity values decreased significantly due to prolonged cultivation duration. An attempt to improve productivity by increasing the initial spore population did not yield the expected results. The successful scale-up of fungal cultivations is evidenced by achieving consistent results (compared to flask experiments under corresponding conditions) in both laboratory-scale (Working Volume-Vw = 1.8 L; C/N = 18.3 mol/mol) and semi-pilot-scale (Vw = 15.0 L; C/N = 110.0 mol/mol) bioreactor experiments. To the best of our knowledge, cultivation of the fungus Cunninghamella elegans in glycerol-based substrates, especially in 20 L bioreactor experiments, has never been previously reported in the international literature. The successful scale-up of the process in a semi-pilot-scale bioreactor illustrates the potential for industrializing the bioprocess.

Rational Nitrogen Reduction Helps Mitigate the Nitrogen Pollution Risk While Ensuring Rice Growth in a Tropical Rice–Crayfish Coculture System

The incorporation of aquaculture feed within a rice–crayfish coculture system significantly enhances nitrogen cycling, thereby diminishing the reliance on chemical fertilizers. However, this benefit is often overlooked in practice, and farmers continue to use large quantities of chemical fertilizers to maximize production, resulting in excessive soil fertility and water nitrogen pollution. Thus, avoiding nitrogen pollution in rice–crayfish coculture systems has become a pressing issue. In this study, we conducted a two-year experiment with two rice cultivars, and a 33.3% reduction in nitrogen fertilizer in a rice–crayfish coculture system (RC), to systematically analyze the overall nitrogen balance, rice nitrogen nutrition, and soil fertility, as compared with a rice monoculture system (RM). Our findings revealed the following: (1) Under the 33.3% reduction in nitrogen fertilizer, the nitrogen surplus in the rice–crayfish coculture system was comparable to that in the rice monoculture, and was controlled at an environmental safety level. (2) Nitrogen utilization efficiency and the accumulation of nitrogen in the rice–crayfish coculture were comparable to those in the rice monoculture. The nitrogen cycle in this system was able to provide the nitrogen required for rice growth after nitrogen fertilizer reduction. (3) The rice–crayfish coculture significantly improved the overall soil fertility and the effectiveness of soil nitrogen nutrition. Furthermore, cutting off the application of nitrogen fertilizer after the mid-tillering stage effectively controlled the total nitrogen content in soil after rice maturity. In conclusion, reducing nitrogen fertilizer in a rice–crayfish coculture system is feasible and beneficial. It ensures rice production, reduces the risk of excessive nitrogen surplus and surface pollution, and promotes a greener, more environmentally friendly paddy field ecosystem.

Financial Barriers to Reducing Nitrogen Pollution in Dutch Dairy Farms

SummaryNitrogen fertiliser boosts agricultural yields, but its excessive use destabilises ecosystems. That is why Dutch policy makers want to reduce nitrogen pollution on dairy farms. Cleaner technologies and structural changes could reduce farm emissions. We benchmarked farms, organised an expert consultation, and reviewed the literature to determine the degree to which the lack of available internal and external finance is a barrier to reducing nitrogen pollution. Although the average dairy farm in our sample can finance these investments, a significant share of farmers cannot. We find that investments vastly drain the currently accessible finances available to dairy farmers. Subsidies to reduce the price of investments and measures to increase farm net cash flows could mitigate this problem, while equity funds or preferential interest rate systems would be ineffective. Farm management is not bound by access to finance. Our findings suggest that improved management could vastly reduce the accumulation of nitrogen surplus on farms. Interestingly, we estimate that this can be achieved while increasing profits. The wide‐scale adoption of best practices can be facilitated by establishing and financing advisory services and peer learning programmes to spread knowledge and awareness.

