Nitrate Losses Research Articles

Extended soil surface drying triggered by subsurface drip irrigation decouples carbon and nitrogen cycles and alters microbiome composition

IntroductionIrrigation management dramatically alters soil water availability and distribution and could impact soil microbial communities and carbon (C) and nitrogen (N) cycling to an even greater degree than observed in rainfed systems. Adoption of subsurface drip irrigation (SDI) in California’s Mediterranean agroecosystems provides agronomic benefits but wets only a portion of the soil volume near the root zone, leaving the rest dry throughout the growing season. In contrast, traditional furrow irrigation (FI) has periodic wetting events with more homogenous moisture distribution. With conversion to precision irrigation methods, how will the microbiome respond to changes moisture availability, and how is their response influenced by soil C and N resource levels?MethodsIn a field experiment in California, we compared SDI and FI’s effects on microbial communities and evaluated how long-term organic and conventional management systems impact outcomes. Throughout the growing season, soil samples were collected at two depths (0-15, 15-30 cm) and three distances from bed center (10, 25, 45 cm) where the drip tape is located.ResultsAt harvest, soils irrigated using SDI had lower microbial biomass C (MBC) than under FI at the surface and showed a build-up of soluble C and N relative to MBC at the bed edge, indicating reduced microbial uptake. Community composition at the bed edge also diverged between SDI and FI, favoring Actinobacteria in the former and Acidobacteria and Gemmatimonadetes in the latter. Regardless of irrigation type, dry areas of the bed had the highest alpha diversity indices. Response to SDI was similar in organic and conventional systems, though organic had higher MBC, DOC, and relative abundance of Proteobacteria and fungal lipids, regardless of irrigation.DiscussionProlonged dry conditions in SDI appeared to limit microbial access to resources and changed community composition. As seen in non-agricultural systems, the severity and frequency of moisture changes, adaptation of the communities, and resource availability affect microbial response. Decoupling of C and N pools in dry surface soils under SDI may increase the potential for losses of DOC and nitrate with the first winter rains in this Mediterranean climate.

Residue recycling options and their implications for sustainable nitrogen management in rice–wheat agroecosystems

BackgroundIn the Indo-Gangetic Plain, rice–wheat is the most extensively practiced crop rotation. The escalating issue of crop residue burning, particularly rice straw, and the necessity to lower the exorbitant expenses associated with fertilizer inputs stand out as significant challenges for farmers in the region. A well-suited integrated nutrient management (INM) strategy that focuses on recycling crop residues can serve as a solution to address these issues. Such a strategy not only mitigates air pollution resulting from residue burning but also helps combat water pollution due to nitrate losses from agroecosystems. Field experiments were used to evaluate the suitability of eight INM-modules that included various combinations of inorganic fertilizer rates (50%, 100%, 150% of recommended dose), crop residues (wheat and rice stubble retention at 30 cm standing stubble equivalent to 1/3 the straw yield), rice straw compost (RSC), farmyard manure (FYM), and green manuring (GM), compared to 100% recommended dose of fertilizers (F) and no fertilizer application.ResultsThere was a considerable improvement in nitrogen mineralization, grain yields, and nitrogen use efficiency under GM + RSC-F50 and GM + FYM-F50. These INM modules would permit a 50% reduction in the use of chemical fertilizers. There was a little yield penalty with in situ rice residue incorporation at 100% F; however, this could be overcome with 150% F fertilizer application. In situ retention of wheat straw with a full application of fertilizer resulted in steadily rising crop yields over time. Changes in the redox potential, soil pH, and soil organic carbon best accounted for the observed trajectories in nitrogen use efficiency.ConclusionThe most promising INM modules for adoption by farmers in the Indo-Gangetic Plain to judiciously use crop residues and curtail chemical fertilizer inputs are green manuring with Sesbania aculeata + rice straw compost at 5 t ha−1 + only 50% of recommended dose of fertilizers (GM + RSC-F50), and green manuring with Sesbania aculeata + farmyard manure at 5 t ha−1 + only 50% of recommended dose of fertilizers (GM + FYM-F50). Sole incorporation of crop residues without nitrogen augmentation from other sources might not help curtail chemical fertilizer use. Composting rice straw, which otherwise is widely burnt, proved a useful nitrogen source and a vital component of INM. Waste rice straw composting at the community scale and its application as a nutrient source can help achieve sustainable nitrogen management in the agroecosystems of Indo-Gangetic Plain.

