Improving brassica crop yields in areas cultivated out of hawkweed

Abstract

Hawkweeds (Hierucium species) presently dominate 500 000 ha of the South Island high country. Their spread threatens the ecology of the tussock grasslands and the livelihood of runholders. Management practices have been partially 'i successful at controlling hawkweed spread, but increasingly runholders are cultivating suitable areas. Crops planted into this environment are usually poor with negligible yield. Over 2 seasons 5 trials investigated the role of nitrogen, lime and molybdenum, boron superphosphate in the growth of soft turnips (Brassica campestris ssp. rapifera Green Globe) and Italian ryegrass (Lolium multiflorum). The results showed the importance of nitrogen. The nitrogen response of total yield was curvilinear or linear in every trial. Up to 48 kg DIWkg N was grown when 80 kg N/ha was applied, There was no significant reponse to molybdenum, boron, superphosphate or lime. Vegetation and soils dominated by hawkweeds are low in nitrogen, therefore little nitrogen is released after cultivation. Keywords: crop-yields, dryland, Hieracium pilosella, nitrogen, toe slopes, Brassica campestris ssp. rapifera, tussock grasslands, Lolium multiflorum