Oxygen measurements in the root zone facilitated by TDR

Abstract

Deleterious soil structural conditions, as from compaction, can reduce plant growth and yields by reducing aeration and oxygen in the rooting environment. Using a double-membrane oxygen cathode in each of four corn plots, we measured soil oxygen concentrations in duplicate at depths of 5, 10, 20 and 30 cm during the growing season. In addition, temperature, water content and bulk density determinations allowed the monitoring of O2 concentration trends under no-till and conventional-till corn management. Carbon dioxide flux from the soil surface was measured weekly. Temporal patterns of O2 levels fluctuated in response to rainfall at all depths but much less so at 30-cm depth. At 30 cm the O2 concentration remained inadequate for optimum plant growth (<0.01 kg m−3) for over 2 mo after planting under no-till with poorly timed trafficking. Under conventional till and appropriately timed trafficking adequate aeration occurred more than a month earlier than under no-till. The CO2 output was generally lower by 10 to 30% in no-till than that in conventional till, indicating measurably lower levels of biological activity. The relative magnitudes of mid-season O2 concentrations and CO2 flux densities showed the same pattern as the crop yields for all tillage treatments. More analyses of seasonal O2 consumption patterns are required to determine if lack of O2 is a causal factor for the reduced crop yield. Key words: TDR, aeration, oxygen measurement, carbon dioxide, tillage, root zone