Canopy photosynthesis, growth, yield, and bell N-15 accumulation under nitrogen stress in cotton

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 bell N-15 accumulation from foliar-N-15 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 late-season canopy photosynthesis, growth, yield and foliar applied-N-15 accumulation by bells 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, bell number, and dry weights of leaf and bell 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 bell N-15 accumulation from foliar fertilization, three foliar-N sprays with the last foliar-N spray consisting of N-15 was applied in each pre-plant fertilizer N regime. The middle canopy bells accumulated significantly more N-15 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 N-15 accumulation by bells positioned in different portions of the canopy.