Nitrate Losses Research Articles

Reactive Transport of Manure‐Derived Nitrogen in the Vadose Zone: Consideration of Macropore Connectivity to Subsurface Receptors

Core Ideas Manure N transformation was modeled with different soil pore connectivities to tile drains. Macropores facilitated NH4+ oxidation reaction products deeper in the profile. Nitrate losses to tile were best predicted by models using pores connected to tile drains. Macropores can be important conduits for surface‐derived nutrients to reach subsurface receptors. Accordingly, nutrient reactive transport processes in macroporous soils need to be well understood. In this study, steady‐state two‐dimensional reactive transport simulations with MIN3P‐THCm (version 1.0.519.0) were used to elucidate how soil macropore connectivity to tile drains can influence N transformations following liquid swine manure (LSM) applications to soil. Four different soil scenarios were considered: homogeneous sand, homogeneous clay loam, and clay loam with discrete macropores connected to or disconnected from the bottom boundary used to represent tile drain outflow. In relation to the homogeneous soils, macropores, overall, facilitated chemical diffusion into the adjacent soil matrix along their length and broadly augmented O2 ingress into the soil profile. These processes combined to critically control the spatial distribution of NH4+ oxidation reaction products. When used in transient simulation mode with field data observed at experimental tile‐drained plots that received LSM application, the model showed that simulated nitrate mass losses to tile are considerably higher and most realistic under the connected macropore scenario compared with the homogeneous or disconnected macropore scenarios.

High temperature-produced biochar can be efficient in nitrate loss prevention and carbon sequestration

The effects of biochar on soil properties including nutrients have been reported in previous studies, but few studies targeted on soil nitrogen. Moreover, there remains a lack of studies considering the liberation of ammonia during the ammonium (N-NH4+) adsorption process. Our study aimed to fill this research gap. A pot incubation experiment was conducted for 84 days, with ten different soils and four rates of wood chip-based biochar (0.5, 2, 4, and 8%). Biochar's effect on soil ammonium was inconsistent and insignificant in most of the incubated soils at all biochar rates. This finding contradicted our Langmuir model, which estimated maximum ammonium adsorption capacity of biochar as 6.66 mg of N-NH4+ per g of biochar. Soil response in nitrate (N-NO3−) and dissolved organic carbon (DOC) followed a similar declining trend in all soils in both incubation periods, with the effect boosted according to the biochar application rate. The Langmuir isotherm estimated the maximum N-NO3− adsorption capacity of our biochar as 11.3 mg g−1. Soil original properties determined amount of nitrate and DOC reduction after biochar addition. Our result also indicated poor estimation of ammonium adsorption by biochar due to the liberation of ammonia. As a result, we strongly recommend that ammonia liberation should be considered during adsorption experiments and more studies in this field.

Hydrologic controls of controlled and free draining subsurface drainage systems

One of the strategies proposed for reducing nitrate losses from subsurface tile drain systems in Midwestern agricultural lands, controlled drainage, is known to reduce drain flow on an annual basis, but is not well understood for individual events. Understanding hydrologic controls that regulate outflow from free and controlled drainage systems during drainage events can offer improved insight on the overall functioning of these systems so that they can be better managed or retrofitted to increase their environmental benefits. This study used data from a monitoring site in east central Indiana to investigate the hydrology of 22 drainage events in free and controlled subsurface drainage systems. Relationships between event drainage volume, drain flow hydrograph metrics, column soil moisture, water table depth, and precipitation time series for each event were explored to determine the effect of precipitation characteristics and antecedent conditions on these metrics. Controlled drainage reduced event drainage volume and peak flows by 22% ± 12% and 29% ± 16% respectively, and increased the time to peak of drainage by 98% ± 52%. Higher total precipitation and precipitation time spread increased infiltration, while the average precipitation intensity did not correlate with drainage volumes in either system. Peak flow rate in free draining quadrants were positively affected by higher precipitation and average precipitation intensity, while in managed quadrants, the antecedent soil moisture appeared to be more influential in affecting peak flow rate than precipitation characteristics. Surface runoff potential increased with the increase in average precipitation intensity in all quadrants. Saturation excess ponding or possibly overland flow occurred in events that have a low average precipitation intensity, and a high precipitation time spread. Field observations indicate that saturation excess overland flow was more pronounced in controlled quadrants because water table levels rose higher than the water table levels of their free draining counterpart.

