Soil Carbon, Nitrogen, and Water Chemistry Three Years After Conversion of Marginal Agricultural Soils to Switchgrass and Cottonwood Bioenergy Cropping Systems.

Switchgrass and cottonwood are two cellulosic crops being considered for bioenergy feedstock production in the Lower Mississippi Alluvial Valley.  Marginal soils in this region, which are typically planted to soybean-grain sorghum rotations, are thought to be likely areas for cellulosic biofuel crop production.  Conversion of these conventional cropping systems to switchgrass or cottonwood for bioenergy feedstock production may have additional benefits if soil carbon sequestration is increased or soil nutrient leaching is reduced.  As part of a project determining the viability of producing bioenergy feedstocks from cottonwood-switchgrass agroforests on these marginal soils, we are monitoring soil carbon, soil nitrogen, and soil water chemistry at three sites in Arkansas and Louisiana planted to cottonwood, switchgrass, and a soybean-grain sorghum rotation.  Soil carbon (27.2-40.7 Mg ha^-1) and nitrogen (2.5-3.8 Mg ha^-1) pools to a depth of 30 cm, which were determined prior to planting in 2009, will be compared to those calculated from soil samples collected in 2011 at the end of the growing season.  Soil water has been collected bi-monthly at a depth of 30 cm using tension lysimeters since the first growing season following crop establishment.  Soil chemistry during the first year of collection did not significantly differ among crops.  Differences in soil water chemistry among crops during 2012 will also be presented.