Quantification of Foliar Nitrogen Uptake By Cotton Leaves with Time.

The use of foliar-applied nitrogen (N) fertilizers in cotton (Gossypium hirsutum L.) production can be beneficial towards overcoming N deficiencies as well as increasing overall yields. However, the rates over time at which these foliar-N fertilizers can penetrate or be lost from cotton leaves are less understood. Experiments were conducted in 2014 in a controlled climate growth chamber at the University of Arkansas in Fayetteville, AR. In the first trial, foliar-N treatments consisted of: (1) a no foliar-N applied control; (2) foliar urea; and (3) a slow-release foliar-N fertilizer Nitamin^®, all applied at rates equivalent to 10 lbs N/acre. Measurements of the amount of foliar-N lost in rinsate samples and by ammonia (NH₃) volatilization were collected at time intervals of 1, 6 and 12 hours after foliar applications and used to determine the amount of foliar-N either absorbed and/or adsorbed by cotton leaves. In the second experiment, foliar-N treatments consisted of: (1) a no foliar-N applied control; (2) foliar urea; (3) Nitamin^®; and (4) foliar UAN 32, all applied at rates equivalent to 10 lbs N/acre. Measurements of the amount of foliar-N lost in rinsate, NH₃ volatilization and by adsorption to the cuticle wax were collected at sampling times of 4, 8 and 16 hours after foliar applications. In the first experiment, Nitamin had a significantly higher percentage of total N (%TN) absorbed and/or adsorbed by cotton leaves over foliar urea at all sampling times; most likely the result of foliar urea treated leaves losing the majority of foliar-applied N via rinsate off of the leaf surface. In the second experiment, Nitamin and UAN 32 had a significantly higher %TN absorbed in cotton leaves than foliar urea at 4 and 8 hours after foliar applications while no significant differences were observed at 16 hours. Similar to the first experiment, the major foliar-N loss mechanism for foliar urea was through rinsing while UAN 32 lost significantly more foliar-applied N via NH₃volatilization than Nitamin and foliar urea respectively. These results demonstrate the variability of different foliar-N fertilizers regarding their respective N loss pathways along with their relative effectiveness in cotton leaf uptake potential.