Soil organic carbon (SOC) changes indicated by hot water extractable carbon (HWEC).

Abstract

Labile carbon responds readily to changes in soil management practices and has been identified as a site-independent indicator for monitoring soil organic carbon (SOC). The problem is, however, that there are no easy, reliable methods available to measure this fraction. For this paper the hot water extractable carbon (HWEC) method has been evaluated to determine whether it is able to quantify carbon from the labile pool of soil and to detect short term changes in carbon content. Samples from long-term experiments in Germany and South Africa with a well established differentiation in SOC were exchanged. The SOC and HWEC were determined to establish the relationship between them. The effect of management practices on the HWEC fraction was tested using soils from selected sites of the sugarcane growing areas in South Africa under different management (trashed, burnt, uncultivated). The relationships derived between SOC and HWEC were comparable to the German results for soils with clay contents ranging between 10 and 40%. For these soils the analysed HWEC values multiplied by a factor of 15 to 19 gave a good estimate of the labile carbon portion in the soils. The virgin (uncultivated) soils generated the highest HWEC values (87% higher than burnt), followed by the trashed soils (66% higher than burnt). The HWEC method showed reproducible results.