Individual study: A finer potting mix enhances initial Eucalyptus tree seedling survival in heavy clay soils near Birregurra, Victoria, Australia
Noble P. (1993) Effect of potting mix texture on farm tree seedling survival in heavy soils. Agroforestry Systems, 21, 75-78
Thousands of tree seedlings are planted on farmland each year in the Western District of Victoria in southeast Australia. In this region, heavy clay soils, prone to water-logging in winter and drying out in summer, are prevalent in some areas. If soil moisture is adequate at planting, combined with weed control, watering of seedlings subsequent to planting is usually considered unnecessary. However, the use of coarse, bark-based potting mixes in heavy clay soils upon seedling survival is questioned, as during very wet periods the potting mix may act as a water sump, and during dry periods it dries more rapidly than the surrounding soil and once dry, is very difficult to rewet. To test the effect of different potting mixes on initial survival of two native Eucalyptus species, a simple trial was undertaken.
Tree seedlings and planting: Tree seedlings of Eucalyptus maculata and E.viminalis were grown at the Victorian College of Agriculture and Horticulture in two different potting media:
i) a coarse mix (bark and sand) - 21 seedlings of each species;
ii) a finer mix (bark and sandy loam) - 18 E.maculata, 23 E.viminalis.
The tree seedlings (no indication of size/age given in original paper) were planted out on 9 November 1991 in heavy clay soils at a site north of Birregurra in the Western District. The planting area was sprayed with Roundup herbicide to control weeds. A Hamilton Tree Planter was used to plant the seedlings which were watered in at planting, and subsequently watered four times during the first six weeks after planting. Plastic guards were placed around the seedlings to protect them from lagomorph damage.
Seedling survival: Tree seedling survival was recorded on 8 January and 24 March 1992.
All 21 E.maculata seedlings planted in the coarse mix had died over the dry period by 24 March, whereas 4 (22%) in the finer mix survived. E.viminalis survival to 24 March was 4 (19%) in the coarse mix and 6 (26%) in the finer mix. Survival of each tree species recorded on the two observation dates in the two potting media were:
8 January 1992 – coarse 11 (52%) alive, 10 dead; finer 14 (78%) 4 dead.
24 March 1992 – coarse 0 (0%) alive, 21dead; finer 4 (22%) alive, 14 dead.
8 January 1992 – coarse 11 (52%) alive, 10 dead; finer 13 (56%) alive, 10 dead.
24 March 1992 - coarse 4 (19%) alive, 17 dead; finer 6 (26%) alive, 23 dead.
During the survey period, no seedling pests or salt indicator plants were observed at the planting sites. Overall, the finer potting mix enhanced survival of the two species of eucalypt seedlings planted.
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