Seedling growth and survival of Oryzopsis holciformis (ricegrass) sown at different densities and moisture levels.
Oryzopsis holciformis (M.B.). Hack. (hairy ricegrass) was sown in loess soil in containers 60 cm deep at densities of between 160 and 3200 seedlings/m2 in a study of 'interference' between seedlings, including competition for water and density-dependent phenomena assisting seedling growth and survival. Moisture stress was varied by sowing at 3 levels of initial soil moisture and giving no additional water. Shoot dry weight generally showed the negative effect of increasing density and moisture stress. Total root dry weight was reduced at high density and low moisture. The effect of stress on root penetration expressed as percentage of roots below 20 cm was not consistent and did not indicate that deeper rooting was an adaptive reaction to drought. Shoot:root ratio at 20 and 50 days was sharply reduced by both density and low moisture, but at 50 days the low density with medium moisture treatment resulted in the highest shoot:root ratio and also the least root penetration. Survival, both as number of plants and as amount of live shoots, was generally reduced by density and low moisture. Whereas the densest and driest treatment showed high initial mortality, the sparser and moister treatments surpassed it in both rate and percentage mortality. This could be due to drought hardening or to better moisture extraction by dense roots.