Responses of soil respiration and barley growth to modified supply of oxygen in the soil

Roots of dry-land plants are supplied with oxygen mainly by molecular diffu sion from soil air. Roots may suffer from hypoxia if soil aeration is reduc ed by compaction and wetting. Although the mechanisms involved are well kno wn, more research is needed to relate soil aeration status to plant growth. The effects of reduced oxygen supply on soil respiration and the growth of barley seedlings were studied in pot experiments with fine sand soil, wher e the soil air composition was varied by flushing the soil with gas streams containing 0%, 2%, 6%, 10% or 20% O-2 independently of compactness (bulk d ensity 1.4, 1.6 Mg m(-3)) and wetness lair space 0-5%, >5%). Plant growth d ecreased only at O-2% O-2 in the loose moist soil but as early as 20% O-2 i n the wet soil. Soil compaction impaired plant growth regardless of wetting and aeration. In the loose moist soil cropped with barley, the respiration rate (emission of CO2) did not decrease at 6% O-2 but decreased clearly at 0-2% O-2. The results compared fairly well with the critical oxygen concen trations calculated by a simple multicylindrical model, in which the water- film thickness around the roots was estimated using soil water retention da ta.