Effects of cultivar introduction and fertiliser on characteristics of white clover (Trifolium repens L.) plants and populations in a hill pasture

Abstract

Pastures based on the white clover cultivars Grasslands Tahora and Grasslands Huia were established by oversowing into unimproved hill country at Ballantrae in May–June 1986. Each pasture type occupied 2.2 ha, and a further 2.2 ha of unamended pasture containing the resident clover ecotype was also included. From August 1988, four fertiliser treatments (control, receiving no fertiliser; reactive phosphate rock; partially acidulated phosphate rock; and a superphosphate/phosphate rock blend, the latter three applied at 35 kg P/ha per year) were superimposed upon pasture types. Emphasis was placed on identifying the population and plant characteristics which responded to treatment, and defining the relative benefits to pasture performance resulting from the two approaches to pasture improvement (cultivars versus fertiliser). Based on measurements of the frequency of occurrence of cyanogenic plants in populations nearly 4 years after sowing, 58% of white clover plants in the Tahora-sown pastures and 43% of plants in the Huia-sown pastures were estimated to have derived from the original seedlines. The rest of these populations were volunteer plants of the resident ecotype; these were much smaller than plants of Tahora and Huia (mean total plant weights, including root material, were 49.5, 112.2, and 139.2 mg, respectively). When both genotype frequency and plant weight differences were accounted for, the introduced cultivars were estimated to have contributed 70% of the total white clover biomass present in sown pastures, averaged across fertiliser treatments. White clover herbage accumulation was greater in the sown pastures than in the resident pasture (558 and 586 kg DM/ha per year for Huia-sown and Tahora-sown pastures respectively, versus 305 kg DM/ha per year for resident pasture, means for Years 3 and 4 after sowing), and in the fertilised treatments compared to the Control (518-597 kg DM/ha per year versus 231 kg DM/ha per year respectively). Applying 35 kg P/ha per year had a greater influence on clover herbage accumulation than cultivar introduction, though returns on cultivar introduction can be seen as accruing each year (if cultivars are persistent) for a one-off cost whereas fertiliser must be financed annually. Fertiliser application increased mainly the population density of clover plants (number/m²) whereas cultivar introduction affected mainly the mean size of plants in the population. Limited evidence was obtained to suggest that Tahora and Huia responded differently to fertiliser application.

Keywords:

• white clover
• Trifolium repens L.
• hill country
• cultivars
• phosphate fertiliser
• plant populations
• plant morphology
• legume performance