The role of stoloniferous red clover cv. Rubitas in establishing irrigated grass based pastures

Irrigated dairy pastures go through three phases, establishment, production and decline. What occurs during the establishment phase influences the subsequent phases. In established productive pasture a symbiotic relationship exists between clover root nodules and the nitrogen (N) fixing bacteria rhizobia. Nitrogen becomes available to grasses during the production phase, as roots are replaced or nodules are cast off. During the establishment phase, grass/clover root interactions are less understood.

In a series of pasture establishment experiments red clover (RC; Trifolium pratense) cv. Rubitas and white clover (WC; T.repens) cv. Bounty were sown as companion legumes with perennial ryegrass (PRG; Lolium perenne) cv. Reward, phalaris (PA; Phalaris aquatica) cv. Advanced AT and Atlas, and coloured brome (CB; Bromus coloratus) cv. Exceltas. Pot experiments, showed Rubitas when sown with PRG or PA compared to PRG or PA sown alone, produced higher grass DM yields. A field experiment also showed Rubitas sown with PRG increased grass yield during the establishment phase compared to PRG sown alone.

In comparison, WC cv. Bounty sown with grasses showed no increase in grass yield during establishment, compared to grasses sown alone. Preliminary results suggest Rubitas increases the yield of companion grasses during the establishment phase, although by what mechanism is unknown. Establishing legume roots have been shown to exude substances reported to attract bacteria required for nodulation. The increased yield of establishing grasses sown with Rubitas could be attributed to grass roots sharing clover root exudates.

Future research will investigate possible sharing interactions.