Differential Potassium Influx Influences Growth of Two Cotton Varieties in Hydroponics

Potassium uptake rate of two cotton (Gossypium hirsutum L.) varieties viz., NIBGE-2 and MNH-786 was investigated in nutrient solution culture having deficient K @ 0.3 mM and deficient K+ Na @ 0.3 +2.7 mM. Depletion of K from solution was monitored over a period of 24 h at regular time intervals after 0, 0.5, 1.0, 1.5, 2, 3, 4, 5, 6, 8, 10, 12 and 24 h to estimate K uptake kinetics of the roots i.e. maximum influx, Imax and the Michaelis-Menten constant, Km. NIBGE-2 had about 2-fold higher (2.0 mg g rdw hr) Imax value for K uptake rate at deficient K+Na than that (1.207 mg g rdw hr) for MNH-786. Higher, Michaelis-Menten constant, Km (12.82 ppm) for K uptake rate was observed in both cultivars NIBGE-2 and MNH-786 at deficient K+Na than that at deficient K. Main effects of treatments and varieties had significant (p< 0.05) effect on shoot dry matter, root dry matter, total dry matter and leaf area per plant. Maximum K influx in NIBGE-2 at deficient K and deficient K +Na was attributed to enhanced growth response as compared to that in MNH-786.