Nitrate Losses Research Articles

Diffuse water pollution during recent extreme wet-weather in the UK: Environmental damage costs and insight into the future?

Periods of extreme wet-weather elevate agricultural diffuse water pollutant loads and climate projections for the UK suggest wetter winters. Within this context, we monitored nitrate and suspended sediment loss using a field and landscape scale platform in SW England during the recent extreme wet-weather of 2019–2020. We compared the recent extreme wet-weather period to both the climatic baseline (1981–2010) and projected near- (2041–2060) and far- (2071–2090) future climates, using the 95th percentiles of conventional rainfall indices generated for climate scenarios downscaled by the LARS-WG weather generator from the 19 global climate models in the CMIP5 ensemble for the RCP8.5 emission scenario. Finally, we explored relationships between pollutant loss and the rainfall indices. Grassland field-scale monthly average nitrate losses increased from 0.39-1.07 kg ha−1 (2016–2019) to 0.70–1.35 kg ha−1 (2019–2020), whereas losses from grassland ploughed up for cereals, increased from 0.63-0.83 kg ha−1 to 2.34–4.09 kg ha−1. Nitrate losses at landscape scale increased during the 2019–2020 extreme wet-weather period to 2.04–4.54 kg ha−1. Field-scale grassland monthly average sediment losses increased from 92-116 kg ha−1 (2016–2019) to 281–333 kg ha−1 (2019–2020), whereas corresponding losses from grassland converted to cereal production increased from 63-80 kg ha−1 to 2124–2146 kg ha−1. Landscape scale monthly sediment losses increased from 8-37 kg ha−1 in 2018 to between 15 and 173 kg ha−1 during the 2019–2020 wet-weather period. 2019–2020 was most representative of the forecast 95th percentiles of >1 mm rainfall for near- and far-future climates and this rainfall index was related to monitored sediment, but not nitrate, loss. The elevated suspended sediment loads generated by the extreme wet-weather of 2019–2020 therefore potentially provide some insight into the responses to the projected >1 mm rainfall extremes under future climates at the study location.

Effects of moisture contents in incorporated residues and soil on net nitrogen mineralization in a laboratory study

AbstractIn Mediterranean climates, winters are mild, and decomposition of crop residues generally continues during the rainy winter season. The objective of this study was to determine whether letting crop residues dry before incorporation slows down net nitrogen (N) mineralization and reduces the risk of nitrate losses with rain during the winter months. Incubation experiments were performed with processing tomato (Solanum lycopersicum L.) and broccoli (Brassica oleracea L. var. italica) residues. Three residue moisture treatments, ranging from fresh to air‐dry residues, and three soil moisture levels were included in the study. Net N mineralization was observed during the first week in the broccoli treatments, whereas tomato residues led to net N immobilization. Increasing moisture of incorporated residues increased net N mineralization or immobilization. An exception was the fresh broccoli residue, which resulted in a lower net N mineralization rate than the drier residues, likely due to anaerobic microsites created by high microbial activity. The moisture content of the residues only had a short‐term effect on N turnover. Over the 12 wk of the incubations, the incorporation of both residues resulted in net N mineralization when compared with the unamended control. Nitrogen mineralization increased as soil moisture content increased and approached field capacity. These results indicate that residue moisture at the time of incorporation will not affect N mineralization beyond the initial weeks.

Efficiencies of best management practices in reducing nitrate pollution of the Sebdou River, a semi‐arid Mediterranean agricultural catchment (North Africa)

