Nutritional aspects of the decline in Banksia integrifolia at Wilsons Promontory National Park, Victoria.  P. Hopmans.  July 1993.  13pp. (unpubl.)

SUMMARY

Mortality of Banksia integrifolia L.f. (coast banksia) has affected some 1500 ha along the Yanakie Isthmus of Wilsons Promontory National Park since it was first observed in 1980. Trees of all ages are affected and early symptoms of the decline include chlorosis of foliage followed by necrosis of older leaves. A study was undertaken to determine if the decline was associated with inadequate plant nutrition. This hypothesis was tested at first in a glasshouse trial at Kew and subsequently in a field trial at the Yanakie Isthmus.

Chlorosis of B. integrifolia grown in pots with calcareous sand (pH 8.9) from the Big Hole area was associated with low concentrations of Fe and Mn in foliage. Critical levels of Fe and Mn were estimated at 40 and 80 µg g^-1, respectively, based on relationships between the level of chlorosis and concentrations of Fe and Mn in foliage. Regular foliar applications of Fe chelates (FeEDDHA, FeDTPA, and FeEDTA) decreased chlorosis, while soil applications of complete fertilisers failed to correct the disorder.

A field trial was established in young B. integrifolia at Middle Yards with soil pH increasing from 7.9 at the surface to 9.0 at a depth of 70 cm. A single soil application of FeEDDHA and a complete micronutrient fertiliser with FeEDTA increased uptake of Fe, Mn, and Cu for a short period only. In the long term, these treatments did not improve uptake of Fe and Mn and did not alleviate chlorosis of B. integrifolia. Levels of Fe in foliage were well in excess of the critical level for Fe, indicating that the symptoms observed in the field were probably not associated with Fe deficiency. Likewise, levels of Mn in mature and in older foliage with chlorosis were well in excess of the estimated critical level. However, levels of Mn in young foliage were comparatively low indicating low availability of Mn on these calcareous sands. It is suggested that at least some of the chlorosis may be associated with inadequate uptake of Mn. However, the primary cause of the decline of B. integrifolia is likely to be poor root development, rather than a nutrient disorder. Laboratory tests showed that is feasible to lower the pH of these sands with elemental S, at least on a small scale. It is suggested that further investigations be carried out to determine the role of soil alkalinity in the decline of B. integrifolia at the Yanakie Isthmus.