The Effect of Grazing Intensity on Transition of White Clover Varieties in the Perennial Ryegrass-White Clover Sward

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  • ペレニアルライグラス-シロクローバ混播草地において放牧強度がシロクローバ品種の移行に及ぼす影響
  • Effect of Grazing Intensity on Transition of White Clover Varieties in the Perennial Ryegrass White Clover Sward

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Abstract

Two different size of leaflet of white clover varieties, Grasslands Kopu (large-leaved) and Grasslands Tahora (small-leaved) were sown at the weight ratio of 1:1 with perennial ryegrass in 1994. Treatments with intensive and extensive grazing using Jersey heifers were carried out over four years, 1995-1998. The number of heifers per a unit of acreage in the extensive grazing treatment was a half of that in the intensive grazing treatment. Observed herbage mass from the extensive grazing treatment was higher than that from the intensive grazing due to different intensity of grazing. The proportion of white clover in the sward was significantly lower in the extensive grazing treatment compared with the intensive treatment. The proportion of white clover in a sward for the intensive grazing treatment was a proper content of 20-30% during the experiment period. One hundred samples collected from each sward after the experiment of grazing for four years were measured for the length of central leaflets. The stolon tips of sample plants were cut and transferred to new pots two times with the plants of original varieties, Grasslands Kopu and Grasslands Tahora for the purpose of removing the effect of plasticity through a different grown environment. A wide variation was observed in samples from the extensive treatment with the higher proportion of plants having long leaflets. In contrast, for the intensive grazing treatment, a variation was found with the similar to that of Grasslands Tahora, small-leaved variety. This strongly suggested that Grasslands Tahora dominated gradually during the experiment period. The small-leaved variety of white clover would be adapted to the intensive grazing system and become dominant in such swards. Grasslands Tahora was bred for hill country of New Zealand and had greater stolon density giving improved persistence under intensive grazing in addition to good winter survival. From this experiment it was suggested that small-leaved variety, Grasslands Tahora would be recommended for intensive grazed swards in the cool regions of Japan when grown with perennial ryegrass.

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