© 2004 Heron Publishing—Victoria, Canada
Root distribution of Pinus pinaster, P. radiata, Eucalyptus globulus and E. kochii and associated soil chemistry in agricultural land adjacent to tree lines
R. A. Sudmeyer (1, 2), J. Speijers (3) and B. D. Nicholas (1)
1. Department of Agriculture WA, PMB 50, Esperance 6450, Australia / 2. Corresponding author (rsudmeyer@agric.wa.gov.au) / 3. Department of Agriculture WA, Perth 6151, Australia / Received December 12, 2003; accepted April 12, 2004; published online October 1, 2004
Summary
We quantified the extent and distribution of roots of four commonly planted tree species (Eucalyptus globulus Labill., Pinus radiata D. Don, P. pinaster Aiton and E. kochii Maiden & Blakely subsp. plenissima C.A. Gardner) in agricultural land adjacent to tree lines, and examined the effect of soil type and root pruning on root
morphology. Root distribution in soil adjacent to tree lines was mapped by a trench profile method at 13 sites on the south
coast of Western Australia. Soil samples were collected to determine water content and fertility.
The lateral extent of tree roots ranged from 10 m for E. kochii to 44 m for P. pinaster. This equated to between 1.5 and 2.5 times tree height (H) for E. globulus and Pinus spp. to 4H for E. kochii. Root density declined logarithmically with distance from the trees and was greatest for P. pinaster and least for E. globulus (P < 0.001). The rate of decrease in root density with distance from the trees was greatest for the Pinus spp. and least for E. kochii (P < 0.05). Root density was generally greatest in the top 0.5 m of the soil profile and decreased with increasing depth. This
decrease was relatively gradual in the deep sands, but abrupt in clay subsoil. Root dry mass in the sandy top soil beyond
0.5H ranged between 1.0 and 55.5 Mg kmtreeline–1 for 6-year-old E. kochii and 50-year-old P. pinaster, respectively. Soil water content generally increased with distance from the trees (P < 0.001). There was no evidence of reduced soil fertility in the top 1.4 m of the soil profile adjacent to the trees. Two
to four years after trees had been root pruned, both the lateral extent and vertical distribution of roots were similar for
pruned and unpruned trees. The density of roots < 2 mm in diameter was greater for root-pruned trees than for unpruned trees
(P < 0.05). We conclude that the study species can compete with agricultural crops based on the lateral extent of their roots
and the occurrence of greatest root density within 0.5 m of the soil surface.
Keywords:
alley farming, tree/crop competition, tree/pasture competition, tree root morphology, windbreaks.