The Effects of Organic Mulches on Water Erosion Control for Skid Trails in the Hyrcanian Mixed Forests

Ground-based skidding can lead to severe soil disturbance by increasing surface water flow and soil erosion. Organic mulches have been shown to be effective in contrasting this type of soil disturbance, although the cost/benefit aspect has yet to be studied. This study, by installing runoff sample plots, aims to elucidate the effects of litter (LM) and sawdust (SM) mulches with three application rates (litter: 7.6 Mg ha−1 LM7.6, 14.6 Mg ha−1 LM14.6, 22.5 Mg ha−1 LM22.5; sawdust: 5.3 Mg ha−1 SM5.3, 11.4 Mg ha−1 SM11.4, 16.7 Mg ha−1 SM16.7) on runoff, soil, and nutrient loss (nitrate and phosphate) in skid trails established in the Hyrcanian forest. The results were also compared to the undisturbed area (UND) and to an untreated skid trail (UNT). The results showed that both litter and sawdust mulch significantly decreased runoff, soil loss, and nitrate and phosphate loss. The values of runoff, runoff coefficient, soil loss, NO3, and PO4 were at the highest level in the untreated skid trails (UNTs). The runoff, runoff coefficient, soil loss, NO3, and PO4 gradually decreased as the application rate of both the litter (LM) and sawdust (SM) mulches increased. According to the results, it is possible to conclude that the mulch application rates of 7.6–14.6 Mg ha−1 and 5.3–11.4 Mg ha−1 for litter and sawdust mulch, respectively, can be applied to maintain soil and water conservation after logging operations on skid trails. The obtained findings can help to shape specific best-management practices for the implementation of sustainable forest operations in the context of the study area, by indicating suitable mulch types and application rates to decrease the negative effects of erosion.

Quantifying the spatiotemporal variability of nitrate in irrigation water across the Wisconsin Central Sands.

The Wisconsin Central Sands is home to large scale vegetable production on sandy soils and managed with frequent irrigation, fertigation, and widespread nitrogen fertilizer application, all of which make the region highly susceptible to nitrate loss to groundwater. While the groundwater is used as the primary source of drinking water for many communities and rural residences across the region, it is also used for irrigation. Considering the high levels of nitrate found in the groundwater, it has been proposed that growers more accurately account for the nitrate in their irrigation water as part of nitrogen management plans. Our objectives were to 1) determine the magnitude of nitrate in irrigation water, 2) quantify the spatiotemporal variability of nitrate, and 3) determine key predictors of nitrate concentration in the region. We sampled irrigation water from 38 fields across six farms from 2018 to 2020. Across the 3 years of our study, nitrate concentration varied more across space than time. On average, our samples were tested at 19.0mg L-1 nitrate-nitrogen, or nearly two times the U.S. Environmental Protection Agency (EPA) threshold for safe drinking water, equivalent to 48.1kg ha-1 of applied nitrate-nitrogen with 25.4cm (or 10 in.) of irrigation. To better understand the spatiotemporal variability in nitrate levels, week of sampling, year, well depth, well casing, and nitrogen application rate were analyzed for their role as predictor variables. Based on our linear mixed effects model, nitrogen application rate was the greatest predictor of the nitrate concentration of irrigation water (p<0.05).

Effect of a Prolonged-Release System of Urea on Nitrogen Losses and Microbial Population Changes in Two Types of Agricultural Soil.

Urea is the nitrogen-containing fertilizer most used in agricultural fields; however, the nutrient given by the urea is lost into the environment. The aim of this research was to determine the effect of two soil textures by applying a prolonged-release system of urea (PRSU) on the N losses. This research shows an important decrease of the nitrate and ammonium losses from 24.91 to 87.94%. Also, the microbiological population increases after the application of the PRSU. It was concluded that both soil textures presented the same loss-reduction pattern, where the N from the nitrates and ammonium was reduced in the leachates, increasing the quality of the soil and the microbial population in both soil textures after the PRSU application.