Do enzyme inhibitors dicyandiamide and NBPT influence the microbial immobilization of phosphorus in Humic Cambisol?

ABSTRACT The application of nitrogen fertilizers, both organic and mineral, can cause nitrate losses by leaching. To minimize this effect, enzyme inhibitors are used. However, the effects on microbial biomass, which is the most sensitive and dynamic compartment of nutrients in the soil, as well as its effect on nutrients such as phosphorus (P) are unknown. This study aimed to evaluate the influence of the enzyme inhibitor (EI) on soil microbial phosphorus (Pm) when mineral fertilizer (NPK) or liquid swine manure (LSM) was applied in corn cultivation. The experiment was installed in a Humic Cambisol in Lages – SC, Brazil (27° 47’ 08” S; 50° 18’ 09” W) in the 2012/2013 season. The treatments consisted of: i) NPK; ii) NPK + EI; iii) LSM; iv) LSM + EI, applied before sowing of corn, and v) control (without application of fertilizer and enzyme inhibitor) arranged in a randomized block design, under no-tillage system. Soil samples were collected from the 0-0.10 m layer at 0, 10, 25, 58, 90, 135 and 202 days after application of the treatments. The Pm content was not affected by the enzyme inhibitor application but was influenced throughout the crop cycle in response to water balance and corn cultivation.

Aluminum Oxide Thin Films from Aqueous Solutions: Insights from Solid-State NMR and Dielectric Response

Here, we employ a combination of 27Al solid-state nuclear magnetic resonance (SSNMR) and conventional spectroscopic and microscopic techniques to investigate the structural evolution of aqueous aluminum precursors to a uniform and smooth aluminum oxide film. The route involves no organic ligands and relies on dehydration, dehydroxylation, and nitrate loss for condensation and formation of the three-dimensional aluminum oxide structure. Local chemical environments are tracked as films evolve over the temperature range 200–1100 °C. 27Al SSNMR reveals that Al centers are predominantly four- and five-coordinate in amorphous films annealed between 200 and 800 °C and four- and six-coordinate in crystalline phases that form above 800 °C. The Al coordination of the aqueous-deposited aluminum oxide films are compared to data from SSNMR studies on vapor-phase-deposited aluminum oxide thin films. Additionally, dielectric constants of aluminum oxide-based capacitors are measured and correlated with the SSNMR results. Aluminum oxide is an important material for protective coatings, catalysis, and microelectronic applications. For the latter application, amorphous materials are preferred, but a lack of long-range order complicates structural characterization and determination of structure–property relationships. Solution deposition approaches are attractive alternatives to traditional vapor-phase deposition methods because precursors are commonly stable in air, and they enable printing and direct lithographic patterning on common semiconductor wafers as well as large-area and flexible substrates—useful for scale-up to applications in windows and photovoltaic devices.

