Medics in southern Queensland: Effects of sowing method, weed control and phosphorus application on plant population and biomass

Abstract

Declining sown pasture productivity as a result of a tie-up in plant available soil nitrogen is an ongoing constraint to grazing production across the brigalow bioregion of central and southern Queensland. Research suggests that legume establishment offers the most cost effective long-term remediation strategy for improving pasture quality and yield. Within southern Queensland, medics (Medicago spp.) can provide valuable winter contributions to dietary protein and soil nitrogen, however establishment and yields are frequently poor and soil phosphorus often limiting. An experiment was established across two soil types (brigalow clay and poplar box red loam) 70 km north of Goondiwindi, Queensland to investigate the effects of sowing method, weed control and phosphorus fertiliser application on the establishment and yield of a mix of three medic cultivars (Medicago truncatula cv. Jester & cv .Caliph and Medicago orbicularis cv. Bindaroo Gold). On both soil types, plant population and biomass were significantly improved via direct drilling of seed as compared to broadcasting. On the loam, drilling increased average populations by between 519 and 1,900% above those recorded in broadcast treatments and improved biomass by between 144 and 315%. On the clay soil, drilling increased populations by between 339 and 983% above those measured in broadcast treatments. Clay soil drilling showed biomass improvements of between 124 and 1,368%. No significant biomass or legume population treatment effects were observed on the clay soil. No significant treatment effects were observed for yield on the loam soil. This study implies that medic establishment, plant populations and biomass can be greatly improved through the application of seed drilling.