Defining critical leaf‐ and petiole‐potassium concentrations for monitoring cotton nutritional status

Abstract Plant tissue testing is an effective tool for diagnosing crop nutritional status; however, critical tissue‐potassium (K) concentrations have not been established for modern cotton ( Gossypium hirsutum L.) cultivars. We aimed to define critical leaf‐ and petiole‐K concentrations at various growth stages for optimal cotton production. Nine fertilizer‐K rate (0–187 kg K ha −1 ) trials were conducted in a randomized complete block design on silt loam soils with very low to above optimum soil‐test K in Arkansas, during 2023 and 2024. Leaf and petiole samples were collected from first square through the beginning of boll and fiber maturation, to quantify tissue‐K concentrations. At maturity, cotton lint yield was measured. Lint yield was significantly affected by K fertilization ( p ≤ 0.10) in seven out of nine trials, where the unfertilized control yield was 35%–79% of the yield‐maximizing fertilizer‐K rates (56, 75, and 112 kg K ha −1 ). Leaf‐ and petiole‐K concentrations increased with increasing K availability (soil or fertilization). Tissue‐K concentrations peaked at first square and declined throughout cotton reproductive development. Critical leaf‐ and petiole‐K concentrations to maximize yield were 11.1 and 47.3 g K kg −1 at first square, 10.3 and 48.0 g K kg −1 at first flower, and decreased to 5.1 and 7.5 g K kg −1 at eight weeks after first flower, respectively. Petiole‐K concentrations had a stronger relationship with relative yield than leaf‐K ( R 2 range of 0.31–0.65 for petioles and 0.19–0.53 for leaves). Our results suggest petioles are more accurate for monitoring cotton K nutrition, and growth‐stage‐specific critical K concentrations are key for accurately assessing cotton K nutritional status.