Development of sulla (Hedysarum coronarium) for better adaptation to grazing

Abstract

Sulla is potentially useful in New Zealand as a forage for grazing, hay and silage, in addition to its established use for soil conservation. The plant produces up to 25 t DM/ha/year and is a highly nutritious feed; it contains condensed tannins (CT) which prevent bloat and improve protein utilisation; and high livestock utilisation of leaf and stem is possible. Established stands of sulla can be maintained for several years under good management, but there have been many reports of poor persistence. In an effort to improve stand persistence, particularly under grazing, two evaluations were conducted near Palmerston North in 1995-97. Trial 1 screened 32 lines of sulla, including commercial cultivars, for a range of morphological attributes (e.g., habit, height, spread, vigour, herbage mass), whereas Trial 2 assessed similar attributes for 134 plants of cv. Grasslands Aokau, involved in an earlier grazing trial. Foliar levels of extractable CT were also determined in Trial 1, which is the first documentation of CT variation in the species. In both trials, plants survived for up to 2.5 years and seed was collected from 145 (Trial 1) and 31 (Trial 2) selected plants in early 1997. The plants selected typically had prostrate growth habit, moderate to high plant diameter and branch number, and high plant vigour. CT levels, assayed by a vanillin/HCl procedure, averaged 1.2-3.5% DM in most lines and were 36-81% higher for six samples assayed by a butanol/HCl method. Some CT levels may be sufficiently high to have a slight nutritional disadvantage to ruminants, but this could potentially be overcome by growing sulla with non- CT containing forages. Progeny from selected plants in each trial are being evaluated under more frequent grazing, and their seed will be harvested in autumn 1999. Keywords: condensed tannins, cultivars, Hedysarum coronarium, legume, persistence, sulla