Synechococcus nitrogen gene loss in iron-limited ocean regions

Synechococcus are the most abundant cyanobacteria in high latitude regions and are responsible for an estimated 17% of annual marine net primary productivity. Despite their biogeochemical importance, Synechococcus populations have been unevenly sampled across the ocean, with most studies focused on low-latitude strains. In particular, the near absence of Synechococcus genomes from high-latitude, High Nutrient Low Chlorophyll (HNLC) regions leaves a gap in our knowledge of picocyanobacterial adaptations to iron limitation and their influence on carbon, nitrogen, and iron cycles. We examined Synechococcus populations from the subarctic North Pacific, a well-characterized HNLC region, with quantitative metagenomics. Assembly with short and long reads produced two near complete Synechococcus metagenome-assembled genomes (MAGs). Quantitative metagenome-derived abundances of these populations matched well with flow cytometry counts, and the Synechococcus MAGs were estimated to comprise >99% of the Synechococcus at Station P. Whereas the Station P Synechococcus MAGs contained multiple genes for adaptation to iron limitation, both genomes lacked genes for uptake and assimilation of nitrate and nitrite, suggesting a dependence on ammonium, urea, and other forms of recycled nitrogen leading to reduced iron requirements. A global analysis of Synechococcus nitrate reductase abundance in the TARA Oceans dataset found nitrate assimilation genes are also lower in other HNLC regions. We propose that nitrate and nitrite assimilation gene loss in Synechococcus may represent an adaptation to severe iron limitation in high-latitude regions where ammonium availability is higher. Our findings have implications for models that quantify the contribution of cyanobacteria to primary production and subsequent carbon export.

Distinct soil health indicators are associated with variation in maize yield and tile drain nitrate losses

AbstractAssociations between nitrogen (N) management and losses with soil health indicators (SHI) are widely presumed but relatively untested. An on‐farm experiment conducted in central Illinois was conducted to test potential relationships of SHI with agroecosystem outcomes of maize (Zea mays L.) yield and N losses under bounding N‐fertilization rates of 168 and 252 kg/ha. Chemical (n = 19), physical (n = 11), and biological (n = 14) SHI were measured at 24 locations within a 30 ha field at five timepoints (V3, V10, RT, R6, and post‐harvest). Yields did not necessarily reflect N‐fertilization rates, with lowest yields (14.5 Mg/ha) under 224 kg/ha. Flow‐weighted nitrate‐N concentrations were significantly higher under 168 kg N/ha (10.6 mg/L) relative to higher application rates, though cumulative tile nitrate‐N loads were similar. SHI varied more by sampling location and time than by N fertilization rate. Depending on the time of sampling, distinct SHI were related to yield and tile N losses. Total soil carbon and permanganate oxidizable carbon (POXC) best explained yield variation, whereas POXC and sand content best explained variation in nitrate‐N loss. Nematode indices helped explain variability in yield (Simpson and Shannon indices) and nitrate‐N losses (maturity index), supporting recent propositions to integrate nematode measures into soil health assessments. This study provides a basis for expanding to multiyear assessments of SHI linkages with nutrient losses and crop productivity in the North Central United States.

CNN deep learning performance in estimating nitrate uptake by maize and root zone losses under surface drip irrigation

Optimal fertigation regimes will minimize the leaching of agrochemicals while providing crops with sufficient nutrition for growth. A comprehensive objective function of optimization involves minimizing (i) difference between weekly plant nitrogen uptake and requirement and (ii) nitrate losses (nitrate leaching and accumulated nitrate in the root zone). Coupling a simulation model to an optimization algorithm for obtaining the objective function variables (N plant uptake and nitrate losses) typically requires long runtimes as the simulation model is repeatedly applied over iterations of the optimization algorithm. One attractive way to reduce the programming and computational demands associated with optimization is to construct a simpler, faster, but sufficiently accurate emulator of the simulation model based on machine-learning model. This study assessed the performance of convolutional neural networks (CNN) in modelling nitrate uptake by maize and estimation of nitrate losses in surface drip irrigation in three texturally different soils. To do this, the CNN was trained on output of the simulation model HYDRUS-2D. Various combinations of parameters influencing daily nitrate uptake (daily potential crop evapotranspiration, irrigation water and injected fertilizer amount) were evaluated as model inputs. Results indicated that daily nitrate uptake at any time t was predicted best with inputs of daily potential evapotranspiration at time t, irrigation and fertilizer amounts of the previous 1–7 days and the previous day’s nitrate uptake amount. Estimated nitrate losses for constant weekly fertigation (CWF) were about 32% in sandy loam and 38.5% in sandy clay loam soil. Variable weekly fertigation (VWF) reduced the nitrate losses to 24.5% in sandy loam and 31.5% in sandy clay loam soil, while losses in loam soil were intermediate to these. The study demonstrates that CNN estimation of nitrate uptake and root zone losses can be widely used in optimization of fertigation management.