Mn-based mixed oxides for low temperature NOx adsorber applications

Pd-promoted ternary oxides of the type Mn-Ce-Zr and Mn-Pr-Zr were characterized and evaluated for low temperature NOx storage applications such as diesel vehicle cold starts. While X-ray diffraction data were in all cases consistent with the formation of solid solutions, Mn/Zr and Mn/Ce(Pr) ratios found by XPS were consistently higher than the bulk values, indicative of an enrichment of Mn at the surface of the solids. Both sets of Pd-promoted mixed oxides showed remarkably high NOx storage efficiency in the range 80–160 °C, while a 1.8% Pd/Mn(27)-Ce(7)-Zr catalyst showed excellent NOx storage in simulated cold start experiments. Moreover, ramping the temperature to 370 °C in these experiments, simulating higher speed operation, resulted in near complete purging of stored NOx from the catalyst. NOx storage efficiency in isothermal storage experiments was found to improve with increasing Mn content for the 1%Pd/Mn(x)-Ce(7)-Zr series (x = 9, 18, 27 wt.%), DRIFTS measurements showing that relative to Ce-Zr mixed oxides, Mn incorporation favored NOx storage as nitrate. During temperature programmed desorption (TPD) two main desorption events were observed, corresponding to decomposition of nitrites (up to 200 °C), followed by loss of nitrates (⁓200–400 °C). Nitrates stored on Pd/Mn-Ce(Pr)-Zr mixed oxides desorbed during TPD at lower temperatures than for CeO2-ZrO2 mixed oxides, a finding attributed to the lower basicity of Mn compared to Ce. Hydrothermal aging of 1.8%Pd/Mn(27)-Ce(7)-Zr at 700 °C reduced NOx storage efficiency, although the catalyst was still able to store significant amounts of NOx. However, catalyst sulfation led to a large decrease in NOx storage efficiency and the efficiency could not be completely recovered with lean or rich desulfations at high temperatures.

Control of soil N cycle processes by Pteridium aquilinum and Erica cinerea in heathlands along a pH gradient

AbstractNitrate is a limiting resource in heathland acid soils. Nitrate levels increase in heathland soils after Pteridium aquilinum invasions, and this species is assumed to biologically control nitrogen cycle processes, thus increasing nitrate availability. We compared how P. aquilinum (bracken) and Erica cinerea (bell heather) modify processes driving nitrate availability along a soil pH gradient in a Natura 2000 reserve facing bracken invasion. Soil nitrate and ammonium concentrations, substrate‐induced respiration (SIR), denitrification and nitrification enzyme activities (DEA and NEA, respectively), root procyanidin concentrations, and denitrification inhibition by procyanidins were measured on five sites under P. aquilinum and E. cinerea stands. NEA and nitrate levels were higher, and ammonium levels and SIR lower, for P. aquilinum in the most acid soils. Procyanidins from both species induced the same level of denitrification inhibition, soil nitrate being correlated with root procyanidin concentration for both species. Soil nitrate correlated with NEA only for P. aquilinum. Our results show that both species increased procyanidin production in the most acid soils, thereby reducing denitrification and decreasing nitrate loss, this process being more efficient for E. cinerea. However, P. aquilinum additionally increased nitrification, and this double control on nitrification and denitrification was very efficient to increase soil nitrate availability in the most acid soils. This may participate to the success of P. aquilinum invasions in heathlands. This shows that approaches for bracken control in heathlands should better account for belowground processes and, more generally, that biological denitrification inhibition by plants may be a widespread phenomenon influencing soil N dynamics in N‐poor environments.

Controls on nitrogen transformation rates on restored floodplains along the Cosumnes River, California

Levee construction results in the systematic replumbing of river systems and reduces the frequency of floodplain inundation, which impacts nutrient delivery and transformations in floodplains. Floodplain restoration via levee removal affects downstream water quality by restoring soil microbial metabolic pathways such as denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA). Although these metabolisms are important for the nitrogen cycle, few studies have quantified the contribution of all three pathways to nitrate retention or loss in restored floodplains. The objectives of this study were to quantify the relevance of denitrification, anammox and DNRA to nitrogen retention, characterize the hydrologic conditions most favorable to each pathway, and estimate the potential for floodplain restoration to improve nitrogen cycling in the Cosumnes River watershed. To address these goals, we simulated flood conditions in soil mesocosms collected from two floodplains where levees were breached in 1997 and 2014 along the Lower Cosumnes River in the San Joaquin Basin of California. River water enriched with K15NO3 tracer was pumped into each mesocosm at a constant rate for a period of 3 months. Samples were collected from the surface water and soil pore water for measurements of NO3−, NO2−, and NH4+ concentrations, and δ15N of dissolved gases (N2 and N2O). To the best of our knowledge, this study reports the highest relative contribution to N2 production due to anammox for freshwater systems (41 to 84%) to date. High anammox rates were associated with heterogeneous grain size distribution across depth and high nitrification rates. We quantify the capacity of restored floodplain soils with distinct textural and chemical characteristics to retain or release nitrogen during large and small floods in a particular water year.

