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

Current fertilizer recommendations for cellulosic fuel crops in Arkansas are based on native warm-season grasses used as forages. These crops are normally harvested as hay in early to mid-summer when N, P and K removal rates are typically much greater than when harvested in the fall after the crop senesces and dries down. Fall harvest of a grass crop for bioenergy returns a large fraction of the plant macronutrients back to the soil or to the roots and crowns for recycling back into subsequent year's regrowth. This phenomenon probably would result in P and K fertilizer recommendations that are lower than when the same grasses are utilized as forages. Studies are being conducted in Northwest Arkansas to evaluate the effect of N, P and K fertilization on switchgrass production when grown as a fuel crop.

There were no significant differences in biomass yield due to P or K fertilization in 2013. The biomass yields in the P fertilization trial ranged from 12.3 to 13.3 t/ha, but yields were not significantly different among the P fertilizer application rates (0 to 120 kg/ha). The yields in the K fertilization trial ranged from 12.9 to 13.6 t/ha among the K fertilizer rates (0 to 240 kg/ha), but yield differences were not significantly different. The yields in the N fertilization trial ranged from 9.3 to 20.8 t/ha, which represented a significant yield boost with increasing N application rates. These studies will be continued in 2014.