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Valorisation de biomasses pour une production durable de biocarburant

The research conducted through this grant evaluated combinations of biofuel feedstock crop (switchgrass, reed canarygrass and hybrid poplar), biochar (0 and 20 t ha-1), nitrogen fertilizer (0, 50, 100 kg N ha-1 for switchgrass; 0 75, 150 kg N ha-1 for canarygrass; 0, 70, 140 kg N ha-1 for poplar) and plant growth promoting microbes (those helping sequester phosphorus from the soil and those fixing nitrogen from the atmosphere).

SWITCHGRASS: Switchgrass is a warm-season adapted C4 grass that is reasonably well characterized as a biomass feedstock crop in the United States, but is has been less investigated at higher latitudes and has not been examined in the  context of plant growth promoting micro-organisms and biochar. The work was conducted on three sites, on two soil types at the Macdonald Campus of McGill University and at a site associated with Laval University in southeastern Quebec (St Augustin), so that a range of soil types and climatic conditions were sampled. This study demonstrated a positive effect of biochar, along with PGPR, on plant growth variables (i.e. height, stand count, dry biomass), aboveground N concentration, aboveground N export (kg N ha-1). Overall, plant growth promoting rhizobacteria and biochar resulted in 9-30 % increases in dry biomass when applied separately.  However in the field, biochar and plant growth prmoting rhizobacteria tended to interact. Overall, yield increased approximately 30% with biochar application and PGPR inoculation together, demonstrating a possible biochar by plant growth promoting rhizobacteria interaction or, in some cases, their main effects. The highest biomass yield resulted from 50 kg N ha-1 at one of the Macdonald sites and 100 kg N ha-1 along with biochar at the other Macdonald site and the Laval site. Biochar-amended soils had greater nitrogen use efficiency at 50 kg N ha-1 while comparatively high apparent nitrogen recovery was observed at 50 kg N ha-1 along with biochar at spring harvest. Biochar-amended soils tended to have greater nitrogen use efficiencies at 50 kg N ha-1. Higher apparent nitrogen recovery occurred at fall harvest when 100 kg N ha-1 was applied, while 50 kg N ha-1 along with biochar application resulted in the same trend for the spring harvest. Overall, biochar with 50 kg N ha-1 enhanced swithgrass biomass yield, nitrogen export, apparent nitrogen recovery and nitrogen use efficiency across all three field sites over three years (nine site years). The carbon content was approximately 30% higher with biochar application to the surface soil. Biochar application increased the water content of the soil in the top 15 cm because it has a high water retention capacity. These findings have the potential to accelerate the development of more sustainable low-input energy grass production systems for temperate regions.

REED CANARYGRASS: Reed canarygrass is a relatively cool adapted C3 grass. It has potential as a biofuel crop for production in cool season areas, such as northern Europe and northern North America. Among the cool-season grasses, it matures quickly and is well adapted to cool conditions and has high biomass yield, a wide range of adaptation and low N fertilizer requirement. There have been no previous investigations related to effects of biochar, plant growth promoting rhizobacterial and nitrogen fertilizer on the productivity of reed canarygrass. This crop was investigates at just one site, at the Macdonald Campus of McGill University, for 2 years. The overall objective of the work was the same as for switchgrass, but with a reed canarygrass focus. Overall, biochar treatments increased reed canarygrass nitrogen use efficiency from 10 to 52%, whereas the greatest N export (kg N ha-1) occurred with combined plant growth promoting rhizobacteria (nitrogen-fixing and phosphorus-solubilizing plant growth promoting rhizobacteria) inoculation, which was about 90% greater than the control. A biochar by N fertilizer interaction existed for both years of field testing, whereby the greatest level of dry biomass was produced with 150 kg N ha-1 plus biochar applied as a soil amendment. The greatest carbon content (increase of 38.5% over the control) resulted from addition of 150 kg N ha-1 plus biochar. Biochar application, in conjunction with plant growth promoting rhizobacteria inoculation, enhanced reed canarygrass plant growth and biomass yield over the two years of field experimentation. The combination of increased biomass production plus improved nitrogen use efficiency and nitrogen recovery indicate that a production system like the one tested here can be an efficient low-input system for reed canarygrass production as a biomass feedstock for Québec.

POPLAR: There was an effect of mineral nitrogen fertilization on biomass production, with a 25% increase in biomass for 140 kg N ha-1, as compared to the control treatment, after 3 years at the McGill site. The effects of the fertilization on poplar are known and these results were expected. However, the Laval site did not respond the same way to nitrogen fertilization. After 2 years, only the 70 kg N ha-1 treatment increased poplar growth. After 3 years, N fertilization had no effect on growth. This could be due to the structure of the soil, a clay loam, which limits the nitrate leaching and promotes the accumulation of N in the soil. Analyses of the leaf composition showed that after two growing seasons there were differences in the nitrogen content of plants receiving the 140 kg N ha-1 treatment and the control, but the difference was no longer present in the third growing season. Biochar and plant growth promoting rhizobacteria did not increase the yields of hybrid poplar biomass after two and three growing seasons, respectively. To better understand the possible effects of PGPR bacteria, a greenhouse experiment, under controlled environment conditions, was conducted in the spring of 2011. The survival of bacteria after inoculation, at specific cell concentrations and effects on poplars were tested. No significant effect on growth appeared after 4 months. There was no effect of biochar on growth and no interaction of biochar with fertilizer application. Leaf analyzes did not show effects of biochar on nutrient retention. A greenhouse experiment showed a tendency of biochar to promote growth under conditions of water stress. There was a difference in the growth between the two poplar clones included in this research. Clone 3729 clone was more productive, both in Québec and Montréal areas, and may be preferred for the production of biomass energy. Poplar yields were 60 to 80% higher the Montréal site than at the Laval site (St Augustin.)


Chercheur principal : Donald Smith, Université McGill

Titre original : Valorisation de biomasses à faibles intrants pour une production durable de biocarburant

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