NO3 Leaching Research Articles

Earthworm ecosystem service and dis-service in an N-enriched agroecosystem: Increase of plant production leads to no effects on yield-scaled N2O emissions

Earthworms can enhance plant productivity by promoting nitrogen (N) mineralization in N-limited agroecosystems and may also enhance the risk of N2O emissions and NO3−–N leaching in N-enriched agroecosystems. However, direct evidence demonstrating the enhancement by earthworms of N2O emissions and NO3−–N leaching in the field is scarce, particularly in intensively managed systems. In addition, the interaction of earthworm feeding strategies and organic amendment may profoundly modulate N cycling. We examined these impacts using two earthworm species with distinct ecological strategies (epigeic Eisenia foetida and endogeic Metaphire guillemi) in combination with two manure application methods (surface mulch and incorporation into the soil) in a field experiment. Our results demonstrated that earthworm addition significantly increased the crop yield by 18%–47% and cumulative N2O emissions by 19%–25% largely regardless of earthworm species and manure application methods, respectively. However, earthworms did not significantly increase the leachate NO3−–N concentration. Earthworm-induced N2O emissions were primarily attributed to increased soil N availability (NO3−–N and microbial biomass N) and carbon (C) availability (dissolved organic C). In contrast, a stepwise regression revealed that an earthworm-promoted soil macroaggregation exerted negative effects on N2O emissions. Irrespective of earthworm species and manure application methods, earthworms had no stimulatory effects on the yield-scaled N2O–N because the promotion of crop productivity counteracted the extent of N2O increase. In conclusion, understanding the trade-off between earthworm services and dis-services will contribute to the development of environmentally justified soil management by allowing the full utilization of biological resources.

Dissolved nitrogen release from coarse woody debris of different tree species in the early phase of decomposition

In forest ecosystems, coarse woody debris (CWD) can represent a large stock of organic matter that contributes to the C and N cycling in forest ecosystems. Here we investigated the net release of dissolved organic N (DON), NH4 and NO3 from CWD of different tree species in the early phase of decomposition. Logs of 13 tree species were exposed in the winter 2008/2009 on the soil in a temperate Fagus sylvatica L. forest in Germany. Runoff solutions were periodically collected underneath logs for 17months from June 2011 to November 2012 in the third to fourth year of decomposition. The net release of N was calculated for each log on an annual scale as difference of N fluxes in runoff and throughfall.Nitrogen was net released from CWD of all tree species with DON as the dominant N form, but leaching of NH4 and NO3 was also observed. Differences in total N release between tree species were not statistically significant due to high intra-specific variation. The net release of N ranged from 0.42 (Pseudotsuga) to 1.39 (Carpinus) gNm−2 log projection area yr−1 The variation in net release of N was not related to the initial C/N ratio of bark and sapwood of the different species. The DOC/DON ratios in runoff were positively related to the initial C/N ratio of bark and sapwood. Net release of NH4 was larger in the dormant than in the growing season, opposite to the release of NO3, but no seasonality was found for DON release. Average ratios of NH4/NO3 in runoff from CWD did not significantly differ between species. Precipitation amount and temperature had only minor effect on the total N release, suggesting other dominating drivers.Our results demonstrate that CWD is a source of solute N, even in the early phase of decomposition.

