RAMBUTAN LEAF ANALYSIS
SCIENTIFIC NAME: Nephelium lappaceum
FAMILY: Sapindaceae
Leaf analysis is an important tool for understanding the nutrient needs of crops. It is particularly valuable in tree crops. Unfortunately, we are not yet in a position to offer rambutan growers critical levels at particular times of the year.
Unlike lychee which is very seasonal, we cannot yet predict the flowering time of rambutan precisely - either as a single crop or partial crops over many months. We need to understand the role of nutrition both in tree health and in its effects on flower initiation and successful fruit development.
Obviously we need to be able to provide good leaf cover on the tree, in order to maximise production but not to provide elements in excess, which for nitrogen may or may not delay flowering and cause excessive fruit drop at the seed hardening stage.
WHAT WE KNOW
We have done limited surveys of properties in mid-summer, but need more, and particularly in the June/July period after summer leaf flushes and before flowering, except of course some trees may harvest in the autumn/winter, which presents a different scenario.
NUTRIENT REMOVAL
Malaysian records document that for a 7.36 tonnes of fruit/ha harvest (fruit and stems), the following quantities of nutrients are removed: Potassium 15 kg, Phosphorous 2 kg, Potassium 11.7kg, Calcium 5.9kg and Magnesium 2.7kg. We need to replace these to maintain tree health. We also need to add nutrients to counteract leaching and runoff losses.
CRITICAL LEAF LEVELS FOR NUTRIENTS
A preliminary assessment of leaf levels (taken from the last fully mature leaflets on branch tips) in north Queensland are shown in Table 1. A recommended range based on overseas literature and comparisons with other crops is also presented. Marginal leaf necrosis and leaf loss in winter and spring is most often caused by too much chloride. Fertilisers containing muriate of potash (or any chloride) should not be used on rambutans. Potassium nitrate and potassium sulphate are suitable.
TABLE 1. Suggested range of leaf nutrient levels for Rambutan
| Element | Survey (1) | Suggested (2) | |
| N | % | 1.5 - 2.5 | 2.0 - 2.5 |
| P | % | 0.14 - 0.26 | 0.2 - 0.3 |
| K | % | 0.4 - 0.8 | 0.7 - 0.9 |
| Ca | % | 0.7 - 1.5 | 0.25 - 0.35 |
| Mg | % | 0.18 - 0.37 | 0.25 - 0.35 |
| Cl* | % | 0.11 - 0.4 | below 0.2 |
| Fe | % | ppm | 35 - 81 |
| Mn | ppm | 180 - 1125 | 60 - 100 |
| Zn | ppm | 20 - 34 | 30 - 35 |
| Cu | ppm | 9 - 105** | 10 - 15 |
| Na | ppm | 34 - 269 | ? |
| B | ppm | 19 - 49 | 40 - 50 |
(1) Suggested mean ranges from four cultivars on four properties, January 1986.
(2) Suggested tentative range required before flowering.
* Data from a separate survey from properties with and without muriate of potash application and trees with and without leaf 'burn'.
** High range may be applied Cu not adequately washed off.
DATE: January 1992
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