Leaf age and position on mineral composition of mangosteen leaves

Before leaf analysis can be successfully used as a guide in diagnosing nutritional status and as a basis for fertilizer recommendations in fruit trees, a standardized leaf sampling technique must be established. Position of sampled leaves and time of sampling are the most important factors in ascertaining the nutritional status of fruit trees. The sampling should be done when the variation in nutrient concentration is minimum during the period of plant development. The present study on mangosteen is directed toward the objective above. Mineral nutrient concentrations in mangosteen leaves were investigated at three mature orchards and one experimental plot in Chantaburi province, Eastern Thailand. Fifteen uniform and representative mangosteen trees from each orchard were sampled monthly and nutrient concentrations of N, P, K, Ca, Mg, Fe, Mn, Cu and Zn in their leaves were analyzed. The leaves sampled were the only pair of leaves from the current flush started when they were two months old (December 2000). At the first sampling date, the effects of 4 leaf directions (North, East, West, South) and two branch positions on the tree canopy, lower (1-2 m height) and middle (3-4 m height), on leaf mineral composition were investigated. Thereafter, leaves from all four directions were pooled to create one sample for each tree. The sampling continued until November 2001. As leaves matured, concentration of N and P decreased. The concentration of K also decreased with leaf age especially during fruit development (January April). Then, the K concentration increased slightly before it again decreased. Concentration of Ca increased slightly at the beginning of the sampling period and gradually decreased while Mg changed only slightly throughout the sampling period. In contrast, concentrations of Fe and Mn increased with leaf age, but the patterns of the two elements were slightly different. Zn was rather stable except at some sampling dates due to foliar Zn spray. Fluctuations in Cu concentrations were observed during the growing season due to pesticide spray. The effects of leaf direction were observed in N, K, Ca and Mg. On the other hand, K is the only nutrient that was significantly influenced by the position of leaves on the tree canopy. However, the differences among nutrients found at different positions were relatively small. Seasonal variations in mangosteen leaf nutrient concentrations are similar to those of other tree crops but the concentration of most nutrients were relatively low compared to other fruit trees growing in the same soils. Minimum variations in nutrient concentrations in mangosteen leaves occurred over a wide range of sampling dates. However, considering the practical time for both growers and service laboratories, it is suggested POOVARODOM ET AL. 17 WCSS, 14-21 August 2002, Thailand 2272-2 that mangosteen leaves should be sampled for diagnostic purposes when leaves are 8-10 months old, which is usually after fruit harvest.