EFFECTS OF DIFFERENT SOIL MOISTURE TENSIONS ON GRASS AND LEGUME SPECIES

Established stands of three grasses and legumes, grown in a greenhouse, were subjected to flooding treatments consisting of soil moisture tensions of approximately 0, 25 and 40 centimetres of water which were equivalent to field conditions where the water table is at the soil surface, 25 and 40 centimetres below the soil surface, respectively. Herbage and root yields were measured.Grasses were more tolerant to flooding than were the legumes. The order of decreasing tolerance to flooding was: reed canary grass, timothy, brome grass, birdsfoot trefoil, Ladino clover and alfalfa. The yields of grasses tended to increase with increasing moisture levels and with durations of flooding, whereas the yields of legumes tended to decrease with increasing moisture levels and with the duration of flooding.The effect of flooding on yields was more pronounced on the first than on the second harvest. Highly significant positive correlation coefficients were obtained between total top and root weights of reed canary grass, birdsfoot trefoil, Ladino clover and alfalfa. Corresponding correlation coefficients for timothy and brome grass were negative and highly significant.Oxygen diffusion measurements indicated that, in general, the yields of legumes increased with increasing availability of oxygen whereas the yields of grasses showed a tendency to decrease. As the soil temperature under flooding conditions increased from 41° to 80°F. the forage yields usually decreased.