Management of Furrow Irrigation and Nitrogen Application on Summer Maize

The efficient use of water and N represents a primary concern to agricultural production in Northwest China. The objective of this study was to assess the impacts of irrigation and fertilization on water and N use, soil volatilized NH3, soil NO3 leaching, and NO3 transfer in soil profiles. A 2‐yr field experiment was conducted to assess the separation of N fertilizer and water with alternating furrow irrigation (SNWAFI) and conventional irrigation and fertilization (CIF) in a maize (Zea mays L.) production system. The yields with SNWAFI were 10 to 16% greater than with CIF. Compared with CIF, SNWAFI increased water use efficiencies (WUEs) by 13 to 33%, agronomic efficiency of fertilizer N by 36 to 56%, and NO3−–N in the upper soil layers (0–60 cm) by 30 to 60%. However, SNWAFI reduced NO3−–N in the deeper soil layers (60–200 cm) by 8 to 44% compared with CIF. The use of SNWAFI also decreased soil NH3 emission with the combination with lower irrigation (40 mm) and N rate (100 kg N ha−1), which indicated that SNWAFI emitted less soil NH3 than CIF. Therefore, compared with CIF, SNWAFI increased maize yield WUE and N use efficiency, reduced N leaching, and curtailed soil NH3 loss with appropriate irrigation and N rates. The use of SNWAFI, leading to better spatial management of irrigation water and N application, can provide both agronomic and environmental benefits.

Leachability of Nitrate from Sandy Soil using Waste Amendments

Environmental issues associated with intensive use of nitrogenous fertilizers have generated an interest in alternative management systems. An experiment was conducted to mitigate nitrate leaching from sandy soil using different waste materials such as charcoal, manure, sawdust, wood ash, and control (no amendment). Urea was applied at the rate of 300 kg nitrogen (N) ha−1. Nitrate was determined during six leaching events. During an incubation experiment, nitrate release was also determined in soil amended with charcoal at the rates of 0, 10, 20, and 40 t ha−1. Urea was applied at the rates of 0, 100, 200, 400, and 1000 ppm N. Results indicated that urea application increased nitrate (NO3) concentration in leachate. Soil amendments substantially reduced NO3 in leachates irrespective of the type of material used. Waste amendments differed for NO3 leaching as follows: charcoal < wood ash < sawdust < manure. Leaching of NO3 enhanced up to the fourth leaching event and thereafter reduced significantly. Nitrate retention in soil varied among material in the order of manure > charcoal > wood ash > sawdust. Nitrate accumulation occurred in the lower layer (25–50 cm) of soil column after the leaching process. Application of charcoal retained greater NO3 level as compared to control soil during an incubation. Enhanced urea applications also enhanced NO3 release. This experiment suggests that waste material can be viably recycled to mitigate NO3 concentration in water.

Long-term fate of nitrate fertilizer in agricultural soils is not necessarily related to nitrate leaching from agricultural soils

Accounting for the fate of inorganic N fertilizer in agricultural systems is critical to sustainable production. Sebilo et al. (1) provide a unique long-term record of 15NO3 fertilizer fate that demonstrates N molecules from a discrete fertilizer application are transferred to soil organic matter (SOM) and subsequently mineralized over the course of approximately 100 y, during which they contribute to NO3 leaching. The authors conclude “attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers” (1). Furthermore, Sebilo et al. suggest that a recent decrease in anthropogenic N inputs to the Mississippi River Basin, without a concomitant decrease in riverine NO3 loads, is consistent with their conclusion.

Irrigation with Treated Wastewater: Quantification of Changes in Soil Physical and Chemical Properties

Land application of treated wastewater is increasing particularly in areas where water stress is a major concern. The primary objective of this study was to quantify the effect of irrigation with aerated lagoon treated wastewater on soil properties. Core and bulk soil samples were collected from areas under the canopies of mesquite and creosote and intercanopy areas from each of the three plots. Irrigation water quality from 2006 to 2008 showed that average sodium adsorption ratio (SAR), electrical conductivity (EC) and pH of irrigation water were 37.16, 5.32 dS m-1 and 9.7, respectively. The sprinkler uniformity coefficients of irrigated plot-I was 49.34 ± 2.23 % and irrigated plot-II was 61.57 ± 2.11 %. Within irrigated and between irrigated and un-irrigated plots, most soil physical properties remained similar except saturated hydraulic conductivity (Ks) which was significantly higher under mesquite canopies than in the intercanopy areas. Chloride (Cl-) concentrations below 60 cm depth were higher under creosote than mesquite canopies in irrigated plots indicating deeper leaching of Cl-. Nitrate (NO3 -) concentrations below 20 cm depth under canopy and intercanopy areas were low indicating no leaching of NO3 -.The average SAR to 100 cm depth under shrub canopies was 18.46 ± 2.56 in irrigated plots compared to 2.94 ± 0.79 in the un-irrigated plot. The Na+ content of creosote was eleven times higher un-irrigated than un-irrigated plot and Na+ content of herbaceous vegetation was three times higher in the irrigated than unirrigated. Thus irrigation with high sodium wastewater has exacerbated the soil sodicity and plant Na+ content. Since the majority of mesquite roots are found within 100 cm, and creosote and herbaceous vegetation roots are found within 25 cm from soil surface, a further increase in sodicity may threaten the survival of woody and perennial herbaceous vegetation of the study site.

