Semiarid land rehabilitation by direct drilling in the South Island, New Zealand—plant species and establishment technology

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AbstractLarge areas of the east coast and inland basins of the South Island, New Zealand, are affected by periodic drought and/or semiarid climatic conditions, particularly during cyclic El Niño climatic events. The severity of these environmental conditions places great stress on introduced and native pasture species and frequently results in poor establishment of new pastures using standard drilling techniques. The objective of this study was to determine effective, practical means of rehabilitating semiarid land (about 470 mm annual rainfall) on a site in Central Otago.A comparison of two direct drilling methods, a novel strip‐seeder drill and a standard hoe‐coulter drill, was conducted in a trial initiated during spring 1998. Five drought‐tolerant forage species were established: wheatgrass (Thinopyron intermedium), tall oat grass (Arrhenatherum elatius), birdsfoot trefoil (Lotus corniculatus), hairy dorycnium (Dorycnium hirsutum) and bluebush (Kochia prostrata).For the 2000/2001 growing season, species established with the strip‐seeder drill had an overall mean herbage biomass of 235 g m −2 , three‐times that for the hoe‐coulter drill (77 g m −2 , P < 0·001). Differences in herbage biomass between species were observed, with hairy dorycnium (mean 328 g m −2 ) producing significantly (P < 0·001) more herbage biomass than the other species.After the third spring, the percentage ground cover recorded from transects across the strip‐seeder drill plots (cf. the hoe‐coulter drill) was: wheatgrass—41 per cent (10 per cent); tall oat grass—44 per cent (25 per cent); birdsfoot trefoil—25 per cent (5 per cent); hairy dorycnium—50 per cent (19 per cent); and bluebush—4 per cent (0 per cent). The native plant content of the resident vegetation was reduced as a result of the drilling treatments and also when fertilizer was added to undistrubed pasture.The strip‐seeder drill is capable of providing superior plant growth on dryland sites even during adverse drought conditions. It produces a furrow approximately 16 cm wider than the hoe‐coulter drill, exerts a greater shattering effect on the soil structure and places fertilizer at depth. It is suggested that this assists plant establishment by providing good seedling protection from wind and sun, and subsequent plant growth by allowing easier root penetration to the subsoil where nutrients and moisture are available. Copyright © 2004 John Wiley & Sons, Ltd.