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Canopy Photosynthesis, Growth, Yield, and Boll ¹⁵N Accumulation under Nitrogen Stress in Cotton

Citrus Res. and Education Center, Univ. of Florida, 700 Experiment Station Rd., Lake Alfred, FL 33850

D. M. Oosterhuis and R. J. Norman

Univ. of Arkansas, Dep. of Agronomy, Fayetteville, AR 72701

W. H. Baker

Cotton Branch Exp. Stn, P.O. 789, Marianna, AR 72360

^* Corresponding author (brbo{at}gnv.ifas.ufl.edu).

Comprehensive knowledge concerning the influence of pre-plant fertilizer N rates on canopy photosynthesis, growth, and yield of cotton (Gossypium hirsutum L.) is lacking, while no research has been conducted on boll ¹⁵N accumulation from foliar-¹⁵N fertilization. Field studies were conducted on long-term N fertilizer plots on Loring silt loam (fine-silty, mixed, thermic Typic Fragiudalt) to investigate how varying levels of pre-plant fertilizer-N applied to soil affected lateseason canopy photosynthesis, growth, yield and foliar applied-¹⁵N accumulation by bolls in the top, middle, and bottom portions of the canopy. Four pre-plant soil incorporated fertilizer N treatments were imposed: 0, 55, 82, and 110 kg N ha^-1. Plant height, number of main-stem nodes, and first fruiting branch node were increased by increasing soil-N regime. Leaf number, leaf area, boll number, and dry weights of leaf and boll were higher in the middle of the canopy than in the top or bottom portions. Lint yield was strongly associated with soil N and canopy photosynthesis, and the photosynthetic capacity of the canopy was proportional to availability of N. To determine boll ¹⁵N accumulation from fofiar fertilization, three foliar-N sprays with the last fofiar-N spray consisting of ¹⁵N was applied in each pre-plant fertilizer N regime. The middle canopy bolls accumulated significantly more ¹⁵N than those in the upper or lower canopy. This study extended previous cotton N studies by showing that yield differences due to N can largely be explained by variation in canopy photosynthesis and plant size, and provided new information on differential ¹⁵N accumulation by bolls positioned in different portions of the canopy.

Received for publication September 30, 1994.