Mitigating runoff nitrate loss from soil organic nitrogen mineralization in citrus orchard catchments using green manure.

Nitrate-nitrogen (NO3--N) loss is a significant contributor to water quality degradation in agricultural catchments. The amount of nitrogen (N) fertilizer input in citrus orchard is relatively large and results in significant NO3--N loss, compared to cropland. To promote sustainable N fertilizer management, it is crucial to identify the sources of runoff NO3--N loss in citrus orchards catchments. Particularly, we poorly know the sources of NO3--N and the mitigation mechanisms in these areas, which are highly polluted with NO3--N in water bodies. In this study conducted in central China, we conducted a field experiment with four treatments (CK: no N fertilizer; CF: conventional N fertilizer, 371.3kg N ha-1 yr-1 urea; OM: CF with organic manure; GM: CF with legume green manure) and a catchment-scale experiment in two citrus orchards (34.3%; 51.6%) catchments. To determine the source of runoff NO3--N loss, we used the dual isotope tracer method (δ15N and δ18O of NO3-) to identify the sources of NO3--N, and a 15-day incubation experiment to determine the potential and rate of soil N mineralization. Our findings revealed that soil organic nitrogen (SON) mineralization was the primary contributor to runoff NO3--N loss, and soil N mineralization potential (0.65⁎⁎⁎) and rate (0.54⁎⁎⁎) were the key factors impacting NO3--N loss. Interestingly, organic manure significantly increased 29.0% of NO3--N loss derived from SON in the runoff by enhancing soil N mineralization potential (+36.6%) and rate (+77.1%). But green manure mulching significantly reduced the soil N mineralization rate (-18.6%) compared to organic manure application, making it the most effective measure to reduce NO3--N loss (-12.4%). Our study highlights the critical role of regulating SON mineralization in controlling NO3--N pollution in surface waters in citrus orchard catchments.

Industrial demonstration of indirect mineral carbonation in the cement and concrete sector

This paper reports on the successful construction, commissioning and operation of a mobile indirect mineral carbonation (IMC) pilot plant in the concrete sector. This work confirms the technical feasibility of IMC at large scale, while producing precipitated calcium carbonate (PCC) and leached recycled concrete aggregate (RCA) as useful products. The plant is capable of handling industrial flue gas or pure CO2 as carbon feedstock, while processing around 80 kg/h of RCA as calcium feedstock, and storing around 0.9 kg/hr of CO2. Good recyclability of the aqueous ammonium nitrate mother liquor is suggested, although small changes occurred over time, with only small effects on the operation. Importantly, some CaCO3 precipitates in the dissolution reactor, especially at high CO2 feed rates; this does not decrease the CO2 storage rate, but it reduces the PCC production rate. The plant may be operated at a variety of operating conditions and it responds to them as expected from thermodynamic considerations. Similarly, the trade-offs in terms of performance parameters also change as expected. The observed calcium extraction efficiency is rather low due to the thermodynamic nature of the batch dissolution step. Also, the ammonium nitrate losses are rather high due to the plant not having a solvent recovery step integrated. Potentially alternative reactor concepts for the dissolution section can improve the calcium extraction efficiency while including a washing step, thus alleviating the main limitation. Material tests with the products of the process suggest that leached RCA is as good as, or even better than fresh RCA for use as aggregate in concrete; ground PCC performs similar as ground limestone in cement, however it is not the most attractive use of fine PCC, as higher value applications exist. Although improvements to the plant design are necessary to make the process economically and environmentally viable, this work represents an important steppingstone towards industrial implementation of IMC, and confirms its technical feasibility in the concrete sector.

