Effect of nitrogen, phosphorus and potassium fertiliser rates on fruit yield, leaf mineral concentration and growth of young orange trees in the Sunraysia district

Abstract

Fruit yield, leaf nutrient concentrations and growth response of young Valencia orange trees to 4 rates of nitrogen (N, 75-450 kg/ha), phosphorus (P, 0-180 kg/ha) and potassium (K, 0-360 kg/ha) were studied using 2 soil management systems (sod-sown and bare ground) and 2 rootstocks (Troyer Citrange and Sweet Orange). Eight-year-old Sweet Orange produced maximum yield at the higher rates of applied N and P and medium level of K, but at 12 years of age, highest yields occurred at the lowest rate of applied N, medium P and nil K. High N without P at year 12 strongly depressed yield especially on bare soil. Phosphorus application at high rates of N greatly increased yield but had no effect at lower rates of N. The effect of nutrients on yield was smaller on Troyer than on Sweet Orange rootstock. Leaf N concentration increased with amount of N applied and slightly increased with K applications but not with applied P. Leaf P concentrations increased with higher rates of applied P, especially in year 12 and at the lowest rate of applied N. Both rootstock and management affected leaf P concentration. Leaf K increased with amount of applied K. Highest concentrations of leaf K were from Troyer trees under bare soil management but this trend declined with time. The effects of fertilisers on tree size were small and varied with rootstock and management.