Effect of season (vegetative flushing) and leaf position on the leaf nutrient composition of Annona spp. hybrid cv. Pink's Mammoth in south-eastern Queensland

Seasonal patterns of leaf nutrient concentrations and leaf sampling procedures were established for the Annona spp. hybrid cultivar, Pink's Mammoth in subtropical Queensland (27°S.). One group of nutrients showed a general decline in concentration in the leaves with time (K, 1.448%; P, 0.3-0.15%) while another group showed an overall increase (Ca, 0.4-1.4%; Mg, 0.3-0.54%; B, 24-66 μg/g). Nitrogen leaf levels decreased throughout the growing season (3.5-2.5%), with the pattern of decline strongly influenced by vegetative flushing.

Leaf concentrations of Ca, Mg, Mn and B generally increased, and N, P, K, Cu, and Zn decreased with leaf age. Movement of the more mobile elements (i.e. N, P. K, Cu, and Zn) from the older into the younger leaves was more rapid when trees were flushing compared with trees that had completed flushing. Irrespective of the state of flushing, higher concentrations of the less mobile elements Mg, Ca, B and Mn were recorded in the older compared with the younger leaves, indicating that their movement into younger leaves is relatively slow. Our results suggest that the most suitable time to sample leaves is after the completion of vegetative flushing when the concentration of most leaf elements have stabilised. Depending on the element, it may be more appropriate to sample either young or old leaves rather than compromise by sampling only the most recently mature, fully expanded leaf.