On-Farm Evaluation of Sorghum As a Dedicated Bioenergy Crop on Swine-Effluent Spray Fields.

Sorghum (Sorghum bicolor spp.) has potential as a dedicated bioenergy crop on effluent spray fields in North Carolina. However, additional information is needed to determine potential dry matter (DM) production and nutrient management practices for this production system. Our objectives were to determine DM production and nutrient removal of two hybrid sorghums at three different farms of established swine effluent spray fields. The study was conducted for two years (2012 and 2013). Liquid effluent nutrient application was done using a traveling irrigation sprinkler system and application schedules followed each farms’ specific management practices. The sorghums were planted in a randomized complete block design replicated three times. Sorghums were Blade ES5200 (biomass sorghum) and M81E (sweet sorghum). Total DM production of Blade ES5200 (20.7 Mg ha^-1) was greater than M81E (16.4 Mg ha^-1) in 2012 but was similar in 2013 (14.0 and 15.6 Mg ha^-1 for Blade ES5200 and M81E, respectively). Nitrogen concentration and removal in the harvested plant tissue were greater in 2012 (9.1 g kg^-1 and 176.4 kg ha^-1 for N concentration and removal, respectively) than 2013 (7.6 g kg^-1 and 111.1 kg ha^-1 for N concentration and removal, respectively). There was a trend towards greater P and K concentration in the plant tissue for Blade ES5200 (2.1 and 20.1 g kg^-1 for P and K, respectively) compared with M81E (1.8 and 18.1 g kg^-1 for P and K, respectively). Plant P and K removal was greater in Blade ES5200 (34.2 and 379.0 kg ha^-1 for P and K, respectively) than M81E (28.2 and 279.5 kg ha^-1, respectively). The results indicate that sorghum DM production of at least 14 Mg ha^-1 is possible in the swine-effluent spray fields under current on-farm management practices. Additionally, there are differences in P and K removal between sorghum types evaluated.