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

Abstract

An investigation was made during 1988 to test the hypothesis that ‘Grasslands Huia’ white clover (Trifolium repens L.) could be eliminated under close sheep grazing. The effects of grazing management, topography and fertilizer on the contribution of Huia plants to the white clover population in an 85 ha experimental upland pasture ecosystem in the southern North Island, New Zealand (lat. 40° 20′ S, long. 175° 50′ E, 125–350 m altitude) were quantified 11 years after oversowing. Replicated sampling sites (108 in total) were located on nine combinations of slope and aspect within grazing 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 occurrence, leaf area, phosphoglucoisomerase-2 (PGI-2) allele frequencies and the proportion of Grasslands Huia plants in the white clover population were determined at each site. White clover frequency was lower on steeper slopes. Aspect, slope and grazing management affected area of individual clover leaves. 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 concluded 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.