AbstractA major problem facing the water sector in Algeria is deteriorating water quality, which is strongly influenced by nutrient inputs to agricultural watersheds. To mitigate the effects of agricultural activities and enhance water quality, this study considered the impact of different best management practices (BMPs) in agriculture. The objective of the research was to evaluate the impacts of various agricultural BMPs on nitrate losses in the Sebdou catchment in north‐west Africa using the Soil and Water Assessment Tool (SWAT) model in order to identify and recommend the most appropriate BMP. The study was carried out in two parts: first, the SWAT model was calibrated and validated to simulate discharge and nitrate losses at the outlet of the catchment, and second, the calibrated model was used to assess the effects of BMPs on nitrate losses. The hydrological modelling fitted well with the observed data for the calibration and validation periods (NSE between 0.63 and 0.65 and R2 between 0.80 and 0.92). Nitrate simulation was also satisfactory (NSE = 0.58 and R2 = 0.58), with the average nitrate exports at the outlet varying between 136 and 149 t N year−1. Agricultural tillage practices were the main N input and plant uptake was the main N output. The simulation results of BMP scenarios (contour farming, strip cropping and terracing) showed a significant decrease in nitrate quantity in soil, nitrate yield in surface run‐off and nitrate exports. The maximum reduction was observed from the use of parallel terraces, which reduced nitrate in soil by 17% (41 kg ha−1) and decreased nitrate flux exportation to below 133 t N year−1 (a reduction of about 11%). This study provided useful information for implementation of the most effective agricultural BMPs in the catchment for stakeholders who are interested in soil and water management.

Evaluation of the ammonia emission sensitivity of secondary inorganic aerosol concentrations measured by the national reference method

A national reference method for fine particulate matter mass measurement usually specifies Teflon-membrane filter for the collection of ambient particles. Ammonium nitrate, one of the major components of fine particulate matter, is semi-volatile and susceptible to evaporation loss during and after field sampling by Teflon-membrane filter. The goal of this study is to evaluate the ammonia emission sensitivity of secondary inorganic aerosol (SIA) concentrations measured by the national reference method. The evaporation loss of particulate ammonium nitrate during and after field sampling was included in the analysis to cover a wide range of emission scenarios and meteorological conditions. The global to mesoscale air quality forecast and analysis system was used to predict the PM2.5 concentrations and chemical compositions. The predicted relative humidity and temperature were used to calculate the amount of ammonium nitrate evaporation loss from the thermodynamic equilibrium model. Except for the cool months, the particulate ammonium nitrate evaporation loss significantly decreases the ammonium nitrate contents in the SIA and subsequently degraded the effectiveness of ammonia emission control over the SIA. The SIA concentration decrease achieved by a 30% reduction of ammonia emission is lessened by 27–33% in the spring, 49–79% in the summer, 21–41% in the fall when the ammonium nitrate evaporation loss is included. We also proposed the normalized ammonia emission sensitivity of ammonium nitrate concentrations (γ(NH4NO3)) as a measure of the effectiveness of ammonia control and derived a mathematical relationship between γ(NH4NO3) and ammonia reduction rates in ammonia-rich conditions.

Connecting soil characteristics to edge-of-field water quality in Ohio.

Soil health and water quality improvement are major goals of sustainable agricultural management systems, yet the connections between soil health and water quality impacts remain unclear. In this study we conducted an initial exploratory assessment of the relationships between soil chemical, physical, and biological properties and edge-of-field water quality across a network of 40 fields in Ohio, USA. Discharge, dissolved reactive P (DRP), total P (TP), and nitrate (NO3 ) losses associated with precipitation events via surface runoff and tile drainage were monitored. Agronomic soil tests and a suite of soil health indicators were measured, then predictive relationships between the field average soil properties and tile drainage and surface runoff discharge and DRP, TP, and nitrate loads were explored with random forest and multiple linear regression approaches. Among the soil health indicators, water extractable C and N were consistently found to be positively related to tile nitrate loads, but other soil health indicators had little or inconsistent importance for water quality impacts. Several other soil properties were important predictors, particularly soil P pools for surface and tile DRP and TP losses as well as Mehlich-3 (M3) extractable Fe and Al for surface and tile discharge. Thus, we did not observe strong evidence that soil health was associated with improved edge-of-field water quality across the edge-of-field monitoring network. However, additional studies are needed to definitively test the relationships between a broader array of soil health metrics and water quality outcomes.

