Effect of different types of branches, growth stages, and rootstocks on mineral nutrients concentration in the leaves of citrus

Summary To clarify the difference of leaf mineral nutrients affected by types of branches, growth stages, and rootstocks of navel orange, a field experiment was conducted on nine-year-old ‘Newhall’ navel orange grafted on trifoliate orange or citrange, which were similar in size and tree vigor. Branches were divided into three types (leaves of spring shoots (LSP), summer shoots (LSU), and autumn shoots (LAU)), and the observation period were divided into four stages (stage I, II, III, and IV). Their leaves were sampled monthly, and mineral nutrient concentrations were measured subsequently. The results showed that the patterns of annual change in the concentrations of leaf nutrients in two rootstocks grafted navel orange were generally similar, but there were significant differences among branch types. For all kinds of branch types, the concentrations of P, K, and Mg in the leaves of two rootstocks grafted navel orange showed decreased tendency with leaf age, and rapidly decrease was observed for P and K concentrations at stage III and early stage IV, but increased at the last sampling point. For Ca concentration in LSP, it was only decreased at the end of stage IV in trifoliate orange-grafted navel orange. In LSP, the concentration of Fe and Mn increased during stage I and II but declined during stage III of navel orange grafted on two rootstocks. Mn concentration was significantly higher in LSP than in LSU and LAU. B concentration in LSP increased during stages I and IV, decreased during stages II and III. n concentrations decreased during stage I and increased during stage IV, and they were generally similar in the leaves of all branch types. The concentration of Mo decreased from a maximum just after stage I to a minimum at stage II and then remained steady from stage II to IV in LSP. There were strong positive correlations among P, K, and Mg in all branch types. Principal component analysis revealed that the mineral nutrients in LSP were particularly important than LSU and LAU for navel orange trees. Overall, the results of this study provide new insights for development of precision fertilization in citrus production.