Florida’s environment is often hot and humid when cotton is defoliated in the fall. This may result in high levels of hard locked bolls that can not be harvested. Nitrogen is often implicated in creating conditions that result in high levels of hard locked bolls and boll rot. Four rates of N (0, 60,120,and 180 lbs./A) were applied at three different timings (all at plant, or 1st square, or 3rd week of bloom). Studies were conducted in 1999 and 2000 at the University of Florida, NFREC in Quincy, FL. Yields were typically lower with the 180lbs. of N, and when applied the 3rd week of bloom for all rates of N in treatments harvested with a spindle picker. Yield, plant height and boll number were usually highest when N was applied at first square. Yield from plots with 180lbs. of N applied at third week of bloom was similar to no N in both years of study. In both years, 0 N gave a similar yield as any N treatment applied at any time. Highest N rate applied late and at planting in another year resulted in lowest yield. Soil test of nitrates showed that as much as 60 lbs./A of residual N was available to the cotton crop and was probably adequate for top yields under environmental conditions present at boll opening. Most hard locked bolls did occur under highest N rates applied the third week of bloom. These data indicate that knowledge of residual soil N and moderate rates of N applied at squaring is best for top yield and reduced hard lock. Messenger, a plant health material, applied 4 times after squaring reduced hard lock by 41% while increasing boll number by about 15%. Because hard lock has often reduced yield by more than 50%, research needs to be done to determine management to further reduce it’s incidence.

One day prior planting 100 lbs/A of 0-0-60 N-P _2O5-K2O fetilizer was broadcast applied on the entire study. Deltapine DP 458 BRR cotton was planted in UNR (7" row spacing) at 120,000 seeds/A with a Great Plains No-till Drill and conventional rows (36" row spacing) strip tilled at 4 seeds/ft of row with a Brown Ro-till implement and KMC planters on late May to early June each year.

Cotton was broadcast sprayed with Cotoran @ 1 qt/A + Prowl @ 1 qt/A + Gramoxone @ 1.5 pt/A + Induce @ 1pt/100 gal immediately after planting each year, Roundup Ultra @ 1 pt/A was applied each year at 2nd and 4th node stage on cotton and, and Staple @ 1 oz/A + Induce @ 1 qt/100 gal. was applied about 6 weeks later.

All nitrogen treatments were applied according to the schedule (at plant, 1st square, and 3rd wek of bloom). Cotton was irrigated on an as need basis each year and each of the three years were dry years.

The studies were defoliated with Finish @ 1 qt/A + Dropp @ 0.2 lb/A when 60% of the crop was open. Cotton was picked by hand or with a modified cotton picker to determine amount of hard lock or unpickable cotton. At defoliation 5 plants were selected from each plot and the height and boll number was determined to determine if the treatments affected boll positioning within the plant canopy.

The study was Two Factor Completely Randomized Block Design with four replications. Analysis of Variance and the Least Significant Difference Test were calculated at 5% probability level.