Effects of dietary protein concentration on ammonia volatilization, nitrate leaching, and plant nitrogen uptake from dairy manure applied to lysimeters.

This lysimeter experiment was designed to investigate the effects of dietary crude protein (CP) concentration on nitrate-N (NO-N) and ammonia (NH) losses from dairy manure applied to soil and manure N used for plant growth. Lactating dairy cows were fed diets with 16.7% CP (HighCP) or 14.8% CP (LowCP) content. Feces and urine were labeled with N by ruminal pulse-doses of NHCl. Unlabeled and N-labeled feces and urine were used to produce manure for a study with 21 lysimeters in a greenhouse. Manure application rate was 277 kg N ha. Ammonia emissions were measured at 3, 8, 23, 28, 54, and 100 h after manure application. Manure was incorporated into the soil, and a leaching event was simulated. Spring barley was planted (387 plants per m) 7 d after the leaching event and harvested at senescence. Ammonia emission rates and the contribution of urinary N to NO-N were on average about 100% greater for HighCP vs. LowCP manures. With both LowCP and HighCP manures, a greater proportion of urinary vs. fecal N was recovered in leachate NO-N. There was no difference in whole-crop barley N yields between LowCP and HighCP manures, but barley kernel N yield tended to be greater ( = 0.09) for lysimeters treated with HighCP manures. Using a unique labeling approach, this lysimeter experiment demonstrated that when applied at equal soil N application rates, manure from cows fed the HighCP diet resulted in markedly greater NH emissions and urinary N losses with leachate NO-N than manure from cows fed the LowCP diet.

N2O and CH4 Emissions, and NO3 − Leaching on a Crop-Yield Basis from a Subtropical Rain-fed Wheat–Maize Rotation in Response to Different Types of Nitrogen Fertilizer

Guaranteeing high crop yields while reducing environmental impacts of nitrogen fertilizer use due to associated losses of N2O emissions and nitrate (NO3 (-)) leaching is a key challenge in the context of sustainable intensification of crop production. However, few field data sets are available that explore the effect of different forms of N management on yields as well as on N losses in the form of N2O or NO3 (-). Here we report on a large-scale field lysimeter (8 x 4 m(2)) experiment, which was designed to determine soil CH4 and N2O emissions, NO3 (-) leaching losses and crop yields from a subtropical rain-fed wheat-maize rotation in the Sichuan Basin, one of the most intensively used agricultural regions in China. One control and three different fertilizer treatments with the same total rate of N application (280 kg N ha(-1) y(-1)) were included: NF: control (no fertilizer); NPK: synthetic N fertilizer; OMNPK: synthetic N fertilizer plus pig manure; RSDNPK: synthetic N fertilizer plus crop residues. As compared to the standard NPK treatment, annual NO3 (-) leaching losses for OMNPK and RSDNPK treatments were decreased by 36 and 22%, respectively (P < 0.05). Similarly, crop yield-scaled NO3 (-) leaching for NPK treatment was higher than those for either OMNPK or RSDNPK treatments (P < 0.05). Direct N2O emissions for RSDNPK treatment were decreased as compared with NPK and OMNPK treatments (P < 0.05). Furthermore, the yield-scaled GWP (global warming potential) was lower for the treatments where either pig manure or crop residues were incorporated as compared to the standard NPK treatment (P < 0.05). Our study indicates that it is possible to reduce the negative environmental impact of NO3 (-) leaching and N2O emissions without compromising crop productivity. Yield-scaled NO3 (-) leaching, similar to the yield-scaled GWP, represents another valuable-integrated metric to address the dual goals of reducing nitrogen pollution and maintaining crop grain yield for a given agricultural system.