Dinoflagellate vertical migration fuels an intense red tide

Harmful algal blooms (HABs) are increasing globally, causing economic, human health, and ecosystem harm. In spite of the frequent occurrence of HABs, the mechanisms responsible for their exceptionally high biomass remain imperfectly understood. A 50-y-old hypothesis posits that some dense blooms derive from dinoflagellate motility: organisms swim upward during the day to photosynthesize and downward at night to access deep nutrients. This allows dinoflagellates to outgrow their nonmotile competitors. We tested this hypothesis with in situ data from an autonomous, ocean-wave-powered vertical profiling system. We showed that the dinoflagellate Lingulodinium polyedra's vertical migration led to depletion of deep nitrate during a 2020 red tide HAB event. Downward migration began at dusk, with the maximum migration depth determined by local nitrate concentrations. Losses of nitrate at depth were balanced by proportional increases in phytoplankton chlorophyll concentrations and suspended particle load, conclusively linking vertical migration to the access and assimilation of deep nitrate in the ocean environment. Vertical migration during the red tide created anomalous biogeochemical conditions compared to 70 y of climatological data, demonstrating the capacity of these events to temporarily reshape the coastal ocean's ecosystem and biogeochemistry. Advances in the understanding of the physiological, behavioral, and metabolic dynamics of HAB-forming organisms from cutting-edge observational techniques will improve our ability to forecast HABs and mitigate their consequences in the future.

Regionalized life cycle inventory data collection and calculation for perennial forage production in Canada: methodological best practices and limitations

Abstract Purpose In Canada, 95–99% of produced forages are consumed domestically each year, mainly by beef cattle. Despite their importance, their contribution to the Canadian livestock industry and associated ecosystem services has not been investigated. This study developed a life cycle inventory (LCI) of perennial forage production in Canada averaged from 2009 to 2018. Methods LCI data were sourced or calculated from up-to-date, regionally resolved sources and models. Inputs to perennial forage production included the following: concrete, steel, and plastic usage; machinery fuel consumption; electricity, natural gas, and water use for irrigation; and synthetic and organic fertilizer, lime, and herbicide use. Assessed emissions included ammonia and nitrous oxide (N2O); carbon dioxide from energy use; herbicide, nitrate, and phosphate losses; and soil carbon accumulation. Results were expressed per metric tonne of harvested perennial forage dry matter at provincial and regional scales—Western Canada [British Columbia (BC), Alberta (AB), Saskatchewan (SK), Manitoba (MB)] and Eastern Canada [Ontario (ON), Québec (QC)]. Results and discussion Rates of inputs varied, with generally lower nutrient but higher herbicide application in West vs. East. Irrigation was highest in BC, followed by AB and SK; energy consumption was highest in BC and lowest in QC. Higher N2O losses and nutrient losses via leaching and runoff in the East were partially due to greater soil moisture. Although total harvested perennial forage area declined from 6.43 to 5.23 million hectares from 2009 to 2018, these lands continued to accumulate soil carbon. The time period used to calculate average yields affected LCI estimates, as prairie yields were lower 1994–2003/1999–2008 due to drought. Furthermore, soil carbon sequestration estimates were affected by the annual change coefficients employed, underscoring the need for careful interpretation of LCI outputs. Results were compared to other studies and highlighted the importance of the choice of data and methods in creating LCI, and the need for transparency. Conclusions This first national LCI of perennial forage production in Canada provides a baseline for LCI inputs and outputs associated with this sector, highlighting provincial and regional differences. Outputs can be used to conduct future life cycle assessments to assess the environmental impacts of forage production and generate recommendations to improve sustainability, and for education and marketing purposes. This study demonstrates methodological best practices for LCI data mining and calculations, within available data and model limitations, thereby identifying gaps and providing a roadmap for other countries or sectors to develop detailed forage LCI.

