Estimation of oxygen concentration in the soil gas phase beneath compost mulch by means of a simple method

A simple method for measuring oxygen level in the root zone of plants growing in non-saturated humidity conditions is presented. The oxygen concentration of soil air under layers of compost mulch was measured using galvanic oxygen sensors mounted in diffusion chambers and the results were compared with infrared gas analyses of soil air samples. Two trials showed that a moderate (5-10 cm) layer of compost mulch has no major effect on the oxygen level in soil under dry conditions, while a 15-cm mulch layer results in an oxygen depletion of short duration. In wet conditions, oxygen depletion under even a 5-cm layer of compost mulch results in a significant lowering of the oxygen level in soil and lasts for days in conditions of much precipitation. Root functions can be negatively affected at <10% oxygen concentration of the soil air. Compost mulch can decrease oxygen concentrations to well below this critical level in wet or poorly drained soils and thereby contribute to the stress load of urban trees. The use of galvanic oxygen sensors proved to be a simple and low-cost method for measuring soil-air oxygen.