Vegetation and Fertilization Effects On Soil Water Soluble Organic Carbon.

Water soluble organic carbon (WSOC) is an important component in soils due to its influence on soil structure, nutrient cycling, and microbial communities.  This study was conducted to determine 1) the proportion of WSOC to organic carbon (OC) and distribution by soil depth; 2) effect of grass species on WSOC content and distribution; and 3) effect of nitrogen (200 Kg ha^-1 yr^-1) and phosphorus (40 Kg ha^-1 yr^-1) fertilizer application on WSOC concentration and distribution.  Soil samples were collected from research plots near Dickinson, North Dakota at 7 depth increments to a depth of 90.  Samples were analyzed for total C (TC), inorganic C (IC), organic C (OC) and WSOC.  In general, WSOC decreased with increasing depth.  The mean proportion of WSOC to OC was 7.28% in the upper 45cm and then significantly increased at lower depths likely due to declining OC and increasing inorganic carbon.  Smooth bromegrass (SB) (Bromis inermus L.) accumulated significantly more WSOC than Kentucky bluegrass (KB) (Poa pratensis L.)and Crested wheatgrass (CW) (Andropogon cristatum L.)when throughout the soil profile.  Nitrogen fertilization significantly decreased WSOC under KB and CW when compared to no fertilizer or phosphorus application.  No significant differences were detected among fertilizer treatments for SB.  Understanding the distribution of WSOC in soil can direct best management practices to improve crop productivity, carbon sequestration, and soil quality.