Seasonal Dynamics of N, P, and K in an Organic and Inorganic Fertilized Willow Biomass System

The seasonal variations in soil nutrient supply and bioavailability were assessed in a willow biomass crop (Salix miyabeana, SX64) treated with 150 and 200 kg available N ha^-1 of commercial fertilizer (CF), biosolid compost (BC), dairy manure (DM), and control (CT0) at Delhi, NY. Plant root simulator probes were used to measure nutrient supply (inside) and bioavailability (outside) of root exclusion cylinders. Measurements were made in September 2008 and May, August, and October of 2009. Soil moisture content (θd) and foliar nutrient concentrations were also determined. The BC treatments increased soil P supply more than CF and CT0. The supply of NH₄⁺ and K in the soil increased in August but their bioavailability increased in May and October. Soil NO₃^- and P supply and bioavailability were both high in May. Foliar N and K concentrations were significantly high in May and low in August which could be due to dilution effect caused by increased soil moisture foliar dry weight. Foliar P concentrations increased in September and October. The observed higher soil NO₃^- mineralization and plant uptake in May suggest that in high soil NO₃^- conditions willow biomass crops can level and minimize leaching out of the root zone into groundwater.