The response of rice seedlings to O2 released from CaO2 in flooded soils

The efficacy of CaO2 as an oxygen-supplying seed coating on the emergence of rice seedlings from flooded soils was studied. Seedling response became increasingly dependent on coating rates of 0–40% (by weight of seed loading with 60% CaO2 material) as the depth of planting increased from 0–2.5 cm. No emergence occurred from 5 cm. The emergence response to 40% CaO2 at 1.5 cm depth of planting was inhibited by the presence of 0.25% finely ground rice straw but was stimulated by increasing pH levels. The organic substrate likely increased microbial competition for available O2 while increasing pH levels improved the rate of CaO2 dissolution during the day 2–8 period of germination. Soil type effects on seedling response were speculated to be due to differences in O2 consumption rates between soils. The addition of CaO to the CaO2 coating improved the emergence response on an unlimed acid soil.