Zeolite intervention in soil nitrate dynamics: insights from column experiments and modelling

This study aims to address the harmful effects of excessive nitrogen fertilizer by investigating the mobility-retardance effect of zeolite on nitrate movement in loam soil columns. Disturbed and undisturbed soil columns, treated with zeolite as well as control soil columns, were analysed over a span of three years. Breakthrough curves generated from the experiments were evaluated using the HYDRUS-1D code with mobile–immobile water (MIM) and dual-permeability (DP) models. Our findings highlight that zeolite application significantly reduced nitrate mobility, with recovery rates decreasing by 8% in disturbed and 11% in undisturbed columns. The DP model, which accurately reflects real soil water flow conditions, outperformed the MIM model in predictive accuracy. This research offers a novel long-term perspective on the benefits of zeolite in enhancing soil properties and mitigating nitrate leaching, recommending the DP model for superior prediction of contaminant transport in structured soils within the vadose zone.

Nonlinear viscoelasticity of filamentous fungal biofilms of Neurospora discreta

The picture of bacterial biofilms as a colloidal gel composed of rigid bacterial cells protected by extracellular crosslinked polymer matrix has been pivotal in understanding their ability to adapt their microstructure and viscoelasticity to environmental assaults. This work explores if an analogous perspective exists in fungal biofilms with long filamentous cells. To this end, we consider biofilms of the fungus Neurospora discreta formed on the air-liquid interface, which has shown an ability to remove excess nitrogen and phosphorous from wastewater effectively. We investigated the changes to the viscoelasticity and the microstructure of these biofilms when the biofilms uptake varying concentrations of nitrogen and phosphorous, using large amplitude oscillatory shear flow rheology (LAOS) and field-emission scanning electron microscopy (FESEM), respectively. A distinctive peak in the loss modulus (G″) at 30–50 % shear strain is observed, indicating the transition from an elastic to plastic deformation state. Though a peak in G″ has been observed in several soft materials, including bacterial biofilms, it has eluded interpretation in terms of quantifiable microstructural features. The central finding of this work is that the intensity of the G″ peak, signifying resistance to large deformations, correlates directly with the protein and polysaccharide concentrations per unit biomass in the extracellular matrix and inversely with the shear-induced changes in filament orientation in the hyphal network. These correlations have implications for the rational design of fungal biofilms with tuneable mechanical properties.

Efficiency of paclobutrazol and gibberellic acid in wheat (Triticum aestivum L.) under different doses of nitrogen fertilization

Application of growth regulators like paclobutrazol and gibberellic acid is a suitable way to prevent excessive nitrogen consumption. Therefore, this 2-year research was conducted in Karaj, Iran. This research was laid out in a randomized complete block design with three replications in a split-plot arrangement in 2019–2021. Treatments included nitrogen at three levels: (60, 105 and 150 kg ha−1) which were placed in the main plots. The second factor was the foliar application of growth regulators at three levels: [gibberellic acid (100 ppm), paclobutrazol (200 ppm) and control]. The results showed that application of paclobutrazol and gibberellic acid raised super wheat yield and quality compared to control. The highest biological yield (27.67 ton ha−1), was observed in the interaction of nitrogen 150 kg ha−1 + gibberellic acid in the second year, which was the same with nitrogen 150 kg ha−1 + gibberellic acid in the first year and also interaction of nitrogen 150 kg ha−1 + paclobutrazol in the second year. The highest grain protein (14.69%) was seen in nitrogen 150 kg ha−1 + gibberellic acid in the second year and nitrogen 150 kg ha−1 + gibberellic acid in the first year. Growth regulators usage and increasing the nitrogen content (150 kg ha−1), improved the yield and grain quality of wheat. Therefore, the interaction of nitrogen 150 kg ha−1 + gibberellic acid and nitrogen 150 kg ha−1 +paclobutrazol, were the best treatments of this study, due to the creation of suitable environmental conditions for wheat, and these treatments can be suggested to the farmers.

