Determination of management and topographic influences on the balance between resident and 'Grasslands Huia' white clover (Trifolium repens) in an upland pasture using isozyme analysis

An investigation was made during 1988 to test the hypothesis that 'Grasslan ds Huia' white clover (Trifolium repens L.) could be eliminated under close sheep grazing. The effects of grazing management, topography and fertilize r on the contribution of Huia plants to the white clover population in an 8 5 ha experimental upland pasture ecosystem in the southern North Island, Ne w Zealand (lat. 40 degrees 20' S, long. 175 degrees 50' E, 125-350 m altitu de) were quantified 11 years after oversewing. Replicated sampling sites (1 08 in total) were located on nine combinations of slope and aspect within g razing management treatments comprising rotational grazing with cattle (RC) , rotational grazing with sheep (RS) and continuous grazing with sheep (CS) , with high and low fertilizer treatments in each case. White clover occurr ence, leaf area, phosphoglucoisomerase-2 (PGI-2) allele frequencies and the proportion of Grasslands Huia plants in the white clover population were d etermined at each site. White clover frequency was lower on steeper slopes. Aspect, slope and grazing management affected area of individual clover le aves. The proportion of Huia plants in the white clover population averaged 54.9, 49.0 and 33.6% for RC, RS and CS, respectively (P < 0.039, 5 D.F.). Fertilizer and topography did not affect the proportion of Huia. It was con cluded that although Huia did persist after 11 years of close sheep grazing , its contribution to the total white clover population was unsatisfactory in some cases, and use of better adapted cultivars is suggested.