Normand Bertrand

N2O fluxes in soils of contrasting textures fertilized with liquid and solid dairy cattle manures

Manure is known to increase soil N2O emissions by stimulating nitrification and denitrification processes. Our objective was to compare soil-surface N2O emissions following the application of liquid and solid dairy cattle manures to a loamy and a clay soil cropped to silage maize. Manures were applied in 2 consecutive years at rates equivalent to 150 kg total N ha-1 and compared with a control treatment receiving an equivalent rate of synthetic N. Soil-surface N2O fluxes, soil temperature, and soil water, nitrate and ammonium contents were monitored weekly in manured and control plots. From 60 to 90% of seasonal N2O emissions occurred during the first 40 d following manure and synthetic fertilizer applications, indicating that outside that period one or several factors limited N2O emissions. The period of higher emissions following manure and fertilizer application corresponded with the period when soil mineral N contents were highest (up to 17 g NO3−-N m-2) and water-filled pore space (WFPS) was greater ...

Ammonia volatilization and soil nitrogen dynamics following fall application of pig slurry on canola crop residues

Land application of liquid manures is a major source of atmospheric ammonia. The presence of crop residues on the soil surface usually increases emissions by retarding slurry infiltration, whereas incorporation of slurry into soil reduces emissions. Our objective was to quantify the relative reduction in NH3 volatilization resulting from the soil incorporation of pig slurry (PS) applied on canola (Brassica napus) residues under fall conditions in Quebec, Canada. Pig slurry was applied at 7.4 L m–2 on six plots covered by canola crop residues. Slurry and residues were incorporated in the top 5 cm of soil (INCORP) in half of the plots, while the other half were left untouched (SURF). Ammonia volatilization was measured following application for 10 d using wind tunnels. Soil NH4+ and NO3− contents, pH, moisture and temperature were also monitored to explain variations in NH3 fluxes. Soil NH4+-N in the surface soil was lower than expected shortly after slurry application, maybe as a result of fixation by clay...

Winter fluxes of greenhouse gases from snow‐covered agricultural soil:intra‐annual and interannual variations

Despite the length of winter in cold temperate climates, few studies refer to greenhouse gas emissions from soils during the nongrowing season. In this study, N2O and CO2 fluxes from agricultural and forest soils in southeastern Quebec (Canada) were measured during winter and spring from 1994 to 1997, and the influences of climate, soil, and snow properties on the gaseous emissions were examined. N2O fluxes were far greater from the agricultural soil (2-187 ng N2O m−2 s−1) than from the forest soil (< 3 ng N2O m−2 s−1), but CO2 fluxes were equivalent for both soil systems (2-102 μ CO2 m−2 s−1). The higher N2O concentrations in the lower soil horizons could be explained by positive temperature gradients with depth and concomitant negative gas solubility gradients. However, the higher N2O concentrations could also be explained by variations in the expression of N2O reductase with depth, which can modify the N2/N2O ratios in relation to the availability of O2. Calculated N2O-N fluxes showed that N losses by gaseous emissions from soils during winter and spring were comparable to, or exceeded, similar reported N losses during the growing season. The highest winter fluxes observed in 1997 were interpreted to be due to favorable meteorological conditions that prevailed for denitrification through high soil water content in summer and fall of 1996. Although interannual and nterseasonal variations of fluxes are important, this study shows that wintertime losses of N2O from agricultural soil can be up to 2 to 4 times greater than emissions measured during the growing season in similar agroecosystems.

Banding of urea increased ammonia volatilization in a dry acidic soil.

