Canopy development and photosynthesis of cotton as influenced by nitrogen nutrition

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Abstract
Nitrogen (N) nutrition influences various important developmental and physiological processes in agricultural crops. However, the extent to which these processes are limited by N deficiency is unclear. Field experiments were conducted to document the effects of N nutrition on photosynthesis, canopy growth, and yield of cotton (Gossypium hirsutum L.). Nitrogen deficiency limited dry matter accumulation of leaves, stems and bolls. Total dry weight of N‐deficient plants was significantly reduced by 7% at 76 days after planting (DAP) and by over 18% at 118 DAP. Leaf area index (LAI) of N‐deficient canopies was significantly decreased at 76 DAP, with an LAI at 118 DAP of 2.5 versus 3.6 for N‐sufficient plants. Single‐leaf expansion was limited by N deficiency with decreased growth rates at 5 days after leaf unfolding and reductions in individual leaf areas exceeding 25% at leaf maturity. Despite these growth limitations, photosynthesis, transpiration, and stomatal conductance of upper‐canopy leaves were not affected by N deficiency. Whole‐canopy photosynthesis, when expressed on a leaf area basis, was increased in N‐deficient plants due to better light distribution associated with a reduced LAI. Canopy photosynthetic rates per unit ground area were similar between the two N treatments.