Effect of nutrient application and herbicides on root competition between green panic seedlings and a Heteropogon grassland sward

Root competition was studied between seedlings of green panic ( Panicum maximum var. trichoglume ) and Heteropogon contortus in a native grassland sward clipped regularly to a height of 5·7 cm, and to which supplementary irrigation was applied. The influence of fertilizer addition and root competition from the grassland sward on seedling growth during the 42 days following emergence was determined. Root competition was excluded by steel tubes, or eliminated by killing the native sward with herbicides.
Seedling growth was poor where neither root competition was controlled nor fertilizer was applied; at 42 days the seedlings were still less than 6 cm high with three leaves and one tiller. When root competition was controlled, either by steel tubes or herbicide, seedling growth increased significantly. Growth was greatest in the herbicide-treated plots where fertilizer was applied, seedlings at day 42 being 48 cm high with sixty-three leaves and nineteen tillers.
Competition for nutrients appeared to be the primary factor limiting seedling growth and this was largely overcome by fertilizer application. Competition for nutrients appeared to increase the fertilizer requirements of pastures oversown into live swards compared with that of pastures oversown into herbicide-treated swards.