Field-scale monitoring of nitrate leaching in agriculture: assessment of three methods

Deterioration of groundwater quality due to nitrate loss from intensive agricultural systems can only be mitigated if methods for in-situ monitoring of nitrate leaching under active farmers’ fields are available. In this study, three methods were used in parallel to evaluate their spatial and temporal differences, namely ion-exchange resin-based Self-Integrating Accumulators (SIA), soil coring for extraction of mineral N (Nmin) from 0 to 90 cm in Mid-October (pre-winter) and Mid-February (post-winter), and Suction Cups (SCs) complemented by a HYDRUS 1D model. The monitoring, conducted from 2017 to 2020 in the Gäu Valley in the Swiss Central Plateau, covered four agricultural fields. The crop rotations included grass-clover leys, canola, silage maize and winter cereals. The monthly resolution of SC samples allowed identifying a seasonal pattern, with a nitrate concentration build-up during autumn and peaks in winter, caused by elevated water percolation to deeper soil layers in this period. Using simulated water percolation values, SC concentrations were converted into fluxes. SCs sampled 30% less N-losses on average compared to SIA, which collect also the wide macropore and preferential flows. The difference between Nmin content in autumn and spring was greater than nitrate leaching measured with either SIA or SCs. This observation indicates that autumn Nmin was depleted not only by leaching but also by plant and microbial N uptake and gaseous losses. The positive correlation between autumn Nmin content and leaching fluxes determined by either SCs or SIA suggests autumn Nmin as a useful relative but not absolute indicator for nitrate leaching. In conclusion, all three monitoring techniques are suited to indicate N leaching but represent different transport and cycling processes and vary in spatio-temporal resolution. The choice of monitoring method mainly depends (1) on the project’s goals and financial budget and (2) on the soil conditions. Long-term data, and especially the combination of methods, increase process understanding and generate knowledge beyond a pure methodological comparison.

Low temperature Moving Bed Bioreactor denitrification as mitigation measure to reduce agricultural nitrate losses

The negative impact of agriculture on the quality of local water streams is widely recognized. Fertilizer residues not taken up by the crops leach into the drainage water and enter the surface water, resulting in eutrophication. Despite various initiatives to prevent this leaching by optimizing fertilizer schemes, the desired effect was not achieved, and the focus has shifted to denitrifying end-of-pipe techniques. Because the available area for installing such treatment systems is often limited, the development of intensified systems is a trend that has emerged recently. In this scope, the main goal of this study was therefore to investigate the suitability of a denitrifying Moving Bed Bioreactor (MBBR) as a low footprint technology, which can compete with conventional technologies. Two parallel lab-scale pilot MBBRs, one at low temperature and one at ambient temperature, were operated for 850 days to investigate the effectiveness and robustness under changing process parameters (hydraulic retention time (HRT), temperature, shutdown). Eventually, the system was scaled up to a full-scale installation and monitored during a full drainage season in the field. The pilot-scale MBBRs achieved removal efficiencies above 90% under optimal conditions (high C/N ratio and minimal HRT of 8 h), even while operating at low temperatures. The robustness of the system was also demonstrated by the immediate start-up after a shutdown period of 220 days. Overall, the full-scale MBBR treated 2910.1 m3 drainage water and removed approximately 59 kg NO3-N. Unfortunately, the average removal efficiency, i.e., 70%, was lower than the lab-scale system, but by intensifying the mixing in the MBBR, improved results were obtained. Nitrite accumulation was furthermore also prevented.

Influence of atmospheric deposition on biogeochemical cycles in an oligotrophic ocean system

Abstract. The surface mixed layer (ML) in the Mediterranean Sea is a well-stratified domain characterized by low macronutrients and low chlorophyll content for almost 6 months of the year. In this study we characterize the biogeochemical cycling of nitrogen (N) in the ML by analyzing simultaneous in situ measurements of atmospheric deposition, nutrients in seawater, hydrological conditions, primary production, heterotrophic prokaryotic production, N2 fixation and leucine aminopeptidase activity. Dry deposition was continuously measured across the central and western open Mediterranean Sea, and two wet deposition events were sampled, one in the Ionian Sea and one in the Algerian Basin. Along the transect, N budgets were computed to compare the sources and sinks of N in the mixed layer. In situ leucine aminopeptidase activity made up 14 % to 66 % of the heterotrophic prokaryotic N demand, and the N2 fixation rate represented 1 % to 4.5 % of the phytoplankton N demand. Dry atmospheric deposition of inorganic nitrogen, estimated from dry deposition of nitrate and ammonium in aerosols, was higher than the N2 fixation rates in the ML (on average 4.8-fold). The dry atmospheric input of inorganic N represented a highly variable proportion of biological N demand in the ML among the stations, 10 %–82 % for heterotrophic prokaryotes and 1 %–30 % for phytoplankton. As some sites were visited on several days, the evolution of biogeochemical properties in the ML and within the nutrient-depleted layers could be followed. At the Algerian Basin site, the biogeochemical consequences of a wet dust deposition event were monitored through high-frequency sampling. Notably, just after the rain, nitrate was higher in the ML than in the nutrient-depleted layer below. Estimates of nutrient transfer from the ML into the nutrient-depleted layer could explain up to a third of the nitrate loss from the ML. Phytoplankton did not benefit directly from the atmospheric inputs into the ML, probably due to high competition with heterotrophic prokaryotes, also limited by N and phosphorus (P) availability at the time of this study. Primary producers decreased their production after the rain but recovered their initial state of activity after a 2 d lag in the vicinity of the deep chlorophyll maximum layer.

