YIELD RESPONSE OF COTTON TO FOLIAR NITROGEN AS INFLUENCED BY SINK STRENGTH, PETIOLE, AND SOIL NITROGEN

Abstract

Foliar-nitrogen (N) fertilization based on petiole nitrate concentration during boll development is a widely used production practice in cotton. The objectives of this study were: (1) to examine the response of cotton plants to foliar-N fertilization based on petiole N, two boll loads (low and high), and two soil-N levels (low: 55 kg Nha−1; high: 110 kg N ha−1), and (2) study the effect of soil-N levels on petiole characteristics of the leaf positioned fourth from the top of the canopy. High boll load plants in both soil-N levels had significantly greater yield than low boll load plants. Also, the foliar-N sprays in high boll load plants out yielded the nonfoliar-sprayed high boll load plants grown in high soil-N, as well as, low and high boll 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 leaves. The same was true for petiole diameter. Petiole diameter, leaf area, and chlorophyll content of small and big leaves from high soil-N levels were significantly greater than in the low soil-N level. Petiole dry weight was similar between low and high soil-N levels, whereas the boll dry weight was significantly greater in the high soil-N level than in the low soil-N level. High soil-N resulted in greater petiole NO3 concentration than the low soil-N. These findings suggested that although petiole characteristics varied 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 foliar-applied N.