Nutritional status and productivity of carabao mango (Mangifera indica L.) trees induced regularly, with potassium nitrate as influenced by fertilizer and indole acetic acid application.

Significant interaction effects were observed on the number of fruits and yield per tree. The application of N, P, and K increased significantly the pH of ripe fruits from 4.77 in the control to 4.96 and 4.98 in those applied with 0.1-0.8-0.8 and 0.4-0.4-0.00 kg N, P2O5 and K2O/tree, respectively. However, the application of different levels of NPK and Zn and Ca did not increase significantly the level of N, P, K, Ca, Mg, Zn, Cu, Mn, and Fe contents of the leaves at flower induction and after harvest. A significant increase in N, P, K, Zn, and Cu contents of the leaves were observed from fertilizer application to flower induction; but the level of N, K, and Cu after harvest did not differ significantly from that before fertilizer application. The level of Mg after harvest was significantly lower than before fertilizer application. On the other hand, Ca and Fe contents before fertilizer application was significantly higher than at flower induction and after harvest. A significant positive correlation was observed between fruit yield and percentage of flowering, length of panicles, number of fruits retained per 50 panicles and number of fruits per tree. The total K and Cu content of the leaves at flower induction was significantly and positively correlated with the percentage of flowering of number of fruitlets per panicle, respectively. The uptake of N was closely associated with the uptake of K and Ca. A direct and significant relationship was noted between Zn and Cu, and Mg and Fe as regards their uptake. The Zn and Cu uptake was inversely and significantly correlated with the uptake of Ca. Also the total C content was positively and significantly correlated with the starch and total N contents of the leaves at flower induction. An inverse and significant relationship was found between C/N ratio and total C and total N content of the leaves at flower induction.