Effect of Fertilizer, Root and Shoot Competition on the Growth of Siratro (Macroptilium atropurpureum) and Green Panic (Panicum maximum var. trichoglume) Seedlings in a Native Speargrass (Heteropogon contortus) Sward

摘要

The effect of root and shoot competition and the application of fertilizer on the growth of Siratro n(Macroptilium atropurpureum) and green panic (Panicum maxinzum var. trichoglume) seedlings under nsupplementary irrigation in an existing native grassland dominated by Heteropogon contortus was nstudied. The seedlings were grown in both the presence and absence of root competition and varying nlevels of shoot competition. Root competition was prevented by the use of steel tubes while shoot ncompetition was varied by: clipping the native pasture to a height of either 3-5 cm or 10-15 cm every n7-10 days, leaving the native sward unclipped, and unclipped sward with wire-netting guards fitted naround each seedling to prevent overtopping and facilitate light penetration. Seedling growth was nassessed by determining dry weights after 29 days and also by measuring plant heights, leaf and tiller nnumbers and the leaf widths at 7-day intervals during this period. nApplication of superphosphate and nitrogen fertilizer increased the growth of both species, the initial neffects being evident within 1-2 days of seedling emergence. However, at both fertilizer levels the growth nof both species was primarily affected by root competition for nutrients. Where fertilizer was applied nand no root competition was present heavy shading in the lower 5-10 cm of the sward canopy restricted nseedling growth by reducing tiller and leaf production. nThe removal of shoot competition increased seedling yields fivefold whereas the removal of root ncompetition and the removal of both root and shoot competition increased yields by 25- and 45-fold, nrespectively. Siratro and green panic yields were the same in the absence of root competition but Siratro nyields were 11 times those of green panic where root competition was present.