Spatial and Vertical Variation of Soil Carbon in a Row Crop Watershed with Buffers.

Increasing levels of atmospheric carbon dioxide and the depletion of soil organic C in many agroecosystems have stimulated extensive research regarding the examination of soil carbon distribution in many regions and for practices.  The objective of this study was to compare spatial and vertical soil carbon distributions among crop, buffer, and grass waterway areas.  The study design consists of three watersheds; west, center, and east.  Four and a half m wide contour grass-legume strips consisting of redtop (Agrostis gigantea Roth), brome grass (Bromus spp.), and birdsfoot trefoil (Lotus corniculatus L.) were established at 17- to 35-m interval on the Center and West watersheds in 1997.  Pin oak (Quercus palustris Muenchh.), swamp oak (Q. bicolor Willd.), and bur oak (Q. macrocarpa Michx.) were planted 3-m apart on the center of grass strips of the Center watershed in 1997.  Soil cores were sampled to a 100-cm depth. Soil C content, texture, pH, and N were determined by 10 cm depth increments.  Conventional and geo-statistical methods were conducted to understand spatial dependence of soil properties.  The highest carbon concentrations were found under grass waterway areas as compared to row-crop areas.  Grass buffers had slightly higher carbon in the surface soil after four years of establishment.  However, C content was not different below 60 cm depths among treatments and concentrations below 80 cm depth were almost the same on crop areas and buffer areas.  The results of the study suggest that establishment of grass waterways and buffers help increase soil carbon sequestration.  It is anticipated as trees grow and roots occupy more soil volume, the increase in soil carbon should increase on the agroforestry watershed and more carbon accumulation in the deeper soils.