Philippe Rochette

Dynamics of soil microbial biomass C, soluble organic C and CO2 evolution after three years of manure application

Application of manure and fertilizer affects the rate and extent of mineralization and sequestration of C in soil. The objective of this study was to determine the effects of 3 yr of application of N fertilizer and different manure amendments on CO2 evolution and the dynamics of soil microbial biomass and soluble C in the field. Soil respiration, soluble organic C and microbial biomass C were measured at intervals over the growing season in maize soils amended with stockpiled or rotted manure, N fertilizer (200 kg N ha−1) and with no amendments (control). Manure amendments increased soil respiration and levels of soluble organic C and microbial biomass C by a factor of 2 to 3 compared with the control, whereas the N fertilizer had little effect on any parameter. Soil temperature explained most of the variations in CO2 flux (78 to 95%) in each treatment, but data from all treatments could not be fitted to a unique relationship. Increases in CO2 emission and soluble C resulting from manure amendments were s...

Toward Improved Coefficients for Predicting Direct N2O Emissions from Soil in Canadian Agroecosystems

Agricultural soils emit nitrous oxide (N2O), a potent greenhouse gas. Predicting and mitigating N2O emissions is not easy. To derive national coefficients for N2O emissions from soil, we collated over 400 treatment evaluations (measurements) of N2O fluxes from farming systems in various ecoregions across Canada. A simple linear coefficient for fertilizer-induced emission of N2O in non-manured soils (1.18% of N applied) was comparable to that used by the Intergovernmental Panel on Climate Change (IPCC) (1.25% of N applied). Emissions were correlated to soil and crop management practices (manure addition, N fertilizer addition and inclusion of legumes in the rotation) as well as to annual precipitation. The effect of tillage on emissions was inconsistent, varying among experiments and even within experiments from year to year. In humid regions (e.g., Eastern Canada) no-tillage tended to enhance N2O emissions; in arid regions (e.g., Western Prairies) no-tillage sometimes reduced emissions. The variability of N2O fluxes shows that we cannot yet always distinguish between potential mitigation practices with small (e.g., <10%) differences in emission. Our analysis also emphasizes the need for developing consistent experimental approaches (e.g., ‘control’ treatments) and methodologies (i.e. measurement period lengths) for estimating N2O emissions.

Short-term C and N dynamics in a soil amended with pig slurry and barley straw: a field experiment

Interactions between animal slurries and crop residues can impact on soil N availability during decomposition. Our objective was to study the short-term decomposition of pig slurry and barley straw incorporated alone or in combination. A field experiment was conducted on a sandy loam unamended (control) or amended with 60 m3 ha–1 pig slurry (PS) or 4 Mg ha–1 barley straw (BS), or both (PSBS). Surface CO2 and N2O fluxes, soil water content and temperature, microbial biomass C, and NO3− and NH4+ contents were monitored during 28 d in the 0- to 20-cm soil layer. Large CO2 fluxes occurred during the first 4 h of the experiment in slurry-amended plots that were attributed to carbonate dissociation when slurry was mixed to the soil. Specific respiration activity (ratio of CO2-C fluxes-to-microbial biomass C) was increased in slurry-amended soils for the first 7 d, likely due to the rapid oxidation of volatile fatty acids present in slurry. After 28 d, 26% more C had been evolved in PSBS than the sum of C releas...

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...

N2O emissions from spring barley production as influenced by fertilizer nitrogen rate

Usage of mineral nitrogen (N) fertilizers for agricultural crop production systems is a major contributor to anthropogenic nitrous oxide (N2O) emissions. As part of a national study to quantify N2O emissions under different cropping systems and in different eco-regions, this study quantified the effect of fertilizer N rate on spring barley (Hordeum vulgare L.) on N2O emissions in 3 yr in a cool maritime climate with humid soil moisture regimes. Treatments were 0, 75 and 150 kg N ha-1 as ammonium nitrate applied as a pre-plant broadcast. N2O emissions were increased by fertilizer N application in each year. In 2003 and 2005, elevated N2O emissions occurred in the 6-wk period following fertilizer application when soil NO3-N concentrations were high. However, in 2004 and 2005, peak N2O emissions occurred near crop harvest. Elevated N2O emissions at this time were attributed to increased carbon availability due to re-wetting of dry soil. Therefore, the effect of fertilizer N management on N2O emissions may no...

