A study of the effects of root and shoot competition on the growth of green panic (Panicum maximum var. trichoglume) seedlings in an existing grassland using root exclusion tubes.
The effect of root and shoot competition and the application of 300 kg molybdenized superphosphate plus 50 kg N/ha on the growth of green panic seedlings in native grassland dominated by Heteropogon contortus was studied under supplementary irrigation. Green panic was grown in steel tubes of 7.5 and 10 cm diam. driven into the soil at different depths to provide root barriers for 0, 3, 9 or 27 cm. Aboveground competition was varied by clipping the native grasses to 5-7 cm once every 7-10 days. Growth was assessed by measuring plant ht., leaf and tiller number and leaf width during the 56 days following seedling emergence. Plant height increased with tube depth and fertilizer application; the response to fertilizer application was greatest in the 0 and 3 cm tubes where inter-species root competition was greatest, indicating that competition for nutrients limited seedling growth. Root competition affected growth of green panic more than competition for light.