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

Field studies were carried out for the fourth year on ‘Alamo’ switchgrass yield response to N fertilizer in northwest Arkansas, and for the second year in eastern Arkansas. The latter location also had trials on P and K fertilization. The N rate study in NW Arkansas (AR) in 2012 (harvested Oct. 8) showed a statistically significant increase in biomass yield with increments of fertilizer applied as urea in one application in early May.

Field studies were conducted for the third year on switchgrass yield response to N fertilizer in northwest Arkansas. Another study evaluating N, P, and K fertilizer response was established in eastern Arkansas in 2011 and switchgrass variety trials were conducted in 2010 and 2011. For the N, P, and K fertilizer trials, average forage yield was 7 ton/A. The fertilizer nutrients were tested in physically separate trials, which were adjacent to each other.

A switchgrass growth and composition trial was conducted in 2009 and 2010 at the University of Arkansas. The trial consisted of 12 sampling dates from early May to mid-February. For the 2009-10 growing season, peak yield (6. 25 t/A) occurred at the August 28 sampling date. Yields were essentially level from September 30 to October 27, and then followed a gradual decline until February 17, 2010.

Two switchgrass field studies were established at the University of Arkansas in 2008. One describes growing-season biomass accumulation and NPK uptake curves and the other determines N response curves for biomass yield. The first study consisted of 12 harvest dates, ranging from May to February. Trends in cumulative growth and nutrient concentration were fitted to regression models as a function of day of year. The 2009 data showed that growth followed a typical S-shaped curve.

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).