EFFECTS OF ENVIRONMENTAL-FACTORS ON THE PERFORMANCE OF DIGITARIA-ERIANTHA AND MEDICAGO-SATIVA IN MONOCULTURE AND MIXTURE

A glasshouse experiment was conducted to test hypotheses concerning di fferences in environmental adaptation of Digitaria eriantha (digitaria ) and Medicago sativa cv. Hunter River (lucerne), and advantages of gr owing them in mixture on a solodic soil on the Far North-West Slopes o f New South Wales. The 2 species were grown in monoculture and mixture in simulated solodic soil profiles, at 2 temperature regimes, 2 level s of available nitrogen (0 and 0.25 g/container after each harvest), a nd 3 moisture levels (drought, adequate, flood), thus providing the ra nge of conditions encountered in the field. The 2 species differed mar kedly in their response to temperature, which explains the complementa ry seasonal growth patterns in the field. Summer temperatures favoured digitaria growth while spring temperatures favoured lucerne growth. A t summer temperatures, digitaria outyielded lucerne at all moisture re gimes with applied nitrogen, as well as the flooded treatment without applied nitrogen. At spring temperatures, lucerne outyielded digitaria without nitrogen applied, as well as in the adequate moisture regimes with nitrogen applied. Yields of each species were reduced by periodi c flooding and droughting; at their respective more favoured temperatu re regimes for growth, the percentage reduction in yield at individual harvests was higher in lucerne than in digitaria, especially for floo ding. Flooding at summer temperatures had the worst effect on lucerne but summer droughting was almost as severe, especially with continued application of these treatments. Both species responded to nitrogen, t he percentage dry matter increase being higher at summer than at sprin g temperatures. The species responded to temperature, moisture and nit rogen in the same way in mixture as in monoculture. The yield response of the mixture was dominated by that of the most responsive species a t that regime. Monocultures rarely outyielded the mixture. The mixture sometimes significantly outyielded both monocultures, mainly with sum mer temperature, adequate moisture and low nitrogen. Long-term exploit ation of the complementary temperature responses of the 2 species and their overall adaptation to the temperature regime of the Far North-We st Slopes may depend on measures to minimise the effects of intermitte nt flooding and droughting in summer.