Standard sampling method of Longkong leaf for evaluation of plant nutrient status

Abstract

Leaf analysis is a tool for effective fertilizer recommendations in fruit trees. To achieve this goal, suitable leaf sampling method is a very important step. This study aimed to investigate leaf age, leaflet from different compound leaf positions and number of trees to be sampled as a representative sample for plant nutrient status of Longkong (Aglaia dookkoo Griff.) tree. The middle pair of leaflets from the 1st, 2nd, 3rd, and 4th compound leaves from growing twigs at the lower canopy of Longkong trees were separately sampled and the following nutrients were determined: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg). The effect of soil fertility management and leaf age collected from twigs flushed at flowering and post harvest stages on nutrient concentration was investigated. Results showed that concentrations of plant nutrients in leaflets collected from different compound leaf positions were not significantly different. The leaf nutrient concentration depended on soil fertility management, higher fertilizer input resulting in higher leaf nutrient concentration. As leaf age increased, concentrations of N, P and K tended to decrease. In contrast, concentrations of Ca and Mg increased with leaf age. However, concentrations of most nutrients showed minimum variation with leaf aged 3-6 months. It is, thus, suggested that the middle pair leaflet of the 2nd compound leaf position aged 3-6 months of the lower twig should be sampled at post harvest stage from 25-35 trees to be used as a composite sample for plant nutrient analysis