Successful drilling of forage species during severe drought in Central Otago - a preliminary report 1998/99

Abstract

Five plant species were established using two direct drilling techniques in a trial initiated in spring 1998 at a dryland site on Earnscleugh Station in Central Otago. The plant species were: wheatgrass (Thinopyron intermedium), tall oat grass (Arrhenatherum elatius), birdsfoot trefoil (Lotus corniculatus), hairy dorycnium (Dorycnium hirsutum) and bluebush (Kochia prostrata). These were established with the New Zealand Agricultural Engineering Institute/AgResearch strip-seeder drill and a conventional hoe-coulter drill. Establishment and subsequent growth during the first two growing seasons are described, and evaluation of this trial will be ongoing. The 1998/99 summer developed into one of the driest and windiest seasons experienced in Otago, resulting from prevailing La Niña Southern Oscillation weather patterns. The extreme drought culminated in two significant grassland fires near Alexandra in late February. Heat and drought during summer adversely affected seedling numbers as the season advanced. However, survival of plant species established with the strip-seeder drill was significantly better than that from the hoe-coulter drill. By autumn 1999, live seedling numbers were heavily reduced in all treatments (-50% and -68% for strip-seeder and hoe-coulter drills, respectively) but recovery was satisfactory during early winter. Wheatgrass, hairy dorycnium and tall oat grass in particular persisted well during the relatively mild winter. Despite a dry spring, by October 1999 these species had achieved ground coverage of 38%, 23% and 33% respectively from the strip-seeder drill (cf. 7%, 7% and 6% from the hoe-coulter drill), thus the vegetation was providing significant and earlier protection for fragile soil resources in a harsh environment. These results are preliminary but we conclude from them that the strip-seeder technique can provide superior plant establishment on dryland sites even during adverse drought conditions. Commercial development of this technology, including simplification of the system, is recommended. Keywords: birdsfoot trefoil, bluebush, dryland drilling, hairy dorycnium, hoe-coulter, strip-seeder, tall oat grass, wheatgrass