Alternate Partial Root-Zone Drip Nitrogen Fertigation Reduces Residual Nitrate Loss While Improving the Water Use but Not Nitrogen Use Efficiency.

The efficient utilization of irrigation water and nitrogen is of great importance for sustainable agricultural production. Alternate partial root-zone drip irrigation (APRD) is an innovative water-saving drip irrigation technology. However, the coupling effects of water and nitrogen (N) supply under APRD on crop growth, water and N use efficiency, as well as the utilization and fate of residual nitrates accumulated in the soil profile are not clear. A simulated soil column experiment where 30–40 cm soil layer was 15NO3-labeled as residual nitrate was conducted to investigate the coupling effects of different water [sufficient irrigation (W1), two-thirds of the W1(W2)] and N [high level (N1), 50% of N1 (N2)] supplies under different irrigation modes [conventional irrigation (C), APRD (A)] on tomato growth, irrigation water (IWUE) and N use efficiencies (NUE), and the fate of residual N. The results showed that, compared with CW1N1, AW1N1 promoted root growth and nitrogen absorption, and increased tomato yield, while the N absorption and yield did not vary significantly in AW2N1. The N absorption in AW2N2 decreased by 16.1%, while the tomato yield decreased by only 8.8% compared with CW1N1. The highest IWUE appeared in AW2N1, whereas the highest NUE was observed in AW2N2, with no significant difference in NUE between AW2N1 and CW1N1 at the same N supply level. The 15N accumulation peak layer was almost the same as the originally labeled layer under APRD, whereas it moved 10–20 cm downwards under CW1N1. The amount of 15N accumulated in the 0-40 cm layer increased with the decreasing irrigation water and nitrogen supply, with an increase of 82.9–141.1% in APRD compared with that in CW1N1. The utilization of the 15N labeled soil profile by the tomato plants increased by 9–20.5%, whereas the loss rate of 15N from the plant-soil column system decreased by 21.3–50.1% in APRD compared with the CW1N1 treatment. Thus, APRD has great potential in saving irrigation water, facilitating water use while reducing the loss of residual nitrate accumulated in the soil profile, but has no significant effect on the NUE absorbed.

Organic nitrogen enhances nitrogen nutrition and early growth of Pinus sylvestris seedlings.

Boreal trees are capable of taking up organic nitrogen (N) as effectively as inorganic N. Depending on the abundance of soil N forms, plants may adjust physiological and morphological traits to optimize N uptake. However, the link between these traits and N uptake in response to soil N sources is poorly understood. We examined Pinus sylvestris L. seedlings’ biomass growth and allocation, transpiration and N uptake in response to additions of organic N (the amino acid arginine) or inorganic N (ammonium nitrate). We also monitored in situ soil N fluxes in the pots following an addition of N, using a microdialysis system. Supplying organic N resulted in a stable soil N flux, whereas the inorganic N resulted in a sharp increase of nitrate flux followed by a rapid decline, demonstrating a fluctuating N supply and a risk for loss of nitrate from the growth medium. Seedlings supplied with organic N achieved a greater biomass with a higher N content, thus reaching a higher N recovery compared with those supplied inorganic N. In spite of a higher N concentration in organic N seedlings, root-to-shoot ratio and transpiration per unit leaf area were similar to those of inorganic N seedlings. We conclude that enhanced seedlings’ nutrition and growth under the organic N source may be attributed to a stable supply of N, owing to a strong retention rate in the soil medium.

