Submitted to: Agricultural & Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2021
Publication Date: N/A
Interpretive Summary: Commercial swine farms in Mississippi typically dispose of lagoon effluent through irrigation to summer forage grasses, but there is lack of study on the performance of napiergrass. This is a case study using napiergrass for production of both animal fodder and bioethanol. Napiergrass was grown for three years using swine-effluent irrigations under the management of a private farm in northeast Mississippi. Effluent applications from May to October provided 649 pounds per acre nitrogen annually (mean of three years). Full-season growth was harvested in November and separated in leaves and stems. The amounts of nitrogen, phosphorus, and potassium removed in biomass in 2011 were 451, 79, 992 pounds per acre, respectively, and increased considerably in 2012 to 923, 170, and 1764 pounds per acre, associated with an 18% reduction in effluent irrigation (7.1 vs. 5.7 inch). Leaves harvested from mature plants are a forage product that would meet nutritional standards as animal fodder, but corresponding stems had lower forage nutritive value, as reflected by lower concentrations of crude protein and greater acid detergent fiber and neutral detergent fiber. Potential ethanol yield was approximately 36% lower in stems than leaves and xylose concentration was 7% lower; however, stems account for a larger amount of lignocellulosic biomass used in estimating bioethanol production than leaves. Results suggest plantings of napiergrass as a dual-purpose, forage and bioenergy crop on existing bermudagrass hay fields receiving swine-lagoon effluent would enable less competition with the regional feed production systems and flexibility to farm-level management decisions.
Technical Abstract: There is a lack of study on the performance of napiergrass (Pennisetum purpureum Schum.) fertilized with swine (Sus scrofa domestica)-lagoon effluent. This study (2011-2013) determined yields of biomass and nutrients, forage nutritive value, and potential ethanol in cultivar ‘Merkeron’ at a single, late-season harvest. Effluent irrigations provided approximately 727 kg ha-1 N annually (mean of three years). Plant N and P removal in 2011was approximately 505 and 88 kg ha-1, respectively, and increased considerably in 2012 to 1034 and 191 kg ha-1. As compared to stems, leaves had greater (p < 0.001) crude protein (80 vs. 108 g kg-1) and less acid detergent fiber (482 vs. 340 g kg-1). Potential ethanol yield was approximately 36% lower in stems than leaves (98 vs. 153 g kg-1, p > 0.01); however, stems account for a larger amount of lignocellulosic biomass used in estimating bioethanol production than leaves.