P. Rochette

Description of a dynamic closed chamber for measuring soil respiration and its comparison with other techniques

Soil respiration is an important component of the net carbon dioxide exchange between agricultural ecosystems and the atmosphere, and reliable estimates of soil respiration are required in carbon balance studies. Most of the field measurements of soil respiration reported in the literature have been made using alkali traps. The use of portable CO2 analysers in dynamic closed chamber systems is recent. The introduction of this new technique requires its evaluation against existing methods in order to compare new information with older data. Nine intercomparisons between dynamic systems and alkali traps were made. Measurements of Fc,s obtained by both chambers showed a good agreement in all but two comparisons in which alkali trap measurements were lower than the dynamic chamber by about 22%. This first report of agreement between both techniques suggests that many measurements made in the past using alkali traps may be comparable to the measurements made more recently using the dynamic chambers. Analysis o...

Evaluation of two process-based models to estimate soil N2O emissions in Eastern Canada

Process-based models play an important role in the estimation of soil N2O emissions from regions with contrasting soil and climatic conditions. A study was performed to evaluate the ability of two process-based models, DAYCENT and DNDC, to estimate N2O emissions, soil nitrate- and ammonium-N levels, as well as soil temperature and water content. The measurement sites included a maize crop fertilized with pig slurry (Quebec) and a wheat-maize-soybean rotation as part of a tillage-fertilizer experiment (Ontario). At the Quebec site, both models accurately simulated soil temperature with an average relative error (ARE) ranging from 0 to 2%. The models underpredicted soil temperature at the Ontario site with ARE from −5 to −7% for DNDC and from −5 to −13% for DAYCENT. Both models underestimated soil water content particularly during the growing season. The DNDC model accurately predicted average seasonal N2O emissions across treatments at both sites whereas the DAYCENT model underpredicted N2O emissions by 32...

The rate of carbon change in agricultural soils in Canada at the landscape level

The Century model [a computer simulation of the dynamics of soil organic carbon (SOC)] was used to estimate the rate of SOC change in agricultural soil in Canada. The analysis was carried out on 180 Soil Landscapes of Canada (SLC) polygons, representing 15% of the SLC polygons within agricultural regions. The analysis was stratified into soil zones and into soil textural classes. For each sampled polygon, Century was run for 1 to 5 types of crop rotations under conventional-tillage as well as no-tillage, providing that no-till was used on at least 5% of the land. From the Century simulations, it was estimated that the overall rate of SOC loss from agricultural soils in Canada for 1990 was 39.1 kg ha−1 yr−1 This implies that 1.93 Mt of SOC (7.08 Mt of CO2) was lost from agricultural soils in Canada. Compared to 1990, the SOC loss was estimated to have been greater by 11.9 kg ha−1 yr−1 in 1980 and 9.1 kg ha−1 yr−1 in 1985. The lower loss in 1990 was primarily due to the incorporation of no-till practices an...

CH4 fluxes from a soil amended with dairy cattle manure and ammonium nitrate

Dairy cows and heifers in Quebec and Ontario produce 19 Mt of manure annually. Most of this manure is applied to soils and may influence the atmospheric loading of greenhouse gases such as CH4 In this study, soil surface CH4 fluxes were measured 36 times during the snow-free season of 1993, and 28 times in 1994, on plots fertilized with organic or inorganic-N. In 1993, stockpiled dairy cattle manure was applied at rates of 0, 56 and 112 Mg ha−1 In 1994, the treatments were: zero N, 100 Mg ha−1 of stockpiled dairy cattle manure, 100 Mg ha−1 of composted dairy cattle manure and 200 kg N ha−1 as ammonium nitrate. Methane fluxes (−0.012 to 0.004 mg m−2 h−1) were usually higher (less negative) on manured than on unmanured plots, but the differences were not statistically significant. No significant effect of mineral-N fertilization was observed as the ammonium nitrate treatment showed uptake rates similar to those of the control. In 1993, episodic above-ambient CH4 concentrations were measured at 0.15 m (8 ppm...

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...

Can soil clay content predict ammonia volatilization losses from subsurface-banded urea in eastern Canadian soils?

Abstract: To determine how soil physical and chemical characteristics affect NH3 volatilization, we measured NH3 losses from eight different eastern Canadian soils with various soil clay contents and cation exchange capacities (CEC). Losses were measured from soil mesocosms banded (0.05 m depth) with urea (equivalent of 140 kg N ha-1) in a dynamic chamber system fitted with an acid trap; with soil properties measured in parallel mesocosms. Regression analysis indicated a negative relationship between 28 d of NH3 volatilization losses and soil clay content (P < 0.001; R2 = 0.978), CEC (P < 0.001; R2 = 0.941), and buffer capacity (P = 0.006; R2 = 0.772), and positive relations with maximum change in soil pH (P = 0.015; R2 = 0.670) and maximum water-extractable NH4+ (P = 0.010; R2 = 0.721). A 90% reduction in NH3 losses occurred when clay content increased from 10% to 20%. Also, the correlation between water-extractable NH4+ and NH3 loss and a lack of correlation between salt-extractable (1 mol L-1 KCl) NH4+ and NH3 loss indicate that NH4+ bound to cation exchange sites does not contribute to the rapid NH3 volatilization. However, more research on soils of different mineralogy is required to ascertain whether this holds in other regions as well.