Direct measurements of oxygen microprofiles and distribution of phospholipid-P in a two-phase soil—manure system

Abstract

Concentrations of phospholipid-P (Plip-P) were used as an estimate of biomass in soil. Plip-P was correlated with biomass-C, as determined by chloroform fumigation-direct extraction, in soil from a fertilizer experiment, although a background of non-biomass Plip-P was suggested. The distribution of Plip-P was followed during three weeks in a two-phase model system designed to study microbial processes in and around a manure-saturated zone. Concentrations of Plip-P in the soil were unaffected by the presence of manure at ⩾ 4 mm distance from the soil-manure interface. A sharp gradient between manure and soil phases was maintained throughout the three weeks. Oxygen microelectrodes (i.d. ca. 5 μm, o.d. 150–200 μm) were used for direct measurements of oxygen penetration into the manure-saturated zone. No decrease in oxygen concentration was recorded in the soil phase. By Day 1 oxygen penetrated only 0.15 mm into the manure, increasing to 2-2.5 mm after 21 days. During this period the diffusive flux of oxygen decreased five-fold. Aerobic decomposition of dissolved C in the manure was apparently restricted to a thin layer of 0–2 mm thickness below the soil-manure interface.