Silver nanoparticles (AgNPs) are present in biosolids from wastewater treatment facilities, a common soil amendment. Exposing earthworms ( Eisenia fetida) to AgNP and AgNO 3 in soil with 0 and 7.5 g biosolids kg −1 for 28 days showed AgNO 3 was more lethal to earthworms in artificial soil (LC20 ≤ 325 mg Ag kg −1 ) than natural soil (LC20 ≥ 573 mg Ag kg −1 ). In contrast, AgNPs were more lethal in natural soil (LC20 ≤ 425 mg Ag kg −1 ) than artificial soil (LC20 ≥ 653 mg Ag kg −1 ). Earthworm response to silver in artificial soil may not reflect toxicity in biosolids-amended natural soils.

Subsurface tile drains under agricultural field crops are a major source of phosphorus (P) discharge to aquatic ecosystems, contributing to the eutrophication of surface waters. Adsorption reactors for P removal from drainage water (P-reactors) could reduce P outflow from agricultural land but were rarely studied in cold, temperate climates. In our study, four low-cost P-reactors were installed in agricultural fields in south-central Québec, Canada. Activated alumina (AA) beads were used as P-adsorptive material, and the reactors were connected to tile drain outlets. Paired water samples (39 events) from reactor inlets and outlets were analyzed for P species and other physicochemical parameters during one calendar year to assess the P removal from tile drain effluent in the P-reactors. Collectively, the P-reactors retained approximately half (48%) of the total mass of P flowing through the tile drains, mostly (92%) as particulate P. The mass of AA beads adsorbed 11% of the dissolved-P fractions. Results are interpreted in the context of the field drainage area and will require adjustments to the P-reactor design to accommodate larger fields. The P-reactors remained structurally intact throughout all four seasons in a cold temperate climate, showing the potential of simple, inexpensive P-reactors to reduce P concentration in tile drain effluent.

Tile drainage is installed in agricultural fields to remove excess soil moisture to allow earlier planting of spring crops. Water moving from soil into tile drainage lines will potentially create a moist environment for earthworms. This study investigated how earthworms were distributed around tile lines, and how their abundance was affected by moisture in field crops on sandy and clayey soils. Earthworm abundance and soil moisture were similar above and between tile lines. Earthworm biomass was low in dry soils, peaked at 41 g moisture 100 g −1 , and declined in wetter soils, which affects the earthworm activity in agricultural fields.

Soil amended with biochar is expected to produce less nitrous oxide (N 2 O), although this may depend on nitrate (NO 3 -N) availability. Our objective was to determine how pine wood biochar, slow pyrolyzed at 500 °C, affects N 2 O production in soil having different denitrification potentials with variable NO 3 -N concentrations under controlled laboratory conditions. Sandy loam surface soils (0–30 cm, pH 5.7) and sandy clay loam subsurface soils (40–60 cm, pH 5.6) were amended with four biochar rates (0, 10, 20, and 30 g·kg −1 ), two nitrogen fertilizer rates (0 and 100 mg·kg −1 NO 3 -N) and two acetylene levels (0% and 10% headspace), arranged as a full factorial. Soil moisture content was adjusted to 80% water-filled pore space, and flasks were incubated at 20 °C for 30 h. Headspace gas was collected from each flask at 25, 26, 28, and 30 h. There was a significant reduction in N 2 O production with an increasing rate of biochar in the surface soil but not in the subsurface soil. On average, less N 2 O was produced in the subsurface soil than in the surface soil. As the NO 3 -N concentration was not a limiting factor for denitrification, the most likely explanation was that denitrifier activity was influenced by the availability of soluble organic carbon in the soil–biochar mixtures. We recommend further study of the coupled carbon–nitrogen transformations during denitrification to understand how biochar influences soil N 2 O production in sandy loam soils.

Conservation tillage and crop residues should increase the soluble organic carbon and nitrate concentration in agricultural soil, which increases the denitrification potential. Basal denitrification (72 h laboratory incubation) was 2.1–2.7 times higher in a sandy loam soil under 15 yr of conservation tillage than conventional tillage and 1.8–2.0 times higher with high-residue (additional input 8.6–9.4 Mg dry matter·ha−1·yr−1) than low-residue inputs. Adding glucose and nitrate increased the soil denitrification potential 3- to 14-fold. Denitrification was limited by carbon availability, even in soil with 15 yr of conservation tillage and high-residue inputs.

Fall-applied manure may have nitrogen (N) fertilizer value for spring-seeded crops. We applied liquid cattle manure or solid cattle manure to plots on a sandy-loam soil in fall. The following sprin...

