The effect of a soil-amended hydrogel on the establishment of a Eucalyptus grandis clone on a sandy clay loam soil in Zululand during winter

Synopsis

To ensure acceptable survival and growth of Eucalyptus grandis clonal material planted in the sandy clay loam soils of the Zululand interior of South Africa, the current planting season is limited to the summer rainfall period. A field trial was initiated with the primary objective of being able to successfully extend the planting period (May to September) within which Eucalyptus grandis clones could be planted. This was done by testing tree growth and survival by the addition of a soil-amended hydrogel (Stockosorb 400K) and comparing it to traditional water planting methods. Five levels of water (0 ml, 500 ml, 1000 ml, 2000 ml and 4000 ml) were combined with five levels of hydrogel (0 g, 3 g, 6 g, 9 g, and 12 g) and applied to the pit at planting in a 5x5 factorial design. The tree variates of mortality, height, groundline diameter, crown diameter, corrected leaf surface index (LSI ^c) and corrected biomass index (BI ^c) were assessed at 7, 47,86 and 118 days after planting.

There was a highly significant (p<0,01) interaction between hydrogel and water which had a positive impact on both transplant survival and growth. There were significant differences between water only treatments when compared with all levels of hydrogel, with the hydrogel treatments performing significantly better. Optimum survival for water only treatments was achieved at the 4000 ml application level (50 %) while optimum survival for hydrogel and water was achieved for 6 g/1000 ml and 12 g/2000 ml ofhydrogel and water (100 %). There were no significant differences for survival within all but one of the hydrogel treatments over all applications of water. Both the variates LSI ^c and BI ^c indicated that tree growth was significantly enhanced by the addition ofhydrogel over all applications ofwater. Optimum tree performance was found to occur at 2000 ml water and 12 g hydrogel.

The results from this trial indicate the possibility of using a soil-amended hydrogel (Stockosorb 400K) to:

i successfully establish a Eucalyptus grandis clone in the Ntonjaneni area during winter, thereby successfully extending the planting season (between May and September);

ii significantly reduce water volumes used at planting without negatively affecting current silvicultural standards.

Keywords:

• Stockosorb 400K
• soil-amended hydrogel
• survival
• leaf surface index
• biomass index