Biomass and Sweet Sorghum Fertilized with Swine Lagoon Effluent for Bioenergy

Abstract

Core Ideas Dry matter yields were not different between the two sorghums in 11 out of 12 yr–location combinations. Nitrogen, P, and K removals averaged 138, 28, and 313 kg ha–1, respectively. Both sorghum cultivars, ES5200 and M81‐E, were productive biomass crops at swine spray fields and may be a feasible alternative for producers that desire the flexibility of an annual crop and high dry matter yields in a single clipping event at the end of the growing season (15.7 ± 5.1 Mg ha–1 yr–1. Land receiving waste effluent from swine (Sus scrofa domesticus) production systems (also known as spray fields) may provide a unique opportunity for bioenergy feedstock supply from sorghum [Sorghum bicolor (L.) Moench]. Information on dry matter (DM) production and nutrient uptake from on‐farm trials is needed to determine the viability of this practice. The objectives of the study were to compare DM production and nutrient removal of two sorghum cultivars (high biomass Blade ES5200 and sweet sorghum M81‐E) planted at three on‐farm swine effluent spray field locations. The study was conducted in North Carolina for 4 yr (2012–2015). Dry matter yields ranged from 8.1 to 27.7 Mg ha−1 and were no different between sorghum entries in 11 out of 12 location‐year combinations. Nitrogen concentration in the plant tissue ranged from 5.9 to 12.9 g kg−1 reflecting the wide range of N loadings (41–624 kg ha−1). Nitrogen removal ranged from 54 to 287 kg ha−1. Phosphorus concentration in the plant tissue ranged from 1.4 to 2.5 g kg−1 and removal ranged from 15.4 to 51.3 kg ha−1. Potassium concentration and removal were not different between entries and averaged 20.4 g kg−1 and 313 kg ha−1, respectively. The results indicate that if sorghum is to be the only crop per annual cycle, then irrigation management and nutrient loading need to be less intensive (lower amounts), specially for N and K, than in current bermudagrass (Cynodonon dactylon L.)‐based systems to prevent soil nutrient accumulation.