Fertilization of willow bioenergy cropping systems in Saskatchewan, Canada

Abstract

The detrimental effects of climate change and the threat of diminishing fossil fuel reserves is forcing society to search for renewable sources of energy. Energy can be derived from the biomass of plant material by co-fire combustion with coal or on its own for the production of electricity. Energy can also be created by converting the plant biomass into ethanol, a gasoline substitute. When converted into bioenergy, plant biomass from Short Rotation Woody Crop (SRWC) systems has the potential to offset the use of fossil fuels if the yields can be maintained at profitable levels. The effect of first year application of nitrogen (N) fertilizer on willow biomass production in a SRWC system is not well understood. Using field and growth chamber studies, the objectives of this study were to 1) determine biomass production in the growing seasons following a single application of N fertilizer in the year of planting, 2) determine the N recovery for five willow clones using a 15N tracer, and 3) evaluate the effects of various types and rates of fertilizers on biomass production. Objectives 1 and 2 were addressed in a field fertilization study conducted on agricultural lands in the Moist Mixed Grassland ecozone and at tree nursery in the Boreal Transition ecozone. Willow cuttings were planted and fertilized with 100 kg N ha-1 of granular ammonium nitrate. Twelve trees were fertilized with 5 kg N ha-1 of double 15N-labeled ammonium nitrate and 95 kg N ha-1 of granular ammonium nitrate. In the first growing season trees were browsed to a uniform height making biomass measurements unrepresentative of production potential. Annual shoot biomass production in the second year, however, was 0.39 to 2.0 Mg ha-1 and was not found to be significantly different between fertilizer treatments. Nitrogen recovery by entire trees ranged from 2.87 to 10.6 % in the first growing season and 0.39 to 2.95 % in the second growing season. Objective three was addressed in a growth chamber study. Willow cuttings were planted in pots and fertilized with 0, 50, 100 and 200 kg N ha-1 of granular ammonium nitrate and 100 kg N ha-1 of composted cattle manure. After a 90 day growth period shoot biomass production was significantly greater on the Prince Albert soil (1.28 to 5.34 g tree-1) than on the Saskatoon soil (1.18 to 3.59 g tree-1). No consistent trend between fertilizer treatments was observed. Further exploration into fertilization of willow SRWC systems should consider the application of multiple nutrient fertilizer blends, various rates and year of application to gain a better understanding of nutrient requirements of willow for the entire growth period.