Using flow gauges to determine leaf specific conductance in hybrid poplars under mesic and xeric conditions

Non-Peer ReviewedA study was conducted using sap flow gauges to determine leaf specific conductance (LSC) in hybrid poplars in an environmentally-controlled greenhouse at Swift Current, Saskatchewan. Sap flow rates were compared between CanAm and Walker poplar clones using stem flow gauges. The primary objectives were to verify differences in LSC observed between the clones under moist field conditions in a previous study and to compare the responses in sap flow and LSC within these trees as imposed soil conditions changed from moist to dry. Walker poplars appear to be well-suited to mesic sites, and, under ample soil moisture, perform better than CanAms. However, they are susceptible to mid-season terminal shoot dieback, while CanAm poplars do not seem to be as susceptible. We suspect that this is primarily attributable to a greater LSC of CanAm poplars and possibly achieving better stomatal responses during periods of extended vapor pressure deficits. The gauges were mounted near the base of each tree. Following gauge installation, the trees were watered to field capacity. No additional water was added during the course of the test. Sap flow, leaf water potentials and tree conditions were monitored for 17 days as the soil conditions evolved from moist to dry. Results indicate that the CanAms displayed a greater LSC under moist as well as dry conditions compared to the Walkers. Throughout the testing period, CanAm mid-day leaf water potentials were slightly more negative than for the Walker poplars. Although CanAm poplars appear to be less water efficient than Walkers, they are better able to function and survive during periods of extended vapour pressure deficits

Using flow gauges to determine stem and root conductance in hybrid poplars.

Non-Peer ReviewedA study was conducted using sap flow gauges to determine stem and root conductance in hybrid poplars at two sites near Swift Current, Saskatchewan. At the Rushlake site, sap flow rates were compared between CanAm and Walker poplars using Dynamax (Model SGA-10) stem flow gauges. The primary objective was to determine if the difference in susceptibility to midsummer terminal shoot dieback in Walker and CanAm poplar clones could be attributed to leaf-specific conductance. Walker poplars appear to be well-suited to mesic sites and, under good soil moisture conditions, perform better than CanAm . However, they are susceptible to mid-season terminal shoot dieback, while CanAm poplars do not seem to be as susceptible. We suspect that this is primarily attributable to a greater leaf-specific conductance (LSC) of CanAm poplars. As a tertiary cause, perhaps CanAm poplars achieve a more complete stomatal closure during periods of extended vapor pressure deficits. The gauges were mounted at the distal ends (where the shoot diameter is about 10 mm) of actively growing branches near the crown of each tree. For a period of 14 days, the sap flow rates of each tree were measured. Preliminary results indicate that CanAms did indeed have a greater LSC and showed higher stem flow rates than Walker poplars. Under the study conditions at the Rushlake site, air temperatures were not of sufficient magnitude to determine differences in leaf stomatal closure between the CanAm and Walker trees. The LSC characteristics, however, would have benefited the CanAm poplars in functioning under extended vapor pressure deficits. A secondary objective was to determine if differences in root conductances of poplars subjected to varying saline conditions were possible to measure using sap flow gauges. Although great care must be taken during gauge installation on tree roots, we found it is possible to measure root sap conductance on trees subjected to varying levels of salinity

Sustainable biomass production in agroforestry systems

Non-Peer ReviewedResearch conducted in 2007 through 2009 on the occasional biomass harvest from willow rings could provide balanced co-existence between agriculture and wetlands. This would provide biomass feedstock while preserving the wetland for future generations. The focus of the research will be on the sustainable production of biomass in agroforestry systems. The goals of this research project are to determine the impact of biomass harvest on re-growth of willow rings; evaluate the feasibility of mechanical harvest using a bio-baler; determine the biomass yield and production costs; and quantify fuel characteristics of harvested willow. Results have shown that the bio-baler tested can efficiently harvest biomass from willow rings at a rate of 6.5 tonnes/hour. The re-growth of the willows was rapid and was not impacted by the harvest. There are thousands of hectares of wetlands and surrounding willow rings available on the Canadian landscape for harvesting at a reasonable cost of production. The willow ring biomass harvested is suitable for small scale heating systems. Additional research will be conducted on the utilization of the biomass harvested from willow rings as a bioenergy source to supply a biomass boiler for heating purposes at the Agriculture and Agri-Food Canada (AAFC) Agroforestry Development Centre (ADC) in Indian Head, Saskatchewan. This research will include the economics and environmental aspects and will consider the life cycle analysis

Using willow riparian buffer strips for biomass production and riparian protection

Non-Peer ReviewedThere is increasing interest in the development of willow biomass as a renewable source of energy and woody lignocellulosic feedstock for bioproducts. Riparian buffers have been identified as an effective barrier to soil and nutrient movement from agricultural fields into watercourse. Willows are ideal riparian species in that they are well adapted to growing conditions in riparian zones and they vigorously re-grow following coppicing which allows them to be harvested for biomass in 3-4 year cycles. Characteristically riparian edges are highly productive due to water availability, therefore it is anticipated that willow biomass yield per unit area in riparian zones would be attractive. Research is being conducted to determine if using riparian buffer strips for willow biomass production provides energy alternatives and economic opportunities for land owners, but also leads to environmental benefits such as reduced erosion and nutrient leaching and preservation of water quality

Poplars and swine manure – can they be compatible?

Non-Peer ReviewedThe results of two Saskatchewan Agriculture Development Fund (ADF) projects and greenhouse studies are presented. Hybrid poplars are the fastest-growing trees in Saskatchewan and may have economic potential as an alternative crop. They also need more moisture and nutrients annually than other tree species for maximum growth. Under the projects, two hybrid poplar plantings were designed at Arborfield and Preeceville, SK, planted in 2002, which were compatible with field application of swine effluent. The nitrogen response of young hybrid poplar trees in the field was assessed and clonal differences were determined that might make some clones more appropriate in such plantings. Effluent was successfully applied to the two plantings at Arborfield and Preeceville with the Prairie Agricultural Machinery Institute (PAMI) effluent application truck to which modifications to the delivery system had been made. Nitrogen growth response was not shown in the newly-planted trees, but there was an increase in annual growth parameters in older trees at Henribourg, SK even though the final height of the trees did not depend on the nitrogen treatment. The projects showed important clonal differences in growth with Walker, Katepwa, WP69 and a clone of Populus tristis (Fisch.) having greater height and diameter than other clones. Greenhouse studies showed that clonal differences exist in nitrogen uptake rates and in preference for the form (ammonium or nitrate) with Hill poplar combining a relatively high productivity with a relatively greater preference for ammonium