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 differ...

A proposed approach to estimate and reduce net greenhouse gas emissions from whole farms

Greenhouse gas emissions from farms can be suppressed in two ways: by curtailing the release of these gases (especially N2O and CH4), and by storing more carbon in soils, thereby removing atmospheric CO2. But most practices have multiple interactive effects on emissions throughout a farm. We describe an approach for identifying practices that best reduce net, whole-farm emissions. We propose to develop a “Virtual Farm”, a series of interconnected algorithms that predict net emissions from flows of carbon, nitrogen, and energy. The Virtual Farm would consist of three elements: descriptors, which characterize the farm; algorithms, which calculate emissions from components of the farm; and an integrator, which links the algorithms to each other and the descriptors, generating whole-farm estimates. Ideally, the Virtual Farm will be: boundary-explicit, with single farms as the fundamental unit; adaptable to diverse farm types; modular in design; simple and transparent; dependent on minimal, attainable inputs; ...

Nitrous Oxide Emissions Respond Differently to Mineral and Organic Nitrogen Sources in Contrasting Soil Types

The use of various animal manures for nitrogen (N) fertilization is often viewed as a viable replacement for mineral N fertilizers. However, the impacts of amendment type on NO production may vary. In this study, NO emissions were measured for 2 yr on two soil types with contrasting texture and carbon (C) content under a cool, humid climate. Treatments consisted of a no-N control, calcium ammonium nitrate, poultry manure, liquid cattle manure, or liquid swine manure. The N sources were surface applied and immediately incorporated at 90 kg N ha before seeding of spring wheat ( L.). Cumulative NO-N emissions from the silty clay ranged from 2.2 to 8.3 kg ha yr and were slightly lower in the control than in the fertilized plots ( = 0.067). The 2-yr mean NO emission factors ranged from 2.0 to 4.4% of added N, with no difference among N sources. Emissions of NO from the sandy loam soil ranged from 0.3 to 2.2 kg NO-N ha yr, with higher emissions with organic than mineral N sources ( = 0.015) and the greatest emissions with poultry manure ( < 0.001). The NO emission factor from plots amended with poultry manure was 1.8%, more than double that of the other treatments (0.3-0.9%), likely because of its high C content. On the silty clay, the yield-based NO emissions (g NO-N kg grain yield N) were similar between treatments, whereas on the sandy loam, they were greatest when amended with poultry manure. Our findings suggest that, compared with mineral N sources, manure application only increases soil NO flux in soils with low C content.

Estimation of maize (Zea mays L.) canopy conductance by scaling up leaf stomatal conductance

Abstract Transpiration is partially controlled by the plant at leaf level through the degree of aperture of the stomata. Mathematical models estimating the transpiration of plant stands using a conductance network approach to water vapor transfer thus need a plant surface control term ( g s ). Techniques involving different degrees of simplification of canopy structure have been proposed to estimate g s , from measurements or estimates of leaf stomatal conductance ( g s ). This study compares the performance of some of these techniques by examining the patterns of diurnal and seasonal variation for a maize crop grown at Ottawa, Canada. Measurements of g s , were made for sunlit and shaded leaves at three levels in the plant canopy and the response of g s , to photosynthetic photon flux density ( Q p ) has been parameterized. Values of g s , obtained by different scaling-up methods were compared among themselves and with those obtained from the Penman-Monteith equation ( g c ). The main results and conclusions were: daily maximum g s , values of sunlit leaves generally occurred on or slightly before maximum radiation; the response of g s to low Q p was a function of leaf levels in the canopy and growth stage; the response of g s to low Q p increased with leaf area index for shaded leaves; modelling of g s , based on Q p , leaf temperature and leaf water potential failed to give good estimates under overcast afternoon conditions; measurement of g s , on horizontal portions of leaves led to an overestimation of g s ; spherical leaf angle distribution assumption gave the best estimates of g s ; the shelter factor (ratio of scaled-up g s , over g c ) tended to increase as the ratio of the canopy aerodynamic conductance to top leaf stomatal conductance increased.