Strong Acids or Bases Displaced by Weak Acids or Bases in Aerosols: Reactions Driven by the Continuous Partitioning of Volatile Products into the Gas Phase

Aerosols are ubiquitous in the atmosphere and profoundly affect climate systems and human health. To gain more insights on their broad impacts, we need to comprehensively understand the fundamental properties of atmospheric aerosols. Since aerosols are multiphase, a dispersion of condensed matter (solid particles or liquid droplets, hereafter particles) in gas, partitioning of volatile matter between the condensed and the gas phases is one defining characteristic of aerosols. For example, water content partitioning under different relative humidity conditions, known as aerosol hygroscopicity, has been extensively investigated in the past decades. Meanwhile, partitioning of volatile organic or inorganic components, which is referred to as aerosol volatility, remains understudied. Commonly, a bulk solution system is treated as a single phase, with volatility mainly determined by the nature of its components, and the composition partitioning between solution and gas phase is limited. Aerosols, however, comprise an extensive gas phase, and their volatility can also be induced by component reactions. These reactions occurring within aerosols are driven by the formation of volatile products and their continuous partitioning into the gas phase. As a consequence, the overall aerosol systems exhibit prominent volatility. Noteworthily, such volatility induced by reactions is a phenomenon exclusively observed in the multiphase aerosol systems, and it is trivial in bulk solutions due to the limited extent of liquid-gas partitioning. Take the chloride depletion in sea salt particles as an example. Recent findings have revealed that chloride depletion can be caused by reactions between NaCl and weak organic acids, which release HCl into the gas phase. Such a reaction can be described as a strong acid displaced by a weak acid, which is hardly observed in bulk phase. Generally, this unique partitioning behavior of aerosol systems and its potential to alter aerosol composition, size, reactivity, and other physicochemical properties merits more attention by atmospheric community.This Account focuses on the recent advancements in the research of component reactions that induce aerosol volatility. These reactions can be categorized into four types: chloride depletion, nitrate depletion, ammonium depletion, and salt hydrolysis. The depletion of chloride or nitrate can be regarded as a displacement reaction, in which a strong acid is displaced by a weak acid. Such a reaction releases highly volatile HCl or HNO3 into the gas phase and leads to a loss of chloride or nitrate within the particles. Likewise, ammonium depletion is a displacement reaction in which a strong base is displaced by a weak base, resulting in release of ammonia and substantial changes in aerosol hygroscopicity. In addition, aerosol volatility can also be induced by salt hydrolysis in a specific case, which is sustained by the coexistence of proton acceptor and hydroxide ion acceptor within particles. Furthermore, we quantitatively discuss these displacement reactions from both thermodynamic and kinetic perspectives, by using the extended aerosol inorganic model (E-AIM) and Maxwell steady-state diffusive mass transfer equation, respectively. Given the ubiquity of component partitioning in aerosol systems, our discussion may provide a new perspective on the underlying mechanisms of aerosol aging and relevant climate effects.

Split-nitrogen application with cover cropping reduces subsurface nitrate losses while maintaining corn yields.

Artificial subsurface drainage is essential to sustain crop production in many areas but may also impair water quality by exacerbating nitrate (NO3 )-nitrogen (N) delivery downstream. Cover crops and split-N application have been promoted as key conservation practices for reducing NO3 -N losses, but few studies have simultaneously assessed their effect on water quality and crop productivity. A field study was conducted to evaluate the effects of N application timing and cover crops on subsurface drainage NO3 -N losses and grain yield in continuous corn (Zea mays L.). Treatments were preplant-N: 224kg N ha-1 split-applied with 60% fall + 40% preplant in 2018, or as single preplant applications in 2019 and 2020; split-N: 40% preplant + 60% side-dress (V6-V7); split-N + cover crop (CC): Split-N + cereal rye (Secale cereale L.); and a zero N plot as the control. Across the 3-yr study period, split-N + CC significantly reduced flow-weighted NO3 -N concentration and NO3 -N loss by 35 and 37%, respectively, compared with preplant-N. However, flow-weighted NO3 -N concentration (4.3mg L-1 ) and NO3 -N loss (22.4kg ha-1 ) with split-N were not significantly different from either preplant-N (4.8mg L-1 and 26.4kg ha-1 , respectively) or split-N + CC (3.1mg L-1 and 16.7kg ha-1 , respectively). Corn yield was significantly lower in the control treatment but did not differ among N fertilized treatments in any year. These results indicate that combining split-N application with cover crops holds promise for meeting the statewide interim milestone NO3 -N reduction target of 15% by 2025 without negatively impacting crop productivity.