Winter cover crops reduce nitrate loss in an agricultural watershed in the central U.S.

Agricultural land use in the Midwestern U.S. is the major source of nitrogen (N) causing recurring hypoxia in the northern Gulf of Mexico. Despite efforts to reduce losses, N export from tile-drained, agricultural watersheds throughout the Corn Belt persists. The use of effective agricultural conservation practices can reduce N loss from fields, yet little is known about how field-scale implementation will translate into watershed-scale reductions in N export. In this study, we used a sampling approach with high spatial and temporal resolution to quantify changes in tile drain load and watershed export of nitrate (NO3−-N) after planting cover crops on >60% of croppable acres in a small, agricultural watershed. We found that median NO3−-N losses from tiles draining fields with cover crops were 69–90% lower than tiles draining fields without cover crops during winter/spring. Measured instantaneous flow was the major driver of NO3−-N losses from tile drains, though results suggest that this relationship differed between tiles with and without cover crops in spring. The signature of cover crops at the field-scale was evident in watershed NO3−-N export, particularly during times of elevated flows; median daily NO3−-N exported in elevated flows was 18–22% lower during years with watershed-scale planting of cover crops compared to years without. Nevertheless, changes in watershed NO3−-N export were smaller than the observed reductions in tile drain loads. Results indicate that tile drain reductions directly reflected the influence of cover crops at the field-scale while watershed export integrated both past and present management, ultimately complicating attempts to distinguish the effect of conservation efforts at larger spatial scales.

Managing controlled drainage in irrigated farmers’ fields: A case study in the Moghan plain, Iran

Conventional free subsurface drainage practices in the Moghan Plan, in northwest Iran, result in low irrigation efficiency and excessive volumes of drainage water causing extensive environmental problems. Controlled drainage (CD) is promoted to boost crop yields and reduce subsurface drainage flows and leaching of nutrients. This study was conducted to test management options for CD in irrigated farmers’ fields in the Moghan plain. Three options were tested: subsurface drains at 2 m with free outflow (FD), controlled drainage at 70 cm below soil surface (CD70) and controlled drainage with a varying depth depending on the crop stage (CDch). Irrigation gifts were based on the daily measured soil water content and thus varied per drainage treatment. In winter, wheat and barley were grown followed by maize in summer. For each crop and treatment, three replicates were made. The highest crop yields (for all crops) were found with CDch, followed by CD70. For wheat, the yields were respectively 27% and 41% higher in the CD70 and CDch compared to FD. For barley these increase was respectively 23% (CD70) and 34% (CDch) and for maize (forage yields) 19% (CD70) and 25% (CDch). The same trends were observed in water use efficiencies (WUE): compared to FD, the WUE was 26% in CD70 and 40% higher in CDch; for barley these increases were respectively 19% (CD70) and 32% (CDch), and for maize (forage yields) 30% (CD70) and 44% (CDch). Controlled drainage not only reduced subsurface drainage rates, but also nitrate and phosphorous losses. The average drain discharges with CDch were respectively 33%, 45% and 44% lower than FD for wheat, barley and maize. Flow-weighted NO3 concentration in drainage discharge of CD70 and CDch were, respectively, 15% and 9% for wheat, 9% and 13% for barley, and 8% and 7% for maize lower than in FD. Soil salinity decreased in FD, but slightly increased in the CD treatments. Thus, although controlled drainage clearly has advantages above free drainage practices, to optimize CD management options, more research is needed on the long-term effects of controlled drainage on soil salinity.

