MSc.

The study on “Characterisation of coconut palms (Cocos nucifera L.) showing general yellowing” was undertaken in selected coconut palms coming under Thiruvallam of Thiruvananthapuram district from March 2016 to March 2017. The objective was to evaluate the field characteristics and nutritional status of soil and coconut palms showing general yellowing and to formulate a management strategy.
Coconut palms of variety WCT showing general yellowing which advance from lower to upper whorls of leaves were identified from farmer’s field of Thiruvallam. Fifteen palms showing uniform pattern of general yellowing and five healthy palms were selected from five farmer’s fields. Field, soil, plant and management practices followed by farmers were studied in the selected palms to identify the pre disposing factors leading to general yellowing.
Observations on morphological and yield characteristics of selected coconut palms were recorded for one year at 60 days interval. Soil and plant samples were collected and analysed for macro and micronutrients. Based on soil test results the quantity of deficient macro nutrients were calculated and applied as per package of practices recommendation of Kerala Agricultural University. The soil and plant sample was again analysed six months after the application of fertilisers.
Data generated on field characterization revealed the type of soils as red loam soils with good drainage in all the selected coconut palms. High soil organic matter was seen in all the healthy coconut palms while eighty percentage of coconut palms showing general yellowing were under medium status of organic matter. Of the coconut palms showing general yellowing, fifty three percent belonged to the age group of 31-35.The disease and pest incidence in the healthy palms was only twenty percent while it was more than fifty percent in palms showing general yellowing.
The morphological, physiological and yield parameters of selected palms indicated significant variation in number of leaves showing yellowing, chlorophyll content, membrane integrity, relative water content, number of bunches, number of female flowers per bunch of inflorescence, number of nuts set per bunch, weight of nut, weight of copra and oil content in coconut palms showing general yellowing compared to healthy palms. However after the application of nutrients significant increase in chlorophyll a content, total chlorophyll content, membrane integrity and relative water content was noticed in coconut palms showing general yellowing.
The soil and leaf nutrient analysis revealed a significant variation in N, P, K, Ca, Mg, S and B content between coconut palms showing general yellowing and healthy palms. However, observations made at six months after the application of manures and fertilisers revealed a significant increase in soil pH, organic carbon, N, P, K, Ca, Mg, B and Cl in the soil and N,P,K of index leaf of coconut palms showing general yellowing. There was no significant variation in the S, Fe, Mn, Zn and Cu before and after the application of manures and fertilisers.
The present study based on nutritional status and visual symptoms revealed that low soil nutrient status of N, P, K, Ca and Mg have resulted in the general yellowing in coconut. The application of fertilisers as per average management recommended by KAU (2016) could only enhance the soil N, P, K and Mg status to medium level while for calcium it still remained in low status. Thus a higher dose of N, P, K, Ca and Mg are required for the palms showing general yellowing to substantially improve the nutritional status of the palm.