A broad-scale spatial analysis of the environmental benefits of fertiliser closed periods implemented under the Nitrates Directive in Europe

Nutrient pollution from agriculture has been an ongoing challenge for decades, contributing to numerous negative environmental impacts. In the European Union policies have been developed to address nutrient pollution, including Nitrate Action Programmes under Council Directive 91/676/EEC. Although Member States report on progress on implementation, there have been few studies that explore how measures have been implemented; the environmental implications of any differences; and how they vary spatially on a European scale. This study aims to address this gap with respect to fertiliser closed periods (1155 different closed periods across 69 Nitrate Action Programmes). This included the development of an approach that can be applied using readily available spatial data. Each closed period was scored for its coverage of risk periods for losses of nitrate; organic material; nitrous oxide and ammonia. Closed periods were then matched to relevant combinations of spatial data for each environmental zone and fertiliser type. The scores for each combination were used to create maps and calculate spatial statistics. The results show that in addition to nitrate, closed periods also reduce the risk of organic material run-off, emissions of nitrous oxide and to a lesser extent ammonia. However, risk reduction is spatially variable across all the impacts and the scope for synergy is also variable (e.g. nitrate loss does not always correlate with nitrous oxide or ammonia risk reduction). Regions in the Atlantic, Lustanian and some areas within the Mediterranean zones appear to provide the greatest combined risk reduction, with other zones, especially in eastern Europe, having a lower combined risk reduction (due to a combination of different risk periods coupled with lower coverage of individual risks). The spatial analysis within this study is relatively simple; is based on a snapshot of closed periods during 2019–2020; and only explores one measure. However, it does provide some useful data and insights that could support policy development in the future. This includes scope for Member States and regions to learn from others where greater coverage of risk periods has been achieved; and highlighting how a more holistic perspective can be taken to the environmental management of nutrients. As we strive towards developing sustainable production systems, farmers and policy makers need to take a more integrated approach to incorporate additional environmental objectives; which increases the complexity of the challenge. Consequently, the demand for pragmatic approaches that take a more holistic approach is likely to increase in the future.

Strong sensitivity of watershed-scale, ecohydrologic model predictions to soil moisture

It is currently unclear how changes to modeled soil water simulations influence key predictions in complex, ecohydrologic models, particularly beyond hydrology. We assessed sensitivity to soil moisture in the Soil and Water Assessment Tool by artificially perturbing simulated soil moisture and analyzing targeted prediction change. Results demonstrated a strong, process-dependent sensitivity of model predictions to perturbations in soil moisture. At the basin scale, the absolute values of differences from a baseline simulation for surface runoff, evapotranspiration, and nitrate loss ranged from 42% to 107%, 29%–76%, and 19%–369%, respectively, for soil moisture changes between 0.5 and 2 standard deviations. Landscape-scale results illustrated the impact of modeled land management actions, notably fertilizer applications, on determining the magnitude of the change. The findings highlight and motivate the need to improve soil moisture simulations, suggesting possible accuracy improvement for key model predictions by more precisely simulating soil moisture.