INVESTIGATION OF VARIOUS MECHANISMS OF RADIATIVE RECOMBINATION OF SILICON NITRIDE AS AN EFFECTIVE WAY TO BROADENING THE PHOTOLUMINESCENCE SPECTRUM

The development of devices combining optical and electrical functions based on silicon-containing materials is one of the challenges in microelectronics. By plasma enhanced chemical vapor deposition synthesis and subsequent annealing, silicon nitride samples with both excess silicon and excess nitrogen were formed. The high concentration of Si-H and N-H bonds was determined by Raman spectroscopy in samples before annealing. By the transmission electron microscopy, it was determined that in addition to silicon nitride, silicon clusters were formed in the sample’s matrix. The photoluminescence spectra changed significantly for both types of samples during annealing in different gas atmospheres. Heat treatment of samples at 1100 °C after synthesis led to the disappearance of the PL spectrum, and after annealing at 800 °C, photoluminescence increases. It is noted that the highest intensity of photoluminescence was detected after annealing in the air atmosphere and the lowest in the nitrogen. The participation of N centers in recombination processes was confirmed by the method of electron paramagnetic resonance. The different mechanisms of particle interaction leading to photoluminescence and charge storage are considered. Thus, the conditions for the synthesis and annealing of silicon nitride layers are selected to obtain controlled luminescent properties in various spectral ranges.

Effects of Irrigation and Fertigation on Seedless Watermelon Yield in Southern Indiana

Indiana cultivates approximately 7000 acres of watermelons (Citrullus lanatus) every year, with the majority of production concentrated in southern Indiana, thus making this region a key area for watermelon production in the United States. Diverse irrigation and fertilization practices are used for watermelon production in the region, yet their effects on production outcomes remain poorly understood. To address this knowledge gap, this study investigated the impact of existing practices on watermelon yield to optimize irrigation and fertilization practices for improved production. The experiment was conducted at the Southwest Purdue Agricultural Center, Vincennes, IN, USA, during the 2022 and 2023 watermelon seasons. The following four treatments were applied: high irrigation, low irrigation, no irrigation, and fertigation. The fertigation treatment received the same water application as the high irrigation treatment, but with frequent fertilizer application with irrigation; however, fertilizers were applied before planting in the high, low, and no irrigation treatments. Although soil moisture levels at the different depths varied notably among treatments, no significant differences in yield by weight were observed. The minimal impact of irrigation on watermelon yield suggested that sufficient water is stored in the soil to prevent yield-reducing stress during dry periods. However, the high irrigation and fertilization treatments produced more fruit than the low irrigation and no irrigation treatments. The dry periods during both years coincided with the watermelon fruit-setting stages, potentially contributing to the lower fruit set in the low irrigation and no irrigation treatments. Fertigation showed a higher early yield in 2022 than that of the other treatments. An analysis of soil and tissue nitrogen levels indicated that solely applying nitrogen before planting could lead to excessive soil nitrogen during vegetative growth. This excess nitrogen might delay flowering and harvest. This project offers insights into enhancing irrigation and fertilization practices for watermelon production in southern Indiana, provides recommendations, and discusses future research directions.

Potential Linkages Between Submarine Groundwater (Fresh and Saline) Nutrient Inputs and Eutrophication in a Coastal Aquaculture Bay

AbstractSubmarine groundwater discharge (SGD) plays a crucial role in nutrient budgets of coastal systems, encompassing both submarine fresh groundwater discharge (SFGD) and recirculated saline groundwater discharge (RSGD). Despite its significance, the specific importance of these components in mariculture bays has not been thoroughly assessed. Here, utilizing Ra isotopes and water‐salt mass balance model, we show that SFGD flux (1.1 ± 0.4 cm d−1) represented only 17% of the SGD in the Zhenzhu Bay, a typical mariculture bay along the South China Sea. Interestingly, the nutrient contribution from SFGD surpassed that from RSGD, accounting for 82% of the dissolved inorganic nitrogen (DIN) flux within the SGD. Analysis of the monthly satellite Chlorophyll‐a (Chl‐a) data confirmed that the decline in phytoplankton biomass can be linked to the limited dissolved silicate (DSi) transported by SFGD. Additionally, the elevated nitrogen to phosphorus ratio (241:1) and reduced silicon to nitrogen ratio (0.5:1) in SFGD compared to the Redfield ratio suggested that SFGD characterized by nitrogen excess and silica deficient, which likely played a role in transitioning from biogenic element constraints in coastal water. This shift may impact the proportions and functionality of the phytoplankton community, potentially mitigating water eutrophication. These findings underscore the significant influence of SGD on nutrient dynamics and the ecological environment in the Zhenzhu Bay.

