Cover crop and nitrogen fertilization influence soil carbon and nitrogen under bioenergy sweet sorghum

Abstract

Sustainable production of sweet sorghum (Sorghum bicolor [L.] Moench) grown for bioenergy production depends on practices that maintain soil C and N levels. The objective of this study was to evaluate the effect of winter cover crops (hairy vetch [Vicia vil-losa Roth], rye [Secaele cereale L.], hairy vetch/rye mixture, and the control [no cover crop]) and N fertilization rates (0 and 90 kg N ha-1) on soil organic C (SOC), total N (STN), NH4 –N, and NO3 –N contents at the 0- to 30-cm depth from 2010 to 2014 in the southeastern USA. Cover crop biomass yield and C content were greater with vetch/rye than vetch and the control and N content greater with vetch and vetch/rye than the control in 2013 and 2014. The SOC and STN at 0 to 5 cm were greater with vetch/rye than the control and at 15 to 30 cm were greater with vetch than vetch/rye. At 0 to 5 cm, SOC increased at 0.55 Mg C ha-1 yr-1 and STN at 0.06 Mg N ha-1 yr-1regardless of treatments. At most depths, NH4 –N content was greater with rye than the control and greater with 0 than 90 kg N ha-1but NO3 –N content was greater with vetch/rye than rye. Because of greater cover crop C and N inputs, soil C and N stocks can be enhanced and N availability can be optimized by growing vetch and vetch/rye mixture cover crops to replace the stocks reduced by the removal of aboveground sweet sorghum biomass.