Cu and Zn relations in fertilised eucalypt plantations

Interactions between plant nutrients are common and high levels of one nutrient are often associated with a reduced concentration of a second nutrient. For example, an increased growth rate of the plant due to the application of one nutrient can lead to dilution and may cause deficiency of that second nutrient. Effects of one nutrient on root system architecture and mycorrhizal infection may interfere with the uptake of other nutrients. Specific interactions between nutrients have also been reported (Robson & Pitman, 1983). These may lead to increased adsorption to soil solids and changes in the rate of diffusion in soil, interference in uptake and transport by competition, and the formation of insoluble complexes within the plant. A reduction of Cu and Zn concentrations due to application of high levels of N and P has been reported for a number of annual crops and in this thesis it will be investigated for Eucalyptus nitens. Australia aims to treble its plantation estate by 2020 and new plantations have been established recently at a rate of 80,000 ha per annum. As a result of policies directed towards the conservation of native forest, land previously used for agriculture is increasingly used for the establishment of plantations. Poor stem form of trees grown on ex-agricultural land is a common problem particularly in combination with high rates of applied N and P. This poor stem form has been linked with Cu deficiency in Pinus radiata (Ruiter, 1969) and Eucalyptus nitens (Turnbull et al., 1994). A preliminary investigation of research data and the field site used by Turnbull et al. (1994) indicated that Zn deficiency and high levels of Mn may have interacted with Cu deficiency to cause the stem deformities. This thesis investigates the interaction of high N and P application with Cu, Mn and Zn nutrition of E. nitens. A series of greenhouse trials were conducted using soil from a site at which stem deformities have occurred. The first experiment investigated the interaction between N, P, Cu, Mn and Zn application on the growth and micronutrient concentration of E. nitens seedlings grown in soil associated with straight or deformed trees in the field. Lycopersicon esculentum was investigated as a test plant for micronutrient disorders in this experiment. In a second the effect of Cu application on Cu concentrations in L. esculentum and E. nitens seedlings on two soils was tested. In the third experiment the effect of Cu, Mn and Zn application on growth, stem form and micronutrient concentration of E. nitens saplings grown at high levels of N and P was investigated. The fourth experiment investigated the effect of N and Cu application on the uptake and distribution of Cu by E. nitens clones. Soil that was associated with stem deformities in the field resulted in a reduced uptake of Cu and Zn and a lower growth response to the application of N and P by E. nitens and L. esculentum than soil that was associated with straight trees in the field. When Cu and Zn were applied there was an increase in tissue concentration of the respective nutrient. L. esculentum proved to be a good indicator plant for Cu deficiency in E. nitens seedlings. The Cu concentration in L. esculentum was in the deficiency range when compared to that reported previously in the literature, while Zn concentrations were adequate. The growth response to the application of micronutrients was small. The largest response occurred with Cu application in combination with high N and P application. High N application reduced the Cu concentration in seedlings grown without Cu application. With applied Cu, high N application resulted in increased Cu concentration. N application improved the root to shoot transport of applied Cu. The root to shoot transport of Cu was subject to genetic variability with one clone of E. nitens retaining a significantly higher proportion of Cu in the roots than the other. Stem deformities like those observed in the field could not be induced during the greenhouse experiments, although Cu concentrations were deficient for growth. This may be due to the short duration of the greenhouse experiments (up to 6 months) as the symptoms in the field occurred only in the second growing season. Another possible explanation may be the absence of wind stress and other triggers of stem deformities in the controlled greenhouse environment. The research in thesis showed that N application was the cause of the induced Cu deficiency observed in the greenhouse. It showed that the effect of N application on the foliar Cu concentration occurred during the root to shoot transport. The deficiency was ameliorated with Cu application and seedlings with high N and P application showed increased growth to applied Cu. The research supported the critical Cu concentration of 1.4 mg/kg proposed by Turnbull et al. (1994), which had previously been based on a single experiment and showed that it is likely to also indicate a growth response to Cu application at high N and P. Cu concentration of L. esculentum was a good indicator of Cu deficiency in E. nitens seedlings in the greenhouse.