Evaluation of Agricultural BMPs’ Impact on Water Quality and Crop Production Using SWAT+ Model

Subsurface (or tile) drainage improves land productivity by enhancing soil aeration and preventing water-logged conditions. However, the continuous expansion of drained agricultural lands and reliance on synthetic fertilizer in the Midwestern United States have increasingly facilitated nitrate transport from agricultural fields to surface water bodies. Hence, there is a need to implement various agricultural best management practices (BMPs) in order to reduce the adverse water quality impacts resulting from excess nitrate, such as eutrophication and the formation of hypoxic zones. In this study, we used a SWAT+ model to assess the overall impacts on the riverine nitrate load and crop yield in the corn–soybean cropping system based on a combination of different management practices. The corn and soybean yields simulated with the model were found to be in good agreement with the observed yields for both the calibration and validation periods. The long-term simulation over a period of 30 years showed a reduction in the nitrate load of up to 32% without impacting the crop yield. The model results suggest that by reducing the current N application rate by 20% and using a 40:60 split between spring pre-plant and side-dressing N applications combined with cereal rye as a cover crop in corn–soybean rotation, one can potentially reduce nitrate losses without impacting crop yields. This study will help researchers, stakeholders, and farmers to explore and adopt alternative management practices beneficial for offsetting the environmental impacts of agricultural productions on the watershed scale.

Unraveling mechanisms behind reduced nitrate leaching with graphite nanomaterials addition with fertilizers in soil column experiments

Overuse or mistimed application of nitrogen fertilizer can cause nitrate contamination in groundwater and surrounding surface waters. Previous greenhouse studies have explored the use of graphene nanomaterials, including graphite nano additive (GNA), to reduce nitrate leaching in an agricultural soil while growing lettuce crops. To investigate the mechanism of GNA addition in suppressing nitrate leaching, we conducted soil column experiments using native agricultural soils under saturated or unsaturated flow conditions to simulate varied irrigation. We investigated the effects of temperature (4 °C compared with 20 °C) on microbial activity and dose effect of GNA was also explored (165 mg/kg soil and 1650 mg/kg soil) for biotic soil column experiments whereas a single temperature condition (20 °C) and GNA dose (165 mg/kg soil) was employed for abiotic (autoclaved) soil column experiments. Results showed GNA addition had minimal effects on nitrate leaching in saturated flow soil columns due to short hydraulic residence times (∼3.5 h). In comparison, longer residence times (∼3 d) in unsaturated soil columns reduced nitrate leaching by 25–31% relative to control soil columns without GNA addition. Furthermore, nitrate retention in the soil column was found to be suppressed at 4 °C compared with 20 °C, suggesting a bio-mediated mechanism for GNA addition to reduce nitrate leaching. In addition, the soil dissolved organic matter was found to be associated with nitrate leaching, where less nitrate leaching occurring when higher dissolved organic carbon (DOC) was measured in leachate water. Following studies of adding soil-derived organic carbon (SOC) resulted in greater nitrogen retention in the unsaturated soil columns only when GNA was present. Overall, the results suggest that GNA-amended soil reduces nitrate loss through increased N immobilization in the microbial biomass or loss of N in gaseous phase through enhanced nitrification and denitrification process.

Effects of native plants on nitrogen cycling microorganisms in soil

Plants modify the nitrogen (N) cycle in soil through plant N uptake, root exudation, and nitrification inhibition resulting from root exudates and changes to the physicochemical properties of soil. Plants with specific traits can be selected to manage N fluxes in the soil following the land application of N-rich wastes thereby reducing losses of N from these systems into the atmosphere (via nitrous oxide) and waterbodies (via nitrate). Previous work has shown that some New Zealand native myrtaceous species can reduce such losses more than other species, but the underlying mechanisms are unknown. It was hypothesized that lower N losses may result from the inhibition of nitrification and denitrification. We aimed to determine the effect of New Zealand native plant species on the abundance of nitrifying and denitrifying microorganisms in the soil using a pot experiment with five native plant species (Carex secta, Coprosma robusta, Kunzea robusta, Leptospermum scoparium, and Metrosideros umbellata) and exotic pasture (Lolium perenne). Half of the pots received fertilisation with N (urea), phosphorus, potassium, and sulphur, while the remainder were unfertilised controls. We quantified the abundance of bacteria, archaea, and the functional genes encoding nitrite reductase (nirK, nirS), nitrous oxide reductase (nosZ), and bacterial and archaeal ammonia monooxygenase (amoA) in the rhizosphere of these plants. Results indicated that plant species had a significant effect on the abundance of nosZ and bacterial amoA. In fertilised soil, the abundance of bacterial amoA was lower under mono- than dicotyledonous species. Similarly, the chemical properties of the soil differed between these groups. Monocotyledonous species took up more N and had lower concentrations of mineral N in the rhizosphere. This indicates that the increased competition for N likely reduced the abundance of amoA and therefore nitrification and nitrate losses. The results support the utilisation of species selection to reduce N losses. In particular, monocotyledonous species may be planted in high-fertility environments to mitigate N contamination of ground- and surface water. Future work should determine the mechanisms of plant specific interaction with ammonia-oxidising bacteria, although plant uptake can explain some of the observed differences.