In cold humid temperate regions, peak nitrous oxide (N2O) fluxes from agricultural soils occur during spring freeze-thaw periods. Fall-applied manure that adds water-soluble nutrients to the soil prior to freeze-up could contribute to spring N2O emissions. The objective of our field experiment was to evaluate the relationship between water-soluble nutrients and N2O emissions during the spring freeze-thaw period in a sandy-loam soil with fall-applied manure and fall-sown cover crops in Québec, Canada. Dairy cattle manure (solid or liquid form) was applied in September, then 100% ryegrass (Lolium multiflorum Lam.) and 50% ryegrass and 50% hairy vetch (Vicia villosa Roth) were sown. In the following spring (March–April), soil N2O fluxes were measured in non-steady-state closed chambers, and soil samples were analyzed for soil reactive nitrogen (ammonium, NH4+ and nitrate NO3−), dissolved organic carbon and nitrogen, soil moisture (water-filled pore space), and denitrification activity. Spring N2O fluxes were not related to the fall-applied manure and cover crop treatments, possibly due to nitrogen transformations or loss from soil after manure application. The NH4+ concentration, water-filled pore space, and denitrification activity were significant predictors of soil N2O emissions during the spring freeze-thaw period, but only explained about 24% of the variation in these N2O emissions. This suggests that N2O was produced by biological processes such as nitrifier denitrification. N2O emission may be the result of stochastic diffusion processes through pores with ice-water mixtures, as well as through cracks that form during freezing-thawing processes. Therefore, water-soluble soil nutrients may be poor predictors of spring N2O emissions from manure-amended soils in our region.

Riparian buffers, located in the transition zone between terrestrial and aquatic ecosystems, are a hotspot for nitrogen (N) removal through denitrification. Earthworms are abundant in riparian buffers and may enhance denitrification. This study investigated earthworm demographics of three earthworm functional groups (anecic, epigeic, and endogeic) and denitrifier activity in temporarily flooded and non-flooded riparian soils from April to October 2012 in southern Quebec, Canada. Nine earthworm species, mostly endogeic, were found in the temporarily flooded soil, while only six earthworm species were found in the non-flooded soil. On average, there were 11.7 times more earthworms with 12.4 times greater biomass (P < 0.05) found in the temporarily flooded soil than in the non-flooded soil. The denitrification enzyme activity (DEA) was of similar magnitude in temporarily flooded and non-flooded soils, with temporal variation associated with rainfall patterns. Endogeic earthworm biomass was positively correlated (P < 0.05) with DEA, while epigeic earthworm biomass was positively correlated (P < 0.05) with 16S rRNA gene copies and nosZ gene copies from bacteria, indicating an association between earthworm functional groups and denitrifier activity in riparian soils. Stepwise multiple regressions showed that DEA in riparian soils could be predicted using soil moisture, inorganic N concentration, and earthworm functional groups, suggesting that endogeic and epigeic earthworms contributed to denitrifier activity in riparian soils.

Fall-applied manure may have nitrogen (N) fertilizer value for spring-seeded crops. We applied liquid or solid cattle manure to plots on a sandy-loam soil in southern Quebec in fall. The following spring, half of each plot received urea fertilizer before planting the spring cereal crop. Total N content of the spring cereal at tillering, flowering, and maturity was lower in subplots without urea, and yields were up to 183% less in the no-urea subplots, regardless of whether liquid or solid manure was applied in fall. Fall-applied manure did not provide plant-available N to spring cereals under our growing conditions.

Applying manure to temperate agricultural soils in the fall season is often justified by the assumption that mineral nitrogen (N) is stable in frozen soils, although pulses of nitrous oxide (N2O) are emitted when the soil thaws during winter months. Nitrous oxide loss was monitored during three freeze-thaw cycles in agricultural soils that received manure and had a growing cover crop before they were frozen. Soil was mixed with N fertilizer treatments (none, liquid dairy manure, solid dairy manure, or urea) and packed in 0.2-L pots, half of which were planted with an annual ryegrass (Lolium multiflorum Lam.) cover crop. After 3 weeks, pots were transferred to a freezer at − 4 °C, or left in a refrigerator at + 4 °C. Frozen pots were thawed at + 4 °C. Production of N2O was measured after 0, 3, 6, and 9 h of thawing; then the pots were destructively sampled to determine the soil mineral N concentration. The N fertilizer and cover crop treatments did not affect N2O production, and only 14% of the variation in N2O production was explained by soil mineral N concentration. However, there was a 6–9-fold increase in N2O production, relative to soil mineral N, in pots that underwent freeze-thaw cycles compared to pots that were left at + 4 °C. It appears that N2O was produced in frozen soils at − 4 °C, trapped under ice, and subsequently released when the soils thawed at + 4 °C, suggesting that N2O-producing reactions do not stop when manured soils are frozen.

