Deficiencies of major plant nutrients in the soil of different coconut growing areas in Sri Lanka have directly affected the growth and yield of the coconut tree. Through special features seen in coconut twigs severe deficiencies in essential nutrients could be detected.
However, studies have shown that in some cases coconut twigs may not show symptoms but could have nutrient deficiencies. Chemical analysis of parts of the coconut tree can confirm these deficiencies, which are invisible to the naked eye or not easily recognized.
Symptoms that can be identified with the naked eye
1.Nitrogen – N
Nitrogen deficiency is usually caused by insufficient soil nitrogen. In the early stages of nitrogen deficiency, all the (Matured) branches of the trunk appear light green. In this way, as the deficiency gradually increases, the limbs turn yellow.
NB – Similar symptoms can occur due to soil dependent water content, severe drought, etc.
Correspondingly, when the deficiency is high, the light green coconut leaves tend to turn yellow and the trunk circumference becomes smaller and the trunk gradually narrows. At this point, the coconut twigs in the lower part of the tree turn golden and then reddish gray, eventually dying.
*Remedies for Nitrogen Deficiency
• If the application of fertilizer has been stopped for a while, it is advisable to apply the recommended fertilizer mixture for coconut trees and coconut seedlings. (Refer to our web page for recommended fertilizer mixtures)
• If the deficiency persists even after application of fertilizer, in addition to the recommended fertilizer mixture, it is recommended to apply 200 gm of urea per year on an adult tree and 100 gm of urea per plant per year.
It is advisable to apply fertilizer every year till the symptoms of malnutrition disappear.
2.Potassium – K
Potassium deficiency can be seen first in the matured coconut branches of the coconut tree. In this case, rust-coloured spots appear all over the coconut leaf on both sides of the line. At this stage, the coconut leaves appear slightly yellow from a distance and the yellow tinge increases towards the tip of the leaf.
Over time, these rusty spots gradually enlarge and become pale. Then you can see the dry burnt nature of the ends of the coconut leaves. At this stage the branches of the trunk are yellow and the branches of the lower level of the tree are in orange colour. As deficiency increases, all the branches on the trunk become smaller and orange-yellow in color, and thinning of the trunk is also a common feature.
*Remedies for Potassium Deficiency
• If the application of fertilizer has been stopped for a while, it is advisable to apply the recommended amount of dolomite with the recommended fertilizer mixture (500 gm) on coconut trees and coconut seedlings. (Refer to our web page for recommended fertilizer mixtures).
• If the deficiency persists even after application of the fertilizer, it is recommended to apply 500 g of Muriate of Potash as an additional dose to the trees in addition to the recommended fertilizer mixture and dolomite.
3.Magnesium – Mg
A special feature of magnesium deficient coconut trees is the yellowing of the mature coconut branches. When observing coconut leaves, they appear light yellow, with two green stripes on either side of the eakle. Similarly, the green leaf remains on the sides of the stalk of the coconut leaf, as the leaf remains near the base of the leaf (the leaf, the base part which connects with the coconut leaf).
Over time, the ends of the coconut leaves become dry and look burnt. When the deficiency is mild or moderate, yellowing of the trunk and the gradual increase in intensity can be clearly seen in the coconut twigs of the lower level turning yellow.
*Remedies for Magnesium Deficiency
• Covering with straw should be done after applying the recommended coconut fertilizer to half of the fertilizer circle on the fruit bearing coconut trees which are showing magnesium deficiency.
• At the same time, about 1 kg of kesarite is applied to the opposite side of the manure circle (the other half circle which is not fertilized).
• As a long-term remedy to prevent this deficiency, it is recommended to apply 1 kg of dolomite per year on a fruit bearing tree and 500 g of dolomite on a coconut plant every six months with the recommended fertilizer mixture. (This is not necessary)
4.Boron – B
Boron deficiency symptoms can be seen in the young branches surrounding the apical bud of the coconut tree. The coconut leaves on the palm branch are not separated from each other and are bent in a “zigzag” pattern and connected to each other. Occasionally there are short, dense coconut branches without coconut leaves.
When the deficiency is severe, the number of branches of the tree decreases and the tree stops growing as the apical bud turns black, eventually causing the tree to die. Boron deficiency affects the inflorescence and the fruit and causes the inflorescence and the fruit to rot.
*Remedies for Boron Deficiency
Deficiency can be corrected by treating the initial stage of the deficiency.
• For this, 10 g of sodium tetraborate should be applied to seedlings and 20 g of mature coconut trees every 6 months. It is recommended to apply sodium tetraborate until the symptoms disappear. Thereafter, proper watering can speed up the results.
5.Phosphorus – P
Common in acidic and alkaline soils. With deficiency the leaves turn purple and the coconut tree shows slow growth. Immature coconut leaf shedding occurs primarily and indicates reduced growth, size and number of leaves.
*Remedies for Phosphorus Deficiency
• If the application of fertilizer has been stopped, it is advisable to apply the recommended fertilizer mixture. (Refer to our web page for this)
• If there is still a shortage even after the application of fertilizer, it is important to seek advice from the Coconut Development Officer in the area.
In cases where deficiency symptoms are caused by more than one nutrient, the above symptoms may not match with the descriptions given. In such a case it is important to seek advice from the Coconut Development Officer in the area.