Responseof subterraneanclover,balansaclover, andglandclover to lime when grown in mixtures on an acid soil

Abstract. This study compared the relative tolerances of subterranean clover (Trifolium subterraneumL.), balansa clover (T. michelianum Savi.), and gland clover (T. glanduliferum Boiss.) to acid soil conditions. Seed yield, seedling density, herbage production,N2fixation, andherbagemineral compositionof the 3 legumeswere assessedwhengrownon an acid soil (pHCa of 4.3 and 15 % exchangeable Al [0–0.10m]) with and without the addition of lime (CaCO3). Annual legume species were sown in a mixed sward together with burr medic (Medicago polymorpha L.), and in mixtures with either lucerne (Medicago sativa L.), chicory (Cichorium intybusL.), or phalaris (Phalaris aquatica L.). Due to drier than average seasonal conditions, none of the perennial species persisted beyond the first summer. Lime increased the herbage production of annual legumes by 18–22 % and total pasture production by 14 % in both 2002 and2003. Subterranean cloverwas themost tolerant of the annual legumes to acid soil conditions, showingnovisible toxicity symptoms and no response to lime in terms of seed yield. In contrast, both balansa and gland clovers exhibited visual symptoms of manganese toxicity in the absence of lime, withMn concentrations in the shoots of 817mg/kg and 626mg/kg, respectively. Both species responded positively to lime with seed yields increasing by 45 % and 124%, respectively. Lime increased the proportion of herbage N derived from N2 fixation by subterranean clover from 29 to 40 % and by gland clover from 30 to 43%. Lime had no effect on the proportion of N2 fixed by balansa clover (29–31%), suggesting a suboptimal symbiosis of rhizobia with that species. Adding chicory or phalaris to the pasturemix increased sward herbage production i