Canola (Brassica napus L.) is a nitrogen (N)-demanding crop, so tissue N analysis should be related to soil N supply. We evaluated canola N uptake in relation to soil N pools in plots receiving 0, 50, 100, and 150 kg N·ha−1 from urea at three sites in eastern Canada in 2012. Soil N pools varied significantly at the rosette, flowering, pod filling, and maturity stages, but responded less predictably to urea. Canola N uptake was inconsistently related to soil N pools and urea input. This confirms the importance of site-specific N fertilizer management when growing canola in eastern Canada.

Many laboratory and mesocosm studies have demonstrated that earthworms influence nitrogen (N) cycling reactions and produce nitrous oxide (N2O) in well-aerated soils, but whether earthworms can stimulate N2O fluxes in realistic field conditions remains to be determined. We conducted two field experiments, in perennial forage agroecosystems for 2 yr and agriculture riparian buffers for 1 yr, to compare N2O fluxes from enclosures with ambient and artificially elevated earthworm populations. Despite a short-term ( 3 month) increase in mean N2O fluxes from the perennial forage enclosures with artificially elevated earthworm populations, this effect disappeared within 1 yr, with no significant difference (p 0.05) in mean N2O flux from enclosures in either field experiment. The elevated earthworm populations declined and stabilized at the same level as the ambient earthworm populations within 1-2 yr after the field experiments began. The homeostatic regulation of earthworm populations under field conditions could be due to inter- and intra-specific competition, related to limitation in the food supply and habitat preferred by earthworms. Mean N2O fluxes in the perennial forage fields were negatively correlated with soil moisture, but not related to earthworm populations. In the riparian buffers, the average N2O flux was negatively correlated with vegetation cover, and positively correlated with soil moisture and the size of the earthworm population at the end of the study. Our results suggest that the effects of earthworm addition on N2O emissions in laboratory studies can not necessarily be extrapolated to field settings. Earthworm field experiments that continue in the longer-term and in a variety of ecosystems should improve our understanding of the seasonal and environmental variability in earthworm activity and N2O production under field conditions.

Commercial growers who wish to apply biochar to their field crops will need to use conventional agricultural machinery to amend large field areas. Biochar produced by fast pyrolysis of hardwood was applied at a target rate of 5.6 t ha-1 to a single swath (10 m x 100 m) in an agricultural field in Quebec, Canada, using a commercial lime spreader. Windborne losses of up to 30% biochar occurred during handling, transportation, and application. We recommend covering and moistening the biochar before spreading, avoiding surface application on windy days, or mixing it with other materials (e.g., compost, manure) to reduce biochar loss. The biochar-amended swath and an adjacent equally sized swath that received no biochar were harrowed. The entire field was seeded with soybean in the first season, followed by an oat-forage mixture in the second season, and forage in the third season. Soybean and oat yields increased by up to 20% with biochar. In the third season, forage in the biochar-amended swath had greater nutrient concentration and higher projected milk production when used as feed for dairy cattle, based on near-infrared spectroscopy analysis. The variable cost of applying biochar was an estimated CA$2,285 ha-1, indicating the need for a complete cost-benefit analysis of farm-scale biochar applications.

Ecotoxicology research on polychlorinated biphenyl (PCB) mixtures has focused principally on short-term effects on reproduction, growth, and other physiological endpoints. Latent cognitive effects from early life exposure to low-level PCBs were examined in an avian model, the European starling (Sturnus vulgaris). Thirty-six birds, divided equally among 4 treatment groups (control=0 mu g, low=0.35 mu g, intermediate=0.70 mu g, and high=1.05 mu g Aroclor 1254/g body weight), were dosed 1 d through 18 d posthatch, then tested 8mo to 9mo later in captivity in an analog to an open radial arm maze. Birds were subject to 4 sequential experiments: habituation, learning, cue selection, and memory. One-half of the birds did not habituate to the test cage; however, this was not linked to a treatment group. Although 11 of the remaining 18 birds successfully learned, only 1 was from the high-dosed group. Control and low-dosed birds were among the only treatment groups to improve trial times throughout the learning experiment. High-dosed birds were slower and more error-prone than controls. Cue selection (spatial or color cues) and memory retention were not affected by prior PCB exposure. The results indicate that a reduction in spatial learning ability persists among birds exposed to Aroclor 1254 during development. This may have implications for migration ability, resource acquisition, and other behaviors relevant for fitness. Environ Toxicol Chem 2015;34:2513-2522. (c) 2015 SETAC