Short Time‐Scale Variability of Ammonium, Nitrate, and Nitrogen Loss Dynamics During an Upwelling‐Induced Bloom at the Oregon Shelf

AbstractAmmonium, a key intermediate nutrient, is typically low to undetectable on the Oregon coast, particularly as active upwelling delivers high onshore flow of ammonium‐poor waters. However, during bloom and post‐bloom conditions large ammonium concentrations and uptake rates have been described. High‐frequency on board nitrate + nitrite and ammonium analysis synchronized with continuous data from a towed profiling vehicle (equipped with in situ temperature, salinity, dissolved oxygen, and beam attenuation sensors), allowed us to describe coupled high‐resolution physico‐chemical dynamics of inorganic nitrogen in seven cross‐shelf transects, over several days, during an active phytoplankton bloom following cessation of upwelling favorable winds. We present first‐of‐their‐kind high‐resolution cross‐sections showing a build‐up, both within a thin plume of onshore‐originated water, and in mid‐to‐bottom on‐shore water columns, from undetectable values to up to 8 µM of ammonium. The plume extended across the shelf at mid‐depth and was identified in all transects. We also detected a decrease of nitrate in distinct water masses close to the mid‐shelf seabed, associated with low dissolved oxygen, and identified and quantified the amount of nitrogen lost. We found that nitrogen loss was minimal on the first days of relaxation conditions, and increased up to 12 μM off Newport. Combining nitrogen fluxes from benthic incubation chambers and N loss calculated with the NO tracer, we estimated that denitrification in sediments could not account for all N loss, requiring 22%–86% to occur elsewhere. Close association of N loss with particle‐rich, low O2 waters suggests the possibility that particle‐aggregate micro‐environments could provide additional sites for water column denitrification.

3,4-Dimethylpyrazole Phosphate Applied on Ammonium Sulfate Nitrate and Urea Reduces the Nitrification Process in Three Tropical Soils: An Incubation Study

ABSTRACT Objectives Nitrification inhibitors applied to soil can reduce nitrogen (N) fertilizer losses by delaying the nitrification process and reducing nitrate losses to environment with enhanced N-fertilizer management. In this study, laboratory-scale experiments were carried out in order to evaluate the efficiency of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) applied on urea and ammonium sulfate nitrate (ASN) sources under three tropical soils (Typic Quartzipsamment, Typic Hapludox and Rhodic Hapludox – contrasting soil textures). Methods Soil samples were incubated over 60 days and the content of nitrate (N-NO3 −), ammonium (N-NH4 +) and pH variations were assessed periodically. In addition, N-NO3 − and N-NH4 + percentage and nitrification inhibition were assessed. Results 3,4-Dimethylpyrazole phosphate application delays the nitrification process across all three tropical soil types, being more evident in the sandy-textured soils (Typic Quartzipsamment > Typic Hapludox > Rhodic Hapludox). DMPP application reduced the N-NO3 − and N-NH4 + percentage in both ASN and urea sources, mainly between 15 and 30 (ASN) and between 7 and 30 days after N fertilization (urea). However, 45 days after N fertilization, inhibition of the nitrification process by DMPP is unlikely, regardless of N source. Conclusions The nitrification process tended to be more intense when conventional urea was applied compared to conventional ASN. Therefore, the use of DMPP would benefit more urea than ASN mainly in sandy-textured soils, where the nitrification was observed to be increased.