Long‐term Cropping Effects on Partitioning of Water Flow and Nitrate Loss between Surface Runoff and Tile Drainage

Surface runoff and tile drainage are the main pathways for water movement and entry of agricultural nitrate into water resources. The objective of this 5-yr study was to characterize the partitioning of water flow and nitrate loss between these pathways for a humid-temperate Brookston clay loam soil under 54 to 59 yr of consistent cropping and fertilization. Cropping treatments included monoculture corn ( L., MC), continuous bluegrass ( L.) sod (CS), and a corn-oat-alfalfa ( L.)-alfalfa rotation (RC-RO-RA1-RA2). Fertilization treatments included annual fertilizer addition (F) and no fertilizer addition (NF). Tile drainage and surface runoff occurred primarily during the nongrowing season (November-April), and they were highly correlated with the mean saturated hydraulic conductivity of the near-surface soil profile. Tile drainage accounted for 69 to 90% of cumulative water flow and 79 to 96% of cumulative nitrate loss from fertilized rotation and CS, whereas surface runoff accounted for the majority of the nitrate losses in MC (i.e., 75-93% of water flow and 65-96% of nitrate loss). Cumulative nitrate losses were highest in the RC-F (152 kg N ha), RC-NF (101 kg N ha), RA2-F (121 kg N ha), and RA2-NF (75 kg N ha) plots, and these high losses are attributed to N mineralization from the plowed alfalfa and fertilization (if applicable). Fertilization increased cumulative nitrate loss in tile drainage from all treatments, whereas no fertilization increased cumulative nitrate loss in surface runoff from the rotation. Cropping system and fertilization on clay loam soil changed how water flow and nitrate loss were partitioned between tile drainage and surface runoff.

Co-design and ex ante assessment of cropping system prototypes including energy crops in Eastern France

Producing biofuels from crops is controversial due to environmental issues and to food security threats linked with the dedication of land to energy crops rather than to food production. The 2009 European Renewable Energy Directive defined the reduction of greenhouse gas (GHG) emissions as an essential requirement for biofuels. Whatever their specific lifespans, energy crops have short- and long-term effects on the following crops, thus requiring assessment at cropping system level, which is rarely done in the literature.This study aimed at designing and assessing cropping system prototypes (CSP) that include energy crops and food/feed crops in Bourgogne (France), before being implemented in the field (i.e. ex ante). CSP were first designed, using a prototyping approach involving scientists and farm advisors, and then ex ante assessed, using indicators covering the environment, energy, economic and food issues. They were compared with two cropping systems based on food/feed crops. Lastly, we analyzed the sensitivity of the CSP profitability to several scenarios of crop yields and prices (i.e. grain and forage prices for food and feed crops respectively).CSP including Miscanthus x giganteus performed better in terms of GHG emissions, energy costs, nitrate losses and pesticide use than CSP that include only annual crops requiring more inputs, but achieved lower profitability and food production capacity. The cropping systems including only food/feed crops frequently achieved higher economic outcomes and food production capacity. Lastly, CSP combining pluriannual or annual energy crops and annual food/feed crops showed satisfactory trade-offs among environmental impacts and food production capacity.

