Soil Organic Carbon Influenced By Bioenergy Sorghum Cropping Systems.

Bioenergy crop production systems can be a net sink or net source of atmospheric CO₂, depending on a number of factors including land management practices. Assessment of soil organic carbon (SOC) is vital to evaluating agricultural management practices to sustain soil health and minimize impacts on climate change. The objective of this study was to determine the effects of crop rotation, nitrogen fertilization, and residue management on net annual change in SOC to 90 cm depth under bioenergy sorghum production. Soil samples were collected annually from a field study located near College Station, TX which was under bioenergy sorghum production from 2008 to 2015. Regressions of the mass of SOC over time (2008 to 2015) were performed to estimate net annual change in SOC at five depth increments from the seven years of study. Initial SOC accrual rates from 2008 to 2012 exceeded 5 Mg ha^-1 in some treatments, but a sharp decline in SOC between 2012 and 2013 led to a longer term accrual rate of less than 1.5 Mg ha^-1 across all treatments. While crop rotation had a significant effect on SOC accrual from 2008 to 2012, SOC accrual rates from 2008 to 2015 were not significantly influenced by any treatment factors. Preliminary results suggest climate and soil moisture conditions may have influenced the sharp decline in SOC between 2012 and 2013, further investigation is warranted.