Sustainability of cover cropping practice with changing climate in Illinois

Climate change could adversely impact the best management practices (BMPs) designed to build a sustainable agro-ecological environment. Cover cropping is a conservation practice capable of reducing nitrate-nitrogen (NO3–N) loadings by consuming water and nitrate from the soil. The objective of this study was to investigate how climate change would impact the proven water quality benefits of cereal rye as a winter cover crop (CC) over the climate divisions of Illinois using the DSSAT model. Moreover, this study explores the sustainability of the CC with the changing climate conditions by using five regional climate models (RCMs) projections of two warming scenarios-rcp45 (a medium emission scenario - radiative forcing of 4.5 W/m2) and rcp85 (a high emission scenario - radiative forcing of 8.5 W/m2)). The CC impact simulated in the warming scenarios for the near-term (2021–2040) and the far-term future (2041–2060) were compared with the baseline scenario (2001–2020). Our results conclude that the climate change may negatively impact [average of CC and no CC (NCC)] maize yield (−6.6%) while positively affecting soybean yield (17.6%) and CC biomass (73.0%) by the mid-century. Increased mineralization caused by rising temperature could increase the nitrate loss via tile flow (NLoss) and nitrate leached (NLeached) up to 26.3% and 7.6% on average by the mid-century in Illinois. Increasing CC biomass could reduce the NLoss more considerably in all the scenarios compared to the baselines. Nevertheless, the NLoss level in the CC treatment can increase from the near-term to far-term future and could get closer to the baseline levels in the NCC treatment. These results suggest that CC alone may not address nitrate loss goals via subsurface drainage (caused by increasing N mineralization) in future. Therefore, more robust and cost-effective BMPs are needed to aid the CC benefits in preventing nutrient loss from the agricultural fields.

Impacts of extreme climate on nitrogen loss in different forms and pollution risk with the copula model

Climate change is a key factor that profoundly affects aquatic environments. Because of climate warming, the increase in the intensity and frequency of extreme climate events has aggravated the uncertainty of nitrogen pollution. However, the risk of nitrogen loss under different climatic conditions has not been well assessed, which is of great significance for controlling diffuse pollution. In this study, we used the upper and middle Wei River Basin (UMWB) as the study area, and selected organic nitrogen (Org-N) and nitrate (NO3-N) as the two forms of nitrogen pollution. Then, we quantified the contributions of 10 climate factors and combined the Soil and Water Assessment Tool (SWAT) and copula to analyze the risk of pollution when extreme weather occurs. Our results showed that during periods of high precipitation and temperature, Org-N loss accounted for 96% and 83% of the total loss, and nitrate loss accounted for 74% and 67%, respectively. Org-N loss responded more strongly to high precipitation than nitrate loss because Org-N was transported with soil particles. The attribution analysis indicated that high precipitation amount (R95P) contributed to the largest Org-N loss. As for the nitrate loss, R95P, normal precipitation amount, and consecutive days with no precipitation were the most important climatic drivers, accounting for 35%, 32%, and 13% of the watershed area, respectively. After selecting critical source areas by identification method, an optimized copula model for nitrogen loss and the main climatic factors was proposed. The risk of nitrogen pollution under the defined climate severity was then quantified. The probabilities of Org-N and nitrate loss exceeding the top 1%–20% were 0.2%–15% and 0.8%–10% when the precipitation exceeded the top 20%. The pollution risk caused by high temperatures is lower than that caused by precipitation. This study emphasized the dominant role of extreme climate in driving nitrogen loss and proposed a method for quantifying the risk of nitrogen pollution under specific climate conditions, which enabled managers to identify high-risk pollution areas and optimize management measures to prevent diffuse nitrogen pollution.

A hydrogenotrophic Sulfurimonas is globally abundant in deep-sea oxygen-saturated hydrothermal plumes

Members of the bacterial genus Sulfurimonas (phylum Campylobacterota) dominate microbial communities in marine redoxclines and are important for sulfur and nitrogen cycling. Here we used metagenomics and metabolic analyses to characterize a Sulfurimonas from the Gakkel Ridge in the Central Arctic Ocean and Southwest Indian Ridge, showing that this species is ubiquitous in non-buoyant hydrothermal plumes at Mid Ocean Ridges across the global ocean. One Sulfurimonas species, USulfurimonas pluma, was found to be globally abundant and active in cold (<0−4 °C), oxygen-saturated and hydrogen-rich hydrothermal plumes. Compared with other Sulfurimonas species, US. pluma has a reduced genome (>17%) and genomic signatures of an aerobic chemolithotrophic metabolism using hydrogen as an energy source, including acquisition of A2-type oxidase and loss of nitrate and nitrite reductases. The dominance and unique niche of US. pluma in hydrothermal plumes suggest an unappreciated biogeochemical role for Sulfurimonas in the deep ocean.