EFFECT OF DIFFERENT LEVELS OF HUMIC-ACID ON THE GROWTH AND NUTRIENT-UPTAKE OF TEAK SEEDLINGS

A greenhouse experiment to study the effect of humic acid (HA) on the growth and nutrient uptake of Teak (Tectona grandis L.f.), a tropical hardwood, was conducted in Ibadan, Nigeria. The plants were grown for four months in top soils (0-30 cm) collected from an Alfisol (high organic matter) and an Oxisol (low organic matter) in Southern Nigeria. Three levels of HA, viz:, 50, 500, and 1000 mg/kg were added to the two soils. The results indicated that HA was beneficial to the growth and nutrient uptake of teak seedlings. Plant monthly growth rates, and height and total dry matter yield increased significantly (p = 0.05) over the controls in the two soils at the three HA application levels. Effects of adding 500 mg/kg and more of HA to the Alfisol were less beneficial while plant parameters and nutrient uptake tended to increase with increasing amounts of HA in the Oxisol. A significant positive correlation was established between rate of HA application and plant height (r = 0.57), stem diameter (r = 0.77) and total dry matter yield (r = 0.67) in the Oxisol, whereas the HA application rate was significantly correlated only with height (r = 0.57) and root/shoot ratio (r = 0.56) in the Alfisol. The addition of HA to the two soils increased the uptake by seedlings of N, P, K, Mg, Ca, Zn, Fe, and Cu, while Mn was decreased.