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

Abstract

Pastures based on the white clover cultivars Grasslands Tahora and Grasslands Huia ",:ere 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 ferti1i~er 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 Plha 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 A92063 Received 1 December 1992; accepted 15 February 1993 of these populations were volunteer plants of the resident ecotype; these were much smaller than plants ~f Tahora and Huia (mean total plant weights, Includmg 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 DMlha per year for Huia-sown and Tahora-sown pastures respectively, versus 305 kg DMlha 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 DMlha per year versus 231 kg DMlha per year respectively). Applying 35 kg Plha 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.

The relative strengths of phosphate fertiliser application and white clover cultivar introduction for hill pasture improvement

“…The experiment was conducted on moderate-steep hill land at Ballantrae Hill Country Research Station, 20 km NE of Palmerston North in the lower North Island of New Zealand. Details of the site and experimental design were presented by Chapman et al (1993b). The mean annual rainfall at the site is 1270 mm, and average temperature is 12.8°C.…”

“…The genetic composition of the white clover plant populations in all Huia-sown and Tahora-sown plots was measured in January 1990 and January 1994 using cyanogenesis as a genetic marker. A full description of the technique can be found in Chapman et al (1993b), which also reports data from the January 1990 sampling. In essence, the resident white clover ecotype, Huia and Tahora all had sufficiently different frequency occurrence of cyanogenesis to allow resident and Huia plants be distinguished from each other in the Huiasown treatment, and resident and Tahora plants to be distinguished in the Tahora-sown treatment.…”

“…Four P fertiliser rates were applied in factorial combination with three pasture type treatments based on different white clover germplasm. Initial results were reported by Chapman et al (1993a) and detailed information on the structure of pasture white clover populations was presented by Chapman et al (1993b).…”

Persistence: the key to legume performance in summer-dry hill country

“…Attempts to increase the clover yield of hill country pastures through the introduction of new genotypes have been largely unsuccessful (Barker et al 1988;Macfarlane et al 1990b;Webby et al 1990;Wedderburn et al 1996;Dodd et al 2001) with few exceptions (see Chapman et al 1993). Either the new high-productivity genotypes have failed to persist, or the new persistent genotypes have shown no productivity gains over the resident ecotypes.…”

Quantifying the value proposition for white clover persistence on a New Zealand summer-dry hill-country farm

“…Numerous field studies have demonstrated an improvement in pasture production and forage quality as a result of introducing both grasses and legumes into hill-country pastures (e.g., Wedderburn et al 1996), but also by introducing clover only into existing swards (e.g. Lambert et al 1986;Chapman et al 1993). The rationale for this approach is based on the role of the legume in improving the nitrogen economy of the soilpasture system, as a pre-requisite to establishing grasses of high productive potential (Ledgard et al 1987).…”