The impact of activated carbon on NO3−‐N, NH4+‐N, P and K leaching in relation to fertilizer use

SummaryThe ability of light‐textured soils to retain nutrients and water is small. In agriculture such soils pose a risk of nutrient leaching when amended with fertilizers. This study investigated the effects of the incorporation of activated carbon (AC) into the soil to determine (i) if it would decrease leaching of major nutrient ions and (ii) if its effect on leaching is influenced by fertilizer use. Nitrate nitrogen (NO3−‐N), ammonium nitrogen (NH4+‐N), phosphorus (P) and potassium (K) leaching through two substrates (sandy loam soil (S) and a sandy loam soil mixed with activated carbon (S + AC), which were unfertilized (NF or control) or fertilized with inorganic fertilizer (F), pig slurry (PS), pig slurry digestate (PD) or sewage sludge digestate (SD) was studied using mini‐lysimeters. In soil enriched with AC mark K‐835, water percolation and NO3−‐N and P leaching were significantly reduced, and K leaching was increased. Ammonium nitrogen leaching was not influenced by the AC amendment. The impact of AC on NO3−‐N and P leaching and water percolation did not change during the two‐year period, from which it is concluded that AC mark K‐835 prevents the leaching of NO3−‐N and P and increases soil water retention ability, and thus it is beneficial for light‐textured soils.

Effects of temperature and amendments on nitrogen mineralization in selected Australian soils

The effects of temperature (18, 24, and 37 °C) and form of nitrogen (N) input from various sources (organic-green waste compost, biosolids, and chicken manure; inorganic-urea) on N transformation in three different Australian soils with varying pH (4.30, 7.09, and 9.15) were examined. Ammonification rate (ammonium concentration) increased with increase in temperature in all soil types. The effect of temperature on nitrification rate (nitrate concentration) followed 24 > 37 > 18 °C. Nitrification rate was higher in neutral and alkaline soils than acidic soil. Mineral N (bioavailable N) concentration was high in urea treatments than in organic N source treatments in all soil types. Acidic soil lacked nitrification activity resulting in low nitrate (NO3) buildup in urea treatment, whereas a significant NO3 buildup was noticed in green waste compost treatment. In neutral and alkaline soils, the nitrification activity was low at 37 °C in urea treatment but with a significant NO3 buildup in organic amendment added soils. Addition of organic N sources supplied ammonia oxidizing bacteria thereby triggering nitrification in the soils (even at 37 °C). This study posits the following implications: (1) inorganic fertilizer accumulate high NO3 content in soils in a short period of incubation, thereby becoming a potential source of NO3 leaching; (2) organic N sources can serve as possible source of nitrifying bacteria, thereby increasing bioavailable N (NO3) in soils regardless of the soil properties and temperature.

Chemical recovery of acidified Bohemian lakes between 1984 and 2012: the role of acid deposition and bark beetle induced forest disturbance