A soil management strategy for ameliorating soil acidification and reducing nitrification in tea plantations

The cultivation of tea requires acidic soils which further acidify in plantations due to increased levels of nitrogen fixation. Ameliorating soil acidification by increasing pH is commonly implemented but as consequence, soil microbial nitrification causes losses of nitrate and limits the availability of NH4+ for tea, the latter being the preferred nitrogen source. Thus, the aim of this study was to analyze a strategy which can ameliorate soil acidification and simultaneously minimize the stimulation of nitrification in a typical tea soil. Net N transformation rates in different amounts of quicklime (CaO) and rice straw biochar addition treatments were determined through an incubation experiment, to test the effects of quicklime and biochar on acidification and nitrification in a typical tea soil. Our results showed that the addition of quicklime resulted in a significant increase in soil nitrification rate when soil pH increased from 3.77 to 4.10, but it decreased when soil pH increased to >5.10. Soil nitrification rate with biochar application continued to rise with increasing soil pH (3.77-3.85-4.01-4.38). When nitrification rates from all treatments were plotted against soil pH, we found that nitrification rate increased linearly with increasing soil pH from 3.63 to 4.38, then sharply declined to the values lower than that in the original soil pH when soil pH was increased from 4.38 to 5.10, and finally remained stable. Our results suggest that nitrification may be optimized in tea soil at ca. pH 4.40. Therefore, when we employed pH-raising practices to alleviate soil acidification, the soil pH should be enhanced to more than the optimum pH range for nitrification (approximately 5.10 in this study) to avoid stimulating soil nitrification.

Assessing resource-use efficiency of land use

We introduce an explicit indicator and the Land Use Management Support System to assess the resource-use efficiency of land use (RUE) at the landscape scale. To estimate RUE, we relate land-use performance with regard to ecosystem services indicators to the maximum possible land-use performance based on an optimised land-use configuration. The test application of the RUE assessment in the Haean catchment, South Korea, shows that the land-use system's RUE could be increased by 11% for both nitrate and sediment loss. The estimated headroom could indicate whether potential contaminant reduction targets for the downstream water reservoir Lake Soyang could be achieved with the current land-use system. The recurring RUE assessment for a given region might indicate the effectiveness of spatial planning and policy measures to improve the RUE in that region. Future work should address the integration of RUE into a participatory spatial planning or resource-management framework.

Reducing nitrogen fertilization of intensive kiwifruit orchards decreases nitrate accumulation in soil without compromising crop production

Excessive nitrogen (N) fertilization of high value horticultural crops is a common problem that not only increases the cost to farmers, but also negatively affects crop growth and the environment. A three-year field experiment was conducted in an intensive kiwifruit orchard in Shaanxi Province, China to compare the effects of reduced N fertilization applied as urea (U), and controlled release urea (CRU) on the N nutrition of kiwi vines, fruit yield and quality, and nitrate-N accumulation in the soil profile. The three treatments included a conventional N application rate (CF-U, 900 kg N ha−1 yr−1 as urea), two reduced N fertilization treatments where the amount of N fertilizer applied as U and CRU was reduced by 25% in 2013 and 2014, and by 45% in 2015. The 25 and 45% reduced N treatments had no adverse effects on the N concentrations in leaves and pruning branches and the fruit yield and quality of kiwi vines. However, they significantly enhanced the partial factor productivity of applied N (PFPN) and the economic benefits, and reduced nitrate accumulation in the 0–200 cm soil profile. The same benefits of reduced N fertilization were observed for both the U and CRU treatments, but the CRU treatment had the added benefit of decreasing the loss of nitrate through leaching. We concluded that the current level of N fertilization in kiwi orchards is very excessive, and reducing the N fertilizer rate by 25–45% could not only guarantee fruit yield, but also reduce N accumulation and loss.

