F.D. HU and R.J. JONES

CSIRO Tropical Agriculture, Townsville, Queensland, Australia

Abstract

In a previous grazing trial, the percentage of Stylosanthes hamata cv. Verano was much lower when grown with Bothriochloa pertusa cv. Bowen than when grown with Urochloa mosambicensis cv. Nixon. Reasons for this depression in the presence of Bowen have been investigated.
In this study, the possibility of allelopathic effects on Verano and on Stylosanthes scabra cv. Seca from leachates of the grasses Bowen and Nixon was examined. Leachates from soil-filled boxes with or without Bowen or Nixon were used to water seedlings of Verano, Seca, Bowen and Nixon grown in pots along with a control treatment watered with demineralised water. Plant height, tiller or shoot number, leaf number and top and root weights were measured over a 12-week period to harvest.
With Verano, there were no significant adverse effects of leachates from swards of the two grasses compared with the water control. Leachates from Bowen actually gave the highest yields of Verano. These results give no support to the hypothesis that Bowen had allelopathic effects on Verano. With Seca, lowest yield and plant height occurred with leachates from Bowen while the highest yield and plant height were obtained with leachates from bare soil. This indicates Seca is more susceptible to adverse effects from some factor in Bowen. Leachates from bare soil had no allelopathic effects on the growth of the four species. Failure to detect endophytes in Bowen or Nixon rules out the possibility that these are involved in the poorer performance of Verano grown with Bowen in the field.