Assessment of temporal trends and rates of change in hydrochemical parameters and forest cover has been conducted to elucidate key drivers of surface water acidification in glacial lakes in the Czech Republic. Since 1984, the key driver in acidification reversal was sulphate (SO4) concentration (median decrease of −3.58 μeq L−1 yr−1) which fell in line with reductions in sulphur (S) deposition. Reduction of nitrogen (N) deposition was followed by proportional reduction in nitrate (NO3) leaching although decline in NO3 concentrations was more pronounced at two sites, the Certovo Lake (CT) and Prasilske Lake (PR) until 2006; only Žďarske pond showed effective catchment N immobilization. Coherent decline of chloride concentration was detected across all sites. The decrease of strong mineral acids was partly compensated by decrease of inorganic aluminium (Alin), especially at sites most acidified in the beginning of observations (ANC1984–1986 between −160 and −90 μeq L−1 at CT, Cerne Lake—CN and Plesne lake—PL) and by reductions of base cations and increases of pH. All lakes (CN, CT, PL, PR and LK) moved to the ANC range between −29 and 30 μeq L−1 (2010–2012) where sensitivity of pH to further reductions in acid anions may be expected. Concurrently, charge of weak organic acids (OAs) increased and partly balanced the strong mineral acid decrease as a consequence of (i) significant DOC (dissolved organic carbon) increase (median change of 0.13 mgC L−1 yr−1 since 1993) and (ii) deprotonation of weak OAs caused by pH rise. Since 2000s, bark beetle induced forest decline accelerated NO3 leaching at most of the catchments (by 200 % at LK, PL and PR). However, elevated N leaching was effectively neutralized by base cations (K, Mg, Ca) originating from decaying fresh litter, thus acidification recovery was not reversed, but slowed down. After cessation of NO3 leaching we hypothesise that collapsed tree canopy across catchments (from 12 to 87 % compared to 1984) will cause lower total acid input in precipitation (S + N) and regrowth of vegetation may stimulate higher N immobilization (in biomass and soil); processes which could lead to further increase of ANC and pH, key indicators for biological recovery.

Atmospheric nitrogen inputs and losses along an urbanization gradient from Boston to Harvard Forest, MA

Urbanization alters nitrogen (N) cycling, but the spatiotemporal distribution and impact of these alterations on ecosystems are not well-quanti- fied. We measured atmospheric inorganic N inputs and soil leaching losses along an urbanization gradient from Boston, MA to Harvard Forest in Petersham, MA. Atmospheric N inputs at urban sites (12.3 ± 1.5 kg N ha -1 year -1 ) were significantly greater than non-urban (5.7 ± 0.5 kg N ha -1 year -1 ) sites with NH4 ? (median value of 77 ± 4 %) contributing thrice as much as NO3 - . Proximity to urban core correlated positively with NH4 ? (R 2 = 0.57, p = 0.02) and total inorganic N inputs (R 2 = 0.61, p = 0.01); on-road CO2 emissions correlated positively with NO3 inputs (R 2 = 0.74, p = 0.003). Inorganic N leaching rates correlated positively with atmospheric N input rates (R 2 = 0.61, p = 0.01), but did not differ significantly between urban and non-urban sites (p ( 0.05). Our empirical measurements of atmospheric N inputs are greater for urban areas and less for rural areas compared to modeled regional estimates of N depo- sition. Five of the nine sites had NO3 leached that came almost entirely from nitrification, indicating that the NO3 - in leachate came from biological processes rather than directly passing through the soil. A significant proportion (17-100 %) of NO3 leached from the other four sites came directly from the atmosphere. Surprisingly, the four sites where atmo- spheric sources made up the largest proportion of leachate NO3 - also had relatively low N leaching rates, suggesting that atmospheric N inputs added to terrestrial ecosystems can move to multiple sinks and losses simultaneously, rather than being lost via leaching only after abiotic and biotic sinks have become saturated. This study improves our under- standing of atmospheric N deposition and leaching in urban ecosystems, and highlights the need to incor- porate urbanization effects in N deposition models.