Nitrate and phosphorus transport through subsurface drains under free and controlled drainage

Controlled drainage (CD) is a structural conservation practice in which the drainage outlet is managed in order to reduce drain flow volume and nutrient loads to water bodies. The goal of this study was to evaluate the potential of CD to improve water quality for two different seasons and levels of outlet control, using ten years of data collected from an agricultural drained field in eastern Indiana with two sets of paired plots. The Rank Sum test was used to quantify the impact of CD on cumulative annual drain flow and nitrate-N and phosphorus loads. CD plots had a statistically significant (at 5% level) lower annual drain flow (eastern pair: 39%; western pair: 25%) and nitrate load (eastern pair: 43%; western pair: 26%) compared to free draining (FD) plots, while annual soluble reactive phosphorus (SRP) and total phosphorus (TP) loads were not significantly different. An ANCOVA model was used to evaluate the impact of CD on daily drain flow, nitrate-N, SRP and TP concentrations and loads during the two different periods of control. The average percent reduction of daily drain flow was 68% in the eastern pair and 58% in the western pair during controlled drainage at the higher outlet level (winter) and 64% and 58% at the lower outlet level (summer) in the eastern and western pairs, respectively. Nitrate load reduction was similar to drain flow reduction, while the effect of CD on SRP and TP loads was not significant except for the increase in SRP in one pair.These results from a decade-long field monitoring and two different statistical methods enhance our knowledge about water quality impacts of CD system and support this management practice as a reliable system for reducing nitrate loss through subsurface drains, mainly caused by flow reduction.

Summer Fertigation of Dairy Slurry Reduces Soil Nitrate Concentrations and Subsurface Drainage Nitrate Losses Compared to Fall Injection

Leaching of nitrate (NO3-N) from manure-applied cropping systems can represent a substantial N-loss to the environment for dairy farms, particularly in fields with artificial subsurface drainage. In this on-farm study, we used a Before/After analysis to assess the effectiveness of summer fertigation with reduced manure rates (years 2010 – 2015) versus fall injection (2007 – 2009) of dairy slurry in terms of subsequent corn silage yield, corn N removal, soil NO3-N distribution, and NO3-N losses in subsurface tile drainage from a 65-ha field in Minnesota, USA. Yield was similar between periods (average of 18.8 Mg ha-1), but crop %N, N removal, and manurial N-use efficiency were 15, 12, and 126% greater during the fertigation than injection period. Fertigation reduced spring soil NO3-N concentrations to 60-cm depth by an average of 53% relative to injection, except in the 15 to 30 cm increment, where no difference was found. Similarly, fall soil NO3-N concentrations from 30 to 90 cm were 48% lower, on average, under fertigation than injection. Weekly flow-weighted mean NO3-N concentration in tile drainage was lower during fertigation (47.7 mg L-1) than injection (56.8 mg L-1), although mean weekly drainage depth was greater during fertigation (2.3 versus 1.1 mm). This resulted in similar weekly loads between periods (mean of 0.96 kg NO3-N ha-1). For non-snowmelt flow, relationships between drainage and NO3-N load showed log–log slopes of near 1.0 for injection and 0.97 for fertigation, indicating dilution of concentrations with increased flow during fertigation, but not during injection. Differing intercepts indicated a treatment effect of fertigation independent of flow effects, and corresponded to loads of 5.9 kg NO3-N ha-1 for injection and 4.7 kg NO3-N ha-1 for fertigation, a reduction of 20% at a 10 mm weekly flow depth. The magnitude of the reduction in load increased to 22% at a 25 mm weekly flow depth. Results suggest that summer fertigation with attendant reduction in application rate is a viable method for reducing drainage NO3-N losses without impacting yield of irrigated silage corn in the U.S. Midwest.

Influence of rare earth gadolinium nitrate addition on structural, dielectric, linear and nonlinear optical properties of glycine single crystals

In this present work, we have successfully grown γ-glycine single crystals in the presence of gadolinium nitrate as an additive by using slow solvent evaporation method. Powder X-ray Diffraction study confirms γ-polymorph structure and it crystallizes into a hexagonal crystal system with a space group of P31. UV–Visible transmittance spectra was recorded for the grown crystal to analyse the transparency in visible and near infrared region (NIR). In Kurtz-Perry powder test, the SHG efficiency of grown crystal is found to be 3.125 times higher than reference KDP crystal. The dielectric constant and dielectric loss of gadolinium nitrate added glycine was carried out as a function of frequency and the obtained results were discussed. The photoconductivity study confirms the positive photoconducting nature of grown crystal.

