Application of exogenous compounds increased the tolerance to aluminum toxicity and improved fruit production of oil palm (Elaeis guineensis Jacq.) grown on Ultisols

Abstract

The low productivity of oil palm grown on suboptimal land Ultisols with high Al saturation requires efforts to improve cultivation techniques in order to increase plant tolerance to Al stress and to improve fruit production. This study aimed to determine the effect of various exogenous compounds on physiological changes and fruit production of oil palm (Elaeis guineensis Jacq.) grown on Ultisols with high Al saturation. This study consisted of 2 treatments, namely: (1) a combination of various exogenous compounds, and (2) application methods. The experiment was arranged in RCBD split plots with 3 replications. Treatment of exogenous compounds was (1) control (untreated); (2) CaCl2 50 ppm; (3) CaCl2 50 ppm + Salicylic acid 50 ppm; (4) CaCl2 50 ppm + Salicylic acid 50 ppm + citric acid 50 ppm; (5) CaCl2 50 ppm + Salicylic acid 50 ppm + citric acid 50 ppm + boron 50 ppm; and (6) CaCl2 50 ppm + Salicylic acid 50 ppm + citric acid 50 ppm + boron 50 ppm + Cu 50 ppm. The application method used was (1) basal drench and (2) foliar spray. Application of exogenous compounds was carried out every 3 months. The results revealed that application of exogenous compounds has enabled plants to increase the tolerance to Al stress, as evidenced by an increase in the number of normal bunches and bunch weight, the increase of which was due to the decrease in the number of rejected bunches, especially in the CaCl2 + salicylic acid treatment, which was selected as the most effective treatment. Increased fruit production in this treatment was associated with improvements in physiological processes; decreased MDA and increased photosynthetic rate and activity of APX and CAT enzymes resulted in improvement fruit production. These positive changes in physiological processes after treatment suggested that the addition of those exogenous compounds has induced signalling processes involved in ROS scavenging, that promoted the tolerance to Al stress. Basal drench application method was more effective than foliar spray, this was related to the increase in soil pH and P available due to the application of exogenous compounds through basal drench method.