Spring barley grown for decades with straw incorporation and cover crops: Effects on crop yields and N uptake

• Four different straw rates were incorporated for four decades. • Minor effects on spring barley yields and N uptake in grain and straw were found. • Grass-clover cover crops improved barley yield and quality. • Ryegrass cover crops had a small but negative impact on barley yield. Straw incorporation and cover cropping are important measures for reducing loss of nitrate by leaching and supporting soil quality in cereal cropping systems. However, cereal straw also represents an important source of bioenergy, while concerns still exist regarding a negative effect of annual straw incorporation on crop yields. Based on a field experiment initiated in 1981 on a sandy loam soil at Askov Experimental Station (Denmark), we examined the effect of annual addition of straw (0, 4, 8 and 12 Mg ha −1 ), undersown cover crops (ryegrass and ryegrass-clover), and ploughing time (autumn and spring) on spring barley yields and N uptake in grain and grain-free aboveground biomass. During 1981–2019, grain yields showed an annual increase of 0.05 Mg DM ha −1 while grain N concentration decreased 0.019 %-point yr −1 . Straw incorporation rate had a significant effect on grain yield in only six out of 31 years. The effect of increasing straw rates was slightly negative in two of the initial years but positive in the extreme drought year 2018. During 2004–2018, an undersown grass-clover cover crop increased grain yield with 0.41 Mg DM ha −1 and grain N concentration with 0.13 %-point, corresponding to relative increases of 9% when compared to no cover crop. In contrast, an undersown ryegrass cover crop reduced grain yield with 0.21 Mg DM ha −1 corresponding to a relative reduction of 5%, and increased grain N concentration with 0.03 %-point corresponding to a relative increase of 2%, as compared to no cover crop. The time of incorporating straw and cover crop residues had a minor effect on barley yield and quality. Our results suggest that removal of straw for bioenergy does not compromise yields of spring barley grown at this site, while an inclusion of undersown leguminous cover crops had a pronounced positive impact on crop yield and quality. However, implementation of these management measures needs to be site-specific and consider trade-offs between effects on crop yield and quality, environmental benefits, and soil quality.

Landscape configuration mediates hydrology and nonpoint source pollution under climate change and agricultural expansion

Climate variability and landscape modifications directly influence watershed hydrology and processes of nonpoint source pollution, while remedial action requires distinguishing their effects. However, nonlinearity and multiple causality limit our ability to diagnose causes. Therefore, this study developed an approach that integrates hydrological modeling, random forests, regression trees, and variation partitioning analysis, to identify the effects of climate and landscape pattern changes upon runoff and nitrate loading in two typical watersheds in the Three Gorges Reservoir area of China. The Soil and Water Assessment Tool (SWAT) was used to track the spatiotemporal dynamics of runoff and nitrate loading (2000–2015). The findings showed that drylands and orchards were the dominant sources of nitrate and baseflow was the key mode of nitrate transport. Water yield and baseflow were mainly influenced by precipitation change, while the surface runoff and nitrate load were affected primarily by landscape pattern changes, especially in the wet season. Although ecological restoration programs have improved forest cover and forest fragmentation, the effects of forest restoration on the reduction of surface runoff and nitrate at the watershed scale have been offset by increased precipitation and agricultural expansion. Nevertheless, the role of landscape configuration is so dramatic that it can override variation in nitrate losses driven by changes in land cover and precipitation. Effective control of nitrate loss under intensive ecological restoration can be achieved by using a mosaic of “sink” patches to divide larger areas of cropland into smaller patches, maintaining cropland fragmentation, and limiting the increase in edge density of cropland. This paper’s proposed and implemented approach provides a new understanding of the interactions and nonlinear relationship between hydrological processes and environmental change, providing explicit ideas and useful insights for landscape planners and managers for improving eco-hydrological functions of watershed at the practical level. We emphasize that the impact of land use change cannot be assumed to be linear in restoration strategies, instead nonlinear impacts, clear details of landscape configuration, and seasonal climatic characteristics should be explicitly considered.

Evaluation of climate change impacts and effectiveness of adaptation options on nitrate loss, microbial respiration, and soil organic carbon in the Southeastern USA

