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

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. In the N rate trial, N concentration increased, P concentrations were unaffected, and K concentrations declined with increments of N fertilizer. In the P trial, no elemental concentrations were affected by P fertilizer rates. In the K trial, there was a slight, nonsignificant trend for an increase in K concentration with K fertilizer increments, whereas N and P were unaffected. The N rate study in 2011 showed a significant increase in biomass yield with increments of fertilizer applied as urea in one application in early May. The trend in response was linear from 0 to 90 lb N/A, then leveled off at the highest increment. This was similar response to that found in 2010. Yields were lower in 2011 than in 2010 because of record high summer temperatures and a prolonged drought. Concentrations and removal rates of N, P, and K are still being analyzed.

The variety trials compare advanced breeding lines ‘Cimarron’, ‘C75’, and ‘C77’ with the standard, commercially available cultivar, ‘Alamo’. All plots received 60 lb N/A in late April each year. At the beginning of 2011, the plot area was found to have low soil test values for P and K. Therefore, 60 and 115 lb/A of P₂O₅ and K₂O, respectively, were applied to the plot area. Cimarron, a new release, exhibited greater biomass yield than Alamo. New, high-yielding cultivars of switchgrass would be expected to remove more N, P, and K from the field than Alamo. The added P and K fertilizer probably explains most of the increase in biomass yield in 2011 compared to 2010; however, somewhat more favorable rainfall in 2011 may explain some of the increase. Although not designed as a fertilizer response study, the results suggest that switchgrass does respond to P or K, with K being the more likely limiting nutrient, as indicated by the increased K tissue concentrations in the K fertilizer trial described above. AR-33