Seasonal variation in the vertical distribution of white clover stolons in grazed swards

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Abstract
Swards under mob stocking or rotational grazing by sheep at Kaikohe, Taupo, Ballantrae, Wairarapa, Palmerston North, Lincoln, and Gore were sampled every three months for three years. The white clover stolon material was dissected into three vertical classes: aerial, surface, and buried. Length and dry weight of stolon in each class were measured. The mean total weight of stolon and the distribution by weight of stolon in the three vertical classes varied among sites (P<0.001). In addition, each year there was a highly significant (P<0.001) seasonal change in the vertical distribution of stolon at each site, with mean levels of approximately 80070 of stolon buried in winter and 40% in summer and autumn. At two sites, Wairarapa and Lincoln, exceptions to the seasonal. pattern of distribution of stolon were observed when low rainfall periods occurred. A significant negative correlation between threemonthly effective rainfall (rainfall minus Penman potential evapotranspiration) and weight per unit length of buried stolon indicated that thicker stolons comprised the bulk of the stolon population after dry periods. Regression analyses also indicated that earthworm biomass (which affects the quantity of surface casting) and effective rainfall (which influences the effect of stock treading) are both equally important in the burial of stolon. We concluded that white clover growth in grazed pastures throughout New Zealand is subjected to an annual cycle, consisting of burial of stolons in winter, re-emergence of growing points in spring, and surface stolon development over summer (unless harsh environmental conditions interrupt this cycle). This paper also reports earthworm numbers, biomass, and different earthworm species contribution to biomass in July each year for all experimental sites.