NODAL STRUCTURE AND BRANCHING OF TRIFOLIUM-REPENS IN PASTURES UNDER INTENSIVE GRAZING BY SHEEP

The nodal structure of white clover plants was studied in New Zealand in pastures stocked at 22.5 ewes plus lambs/ha and either continuously or rotationally grazed. Intact plants were sampled every month for a year (1988/89) by removing turves and washing out the plants. Plants were classified according to the degree of branching as first (unbranched, single-stolon plants), second, third or fourth order (plants with at least one quaternary branch). Where possible from each turf, four plants of each of the four branching orders were sampled and, for each stolon of each plant, nodes were ascribed positions numbered from the stolon apex, and the position of nodes with a live branch and the total number of nodes/stolon were recorded. The mean number (and 5 and 95% quantiles) of nodes/plant was 15.7 +/- 0.26 (9, 24) for the first-order, 42.2 +/- 0.90 (18, 81) for the second-, 91.4 +/- 2.13 (37, 163) for the third- and 163.7 +/- 7.49 (63, 367) for the fourth-order plants. Grazing management and month of sampling had minor effects on these values. The mean number of nodes/stolon within branched plants depended on the category of the stolon within a plant, the presence or absence of an apex and on the branching order of the plant. The first 10, 15, 20 and 25 node positions accounted for, respectively, 64, 79, 90 and 95% of total nodes in the field population and 39, 62, 79 and 90% of all branches. Successful branch initiation occurred at recently formed nodes at positions 3-10, emphasizing the significant contribution of such nodes in growth and persistence of white clover in grazed swards. Where grazing management allows little consumption of stolon and there is adequate moisture, growth and fragmentation maintain the mean node composition of the branching orders reasonably constant throughout the year. Thus, any seasonal variation in the overall mean number of nodes/plant in a population must be driven by seasonal changes in the distribution of plants among the branching orders. However, there was evidence of mean number of nodes/plant decreasing in the third and fourth orders after dry conditions.