Failure of Eucalyptus globulus (Labill.) plantations on previously irrigated pasture sites in south-eastern South Australia

Summary

From the mid-1990s onwards large areas of Eucalyptus globulus (Labill.) were planted in south-eastern South Australia and south-western Victoria (the Green Triangle region) on land which had been under pasture for decades. Within these plantations some well-defined areas had poor tree growth, and in extreme cases trees died in circular patches. The geometry of the affected areas strongly suggested an association with previous irrigation practices: very clear boundaries separated healthy and affected trees. Foliar analyses of both healthy and affected trees indicated adequate levels of most major nutrients (N, P, K and Ca). There were, however, marked differences in foliar manganese concentrations. Analysis of soil from previously irrigated areas showed increased soil bicarbonate concentration and pH compared to soil from areas with no history of irrigation. There was a strong negative correlation between soil pH and DTPA-extractable manganese. Concomitantly, foliar manganese concentrations decreased significantly to deficient levels as the soil-extractable manganese decreased. We conclude that the severe growth problems in E. globulus commonly found in circular patches of previously irrigated areas are due to acute manganese deficiency as a result of increased soil pH caused by irrigation with water containing high levels of bicarbonate. At one site where pasture grass was analysed, manganese concentration in pasture was considerably lower than in pasture from unirrigated areas, suggesting there could be problems in future for other crops in the region receiving repeated irrigation. The evidence that the pre-planting history dramatically influenced the growth of E. globulus plantations is important because plantations were not irrigated after planting, and areas of current eucalypt plantations in the region include land which had been under irrigation.

Keywords:

• plantations
• growth
• mortality
• nutrition
• nutrient deficiencies
• irrigation
• soil pH
• bicarbonates
• manganese
• Eucalyptus globulus