Effect of organic amendments and slow-release nitrogen fertilizer on willow biomass production and soil chemical characteristics

Lime-stabilized sewage sludge and composted poultry manure, at a rate of 250 m³ ha^-1 each, and slow-release N fertilizer (Scott's Osmocote) at 100, 200 and 300 kg N ha^-1, were applied to plots of willow biomass crops during the first season of a three-year growth cycle. Stem biomass production was measured annually and soil chemical characteristics were assessed at the end of the growth cycle. Average annual stem biomass production was 8-11 Mg ha^-1 in slow-release N fertilized plots corresponding to a yield increase of 7-33% relative to control plots. In organically amended plots, annual stem biomass production increased by 30-38% relative to control plots. The study suggests that organically amended willows grew at a slightly faster rate than slow-release N fertilized willows. Statistically, the relationship between slow-release N application rate and stem biomass production was not highly significant; applications of slow-release N in excess of 100 kg N ha^-1 provided no additional yield benefits. Differences in soil characteristics were most strongly expressed in surface soil. The pH at 0-10 cm depth was 1 and 2 units higher on lime-stabilized sludge and composted poultry manure plots, respectively. Concentrations of soil K, P and Mg were dramatically higher in the composted poultry manure soils. The highest soil organic matter and N levels were observed in the surface horizons of organically amended soils. Utilization of organic residuals increases biomass production, provides beneficial use for wastes, reducing production costs and contributing to the sustainability of biomass production systems.