Autotoxicity is not implicated as a cause of a dying-centre growth pattern in lotononis

Abstract

Stands of the highly nutritious, grazingtolerant pasture legume lotononis (Lotononis bainesil Baker) are often unreliable from year to year, in both favourable and suboptimal environments. An observed retreating pattern of lotononis growth resembles the effects of autotoxicity. A seedling germination experiment in the laboratory and an 11 -month greenhouse study of plant growth were conducted to determine if autotoxicity was a factor in the observed behaviour of lotononis. Treatments tested in these experiments were (i) soil infusions from sites where lotononis was growing vigorously, was dead or dying, or had never been grown; (ii) plant tissue infusions from healthy lotononis roots, healthy stolons and leaves ('shoots'), and dead and dying shoots; and (iii) lotononis roots and shoots mixed into and laid upon the soil in pots. In the seedling germination study, none of the treatments was significantly different (P<0.05) from a distilled-water control. In the plant growth study, plants in pots with lotononis roots mixed in the soil and lotononis shoots laid on the soil surface were significantly taller (5-12.8 cm height) and had significantly higher forage DM yields (10.02 g/plant) than plants in control pots (3-8.1 cm and 6.48 g/plant). The stimulating effect of lotononis plant residue on lotononis growth was probably due to additional nutrients and better water relations for plant growth. No evidence was found that autotoxicity is the cause of lotononis stand disappearance.