Cascading impacts of nitrogen deposition on soil microbiome and herbivore communities in desert steppes

Human activities in the last century have intensified global nitrogen deposition, resulting in the degradation of ecosystem function and loss of biodiversity worldwide. Nitrogen addition is a crucial method for examining the effects of atmospheric nitrogen deposition on species composition and structure of soil microbiome and biotic community, as exogenous nitrogen inputs can trigger cascading effects on ecosystem functions. In a 6-year experiment, we evaluated the impact of nitrogen addition on soil microbial-plant-insect systems in desert steppes. Our results show that nitrogen addition significantly altered soil microbial composition and ecological function, leading to a decrease in nitrogen-fixing bacteria and an increase in saprophytic fungi. High levels of nitrogen addition increased total plant biomass while decreasing species diversity. Additionally, high nitrogen addition levels suppressed below-ground biomass of gramineae and legumes compared to low nitrogen addition. Nitrogen addition also increased herbivore abundance by altering insect community structure, particularly benefiting chewing pests over sucking pests, thus heightening the risk of biological disasters through trophic cascading effects. Consequently, excessive nitrogen addition may destabilize desert steppe ecosystems by disturbing soil microbial-plant-insect interactions, hindering the maintenance of biotic community diversity and steppe productivity.

Evaluation of Nitrogen Fertilizer Supply and Soil Nitrate Thresholds for High Yields of Foxtail Millet

Foxtail millet is an important cereal crop in the North China Plain. However, excessive nitrogen fertilizer application over the years has led to declining yield and soil quality. This study investigated nutrient management strategies for foxtail millet based on crop yield levels and soil nutrient availability. In a field where targeted fertilization was conducted over six seasons, nitrogen fertilization effects and the dynamics of soil-available nitrogen were monitored continuously for two consecutive years (2022–2023) across five different foxtail millet varieties with varying yield levels. The study aimed to determine the optimal nitrogen application rate for achieving a high yield of foxtail millet, the minimum soil nitrate threshold required to maintain soil fertility, and the effective nitrogen application rate range for sustaining soil-available nitrate levels. Results showed that fertilization significantly affected dry matter weight during flowering, while variety affected dry matter weight at maturity. The average nitrogen application rate for achieving high yield across all five millet varieties was 141.3 kg·ha−1. Specifically, the average nitrogen application rate of nitrogen-efficient varieties achieving high yield (5607.32–5637.19 kg·ha−1) was 151.5 kg·ha−1, while the average nitrogen application rate of nitrogen-inefficient varieties achieving high yield (4749.77–4847.74 kg·ha−1) was 134.5 kg·ha−1. Soil NH4+-N and NO3−-N content increased when nitrogen application rate exceeded 360 kg·ha−1, posing environmental risks. To achieve high yield, soil nitrate levels would be maintained at an average of 17.23 mg·kg−1 (before sowing) and 9.75 mg·kg−1 (at maturity). A relationship between soil nitrate and nitrogen application rate was established: y = 867.5 − 50z (where y represents the optimal nitrogen application rate for high yield (kg·ha−1), and z represents soil NO3−-N content in the 0–20 cm layer before sowing, ranging from 10.0 to 17.35 mg·kg−1), which provided a practical method for nitrogen fertilization to achieve high yield of foxtail millet. In this study, the fertilization strategy was optimized according to soil nutrient level and yield targets, and the nitrogen application rate was controlled within 360 kg·ha−1 based on the soil nitrate nitrogen content, which will be instructive for reducing fertilizer use, maximizing fertilizer efficiency, and increasing yield.

