DISTRIBUTION AND AMOUNT OF SOIL ORGANIC C IN LONG-TERM MANAGEMENT-SYSTEMS IN TEXAS

Soil organic carbon (SOC) distribution is altered by residue managemen t practices, but the effect on total C mass is not well understood, es pecially in warm regions. The objective of this study was to determine the effect of residue management practices on SOC distribution and am ount across an 1100 km transect (northwest to southeast) of Texas. Lon g-term (>10 years) continuous cropping rotation and residue management plots located near Bushland, Temple, and Corpus Christi, Texas, were sampled incrementally with depth for SOC distribution and mass. The ma ss of SOC varied among locations depending on management, and climatic conditions. No-tillage management resulted in increased SOC concentra tion and mass in the surface 0.07 m in comparison to more intensive ti llage management (e.g., sweep, chisel plow, moldboard plow). Fertiliza tion had little effect on C sequestration at any site. Carbon sequestr ation decreased as mean annual temperature increased. Carbon may be se questered in soil under Texas climatic conditions, but the amounts may be quite small. (C) 1998 Elsevier Science B.V. All rights reserved.