Soil and Water Quality Rapidly Responds to the Perennial Grain Kernza Wheatgrass

Perennial grain cropping systems could address a number of contemporary agroecological problems, including soil degradation, NO3 leaching, and soil C loss. Since it is likely that these systems will be rotated with other agronomic crops, a better understanding of how rapidly perennial grain systems improve local ecosystem services is needed. We quantified soil moisture, lysimeter NO3 leaching, soil labile C accrual, and grain yields in the first 2 yr of a perennial grain crop under development [kernza wheatgrass, Thinopyrum intermedium (Host) Barkworth &amp; D.R. Dewey] relative to annual winter wheat (Triticum aestivum L.) under three management systems. Overall, differences between annual and perennial plants were much greater than differences observed due to management. In the second year, perennial kernza reduced soil moisture at lower depths and reduced total NO3 leaching (by 86% or more) relative to annual wheat, indicating that perennial roots actively used more available soil water and captured more applied fertilizer than annual roots. Carbon mineralization rates beneath kernza during the second year were increased 13% compared with annual wheat. First‐year kernza grain yields were 4.5% of annual wheat, but second year yields increased to 33% of wheat with a harvest index of 0.10. Although current yields are modest, the realized ecosystem services associated with this developing crop are promising and are a compelling reason to continue breeding efforts for higher yields and for use as a multipurpose crop (e.g., grain, forage, and biofuel).

Seasonal variation of water chemistry and sulfur budget in an acid-sensitive river along the Sea of Japan

A long-term declining trend of pH values has been observed for several rivers in areas of central Japan that are geologically dominated by acidic rocks such as granite, rhyolite, or chert. We monitored the seasonal variation in water chemistry in one of these rivers: the Araya River in Niigata Prefecture. During the 4-year survey period, we observed temporary acidification during the rainy and snowmelt seasons when the river flow rate abruptly increased. In the rainy season, the decrease in pH may be attributable to the dilution of almost all ions and increased leaching of NO3− from the catchment. In the snowmelt season, decreases in pH were found to be associated with peaks of SO42−, where the SO42− was possibly derived from that accumulated in the snowpack. The data pertaining to the river showed that it had a sensitive response to meteorological events and was likely to be acid sensitive. The estimated mass balance of the river showed that the SO42− output exceeded the corresponding input to the Araya River catchment. Mobilization of internal sulfur accumulated in forest ecosystems might have contributed to the observed long-term acidification of this acid-sensitive river.

Biosolid and distillery effluent amendments to Irish short rotation coppiced willow plantations: Impacts on groundwater quality and soil

The impact of landspreading organic byproduct (OB) on the quality of groundwater (GW) and soil underlying short rotation coppiced willow plantations was assessed. Organic byproduct, namely biosolid (BS) and distillery effluent (DE), was spread on six plots (each with a plot area of 0.059ha) at OB treatment-rates of 100%, 50% and 0%. The OB treatment rate was defined by the maximum permissible soil-P load defined in Irish regulation. Groundwater was sampled each month and tested for pH, electrical conductivity (EC), NO3, PO43, total soluble phosphorous (TSP), K and six heavy metals (HMs) Cu, Cd, Cr, Pb, Ni, and Zn. Results were assessed in relation to Irish GW threshold values (GTVs), to assess overall quality using a “well bottom” approach. The background concentration of GW K and GW P (established in early 2008, prior to all OB spreading) were above permissible Irish statutory limits, in all cases. There was evidence of percolation of K and TSP to GW; K and PO43 concentrations breached GTVs across all plots. There was also evidence of percolation of Cu through soil profile, though Cu GW concentration did not breach GTV, and no risk to GW quality is necessarily implied. A potential (though small) risk of P- and K-percolation could impact GW quality in commercially scaled-up plantations; however, risk to GW quality from NO3, Cu, Cd, Cr, Pb, Ni, and Zn leaching in soil are minimal. Sites considered for energy crop should be assessed for soil conditions, and vulnerability to leaching, before OB amendment programs are initiated. The study was conducted over two years; the longer term impact of applications of BS and DE on soil organic-matter content, salinity and pH (and subsequent loss through soil profile) should be assessed. The implication of scaling up test-bed sized applications to larger commercial plantation scales needs to be considered.Capsule: Amendments of organic byproduct to short rotation coppice willow may lead to leaching of nutrients to groundwater in certain circumstances.

