Oxygen measurements in the root zone facilitated by TDR

Deleterious soil structural conditions, as from compaction, can reduce plan t growth and yields by reducing aeration and oxygen in the rooting environm ent. 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 a nd bulk density determinations allowed the monitoring of O-2 concentration trends under no-till and conventional-till corn management. Carbon dioxide flux from the soil surface was measured weekly. Temporal patterns of O-2 le vels fluctuated in response to rainfall at all depths but much less so at 3 0-cm depth. At 30 cm the O-2 concentration remained inadequate for optimum plant growth (<0.01 kg m(-3)) for over 2 mo after planting under no-till wi th poorly timed trafficking. Under conventional till and appropriately time d trafficking adequate aeration occurred more than a month earlier than und er 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 biologica l activity. The relative magnitudes of mid-season O-2 concentrations and CO 2 flux densities showed the same pattern as the crop yields for all tillage treatments. More analyses of seasonal O-2 consumption patterns are require d to determine if lack of O-2 is a causal factor for the reduced crop yield .