Sulphur and nitrogen nutrition and their interactive effects on Dothistroma infection in Pinusradiata

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Abstract
Nitrogen and sulphur fertilizers were applied to a 4-year-old Pinusradiata plantation in northern New South Wales and the results were monitored for 7 years. The aim was to study the effects of sulphur and nitrogen nutrition on tree growth and their interactions on Dothistroma infection. Sulphur (300 kg S ha−1), applied as gypsum, elevated foliage sulphate sulphur levels for up to 7 years after treatment, but no direct effects on growth were noted. The low nitrogen fertilizer level (100 kg N ha−1) had a positive influence on volume increment, while the high nitrogen fertilizer application (400 kg N ha−1) significantly depressed volume increment. This latter negative effect was attributed to induced sulphur and phosphorus deficiencies. Sulphur deficiency resulted in highly increased arginine concentrations in current foliage and there was a strong positive correlation between arginine concentration and tree infection level of Dothistroma needle cast fungus, the highest levels of infection being in the nitrogen-treated plots. Relationships between foliar nutrition and foliar fungal infection are discussed.