Adaptation and complementarity of Digitaria eriantha and Medicago sativa on a solodic soil in a subhumid environment with summer and winter rainfall

Summary. A cutting experiment was conducted over 4 years on a solodic soil on the Far North-West Slopes of New South Wales to compare the environmental adaptation of Digitaria eriantha ssp. eriantha cv. Premier and Medicago sativa cv. Hunter River. Adaptation was tested by comparing seasonal yield responses of the monocultures and the mixture at high and low levels of nitrogen (N); monoculture yields were also compared with those predicted by a simple climate-based model. When N was non-limiting, digitaria yields were highest in summer while lucerne yields were highest in spring. Lucerne yields in summer were often much lower than those predicted by the model but the plant recovered well during periods of milder temperature, until decimated by flooding. Yields of the mixture were similar to those of digitaria in summer when it was grass dominant, and similar to lucerne in spring when it was legume dominant. Overall, at high N the mixture did not outyield digitaria. In the absence of fertiliser N, digitaria and lucerne monocultures gave similar dry matter yields. However, over the 3 warm seasons, the mixture produced 72% more dry matter than the monocultures and 263% (325 kg/ha) more N than digitaria. The complementary seasonal responses of digitaria and lucerne, and high yields of the mixture suggest a role for the mixture on solodic soils on the Far North-West Slopes of New South Wales provided the effects of irregular flooding on lucerne can be minimised by management or more tolerant cultivars.