Volatilization of ammonia following application of urea contributes to smog formation and degradation of natural ecosystems. The objective of this study was to evaluate the impact of (i) incorporation and banding of urea and (ii) surface broadcast of slow-release urea types on NH(3) volatilization in a dry acidic soil. Volatilization was measured using wind tunnels for 25 d after standard urea (140 kg N ha(-1)) was broadcast, broadcast and incorporated (0-5 cm), or incorporated in shallow bands (3-5 cm) to a conventionally tilled silty loam soil. Urea supplemented with a urease inhibitor or coated with a polymer was also broadcast at the soil surface. Little N diffused out of the polymer-coated granules and ammonia losses were low (4% of applied N). Use of a urease inhibitor also resulted in a low NH(3) loss (5% of applied N) while maintaining soil mineral N at levels similar to plots where untreated urea was broadcast. The rate of hydrolysis of urea broadcast at the soil surface was slowed by the lack of moisture and NH(3) loss (9% applied N) was the lowest of all treatments with standard urea. Incorporation of broadcast urea increased emissions (16% applied N) by increasing urea hydrolysis relative to surface application. Furthermore, incorporation in band also increased emissions (27% applied N) due to a localized increase in soil pH from 6.0 to 8.7. We conclude that incorporating urea in bands in a dry acidic soil can increase NH(3) volatilization compared to broadcast application followed by incorporation.

Ammonia volatilization and nitrogen retention: how deep to incorporate urea?

Incorporation of urea decreases ammonia (NH) volatilization, but field measurements are needed to better quantify the impact of placement depth. In this study, we measured the volatilization losses after banding of urea at depths of 0, 2.5, 5, 7.5, and 10 cm in a slightly acidic (pH 6) silt loam soil using wind tunnels. Mineral nitrogen (N) concentration and pH were measured in the top 2 cm of soil to determine the extent of urea N migration and the influence of placement depth on the availability of ammoniacal N for volatilization near the soil surface. Ammonia volatilization losses were 50% of applied N when urea was banded at the surface, and incorporation of the band decreased emissions by an average of 7% cm (14% cm when expressed as a percentage of losses after surface banding). Incorporating urea at depths >7.5 cm therefore resulted in negligible NH emissions and maximum N retention. Cumulative losses increased exponentially with increasing maximum NH-N and pH values measured in the surface soil during the experiment. However, temporal variations in these soil properties were poorly related to the temporal variations in NH emission rates, likely as a result of interactions with other factors (e.g., water content and NH-N adsorption) on, and fixation by, soil particles. Laboratory and field volatilization data from the literature were summarized and used to determine a relationship between NH losses and depth of urea incorporation. When emissions were expressed as a percentage of losses for a surface application, the mean reduction after urea incorporation was approximately 12.5% cm. Although we agree that the efficiency of urea incorporation to reduce NH losses varies depending on several soil properties, management practices, and climatic conditions, we propose that this value represents an estimate of the mean impact of incorporation depth that could be used when site-specific information is unavailable.

Soil air sample storage and handling using polypropylene syringes and glass vials

Accurate determination of gas concentration in soil air samples implies adequate sampling and storage procedures to preserve sample integrity. In this study, we tested polypropylene syringes and glass vials for handling and storage of N2O air samples. Losses of N2O were large and rapid when a gas standard was stored in polypropylene syringes (16% after 24 h). Moreover, gas adsorption on the inner walls (and rubber gasket) of the syringes reached a maximum of 5.8% of the initial N2O after 7 h of storage. These results indicated that polypropylene syringes are not reliable for storing air samples. Commercially available glass vials maintained a moderately high level of vacuum over time (89% after 136 d). However, their overall performance was decreased by contamination (approx. 3%) occurring at the end of the evacuation procedure when the hole left by the needle of the evacuation line took a few seconds to close up. The addition of a silicone septum was proposed to reduce this contamination. The modified vi...

Soil nitrous oxide emissions after deposition of dairy cow excreta in eastern Canada.

Urine and dung deposited by grazing dairy cows are a major source of nitrous oxide (NO), a potent greenhouse gas that contributes to stratospheric ozone depletion. In this study, we quantified the emissions of NO after deposition of dairy cow excreta onto two grassland sites with contrasting soil types in eastern Canada. Our objectives were to determine the impact of excreta type, urine-N rate, time of the year, and soil type on annual NO emissions. Emissions were monitored on sandy loam and clay soils after spring, summer, and fall urine (5 and 10 g N patch) and dung (1.75 kg fresh weight dung) applications to perennial grasses in two successive years. The mean NO emission factor (EF) for urine was 1.09% of applied N in the clay soil and 0.31% in the sandy loam soil, estimates much smaller than the default Intergovernmental Panel on Climate Change (IPCC) default value for total excreta N (2%). Despite variations in urine composition and in climatic conditions, these soil-specific EFs were similar for the two urine-N application rates. The time of the year when urine was applied had no impact on emissions from the sandy loam soil, but greater EFs were observed after summer (1.59%) than spring (1.14%) and fall (0.55%) applications in the clay soil. Dung deposition impact on NO emission was smaller than that of urine, with a mean EF of 0.15% in the sandy loam soil and 0.08% in the clay soil. Our results suggest (i) that the IPCC default EF overestimates NO emissions from grazing cattle excreta in eastern Canada by a factor of 4.3 and (ii) that a region-specific inventory methodology should account for soil type and should use specific EFs for urine and dung.