CONTEXTClimate change presents an agricultural challenge in the Southeastern USA with implications for maintaining environmental quality. OBJECTIVEThe objective of this study was to assess climate change impacts and adaptation practices (biochar and irrigation) simulated with the Environmental Policy Integrated Climate (EPIC) model on nitrate-N (NO3-N) losses, microbial respiration (MR) and soil organic carbon (SOC) in the Southeastern USA. METHODSThe EPIC model was used to assess the impacts of climate change and adaptations on NO3-N losses in leachate and runoff from the soil profile (0–100 cm), loss of soil C via MR (0–100 cm), and impacts on SOC stocks (0–10 cm) for representative farms growing C3 and C4 crops within ten Southeastern USA states. The adaptations explored were annual biochar applications and irrigation. Historical baseline (1979–2009) and future (2041–2070) climate scenarios were used for simulations with CO2 concentrations of 360 ppm and 500 ppm, respectively. Four regional climate models (RCMs), nested within global climate models (GCMs) for their boundary conditions, simulated changes in air temperatures, precipitation, and solar radiation. RESULTS AND CONCLUSIONSClimate change increased simulated NO3-N losses in leaching and runoff by 40–80%, compared to historical baseline scenarios that was attributed to overall increased annual precipitation under three of the four RCM_GCM models. For the C4 crops, NO3-N leaching and runoff losses were 16–47% and 31–45% lower than for the C3 crops, respectively. Biochar applications reduced NO3-N leaching in the West region during 2066–2070 under the RCM3_CGCM3 model. The differences in MR between the C4 and C3 crops ranged from 3 to 75%. SOC increased under C4 crops and when biochar was applied. We concluded that inclusion of C4 crops in crop rotations and the applications of biochar under wetter climate scenarios may be a promising adaptation strategy to reduce NO3-N losses and increase SOC content in the soils of the Southeastern USA. SIGNIFICANCEThis study represents one of the first attempts to assess the effectiveness of climate change adaptations such as the agricultural use of biochar and irrigation. The findings from this study strongly contribute to our understanding of potential climate change impacts on a region's agriculture and resulting environmental footprint. This information may be used by the scientific community along with decision and policy makers working on conceptual and practical technologies to mitigate the impacts of climate change on agriculture and the environment.

Development of Ecological Strategies for the Recovery of the Main Nitrogen Agricultural Pollutants: A Review on Environmental Sustainability in Agroecosystems

Nitrogen (N) is a fundamental nutrient for plant growth and for the performance of biological functions. In agroecosystems, nitrogen fertilization is aimed at providing a suitable N dose for crop growth, avoiding the impoverishment or the improper enrichment of nitrogen compounds in soil. The high application of nitrogen fertilizers is the main cause of the increase in nitrate leaching and loss of the quality of natural resources (groundwater and soil). In the last decades, new sustainable technological approaches have been developed and applied on laboratory and field scales to reduce the impacts of nitrogen pollution on the environmental matrices and to improve the sustainability of agricultural management. This review highlights the results of the implementation of sustainable remediation new strategies to reduce pollution from a main agricultural contaminant (nitrate) and describes the benefits obtained from the use of these solutions in agroecosystems.

Drainage, Cover Crops, and Weather Impact Nitrate Loss

CSA NewsVolume 66, Issue 9 p. 20-20 SOCIETY SCIENCE Drainage, Cover Crops, and Weather Impact Nitrate Loss First published: 16 June 2021 https://doi.org/10.1002/csan.20508Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume66, Issue9September 2021Pages 20-20 RelatedInformation

Role of Nitrogen in Assessing the Sustainability of Irrigated Areas: Case Study of Northern Mexico

World’s food production relies on crops grown in irrigated land to feed an increasing population. In the long term, irrigation agriculture may cause environmental deterioration to the area (soil degradation, aquifer contamination) and its surroundings (greenhouse gas emission, eutrophication) to compromise crop production. Three irrigated areas in northern Mexico (Yaqui Valley, Delicias, Comarca Lagunera) were examined with respect to the challenges to achieve sustainability using reported values of nitrogen (N) along with the conventional aquifer depletion and water contamination parameters. N2O emissions, measured in only the Yaqui Valley, amounted to up to 4.5% of applied N, and nitrate losses to about 18%. The water tables of these aquifers are dropping at rates of 0.4 m year−1 (Delicias) to 1.5 m year−1 (Comarca Lagunera). High NO3− concentrations in the Comarca Lagunera (66.2% of wells above 10 mg L−1 NO3–N) pose a threat to human health. Although lower than 10 mg L−1 NO3–N in most wells, NO3− levels in Delicias and Yaqui Valley are increasing with time, although more data are needed to confirm the trend. Overall, and although the efforts by farmers still focus on increasing crop yield, awareness of the advantage of implementing measures towards sustainability is on the rise.