Artificial Cultivation of Aquatic Plants Promotes Nitrogen Transformation and the Abundance of Key Functional Genes in Agricultural Drainage Ditch Sediments in the Yellow River Irrigation Area in China

Excess nitrogen in agricultural drainage poses a serious threat to the water quality safety of the Yellow River basin. Utilizing aquatic plants to modify the rhizosphere microbial community structure and facilitate nitrogen transformation is a crucial strategy for mitigating regional water eutrophication. We here compare key processes of nitrogen transformation occurring in the rhizosphere of sediments of a ditch artificially planted with a mix of species (Phragmites australis, Typha orientalis, Nymphaea tetragon) with the rhizosphere of a ditch occupied by naturally occurring aquatic vegetation, dominated either by P. australis or T. orientalis. Our results revealed a species effect, with an increased denitrification rate (DR) and dissimilatory nitrate reduction to ammonium rate (DNRAR) in the cultivated ditch for P. australis, compared to the naturally occurring T. orientalis vegetation. The nitrogen fixation rate (NFR) increased in the artificial setting with T. orientalis in comparison to natural P. australis vegetation. The richness of the bacterial community and the relative abundances of Bacteroidota, Firmicutes, and Geobacter were significantly greater in the rhizosphere of the artificially cultivated ditch due a greater availability in nitrogen and organic carbon. In the artificially cultivated ditch, the dominant functional genes affecting DRNARs in the rhizosphere sediments of P. australis were nrfC and nrfA, whereas DRs were driven mainly by norB and napA, which were influenced by the nitrogen and carbon levels. The dominant functional genes affecting NFRs in the rhizosphere sediments of T. orientalis were nifD, nifK, and nifH. Our results provide a scientific basis for the use of aquatic plants for mitigating excess nitrogen levels in agricultural drainage.

A review of nutritional recommendations for scuba divers.

Scuba diving is an increasingly popular activity that involves the use of specialized equipment and compressed air to breathe underwater. Scuba divers are subject to the physiological consequences of being immersed in a high-pressure environment, including, but not limited to, increased work of breathing and kinetic energy expenditure, decreased fluid absorption, and alteration of metabolism. Individual response to these environmental stressors may result in a differential risk of decompression sickness, a condition thought to result from excess nitrogen bubbles forming in a diver's tissues. While the mechanisms of decompression sickness are still largely unknown, it has been postulated that this response may further be influenced by the diver's health status. Nutritional intake has direct relevancy to inflammation status and oxidative stress resistance, both of which have been associated with increased decompression stress. While nutritional recommendations have been determined for saturation divers, these recommendations are likely overly robust for recreational divers, considering that the differences in time spent under pressure and the maximum depth could result nonequivalent energetic demands. Specific recommendations for recreational divers remain largely undefined. This narrative review will summarize existing nutritional recommendations and their justification for recreational divers, as well as identify gaps in research regarding connections between nutritional intake and the health and safety of divers. Following recommendations made by the Institute of Medicine and the Naval Medical Research Institute of Bethesda, recreational divers are advised to consume ~170-210 kJ·kg-1 (40-50 kcal·kg-1) body mass, depending on their workload underwater, in a day consisting of 3 hours' worth of diving above 46 msw. Recommendations for macronutrient distribution for divers are to derive 50% of joules from carbohydrates and less than 30% of joules from fat. Protein consumption is recommended to reach a minimum of 1 g of protein·kg-1 of body mass a day to mitigate loss of appetite while meeting energetic requirements. All divers should take special care to hydrate themselves with an absolute minimum of 500 ml of fluid per hour for any dive longer than 3 hours, with more recent studies finding 0.69 liters of water two hours prior to diving is most effective to minimize bubble loads. While there is evidence that specialized diets may have specific applications in commercial or military diving, they are not advisable for the general recreational diving population considering the often extreme nature of these diets, and the lack of research on their effectiveness on a recreational diving population. Established recommendations do not account for changes in temperature, scuba equipment, depth, dive time, work of breathing, breathing gas mix, or individual variation in metabolism. Individual recommendations may be more accurate when accounting for basal metabolic rate and physical activity outside of diving. However, more research is needed to validate these estimates against variation in dive profile and diver demographics.