Biomass crop production: Benefits for soil quality and carbon sequestration

Research at three locations in the southeastern U.S. is quantifying changes in soil quality and soil carbon storage that occur during production of biomass crops compared with row crops. After three growing seasons, soil quality improved and soil carbon storage increased on plots planted to cottonwood, sycamore, sweetgum with a cover crop, switchgrass, and no-till corn. For tree crops, sequestered belowground carbon was found mainly in stumps and large roots. At the Tennessee site, the coarse woody organic matter storage below ground was 1.3 Mg ha(-1) yr(-1), of which 79% was stumps and large roots and 21% fine roots. Switchgrass at the Alabama site also stored considerable carbon belowground as coarse roots, Most of this carbon storage occurred mainly in the upper 30 cm, although coarse roots were found to depths of greater than 60 cm. Biomass crops contributed to improvements in soil physical quality as well as increasing belowground carbon sequestration. The distribution and extent of carbon sequestration depends on the growth characteristics and age of the individual biomass crop species. Time and increasing crop maturity will determine the potential of these biomass crops to significantly contribute to the overall national goal of increasing carbon sequestration and reducing greenhouse gas emissions.