Wu YouXian;Wu YX

;Institute of Soil Sciences, Academia Sinica, P.O. Box 821, Nanjing 210008, China.

interactions red soils;latosols ph voltammetry organic compounds;plant residues;rice straw;decomposition products variable charge soils;soil types chemical;chemical properties;straw

Electrochemical properties (pH, Eh, and voltammetric behaviour) of the decomposition products of rice straw and their interactions with red soils and latosols were studied. pH, Eh, and amounts of organic reducing substances changed markedly during over 60 days of anaerobic decomposition. pH decreased sharply to pH 5 on day 10 and then increased gradually to 7 by day 45. Amounts of organic reducing substances increased almost synchronously with the fall of redox potential during the first 15 days. The differential pulse voltammetric (dpv) behaviour changed not only in the peak current but also in the peak potential. Fractions with apparent molecular weights lower than 200 daltons appeared to be active in dpv behaviour. The electric charge of organic reducing substances was closely related to the decomposition stage. Day 6 of the incubation was the crucial time before and after which the major part of the components were negatively charged and positively charged, respectively. The group with a lowapparent molecular weight and a negative charge were the main components responsible for the lower anodic peak potentials. They were oxidized first during interactions of organic reducing substances with soils.