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 vials maintained an average vacuum level of 98% after 136 d. The average contamination rate of N2O samples during the first 129 d of storage was 0.20 and 0.13% d-1 with one and two septa, respectively. Key words: Nitrous oxide, air sample

Testing the DNDC model using N2O emissions at two experimental sites in Canada

Measured data from two experimental sites in Canada were used to test the ability of the DeNitrification and DeComposition model (DNDC) to predict N2O emissions from agricultural soils. The two sites, one from eastern Canada, and one from western Canada, provided a variety of crops, management practices, soils, and climates for testing the model. At the site in eastern Canada, the magnitude of total seasonal N2O flux from the seven treatments was accurately predicted with a slight average over-prediction (ARE) of 3% and a coefficient of variation of 41%. Nitrous oxide emissions based on International Panel for Climate Change (IPCC) methodology had a relative error of 62% for the seven treatments. The DNDC estimates of total yearly emissions of N2O from the field site in western Canada showed an underestimation of 8% for the footslope landscape position and an overestimation of 46% for the shoulder position. The data input for the DNDC model were not of sufficient detail to characterize the moisture difference between the landscape positions. The estimates from IPCC guidelines showed an underestimation of 54% for the footslope and an overestimation of 161% for the shoulder. The results indicate that the DNDC model was more accurate than IPCC methodology at estimating N2O emissions at both sites. Key words: Nitrous oxide, DNDC, soil model, greenhouse gas, testing

Nitrous oxide production by manure samples collected from six manure-handling systems

Stored manures are often considered to be source of nitrous oxide (N2O). A study was done to identify manure characteristics and handling stages related to N2O production. In two laboratory experiments we investigated the production of N2O from several animal manures collected at different stages of manure handling or locations in stored-manure systems. Denitrifying enzyme activity, denitrification and CO2 production rates and chemical and fibre characteristics of manure samples were also determined. Most samples had low rates of N2O production. Exceptions were open piles of fresh beef manure and the moist surface layer near the base of an open pile of poultry manure. Production of N2O was most highly correlated with nitrite plus nitrate (NO2− + NO3−) content of manure regardless of whether results were expressed on a wet or a dry weight basis. Denitrification was the most probable source of N2O because N2O production with acetylene and denitrifying enzyme activities was higher than N2O production without acetylene. Stored manure is potentially an important source of N2O emissions, particularly when storage conditions are conducive to formation of (NO2− + NO3−). Key words: Nitrous oxide production, denitrification, denitrifying enzyme activity, manure

Tillage and N source influence soil-emitted nitrous oxide in the Alberta Parkland region

Zero tillage systems are receiving attention as possible strategies for sequestering atmospheric carbon. This benefit may be offset by increased N2O emissions, which have been reported for soils under zero tillage (ZT) compared to those under more intensive tillage (IT). Comparisons of N2O emissions from the two systems have been restricted to the growing season, but substantial losses of N2O have been reported during spring thaw events in many regions. Inorganic and organic additions of nitrogen and fallowing have also been shown to increase levels of soil-emitted N2O. The objectives for this study were: (i) to confirm that losses of N2O are higher under ZT than under IT in Alberta Parkland agroecosystems; (ii) to compare the relative influence of urea fertilizer (56 or 100 kg N ha−1), field pea residue (dry matter at 5 Mg ha−1), sheep manure (dry matter at 40 Mg ha−1) additions, and fallow on total N2O losses; and (iii) to investigate possible interactions between fertility and tillage treatments. Gas samples were collected using vented soil covers at three sites near Edmonton, Alberta during 1993, 1994, and 1995. Gas samples were analyzed using a gas chromatograph equipped with a 63Ni electron capture detector. Estimated annual N2O loss ranged from 0.1 to 4.0 kg N ha−1. Emissions during summer were slightly higher, similar, or lower on ZT compared to those under IT, but were consistently lower on ZT plots during spring thaw. Combined estimates (spring plus summer) of N2O loss under ZT were equal to or lower than those under IT. Highest overall losses were observed on fallow plots, followed by fertilizer, pea residue, and then either manure or control plots. We conclude that ZT management systems have potential for reducing agricultural greenhouse gas emissions in the Alberta Parkland region. Key words: Nitrous oxide, thawing soil, tillage, nitrogen fertilizer, manure, fallow

Three methods to estimate N2O fluxes as impacted by agricultural management

This study examines three methods of evaluating N2O flux and accumulation in soil profile over a growing season under three soil management regimes (fallow, fallow with manure addition and cropped to alfalfa). Estimates of N2O flux were made based on measured soil atmosphere concentration gradients in the top 15 cm and compared to flux estimates based on ex situ cores and micro-meteorological measurements made in parallel studies. All methods indicated strong seasonal trends relating to precipitation events. The amounts of N2O accumulating the profile decreased in the order alfalfa < fallow < fallow/manure. The amounts of N2O accumulating in the profile ranged from ambient (0.35 µL L−1) to 490 µL L−1. Diffusion of N2O to the lower profile was shown to provide temporary storage of N2O and thereby provide the opportunity for further reduction to N2 prior to efflux from the surface. In comparing the estimates of surface flux, all three methods were of the same order of magnitude for the fallow site but profile-based estimates were much lower and much higher for fallow/manure and alfalfa sites, respectively. Differences were attributed to the location and timing of carbon addition in each system. Key words: Nitrous oxide, N2O, flux, measurement, soil, management

