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The contribution of insect herbivory to the canopy decline of Eucalyptus largiflorens F.Muell. (black box) was assessed on nine irrigated properties around Deniliquin in southern central New South Wales. Fully expanded leaves less than 1 year old were sampled from 36 mature trees in June 1993 and again in June 1994 after half the trees had been treated with a systemic insecticide in November 1993. Insect herbivory in treated trees fell significantly from 27 to 9%. It also fell, but to a lesser extent (28-19%, P < 0.05), in the untreated trees. The fall in insect herbivory in control trees corresponded to a decrease in rainfall in 1994 when the rainfall was 50% of that for 1993. There was a significant linear relationship between insect herbivory and trunk diameter increment in the untreated trees. There was no consistent relationship between insect herbivory and the visual assessment of crown condition. Although E. largiflorens is described as having both narrow adult and juvenile foliage, adjacent trees in this study differed significantly in their leaf length:breadth ratios. Canopies with a dominance of broader foliage had significantly higher levels of herbivory. Individual trees tended to replace foliage with leaves of similar morphology. It is suggested that this variation in leaf shape may be genetic rather than environmental. If so, landholders could select for trees with narrower foliage which may result in reduced impact of insect herbivory.

The distribution of water and Bray no. 1 phosphate was measured in the surface soil of a Chromic Luvisol that had been under trickle irrigation for 5 years. The region of the soil reaching field capacity after 8 to 12 h of irrigation extended horizontally to at least 65 and up to 90 cm from the outlet and was no deeper than 12 cm from the surface. After irrigation had ceased soil water decreased with time but usually did not become significantly different from field capacity until after about 24 h.Where the soil had not been fertilized, Bray no. 1 phosphate decreased from 42 to 19 ppm over a 25‐cm depth immediately below the trickle outlet, while 65 cm away it decreased from 78 to 16 ppm. Banding fertilizer 50 to 80 cm from the outlet increased phosphate at the surface to 113 ppm but did not increase phosphate at depth. These results imply that trickle irrigation caused both horizontal and vertical movement of native soil phosphate near the outlet, and that phosphate fertilizer applied 50 to 80 cm away from the outlet remained near the soil surface and above the root zone.Irrigation of an 8‐ to 12‐h duration usually increased the concentration of Bray no. 1 phosphate by an average of 63% in a region of radius 30 cm from the outlet and about 12 cm in depth. The phosphate concentration remained above pre‐irrigation levels for between 6 to 23 h after the end of irrigation but fell to pre‐irrigation levels as the soil dried out.A series of linear regression equations of similar slope were found to describe the relationship between Bray no. 1 phosphate and soil water content for all 300 samples collected in the multicycle irrigation experiment. Differences in intercept values were related to the variable phosphate distribution with depth at various distances from the trickle outlet.Phosphate release probably resulted from reduction of amorphous iron phosphates during the anaerobic phase of the irrigation cycle. These results suggest that trickle irrigation leads to cyclic release of both native and applied phosphate during each irrigation cycle. Leaf analysis showed that under these circumstances there was no significant response to applied phosphate fertilizers at rates up to 78 g of P as single superphosphate per plant. Over the period studied trickle irrigation appears to be an agricultural management system with a much lower requirement for the application of phosphate fertilizer when tree crops are grown.