Alternate row sowing: A novel approach to maintain sown species in mixed pasture swards

Establishing and maintaining a balanced mixture of perennial and annual pasture species is often difficult, especially in drier environments. One method to reduce the competition between pasture species and to improve the potential productivity and nitrogen fixed by the pasture is to establish pasture species in separate rows (alternate row sowings). An experimental field site was established in the autumn of 2012 near Mirrool in southern NSW. Medicago sativa and Phalaris aquatica were sown in combination with a range of annual legumes either as a monoculture, mixture, or arranged in alternate rows in 1:1 or 1:2 ratios. Legumes were inoculated with appropriate rhizobia and the sites were fertilised with Starter 15 at 150 kg/ha. Seedling establishment, regeneration and dry matter (DM) were measured each year until 2014. Annual legume seed reserves and nitrogen fixation (N-fix) were measured in 2013. Alternate row sowing improved seedling regeneration and annual legume seed reserves in some situations; however, it did not significantly improve mean DM, mean legume DM or N-fix. In contrast the choice of species combinations impacted on these responses. For example, the inclusion of P. aquatica in the pasture mix tended to increase mean DM, although if N-fix and mean legume DM were to be maintained at acceptable levels, M. sativa and Trifolium subterraneum were important inclusions in combination with P. aquatica.