Molecular Weight Distribution of Soluble Organics from Laboratory‐Manipulated Surface Soils

Abstract

AbstractTransfer of organic matter from solid to solution phase is the first step in the redistribution by leaching of organic C and associated elements in forest soil profiles. To examine the effects of disturbances on solubilization of organics, three A horizons and one O horizon were exposed to air drying, waterlogging, addition of urea, addition of ash, and addition of ash in combination with heating at 250 °C. Following incuhation at 20 to 22 °C for 1 to 50 d, soluble organic C (SOC) was extracted with 0.5 mM SrCl2. The SOC was 0.2 to 0.7% of total organic C in controls. Urea and heat‐plus‐ash treatments yielded up to 17 times more SOC than controls, and other treatments yielded up to three times more than controls. Distribution of SOC among molecular‐weight classes, as determined by dialysis, was 21 to 32% in the <3500‐dalton class, 8 to 20% in the 3500 to 14 000‐dalton class, and 47 to 71% in the >14 000‐dalton class. Urea treatment yielded a higher proportion of SOC in the >14 000‐dalton class than in the controls, while air drying resulted in a lower proportion. Both the quantity and quality of soluble organics can be influenced by soil disturbances, but the specific response varies with the type of disturbance.