Biomass and Macronutrient Accumulation and Losses in Switchgrass During and After the Growing Season

Two switchgrass production field studies were established at the University of Arkansas Agricultural Research and Extension Center in July 2008. Switchgrass generally produces very little above-ground growth in Year 1 as it allocates a large amount of energy to its strong root systems. Harvestable biomass accumulates in Year 2, while maximum yields occur from Year 3 onward. Thus, data from these studies will be collected in Years 2 and 3 (May 2009 to February 2011). One study will describe growing-season biomass accumulation and NPK uptake curves for switchgrass grown for biomass and the other will determine N response curves for biomass yield in second- and third-year switchgrass stands. The first study will consist of 12 harvest dates, ranging from May to February. Trends in cumulative growth, moisture concentration, and nutrient concentration and removal will be fitted to regression models as a function of day of year and accumulated growing-degree days. Regressions will be tested on two phases of the year, in-season from May to September, and post-season from October to February. The second study will include treatments of urea applied on April 1 at the rates of 0, 35, 70, 105, and 140 kg N/ha. One harvest per year will be taken in early October for moisture content and biomass yield. Plant biomass will be sampled to determine N concentration and to calculate N removal and apparent N recovery. AR-33