Characterizing Soil Organic Carbon and Winter Wheat Root Biomass after Twelve Years of Chisel Plow and No-till Management.

Results of past studies on carbon sequestration within reduced tillage agroecosystems are inconsistent.  A better understanding of the relationship among roots, tillage and whole-profile soil organic carbon (SOC) stocks may help to explain the variable results that have been reported.  The aim of this study was the characterization of SOC and winter wheat root biomass after twelve years of chisel plow (CP) and no-till (NT) management.  The study was conducted at the University of Idaho Kambitsch Research Farm in four replicate, 6 m x 80 m NT and CP cropping strips following winter wheat harvest in October 2012.  In each crop strip three replicate soil cores were taken in 10-cm increments to a depth of 90 cm to characterize root density and two 1.5 m continuous soil cores were taken to characterize SOC.  Soil cores were cut into depth sections (0-10, 10-20, 20-30, 30-60, 60-90, 90-120, 120-150 cm).  Carbon concentrations of soil samples were determined by dry combustion using a CNS analyzer.  Percent carbon values across both tillage treatments ranged from 1.75% at the surface to 0.17% at depth.  No-till had a significantly greater (P=0.05) whole mean soil profile carbon (0.81%) compared to 0.69% in CP.  However, mean carbon stock to 150-cm in NT (121 Mg C ha^-1) was not significantly different than that measured in CP (117 Mg C ha^-1) (P=0.66).  Approximately 47% of the carbon stored in both treatments was within the top 30 cm, 58 Mg C ha^-1 in NT and 56 Mg C ha^-1 in CP.  Mean root biomass in the top 20 cm was significantly greater in NT than in CP (P=0.01).  Results indicate that NT promotes a greater abundance of fine roots near the soil surface than does CP, but does not appear to result in greater carbon storage on an equivalent mass basis.