Changes in water-extractable organic carbon as an indicator of changes in soil productivity

Abstract

A factorial experiment was designed in 1991 to determine if quantitative and qualitative changes in water-extractable organic carbon (WEOC) could be related to tree growth at the Longleaf Tract of the Palustris Experimental Forest in Rapides Parish, LA. The treatment factors were compaction at two levels (none and severe) and organic matter removal at three levels (bole, whole tree, and total biomass). The severe compaction treatments produced significantly higher quantities of WEOC than the non-compacted treatments, and the total biomass removal treatments produced significantly lower quantities of WEOC than the other two levels of organic matter removal. The seasonal effect on WEOC quantities was consistent for both compaction and organic matter removal: WEOC from the hot/dry season > WEOC from the hot/wet season > WEOC from the cold/wet season. While there was no significant effect of treatment on the partitioning of WEOC into hydrophobic and hydrophilic fractions, all treatments produced a greater hydrophilic than hydrophobic fraction. WEOC from all treatments and all seasons released more P from iron oxide than from aluminum oxide. Season affected the partitioning of WEOC into hydrophobic and hydrophilic acids, bases, and neutrals that in turn influenced WEOC reactivity. Both compaction and organic matter removal reduced plant growth. However, plant growth could not be related to short-term changes in WEOC quantity or quality.