A study of the germination and establishment of lucerne (Medicago sativa L.) oversown on an uncultivated grass sward : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science (M. Agr. Sci.) at Massey University

Abstract

In this study on the oversowing of lucerne on an uncultivated sward at Massey, three trials were conducted, two in the field and one box trial under glasshouse conditions during the summer of 1975/76 and the autumn and early winter of 1976. The triars compared the effects of two lengths of ground cover, untreated, suppressed for a longer or shorter period with herbicides and burnt on the early establishment of lucerrne sown as bare or pelleted seed. It was found that small amounts of cover at sowing encouraged lucerne germination under high moisture conditions subsequent establishment and early survival was best on the burnt and chemically desiccated, plots. The cover was most useful where it was short (8 cm) and desiccated by long term paraquat or glyphosate treatments. Dense live cover was harmful to lucerne seedlings and smothered them within 5 weeks after sowing. Where recovery of the resident vegetation and weeds was rapid, as on the burnt and short term herbicide plots, lucerne establishnent and survivar was poor and surviviag plants were small and weak. Weed infestation was heavy both on burnt and herbicide treated plots, pointing to the need to introduce an early weed control programme with oversowing. Weeds were found to respond in a similar manner to lucerne to grass competition. In the autumn and early winter tria1s, slug damage was observed and this problem appeared to be of major importance under wet conditions. The effects of slugs were fourd to be most damaging during the first 4-5 weeks after sowing. Metaldehyde slug bait pellets were effective in reducing slug damage if applied at least twice during the establishment period of lucerne. The implications of these findings are reported and discussed with particular reference to the possibilities of oversowing under East African conditions