The chemical and physical nature of the Leaf Surface Of Coffee Arabica L. with Special Reference to its significance in Foliar Nutrition
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A study has been made of the chemical and physical nature of the leaf surface of Coffea arabica L., with special rererence to foliar nutrition. Glasshouse and field-grown plants of cvs.SL28/5134 were used far the investigation. The coffee leaf was found to have an epicuticular wax level which varied from 0.01 mg/cm2 in the young leaf (3rd leaf pair) to 0.05 mg/cm2 in the mature leaf (6th leaf pair). The adaxial surface cuticular membrane weighed 0.17 mg/cm2 in both young and mature leaves, while t he abaxial membrane varied in weight between 0.07 and 0.13 mg/cm2 be twe en young and mature leaves. The occluded wax amounted to 0,02 and 0.01 mg/cm'- for the upper and lower cuticular membranes of younq Leave s, but increased to 0.06 and 0.07 mg/cm2 for the upper and 1ower membrane of mature leaves The principal constituents of both epicut i cuLar and occltded waxes were n-alkanes (major homologues n-C29 and E,-C31), pri.mary alcohols (major homologues n-C30 and n.-C32)' Cutin from coffee leaf contained at least 60% 10,16-dihydroxyhexadecanoic acid and its isomers, the next most important constituent being monohydroxy-l,16-dioic acid and its iomers. C14t CIS and C18 hydroxyfatty acids as well as small amounts of n.onobasi c acids• and alkan-l-ols were also identified • The leaf surfaces of field-grown coffee plants were undulating in nature and had a granular wax cover, which when viewed under the scanning electron microscope was denser on mature than on young leaves. No leaf hairs or trichomes were observed on coffee leaves. The cuticular membranes of coffee Leaves exhibited well-developed V-shaped subcutaneous ridges. Continuous cuticular linings were observed in stomatal cavities. The cation exchange capacity of coffee leaf varied between 7 and 11 ME./IOO g dry cuticle. higher CEC. thanlmature leaves. Absorption Of 32 p by leaves of coffee seedlings was affected by ratio, 2nd a ratio of between 1 and 5 was found to be most favourable for absorption Under non-deficiency conditions, nutritional status did not affect .foliar uptake of 32p by leaves of cropping coffee trees. Uptake of 32p through the upper leaf surfaces was greater in old (mature) than in young leaves. It was concluded that the coffee leaf possessed characteristics both favourable to vet t inq (smooth surface, non-crystalline wax cover) and unfavourable (high content of alkanes and tri terpenoids in wax).Foliar uptake experiments shoved good prospects for foliar application of P in coffee. '