Carbon Pool Dynamics within Bioenergy Sorghum Production Systems in Central Texas.

Bioenergy sorghum is being evaluated for its potential as a dedicated bioenergy crop. Carbon (C) cycling within and between the terrestrial-atmospheric interface is important to sustaining soil and plant productivity as well as its impact on the Earth’s energy balance and global climate regulation. The impact of bioenergy sorghum cropping systems on C dynamics within agroecosystems is not fully understood. This study evaluated the effect of crop rotation, nitrogen (N) fertilization, residue return, and their interactions on various soil, plant, and gaseous C pools. A primary aim of this study was to identify production scenarios capable of sustaining soil health and plant productivity while minimizing CO₂ emissions and offering C sequestration potential. Results showed that crop rotation significantly affected soil organic C (SOC), plant C content, soil microbial biomass-C (SMBC), and cumulative CO₂-C emissions. Returning biomass residue resulted in a significant increase in SMBC, SOC, and cumulative losses of CO₂-C in 2010, but not 2011. Nitrogen fertilization significantly affected SOC, plant C content, SMBC, and CO₂-C in 2011, but not 2010. Cumulative CO₂-C emissions increased by 12% from 2010 to 2011, potentially due to all treatments being in the sorghum sequence of the crop rotation, which likely led to greater respiration, as sorghum was photosynthetically-active longer than corn. Continuous biomass sorghum significantly increased SOC below 45 cm, suggesting potential organic C deposition by root biomass at depth may increase belowground C storage and potential long term C sequestration.