Improving the reliability of establishing legumes into grass pastures in the sub-tropics

Abstract

Poor establishment is the most common reason for failure of pasture legumes sown into existing grass pastures on commercial farms in the sub-tropics. Although good establishment is recognised as critical to the long term productivity and persistence of legumes, most producers use low-cost and low-reliability establishment techniques such as broadcasting after either no or minimal pasture disturbance; one-pass cultivation with seed spread at the same time; or severe soil disturbance and a rough seed bed behind a blade plough. This paper reports the results of a study designed to test the impact of different fallow periods (medium – 4 months; short – 2 months; disturb at sowing and no disturbance); seedbed preparation cultivation or zero tillage); drilling or broadcasting seed and post emergence herbicides when establishing legumes into existing grass pastures. The most common, commercially used establishment techniques of sowing legume seed into grass pastures with no disturbance or single pass cultivation treatments at sowing all resulted in establishment failure. Spraying at sowing resulted in adequate numbers of legumes. Short or medium fallows resulted in similar densities of legumes between all treatments, however treatments with greater control of the grass and post emergence weed control grew better which resulted in more seedling
recruitment in the subsequent year. At 25 months after sowing only fallowed treatments with Spinnaker® post-emergence weed control achieved legume numbers above benchmark figures for establishment success. The study demonstrates that agronomic practices commonly used for grain cropping (such as fallowing to store soil moisture) can improve the reliability of establishing legumes into existing grass pastures.