Competitive ability of Caucasian clover (Trifolium ambiguum) compared with white clover (Trifolium repens) on lowland and high country sites

Abstract

The competitive ability of Caucasian clover and white clover was assessed at three fertile lowland sites of different ages and one low fertility 21 year old high country site during autumn 1996.

The first lowland site examined the sociability of Caucasian clover and white clover 15 months after sowing with five grasses: ryegrass (Lolium perenne), grazing brome (Bromus sitchensis), tall fescue (Festuca arundinacea), cocksfoot (Dactylis g/omerata), and phalaris (Pha/aris aquatica) on fertile (pH 6.1, Olsen P 39) lowland soil. Neither clover illustrated a superior competitive ability in terms of plant canopy height or plant diameter when grown with grasses. The canopy height and spread of both clovers was reduced when grown in association with the more aggressive ryegrass and grazing brome. The height of the two clovers was generally 2/3 that of associated grass height indicating that the clovers were able to intercept sufficient light at this level in the canopy. The spread of Caucasian clover in monoculture (324mm) was significantly (p<0.01) greater than white clover. Poor establishment of the clovers was thought to be limiting the contribution of the legumes to pasture production and % cover at his early stage in sward development.

The second fertile (pH 5.9, Olsen P 23) lowland site assessed the competitive ability of Caucasian clover, white clover and lotus (Lotus pedunculatus) when grown in monoculture and with ryegrass, three years after establishment of legumes from 10 week old seedlings. The mean plant weight of all three legumes in autumn was reduced (p<0.001) when grown in association with ryegrass to approximately 1/5 of that when grown in monoculture. The mean plant dry weight of Caucasian clover (67.2g) was greater than the mean yield of white clover (37.9g) and lotus (41.7g). The mean spread of all three legumes in spring was significantly (p<0.05) greater in monoculture plots (714mm) than in grass plots (476mm), with the mean spread of white clover, Caucasian clover and lotus 865mm, 710mm and 254mm respectively.

Experiments 1 and 2 were subjected to rotational grazing by sheep and had received some irrigation to relieve moisture stress.

The comparative performance of Caucasian clover and white clover in the third year of an ongoing grazing experiment on fertile (pH 5.8, Olsen P 19) lowland was assessed in March, May and September. Caucasian clover performance was better under a rotational grazed system than under set stock grazing. White clover was not as greatly affected by grazing frequency but generally had greater % cover when grazing intensity was severe.

The persistence of white clover, Caucasian clover and lotus on a high country site was assessed in April 1996. The site was sown with three legumes (white clover, Caucasian clover, and lotus) with four establishment P levels (0 kg P/ha, 10 kg P/ha, 50 kg P/ha, and 100 kg P/ha) 21 years previously. For the past nine years the plots have been intensively grazed by deer. All plots were visually scored for current grazing intensity by deer. Plots that received 50 kg P/ha at establishment were sampled for underground biomass and nutrient storage of Caucasian clover, white clover, and browntop (Agrostis capillaris L. syn. A. tenuis) but not lotus which had not persisted.

Plots that were originally sown in Caucasian clover were preferentially grazed. Post grazing pasture mass (PGPM) on Caucasian clover plots was 1600 kg DM/ha while PGPM on white clover and lotus plots was 3200 kg DM/ha and 3000 kg DM/ha respectively. The greater underground biomass of Caucasian clover (roots plus rhizomes - 5.29 t DM/ha) in comparison with white clover (roots plus stolons - 0.46 t DM/ha) may have enabled Caucasian clover to compete more successfully with browntop for scarce nutrients.

Browntop was the dominant grass over the site. The underground biomass of browntop (roots plus rhizomes plus stolons) was significantly (p<0,05) reduced under hard grazing. Both clover species had greater underground biomass under hard grazing sites. White clover root plus stolon herbage contained the greatest % of all nutrients however browntop and Caucasian clover underground biomass contained greater total nutrients. The greater total nutrient storage ability of browntop and Caucasian clover was thought to contribute to their long term persistence at this low fertility site. Caucasian clover had superior persistence to lotus and appeared to have greater competitive ability than white clover with browntop.

It was concluded that further work on the compatibility and competitive ability of Caucasian clover with pasture grasses will further help identify the preferred niche for Caucasian clover in temperate pasture ecosystems.