Department of Plant Sciences

Foliar application of N to cotton (Gossypium hirsutum L.) is a common practice, but there is a lack of published information concerning the absorption and translocation of the N by the cotton plant. Field studies were conducted to study the characteristics of the cotton leaf cuticle, the effects of water deficit stress, and the absorption of foliar-applied nitrogen. Water stress increased the cuticle thickness by 33% and also changed the qualitative composition of cuticular waxes to more long chain molecular waxes of greater hydrophobicity that reduced fertilizer absorption. The thickness of the leaf cuticle increased with leaf age and this was correlated with a decrease in absorption of foliar-applied 15N-urea. Applications made either late afternoon or early morning were more effectively absorbed than those made at mid-day, and this was more pronounced for water-stressed plants. Foliar-applied urea N was rapidly taken up by the sympodial leaf, with 30%, 47% and 70% recovery within 1 h, 24 h and 192 h after application, respectively. Rapidly developing fruits were the major sinks for foliar-applied N with the boll closer to the site of application being the strongest sink. The percentage of 15N recovered in the petioles, bracts, branches, main-stem leaves was negligible. These studies showed that foliar-applied urea is readily absorbed by the cotton plant and translocated to the closest developing fruit.