Estimates of nitrous oxide emissions from agricultural fields over 28 months

Field studies conducted throughout the calendar year are needed to improve flux estimates for the greenhouse gas nitrous oxide (N2O). In this study, we report monthly N2O emissions measured using micrometeorological techniques and a Tunable Diode Laser Trace Gas Analyzer (TDLTGA). Nitrous oxide fluxes were measured at the Elora Research Station (20 km north of Guelph, Ontario) from July to November 1992, and from March 1993 to February 1995, giving a total of 2445 daily averages obtained during the full length of the experiment. The soil at the experimental site was a Conestogo silt loam (Gleyed melanic brunisol). Several fields were monitored including fallow, manured fallow, Kentucky bluegrass, alfalfa, barley, canola, soybeans and corn plots. Spring thaw emissions from fallow or ploughed plots measured from March to April ranged from 1.5 to 4.3 kg N ha−1, corresponding to approximately 65% of the total annual emission. Similar effects were not observed on the vegetated (alfalfa and grass) plots. The lowest total annual N2O emissions were measured for second year alfalfa (1 kg N ha−1 yr−1) and bluegrass (0 to 0.5 kg N ha−1 yr−1). Higher annual emissions (2.5 to 4.0 kg N ha−1 yr−1) were observed for corn, barley, canola, and fallow plots. Highest annual emissions were measured after addition of nitrogen in the form of animal manure on a fallowed plot (5.7 to 7.4 kg N ha−1 yr−1), and alfalfa residue by fall-ploughing (6.1 kg N ha−1 yr−1). Plot management during the previous year affected N2O emissions, particularly on the soybean plot (5.9 kg N ha−1 yr−1) that followed a manured fallow treatment. The micrometeorological technique used in this study was successful at quasi-continuous monitoring of N2O fluxes from several plots, and therefore, useful for detecting long-term effects of management on emissions. Key words: Nitrous oxide, N2O fluxes, trace gases, agriculture, greenhouse gases

DENITRIFICATION IN LOWBUSH BLUEBERRY SOILS

Effects of environmental variables on denitrification in acid (pH 4.0–5.5), infertile soils of lowbush blueberry (Vaccinium angustifolium Ait.) stands were investigated under laboratory conditions. All soils produced N2O when nitrate was added and samples were waterlogged and incubated for 2 d at temperatures of 20 °C or greater. No N2O production occurred at temperatures of 15 °C or lower. Nitrous oxide was the main gas evolved at the natural pH levels of these soils. Mercuric chloride inhibited nitrous oxide evolution. Raising soil pH resulted in increased rates of denitrification, and in more conversion of nitrous oxide to dinitrogen. Soil taken from a site that had been fertilized repeatedly exhibited higher rates of N2O evolution than did soil from a site that had never been fertilized. N2O production from waterlogged samples without added nitrate was positively correlated with percent organic matter and nitrate concentration of soils at the time of sampling. In a field experiment, more N2O was produced by samples from fertilized plots than by those from unfertilized plots, but absolute values from both types of plots were low. Key words: Nitrous oxide, pH, nitrate, moisture

NITROUS OXIDE EMISSIONS FROM SOILS DURING THAWING

We, as well as others, have observed that nitrous oxide (N2O) fluxes increased markedly during soil thaw in early spring. This phenomenon was examined further by determining nitrous oxide concentrations in the soil profile and N2O fluxes from the soil surface during the winter-spring period and evaluating physical release and microbial production of N2O on thawing of frozen soil cores in the laboratory. In mid-winter, soil profile N2O concentrations were close to ambient and surface N2O fluxes were low. At thawing, high N2O concentrations (ranging from 1082 to 2066 mg∙m−3) were found at 10–30 cm in the soil profiles of a coniferous forest, and in manure- and straw-treated plots. Concurrently, N2O flux increased markedly and reached some of the highest values observed during the entire season. When thawing was complete, soil profile N2O concentrations and N2O flux declined. Soil cores were taken from frozen soil, warmed in the laboratory, and N2O release measured. Nitrous oxide was released on warming, and cores treated with CHCl3 had a slower release rate. The results indicate that some of the N2O flux occurring at thawing is due in part to physical release of N2O, and that additional N2O is likely produced by denitrification. Key words: Nitrous oxide, denitrification, frozen soils, nitrogen loss