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Accueil du site → Master → Afrique du Sud → 2002 → The effect of a soil-amending hydrogel on Eucalyptus grandis establishment practices in the Zululand forestry region

Port Elizabeth Technikon (2002)

The effect of a soil-amending hydrogel on Eucalyptus grandis establishment practices in the Zululand forestry region

Viero, Paul Walter Mario

Titre : The effect of a soil-amending hydrogel on Eucalyptus grandis establishment practices in the Zululand forestry region

Auteur : Viero, Paul Walter Mario

Université de soutenance : Port Elizabeth Technikon

Grade : Magister of Technologiae Forestry 2002

To ensure acceptable survival and initial growth of Eucalyptus grandis clonal and clonal hybrid material planted in the cool temperate and sub-tropical climates of Zululand (KwaZulu-Natal, South Africa) the planting seasons are currently restricted to the winter or summer months respectively. The Zululand coast (sub-tropical climate) experiences traditionally hot and humid summers and as a result Eucalyptus planting is largely restricted to the cool and dry winter months when survival is acceptable (90- 95%). In comparison, the Zululand interior (cool temperate climate) experiences moderately cooler summers followed by drier winters. As a result, the Eucalyptus planting season is reversed to that of the Zululand coast, with most of the planting taking place during the summer months with little or no planting occurring during winter. To ensure adequate transplant survival during and beyond these periods, transplants are planted with large volumes of water at a high cost. To determine whether it was possible to significantly reduce current water volumes at planting and therefore reduce costs, and to potentially extend the current planting seasons, two field trials were initiated during traditionally �unsuitable� planting periods (winter months for the Zululand interior and summer months for the Zululand coast). These trials were established near Kwambonambi on the Zululand coast and at Ntonjaneni in the Zululand interior. Five levels of water were combined with five levels of hydrogel and applied to the pit at planting in a 5 x 5 factorial treatment design for both trials. The tree variates of mortality, height, groundline diameter, crown diameter, corrected leaf surface index (LSIC) and corrected biomass index (BIC) were assessed at regular intervals until the final measurement dates (118 and 128 days after planting for the Ntonjaneni and Kwambonambi trials respectively). For the Kwambonambi trial, the response of transplant survival to the application water was highly significant (p<0,01) 128 days after planting, but not to the application of the hydrogel. Transplant survival nevertheless conformed to the silviculturally accepted norms of 90-95% using the hydrogel, thus water volumes could be significantly reduced without negatively affecting current survival standards. The lack of the expected response of significantly reduced transplant survival to increasing levels of hydrogel could possibly be attributed to the significant rainfall event (146 mm) that fell two days after trial initiation. Increasing levels of both water and hydrogel resulted in significantly enhanced growth (LSIC and BIC : p<0.01) for the final measurement date. For the Ntonjaneni trial, there was a significant (p<0,01) interaction between hydrogel and water, 118 days after planting. There were significant (p<0,01) differences between water only and all hydrogel treatments, with the hydrogel treatments performing significantly better. Optimum transplant survival for water only treatments was 50% using 4000 ml water while that for hydrogel treatments was 100% using 6 g hydrogel with 1000 ml of water and 12 g hydrogel with 2000 ml of water. The variates, corrected leaf surface index and corrected biomass index indicated that tree growth was significantly enhanced by the addition of a hydrogel over all levels of water. A pot trial was subsequently implemented to ascertain whether the significant increases obtained for initial transplant growth for the sandy clay loam soils of Ntonjaneni were due to an initial but unsustainable positive response of the roots to the presence of the hydrogel, or whether root growth was sustainably advantaged by the presence of the hydrogel. There was a highly significant (p<0,01) response of root biomass and above ground biomass over all levels of hydrogel, including a significant positive linear (p<0,01) relationship between increased root biomass and above ground biomass. This clearly indicated that initial root growth was not negatively affected by the addition of the soil-amending hydrogel Stockosorb 400K.

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