Nitrates in Petioles of Three Cottons1

Three cotton strains, Gossypium hirsutum L., were grown with two N levels, 56 (soil applied) and 86 kg N/ha (56 kg/ha soil applied plus 30 kg/ha foliar applied). Foliar applications were based on results from petiole nitrate monitoring. The primary objective was to determine if petiole nitrates and phosphorus levels were affected by cotton strains. We chose three cottons which we knew were different in leaf area and rate of fruiting. Significant differences among ‘Stoneville 213,’ Stoneville 817 frego, and Stoneville 7A nectariless, okra leaf were found for levels of petiole nitrates and P when monitored for 11 weeks during the growing season. No significant differences in levels of petiole nitrates or P were found between two levels of N. There was a significant cotton strain by week interaction for petiole nitrates but not P. Petiole nitrates ranged from 310 to 16,000 ppm during the sea‐son. There was a significant increase in lint yields at the second harvest in foliar‐fed plots and an increase of 47 kg lint/ha in total yield. However, total llnt yields were not significantly different between the two levels of N or among the three strains. Yields ranged from 981 to 1,010 kg lint/ha for the three strains. Strains did not respond differently to the two N levels. Follar feeding did not affect boll size or lint percent. These data illustrate some of the inherent difficulties associated with the use of petiole nitrate monitoring as a useful tool for assessing N application.