Cotton Leaf Age, Epicuticular Wax, and Nitrogen-15 Absorption
- Bhaskar R. Bondada ,
- Derrick M. Oosterhuis and
- Richard J. Norman
Foliar N fertilization is sometimes used as a supplement to soil application in cotton (Gossypium hirsutum L.) production; however, information is lacking about the absorption of foliar-applied N in relation to leaf age and epicuticular wax. A 2-yr field study was conducted to examine the effect of leaf age and epicuticular wax on foliar-applied 15N-urea absorption and subsequent distribution within the subtended boll. Cotton (cv. Stoneville 506) leaves of different ages (20, 30, 40, and 60 d), at main-stem node 10, fruiting position 1, were selected and treated with 15N-urea solution using a paint brush. The 15N analysis of tissues 1 wk after treatment indicated that maximum absorption of 80% was achieved by 20-d-old leaves compared with 27 to 38% for 60-d-old leaves. As the leaves aged, 15N absorption decreased in concert with increased total wax concentration. A negative relationship between 15N absorption and total wax concentration of leaves of different ages (r2 = 0.97) suggested waxes were an important barrier to 15N absorption in older leaves. The subsequent translocation and distribution of 15N within the boll indicated that most of the absorbed 15N was retained in the 20-d-old leaf. As the leaves aged, more 15N was translocated to the subtended boll. Within the boll, most of the 15N was compartmentalized to lint and seed, and less was partitioned to the capsule wall, which implicated lint and seed as the major sinks. This study demonstrated that increased wax concentration during leaf aging was associated with reduced 15N absorption.
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