Comparative evaluation of different organic fertilizers on the soil fertility, leaf mineral composition and growth of bitter kola seedlings

The effect of oil palm bunch ash, spent grain, poultry and turkey manures applied solely and their supplemented forms, as sources of fertilizer on soil fertility, leaf mineral composition and growth of bitter kola (Garnicia colae) seedlings was investigated at Akure in the rainforest zone of Nigeria. The eight organic fertilizer treatments: spent grain, oil palm bunch ash, poultry manure, turkey manure, spent grain + poultry manure, spent grain + turkey manure, oil palm bunch ash + poultry manure and oil palm bunch ash + turkey manure were applied at 40g per 10kg soil filled polybag (8t/ha dry weight) with a reference treatment 400kg/ha NPK 15-15-15 fertilizer (2g per bag) and arranged in a completely randomized design (CRD) and replicated three times. The supplemented or amended treatments were applied at a 50:50% by weight (20g each). The results showed that these organic fertilizers increased the growth parameters, soil and leafN, P, K, Ca and Mg, soil pH and organic matter significantly (P 0.05) compared to the control treatment. The supplements of oil palm bunch ash and wood ash with poultry and turkey manures increased consistently the growth, soil and leaf mineral compared to their sale forms. Oil pal bunch ash + poultry manure increased the leaf N (52%), P (27%), K (44%), Ca (39%) and Mg (51%) compared to the sole application of poultry manure. When compared with NPK 15-15-15 fertilizer, the oil palm bunch ash + poultry manure treatment increased the plant height (40%) leaf area (50%), stem girth (450/0) number of leaves (53%), and fresh shoot weight (29%). For soil chemical composition, the oil palm bunch ash + poultry manure treatment increased the soil pH (28%), O.M. (92%), P (26.30/0), Ca (99%), Mg (980/0) and Na (930/0) compared to the NPK 15-15-15 fertilizer. However, the NPK 15-15-15 fertilizer increased the soil K by 11% compared to the former. The high soil K1Ca, K/Mg and P/Mg ratios in the NPK 15-15-15 fertilizer treatment led to an imbalance in the supply of P, K, Ca and Mg nutrient to bitter kola seedlings. In these experiments, oil palm bunch ash + poultry manure applied at 8tJha was most effective treatment in improving bitter kola growth parameters, soil and leaf mineral composition.