Nitrous Oxide Dynamics in a Deep Soil-Alluvial Gravel Vadose Zone Following Nitrate Leaching

Subsoil denitrification is a potential sink for leached nitrate (NO₃–) that may otherwise contaminate ground water. A field trial was undertaken to assess the importance of subsoil denitrification and to examine the role of leached NO₃– on subsurface nitrous oxide (N₂O) (a potent greenhouse gas) dynamics. We monitored NO₃–, Br–, N₂O, CO₂, and O₂ concentrations in alluvial vadose materials to a depth of 7 m over a 32-mo period following the application of N (400 kg ha⁻¹ as NH₄NO₃) and Br– to potatoes (Solanum tuberosum L.) followed by a second application (400 kg ha⁻¹ as NH₄NO₃) to ryegrass (Lolium multiflorum Lam.) 24 mo later. Our sampling system consisted of an array of ceramic cups and permeable silicone tubing chambers to sample soil solution and gases. Following rainfall and irrigation, subsoil N₂O concentrations increased rapidly. Within days of NO₃– leaching below 1 m, high concentrations of NO₃–, Br–, and N₂O were observed at 7-m depth. Based on N to Br– ratios, and NO₃– leaching estimates from drainage amounts and leachate NO₃– concentrations, 5 to 10% of the fertilizer and soil N was denitrified. Based on N₂O flux estimates and NO₃––N/Br– ratios, almost all of the net N₂O production occurred in the subsoil above the gravel material (1-m depth). In the gravel matrix the NO₃––N/Br– ratio did not change indicating a low capacity to attenuate NO₃–.

Switchgrass Biochar Affects Two Aridisols

The use of biochar has received growing attention because of its ability to improve the physicochemical properties of highly weathered Ultisols and Oxisols, yet very little research has focused on its effects in Aridisols. We investigated the effect of low or high temperature (250 or 500°C) pyrolyzed switchgrass () biochar on two Aridisols. In a pot study, biochar was added at 2% w/w to a Declo loam (Xeric Haplocalcids) or to a Warden very fine sandy loam (Xeric Haplocambids) and incubated at 15% moisture content (by weight) for 127 d; a control (no biochar) was also included. Soils were leached with 1.2 to 1.3 pore volumes of deionized HO on Days 34, 62, 92, and 127, and cumulative leachate Ca, K, Mg, Na, P, Cu, Fe, Mn, Ni, Zn, NO-N, NO-N, and NH-N concentrations were quantified. On termination of the incubation, soils were destructively sampled for extractable Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Zn, NO-N, and NH-N, total C, inorganic C, organic C, and pH. Compared with 250°C, the 500°C pyrolysis temperature resulted in greater biochar surface area, elevated pH, higher ash content, and minimal total surface charge. For both soils, leachate Ca and Mg decreased with the 250°C switchgrass biochar, likely due to binding by biochar's functional group sites. Both biochars caused an increase in leachate K, whereas the 500°C biochar increased leachate P. Both biochars reduced leachate NO-N concentrations compared with the control; however, the 250°C biochar reduced NO-N concentrations to the greatest extent. Easily degradable C, associated with the 250°C biochar's structural make-up, likely stimulated microbial growth, which caused NO-N immobilization. Soil-extractable K, P, and NO-N followed a pattern similar to the leachate observations. Total soil C content increases were linked to an increase in organic C from the biochars. Cumulative results suggest that the use of switchgrass biochar prepared at 250°C could improve environmental quality in calcareous soil systems by reducing nutrient leaching potential.

