Yield response of cotton to foliar nitrogen as influenced by sink strength, petiole, and soil nitrogen

Foliar-nitrogen (N) fertilization based on petiole nitrate concentration du ring boil development is a widely used production practice in cotton. The o bjectives of this study were: (1) to examine the response of cotton plants to foliar-N fertilization based on petiole N, two bell loads (low and high) , and two soil-N levels (low: 55kg N ha(-1); high: 110kg N ha(-1)), and (2) study the effect of soil-N levels on petiole characteristics of the leaf p ositioned fourth from the top of the canopy. High boil load plants in both soil-N levels had significantly greater yield than low boil load plants. Al so, the foliar-N sprays in high boil load plants out yielded the nonfoliar- sprayed high boil load plants grown in high soil-N, as well as, low and hig h boil load plants growing in low soil-N. Petiole lengths of big leaves in low and high soil-N levels were significantly greater than that of small le aves. The same was true for petiole diameter. Petiole diameter, leaf area, and chlorophyll content of small and big leaves from high soil-N levels wer e significantly greater than in the low soil-N level. Petiole dry weight wa s similar between low and high soil-N levels, whereas the boil dry weight w as significantly greater in the high soil-N level than in the low soil-N le vel. High soil-N resulted in greater petiole NO3 concentration than the low soil-N. These findings suggested that although petiole characteristics var ied between low and high soil-N levels, the size of the sink determined the plants need for additional N, and therefore, governed plant response to fo liar-applied N.