OPTIMIZATION OF SOIL K: NA RATIO FOR COTTON (GOSSYPIUM HIRSUTUM L.) NUTRITION UNDER FIELD CONDITIONS

Abstract

Adequate potassium (K) supply is crucial for cotton growth and development. However, sodium (Na) can share some functions with K. In present study, we investigated the effects of replacing K with Na at different ratios on growth, ionic relations and yield as well as yield attributes of two cotton varieties differed in K use efficiency. Different levels of K and Na giving K: Na ratios of 3.5: 1 (control), 3.75: 1, 4: 1, 4.25: 1, 4.5: 1, 2.8: 1, 3: 1, 3.2: 1, 3.4: 1, 3.6: 1 were arranged in triplicates according to randomized complete block design under natural field conditions. Results revealed that maximum seed cotton yield was obtained at K: Na ratio of 3.4: 1 followed by 3.6: 1 in both cotton varieties. However, NIBGE-2 manifested greater seed cotton yield than MNH-786. The significant (p≤0.05) positive correlation was found between number of bolls plant-1 and seed cotton yield (R2 = 0.62 for NIBGE-2 and R2 = 0.64 for MNH-786) determined at different levels of K and Na. Leaf K: Na ratio also varied significantly (p≤0.05) due to main effects of K, Na, varieties and their interactions. Maximum leaf K: Na ratio was shown by NIBGE-2 with 270 kg K ha-1+60 kg Na ha-1 at ratio of 4.5: 1 followed by 255 kg K ha-1+60 kg Na ha-1 at ratio of 4.25: 1. Although fiber quality of both cotton varieties were markedly influenced by different ratios of K: Na, however these differences between treatments and varieties were not consistent. There was a significant positive correlation between K concentration and fiber length (R2 = 0.97 for NIBGE-2 and R2 = 0.98 for MNH-786). Our results suggested that cotton growth and yield could be improved by adding appropriate amounts of K and Na.