Soil Organic Matter Dynamics in the Pendleton Long-Term Plots.

Producing biofuels from cellulosic materials will entail crop residue removal that could adversely affect soil quality and productivity. Information to ascertain the effects of residue removal on soil productivity is scant and requires long-term experimentation. Fortunately some information on this matter could be garnered from existing long-term plots (LTEs) at the Oregon State University Pendleton LTEs some of which were initiated in 1931. Data obtained from LTEs at the Center, indicated that the effect of residue removal was influenced by the cropping system in question. In the conventional tillage (CT) wheat/fallow system, the predominant cropping system in the Pacific Northwest (PNW), soil organic carbon (SOC) continues to decline in treatments that include residue burning and no burning, and where 2 tons of pea vines were added biennially except where 22.4 Mg ha^-1 of steer manure were added every two years. In the Tillage Fertility experiment, another CT wheat/fallow system with N and tillage treatments, SOC has also been on the decline in all tillage treatments. N additions, from 45 to 180 kg N ha^-1, did not increase SOC in all fallow treatments. In other LTEs involving continuous annual cropping both CT and no-till (NT) systems, SOC was maintained or increased over time. SOC under CT was highly correlated with the amount of above ground biomass whereas there was no correlation under NT. Based on these results, it appears that removal of residues for the production of biofuels would exacerbate SOC decline under the CT wheat/fallow system. There may be a possibility of harvesting some biomass for biofuel production under NT continuous cropping systems but care should be taken to leave enough for SOC maintenance or increase and for soil erosion control.