The most convenient and economical way to apply nitrogen (N) for cotton is as a single application at the preplant or early seedling stage. However, split applications of A may be more practical than single early applications when soil and environmental conditions favor N loss by leaching or denitrification, where nitrate salt damage to cotton seedlings tends to occur, or when it is expedient to adapt fertilization to other management inputs. Mid- to late-season applications of supplemental N, in addition to the recommended rate, may also be used to compensate for N that is lost from the soil or to accommodate a greater than-normal cotton yield potential. Field trials were conducted to measure the efficiency of N applied at different times from preplant to seven weeks after the initiation of flowering.

Three-year field studies were conducted on Rilla silt loam (Fine-silty, mixed, thermic Typic Hapludalfs) and on Calloway silt loam (Fine-silty, mixed thermic Glossaquic Fragiudalfs) in which N was applied at the rate of 75 pounds per acre all preplant and in split applications. The split applications were in increments of 25 pounds of N per acre at the 1) preplant, 2) seedling, 3) squaring, and/or 4) flowering stages. All N treatments increased yields compared to no N, but there were no significant differences among yields produced by treatments in which at least 25 pounds of N were applied at the preplant or seedling stage. During one year, yields were lower where all N was applied in the squaring and flowering stages than where all N was applied preplant. Reduced efficiency of the later N applications appeared to be associated with drouth stress. These results indicate that one-third to onehalf of the soil-applied N for cotton should be applied in the preplant or seedling stage and that the remainder may be effectively applied as late as the second week flowering.

On Calloway silt loam, foliar applications of 5 to 1 pounds of N per acre were applied to N-deficient cotton at weekly intervals from two weeks after emergence through the seventh week of flowering. Foliar nitrogen that was applied from too weeks after emergence to the third week of flowering increased yields by an average of 6.3 pounds of lint for each pound of N applied. Foliar Applications of N during-the fourth, fifth, six and seventh weeks of flowering increased yields by 5.3 pounds of lint for each pound of N applied. These yield responses to foliar-applied N are similar to yield responses commonly obtained with soil applied N.

We conclude that cotton yields may be increased efficiently by N that is applied as needed from preplanting through the seventh week of flowering.