Effects of biofuel activities on soil carbon, nutrients, and sedimentation

Perennial biofuel crops have benefits such as improving soil C storage. However, conversion of agricultural land to biofuel feedstock production presents a potential for pollution of surface and groundwater resources. Therefore, to assess the sustainability and overall feasibility of implementing bioenergy development strategies, these potential environmental problems need to be evaluated. This study investigated the effects of biofuel production activities on soil carbon, nutrients and soil sedimentation on agricultural land converted to short-rotation sweetgum (Liquidamber styraciflua L.) plantations with and without fescue (Festuca elatior L.) and switchgrass (Panicum virgatum L.) bioenergy crops, compared to corn (Zea mays L.), on a Decatur silt loam soil in north Alabama, from 1995 to 1999. Soil C in switchgrass, no-till corn, and sweetgum with a cover crop treatments increased during the first 3 years. However, soil C decreased by 6% in sweetgum plots without a cover crop. Runoff volume was significantly correlated to total rainfall and sediment yield in each year, but treatment differences were not significant. Sweetgum plots produced the highest mean sediment yield of up to 800 kg ha^_1compared to corn and switchgrass plots, which averaged less than 200 kg ha^_1. Runoff NH₄⁺ N losses averaged over treatments and years for spring season (3.1 kg ha^_1) were three to five times those for summer, fall, and winter seasons. Runoff NO₃^_ N for no-till corn and switchgrass plots in spring and summer were five to ten times that for sweetgum plots. No-till corn and switchgrass treatments had 2.4 and 2.1 kg ha^_1 average runoff total P, respectively, which were two to three times that for sweetgum treatments. Our study suggests that in terms of overall sustainability, indicated by increased soil C storage and reduced risk of water pollution by sediment, runoff N, the sweetgum with a fescue cover crop treatment would be feasible.