Ameliorating acidity and Al toxicity in soil cultivated with oil palm using calcium liming materials and dolomite

This PhD thesis presents a comprehensive investigation into the impact of calcium (Ca) amendments on soil properties and oil palm. The research is organized into four distinct experiments, each contributing to a deeper understanding of the effects of various Ca amendments on soil health and plant response. Objective 1 focuses on the initial effects of Ca amendments on strongly acidic soils represented by the Bungor and Jeram series. A randomized complete block design is employed, and a 12-month soil incubation phase precedes controlled oil palm seedling cultivation. Results indicate a significant elevation in soil pH from 4.5 to 6.0, with electrical conductivity stabilizing around 0.8 dS/m. Toxic aluminium (Al) forms decrease from 60% to 25%, and exchangeable cations show a 15-25% improvement in base saturation. Oil palm responses include root dry weight yields ranging from 0.76 to 1.24 g/pot, with shoot dry weight yields reaching up to 1.5 g/pot. Objective 2 delves into the long-term residual effects of Ca amendments on acidic Ultisol soil series (Bungor and Jeram). A 360-day incubation period followed by a 180- day growth phase for oil palm seedlings is employed. The study confirms significant improvements in shoot dry weight yield (SDWY) in the Bungor series, ranging from 14.95g to 16.87g, compared to the control group. Increased levels of essential nutrients are observed, and a negative correlation between SDWY and concentrations of Al and Mn is developed. The study concludes that the residual effects of Ca amendments are attributed to Al complexation with Ca ions and the precipitation of Al due to increased soil pH. Objective 3 investigates nutrient dynamics in acidic soils, focusing on Ca release rates and P availability. The study employs two distinct experiments - Ca Release Experiment and P Sorption Experiment. Various Ca amendments are analyzed, with quicklime exhibiting the highest Ca release, reaching up to 1765.9 mg/kg soil in the Bungor series. The study reveals increased P sorption across all Ca amendments, particularly in calcium carbonate and quicklime treatments. Objective 4 bridges the gap between laboratory findings and real-world agricultural applications. Column leaching tests and field trials are conducted, validating laboratory results and offering practical guidelines for sustainable agriculture. Surface-applied Ca amendments significantly improve subsoil pH, reduce exchangeable Al concentrations by up to 45%, and enhance nutrient availability. The research methodology includes rigorous statistical analyses, employing methods such as Analysis of Variance (ANOVA) and the Duncan test to validate the effectiveness of Ca amendments in improving soil health and nutrient availability. Overall, this Ph.D. thesis provides valuable insights into the potential of Ca amendments for soil amelioration and sustainable agricultural practices, with specific parameter values highlighting the tangible benefits of these amendments.