Changes in soil quality and carbon storage under biofuel crops in central Ohio

The issue of carbon (C) neutrality and the environmental advantages and variations in soil organic C (SOC) stocks under biofuel crops need to be addressed thoroughly and objectively. Thus, the aim of this study was to compare the impact of annual biofuel crops (no-till maize, Zea mays L.; sorghum, Sorghum bicolor L.) and perennial lignocellulosic grasses (switch grass, Panicum virgatum L.; miscanthus, Miscanthus × giganteus; and prairie mix) on soil properties and SOC stock in central Ohio. Two years of perennial energy crops improved soil properties in terms of lower soil bulk density, higher porosity, improved water-stable aggregates (WSA), higher mean weight diameter, pH and electrical conductivity compared with those under maize and sorghum. The WSA in the 0–10 and 10–20 cm soil layers were higher under miscanthus (94.7% and 91.8%, respectively) and switch grass (92.7% and 89.4%) than under maize (89.9% and 86.1%) and sorghum (85.1% and 85.4%). Macroaggregates (>0.25 mm diameter) contained higher concentrations of C and nitrogen (N) than microaggregates. Macroaggregates in soil under sorghum and maize contained 17.3% and 14.2% less C and 22.8% and 15.2% less N in 0–10 cm layer, and 29.8% and 24.2% less C and 22% and 7.1% less N in 10–20 cm layer, than macroaggregates under switch grass (15.82 g C kg–1 in 0–10 cm and 14.06 g C kg–1 in 10–20 cm layers), respectively. The SOC stock in the 0–10 cm layer, on an equivalent soil-mass basis, was significantly higher under switch grass (28.5 Mg C ha–1) and miscanthus (28 Mg C ha–1) than that under sorghum (24.8 Mg C ha–1). Thus, only switch grass and miscanthus sequestered C, whereas other species had no or negative effect, with loss of soil C under sorghum in 2 years. There is a need for long-term studies and estimation of SOC stock in deeper layers to establish the SOC balance under biofuel crops.