Vol. 81 No: 2

Title:
Cuticular penetration characteristics of urea in citrus leaves

Authors:
BHASKAR R. BONDADA, PETER D. PETRACEK, JAMES P. SYVERTSEN and L.G. ALBRIGO

pp: 219-224

Abstract:
Recent interest in reducing nitrate levels in ground water has stimulated a re-examination of the potential use of foliar applications of urea on citrus trees. We examined the penetration characteristics of urea through isolated cuticles in relation to their thickness and surface wax content in citrus (Citrus paradisi Macf.) leaves using a finite dose-diffusion system. Isolated cuticles with the greatest integrity were mounted on diffusion half-cells with the inner morphological surface in contact with citrate buffer solution. ¹⁴C-urea in citrate buffer was applied to the outer wax-rich morphological surface and the penetration of urea was monitored by repeated sampling of the receiver solution. Urea penetration through cuticles exhibited an asymptotic curve characterised by an initial lag phase of about 10 min, a quasi-linear phase of maximum penetration rate, averaging 2% of the urea applied h^-1, occurred about 40 min after urea application, followed by a plateau phase during which the rate of penetration approached zero at 144 h. Total urea penetration averaged approx. 35% and tended to decrease with increased cuticle weight until the cuticles were 6 months-old. Re-hydration of the urea deposit, with water, stimulated additional penetration of about 1%; however, this was not significant. Epicuticular wax occurred as platelets that increased with leaf age. Dewaxing the cuticles significantly enhanced the maximum penetration rates by 30% of the amount applied h^-1 and increased total penetration by 64%. This study provides valuable details on the transport of urea through isolated cuticles which is important in fine-tuning foliar urea fertilisation in citrus trees.

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