Authors:

Abstract

Coconut Rapid Decline (CRD) is a serious disorder of coconut palms
(Cocos nucifera L.) in Sri Lanka. A substantial loss of crop is well evident
due to this disorder. This study aims to determine the effect of micronutrients
and common salt on the performance of CRD-affected palms.
Fifteen-years-old, mild, moderate and severe CRD-affected palms, in
Makandura Research Station (MRS) of Coconut Research Institute were
used for this study. Affected palms were treated with the micro-nutrients
(100 ml of 0.35 % CuS04.5H2 0 and 0.72 % ZnS04.7H2 0 solution/palm, root
feeding at bi-monthly intervals) or common salt (NaCI, 1 kg/palm/year,
surface application in the manure circle). Untreated CRD-affected palms
were used as the control. Leaf nutrient levels before, one and two years
after treatment application were analyzed. Vegetative, reproductive and
physiological parameters were measured during two years, after treatment
application.

Pre-treatment analysis of leaves revealed that Nitrogen (N) and Phosphorus
(P) contents were within the sufficiency range and Potassium (K) content
was above the sufficiency range in CRD-affected palms. Magnesium (Mg),
Calcium (Ca), Sodium (Na), Copper (Cu) and Zinc (Zn) contents of those
palms were below the sufficiency range. The macro and micro-nutrient
contents (except Mg) of apparently healthy palms, adjacent to CRD-affected
palms were within the sufficiency range for coconut. Therefore, it is
suggested that the CRD-affected palms suffer from deficiency of Ca, Na, Cu
and Zn. There was a significant difference in Iron (Fe) content among three
severity stages of CRD-affected palms before initial treatment application,
Fe concentration increased with increasing severity.

Phosphorus and Ca contents significantly increased in micro nutrient and
common salt treated palms after one year, compared to before treatment
application and control. However, there was no significant increase in leaf
Cu, Zn and Na levels, even after two years of the treatment application. The
percentage of drooping fronds, size of the spadix, number of female flowers,
number and size of nuts and circumference of the trunk were not improved
in treated palms one year after treatment. Two years after the treatment, number of total fronds and functional green fronds in the canopy of affected
palms were increased by common salt application. The stomatal diffusive
resistance of these palms was also reduced after two years showing an
improvement in palm water status. The experiment is in progress to.
observe the recovery of symptoms.