Influence of surfactants on potassium uptake and yield response of cotton to foliar potassium nitrate

Abstract

Abstract Foliar potassium (K) applications are intended to supplement soil K uptake, and thereby, increase cotton (Gossypium hirsutum L.) yields. Considerable research has been conducted to evaluate yield response to foliar K, but research evaluating surfactant effects on foliar uptake has been limited. Research was initiated in West Tennessee in 1991 to evaluate effects of foliar applied potassium nitrate (KNO3) with and without surfactants on leaf and petiole K concentrations and on lint yield. Field research was conducted on three sites over a four year period using upland cotton ‘DPL 50’. Treatments included a check (no foliar treatment), 4.1 kg K/ha in water, 4.1 kg K/ha with Penetrator Plus, 4.1 kg K/ha with X‐77, 2.0 kg K/ha with Penetrator Plus, and 2.0 kg K/ha with X‐77. Surfactants were added to KNO3 solutions at 1.25% v/v for Penetrator Plus and 0.5% v/v for X‐77. Kinetic was substituted for X‐77 after 1991 and was applied at 0.12% v/v. Cotton leaves and petioles were collected one, three, and seven days after each foliar application for K concentration determinations. Applying 4.1 kg K/ha (high‐K rate) as KNO3 in water increased four‐year average leaf K but not petiole K concentrations in tissue collected 24 h after treatment relative to the check. Applying the high‐K rate with a surfactant increased the four‐year average concentration of leaves and petioles collected one, three, and seven days after application relative to the check or to the high‐K rate applied with water. Increases in both leaf and petiole K concentrations varied with year, with significant increases in two of the four years of the study. Yearly K concentrations of the day‐one and day‐three petioles were higher after applying the high‐K rate with Penetrator Plus relative to the check. Petiole K was not increased by applying low‐K rates with surfactants or the high‐K rate in water. First harvest lint yields were generally unaffected by foliar treatments. Second harvest and total yields were increased by applying the high‐K rate with Penetrator Plus relative to the other treatments. Yield responses may have been due in part to the nitrate anion (NO3‐) being applied with the K+ cation, but higher K concentrations generally accompanied higher yields. These results suggest that surfactants may enhance K uptake and yield, but that more research is needed to determine why responses vary from year to year.