Effect of synthetic dairy factory effluent containing different acids (H3PO4, HNO3 and CH3COOH) on soil microbial and chemical properties and nutrient leaching

The effects of addition of synthetic dairy factory effluent (DFE) containing phosphoric, nitric or acetic acids as cleaning agents on soil chemical and microbial properties and potential nutrient leaching from a dairy farm soil were studied in an 84-day open incubation/leaching experiment and in a short-term (24 days) closed incubation. Dairy factory effluent resulted in increased leaching of Na+ and Ca2+. The main anion leached in the DFE treatments was Cl−, whilst in the control treatments it was NO 3 − . Leachates from DFE-treated soil had a greater electrical conductivity (EC) and lower pH than those from controls, but type of acid had little effect on the ionic content or composition of leachates. At the conclusion of the experiment, soils from DFE treatments showed a large accumulation of exchangeable Na+, a reduction in exchangeable Ca2+ and significant increases in microbial biomass C, basal respiration and β-glucosidase and arylsulphatase activities. Microbial activity was greatest from the acetic acid-DFE treatment. There was a significant increase in extractable P in the phosphoric acid-DFE treatment, but addition of nitric acid-DFE did not increase leaching of NO 3 − . In the short-term incubation experiment, EC increased over time in all treatments, while pH, microbial biomass and basal respiration decreased. During the first few days after a one-off DFE addition, there was an increase in both microbial biomass C and basal respiration, but these differences dissipated after 3 days. It was concluded that while additions of DFE have significant effects on chemical and microbial soil properties, a change in the form of acid present in the DFE has relatively minor effects on these properties.

The role of nitrogen deposition in the recent nitrate decline in lakes and rivers in Northern Italy

Deposition of inorganic nitrogen (N) in north-western Italy is around 20–25kgNha−1y−1, and has remained constant during the last 30years. This flux of N caused saturation of terrestrial catchments and increasing levels of nitrate (NO3) in surface waters. Recently, monitoring data for both rivers and lakes have shown a reversal in NO3 trends. This change was widespread, affecting high-altitude lakes in the Alps and subalpine lakes and rivers, and occurred at almost the same time at all sites. The seasonal pattern of NO3 concentrations in running waters has shown a change in the last few years, with a tendency towards slightly lower leaching of NO3 during the growing season. Atmospheric input of N has also shown a recent decrease, mainly due to decreasing emissions and partly to the lower amount of precipitation occurring between 2003 and 2009. Surface waters are probably responding to these changing N inputs, but a further decrease of N deposition, especially reduced N, will be required to achieve full recovery from N saturation.

Nitrate production and availability in residential soils

The rapid increase in residential land area in the United States has raised concern about water pollution associated with nitrogen fertilizers. Nitrate (NO3-) is the form of reactive N that is most susceptible to leaching and runoff; thus, a more thorough understanding of nitrification and NO3(-) availability is needed if we are to accurately predict the consequences of residential expansion for water quality. In particular, there have been few assessments of how the land use history, housing density, and age of residential soils influence NO3(-) pools and fluxes, especially at depth. In this study, we used 1 m deep soil cores to evaluate potential net nitrification and mineralization, microbial respiration and biomass, and soil NO3(-) and NH4+ pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types. These were compared to eight forested reference sites with similar soils. Our results suggest that a change to residential land use has increased pools and production of reactive N, which has clear implications for water quality in the region. However, the results contradict the common assumption that NO3(-) production and availability is dramatically higher in residential soils than in forests in general. While net nitrification (128.6 +/- 15.5 mg m(-2) d(-1) vs. 4.7 +/- 2.3 mg m(-2) d(-1); mean +/- SE) and exchangeable NO3(-) (3.8 +/- 0.5 g/m2 vs. 0.7 +/- 0.3 g/m2) were significantly higher in residential soils than in forest soils in this study, these measures of NO3(-) production and availability were still notably low, comparable to deciduous forest stands in other studies. A second unexpected result was that current homeowner management practices were not predictive of NO3(-) availability or production. This may reflect the transient availability of inorganic N after fertilizer application. Higher housing density and a history of agricultural land use were predictors of greater NO3(-) availability in residential soils. If these factors are good predictors across a wider range of sites, they may be useful indicators of NO3(-) availability and leaching and runoff potential at the landscape scale.