Wheat and ryegrass interaction in response to drought

Abstract

Greenhouse experiments compared the growth of wheat and ryegrass in pure culture and mixtures in response to temporary and prolonged droughts. The main experiment was a replacement series with wheat:ryegrass ratios of 12:0, 9:3, 6:6, 3:9, and 0:12 in 19 1 pots. Controls were well watered for the 14 wk experiment. Plants exposed to drought were well watered for 8 wk, had no water for 2 wk, and then were well watered for 4 wk. Despite a much smaller seed than wheat and a similar time of emergence, control ryegrass produced by 14 wk after planting more above and below-ground growth than wheat in pure cultures. But, the greater seed size and height allowed wheat to be more competitive above-around in control mixtures than ryegrass. Wheat maintained a greater leaf expansion rate and area during drought than ryegrass. Drought and rewatering enhanced the growth of wheat relative to ryegrass in pure culture compared to controls. However, the ryegrass in mixtures regrew vigorously during 4 wk of rewatering and was equally competitive with wheat in almost all measures. Ryegrass was equally competitive with wheat for root growth in control and drought mixtures. There was no alleopathic interaction. A companion experiment used rhizotron columns to compare the interaction 7 wk after transplanting seedlings of wheat and ryegrass during continuous well watering and prolonged drought. Above-ground growth of wheat was greater in pure culture than the mixtures and greater in the well watered mixture than the drought mixture. The proportion of ryegrass to wheat as a percent total growth in these mixtures was greater in the drought than the well watered treatment. Thus, the competitiveness of ryegrass relative to wheat was greater in both the temporary drought of the main experiment and the prolonged drought of the companion experiment than in well watered conditions.