Soil N transformation mechanisms can effectively conserve N in soil under saturated conditions compared to unsaturated conditions in subtropical China

The connection between moisture and nitrogen (N) transformation in soils is key to understanding N losses, particularly nitrate (NO3−) losses, and also provides a theoretical framework for appropriate water management in agricultural systems. Thus, we designed this study to provide a process-based background for management decision. We collected soil samples from the long-term field experiment in subtropical China, which was designed to examine tobacco and rice rotations under a subtropical monsoon climate. The field experiment was established in 2008 with four treatments: (1) no fertilization as control; (2) N, phosphorus (P), and potassium (K) fertilizers applied at recommended rates; (3) N fertilizers applied at rates 50% higher than the recommended amounts and P and K fertilizers applied at recommended rates; and (4) N, P, and K fertilizers applied at recommended rates with straw incorporated (NPKS). Soil samples were collected during the unsaturated tobacco-cropping season and saturated rice-cropping season and were incubated at 60% water holding capacity and under saturated conditions, respectively. Two 15N tracing treatments (15NH4NO3 and NH415NO3) and a numerical modeling method were used to quantify N transformations and gross N dynamics. Autotrophic nitrification was stimulated by N fertilizer both under unsaturated and saturated conditions. The rate of NO3− consumption (via immobilization and denitrification) increased under the NPKS treatment under saturated conditions. Secondly, the rates of processes associated with ammonium (NH4+) cycling, including mineralization of organic N, NH4+ immobilization, and dissimilatory NO3− reduction to NH4+, were all increased under saturated conditions relative to unsaturated conditions, except for autotrophic nitrification. Consequently, NO3−-N and NH4+-N concentrations were significantly lower under saturated conditions relative to unsaturated conditions, which resulted in reduced risks of N losses via runoff or leaching. Our results suggest that under saturated conditions, there is a soil N conservation mechanism which alleviates the potential risk of N losses by runoff or leaching.

Probabilistic risk assessment of nitrate groundwater contamination from greenhouses in Albenga plain (Liguria, Italy) using lysimeters

The use of fertilizers in greenhouse-grown crops can pose a threat to groundwater quality and, consequently, to human beings and subterranean ecosystem, where intensive farming produces pollutants leaching. Albenga plain (Liguria, Italy) is an alluvial area of about 45km2 historically devoted to farming. Recently the crops have evolved to greenhouses horticulture and floriculture production. In the area high levels of nitrates in groundwater have been detected.Lysimeters with three types of reconstituted soils (loamy sand, sandy clay loam and sandy loam) collected from different areas of Albenga plain were used in this study to evaluate the leaching loss of nitrate (NO3−) over a period of 12weeks. Leaf lettuce (Lactuca sativa L.) was selected as a representative green-grown crop. Each of the soil samples was treated with a slow release fertilizer, simulating the real fertilizing strategy of the tillage. In order to estimate the potential risk for aquifers as well as for organisms exposed via pore water, nitrate concentrations in groundwater were evaluated by applying a simplified attenuation model to the experimental data. Results were refined and extended from comparison of single effects and exposure values (Tier I level) up to the evaluation of probabilistic distributions of exposure and related effects (Tier II, III IV levels).HHRA suggested HI >1 and about 20% probability of exceeding RfD for all the greenhouses, regardless of the soil. ERA suggested HQ>100 for all the greenhouses; 93% probability of PNEC exceedance for greenhouses containing sand clay loam. The probability of exceeding LC50 for 5% of the species was about 40% and the probability corresponding to DBQ of DEC/EC50>0.001 was >90% for all the greenhouses. The significantly high risk, related to the detected nitrate leaching loss, can be attributed to excessive and inappropriate fertigation strategies.