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. The response trends for 2012 and the 4-year mean were linear. The fitted regression for 2012 indicates that biomass yield increased by 11 kg/ha for every additional kg of N applied above the control. The regression for the 4-year means shows that biomass yield increased by around 20 kg per kg of N applied above the control. The important finding in the current trial is that relatively low N application rates (50 kg/ha) on an upland, drought-prone soil in the Ozark Plateau result in yields of 11 to 12 t/ha (~5 t/A). For the fertilizer trials in eastern AR, there were no significant differences in biomass yield among treatments. There was a numerical response to N in that trial from 10.6 to 15.3 t/ha; however, high field variability among replications prevented a statistical significance. As for P and K, there were no apparent yield responses even though the soil was very low to low in Mehlich III extractable P (8 to 20 ppm) and low to medium in extractable K (50 to 100 ppm). Future work on these trials will include soil sampling every plot to correlate yield response to soil-test levels, which will be used for developing fertilizer recommendations for switchgrass as a bioenergy crop. AR-33