Experiments were conducted at Tifton, Georgia from 1981 to 1986 on a Tifton loamy sand and at Midville, Georgia from 1983 to 1986 on a Dothan loamy sand to measure cotton yield response to soil and/or foliar applied N. Nitrogen rates of 0, 30, 60 or 90 pounds of N per acre were applied either as preplant or sidedress using ammonium nitrate (3 .5% N). Beginning one week before bloom, petioles of the most recently mature leaves were collected at weekly intervals from the center rows of 8-row plots. Nitrates were determined using the procedure outlined by Gaines and Mitchell (1). Nitrate-nitrogen data obtained from petioles selected from individual plots were plotted on graphs (Estimated range of sufficient nitrogen) developed by Walker et al (2). If there was a nitrogen deficiency, plots were sprayed with foliar urea (46% N). Adjacent control plots were left untreated.

The 6-year average yield of lint cotton at Tifton was higher where foliar nitrogen was added regardless of soil-applied nitrogen. Those plots which received 30 lb/Ac of N at planting with additional foliar N as needed produced 121 lb/Ac of lint more than those plots which received only soil applied N.

The 4-year average yield of lint cotton at Midville was significantly higher with additional N added to foliage as needed than where either 0 or 30 lb/Ac N was applied at planting.

The data thus far show that cotton will respond to foliar applied N when based on a petiole nitrate monitoring program.