Ammonia volatilization following application of pig slurry increases with slurry interception by grass foliage

Efficient liquid manure application systems that minimize ammonia volatilization are required for use on perennial forage grasses. Ammonia volatilization was monitored using wind tunnels for 10 d after three pig slurry applications using four boom-mounted applicators: a broadcast splash-plate system, a trailing-shoe system and a drag-hose system with and without previous soil aeration. Average losses of 32, 20 and 15% of the total ammonia-N (TAN) applied to plots were observed for the splash-plate, the trailing-shoe and the drag-hose systems, respectively. The grass canopy intercepted, on average, 14% of pig slurry TAN using the splash-plate system compared with 4% for the trailing-shoe and 5% for the drag-hose systems. Reductions in canopy interception explained 58% of differences in volatilization rates among the application systems. On two of three application dates, NH3 volatilization was lower using the drag-hose than the trailing-shoe system. This was attributed to the sealing of the soil surface by...

Soil-surface carbon dioxide emission following nitrogen fertilization in corn

Abstract: Improvement in use efficiency of N fertilizers can potentially better sustain agriculture by reducing N2O emissions from soils, but little is known about its impact on soil CO2 emissions. A study, involving both a field experiment and a laboratory incubation, was conducted in eastern Canada to determine the N fertilization effect on soil CO2 emissions. In laboratory, we incubated nine different types of soil with and without 150 kg N ha-1 as KNO3 or (NH4)2SO4. The N-fertilized soils had lower CO2 emissions compared with the no-N control soils for six of them. Among fertilizer sources, emissions of CO2 were on average 22% lower with KNO3 than with (NH4)2SO4. The field experiment conducted on a clay soil included three sources of N (urea-NH4NO3, CaNH4NO3, and aqua NH3) at 0-200 kg N ha-1 band-incorporated at the six-leaf corn stage. Under field conditions, most CO2 was emitted between N application and grain maturity with cumulative seasonal soil emissions greater in the control (4.9 Mg C ha-1) than in the N treatments (average of 4.0 ± 0.3 Mg C ha-1). Evidence suggested that both heterotrophic and autotrophic respiration seemed affected, whereas the NO3-based source had a more depressing effect on CO2 emissions than did the NH4 source.

Nongrowing season N2O and CO2 emissions — Temporal dynamics and influence of soil texture and fall-applied manure1

Abstract: Nongrowing season (NGS) greenhouse gas (GHG) emissions may be significant in cold agricultural regions, but the influence of winter conditions, soil type, and fall manuring must be better documented. We monitored NGS N2O and CO2 fluxes and soil atmosphere composition from 2009 to 2013, on sandy loam and silty clay soils, with and without fall-applied pig slurry. Early-winter emission peaks indicated that soil respiration and biogenic N2O production were stimulated during active soil freezing. Soil atmosphere GHG concentrations increased throughout winter, whereas O2 concentration declined, especially when surface fluxes were low. Therefore, soil respiration and denitrification were not stopped by cold temperatures, and low surface fluxes were mainly due to restriction of gas diffusion. Nitrous oxide emissions varied from 0.4 to 8.5 kg N ha-1 and were generally greater in the presence of pig slurry. Emissions were of similar magnitude between soil types, likely because O2 restrictions on denitrification typically found in sandy soils during the growing season were eliminated by high soil moisture content in the NGS. This multiyear assessment highlights the need to include NGS GHG emissions to properly estimate yearly emissions and refine inventories in cold regions, particularly for sandy soils.