Effects of Oil Palm Empty Fruit Bunch and Coal Fly Ash on Soil pH and Nitrogen Status in Post-coal Mining Soil

Aims: This research aims to determine the effect of applying oil palm empty fruit bunches (EFB) organic material and coal fly ash (CFA) application on soil pH, total N, and N availability in post-coal mining soil. Study Design: The method used in this study was a completely randomized design (CRD) with two treatment factors in a greenhouse. Place and Duration of Study: This research was conducted in the greenhouse and Soil Science Laboratory, Faculty of Agriculture, Lambung Mangkurat University, Banjarbaru, Indonesia 70714, from August 2024 to May 2025 Methodology: The treatment factors were EFB (0, 4, 8 t ha-1) and CFA (0, 5,10 t ha-1) with three replicates for a total of 27 experimental units. The experimental units were 3.5 kg of soil sample in a plastic pot for two weeks of incubation. 400 mL of distilled water was added on the first day to make the soil reach the field capacity. In the following days, the field capacity was maintained by adding distilled water equal to the loss of weight. Distilled water and NPK fertilizer were added to guarantee any possible N mineralization. Results: The results showed that the application of EFB significantly improved soil properties in post-mining soil by increasing pH. Among the treatments, the application of 8 t ha⁻¹ EFB was the most effective dose for improving soil pH, while other treatments (CFA) did not show any effects, including the interaction. Conclusion: The application of EFB increased the pH of post-mining soil, but it did not increase N availability, either N-NH4- nor N-NO3-. Similarly, the total-N content of the soil was not affected. The application of 8 t ha-1 of EFB was the best dose for increasing the pH of post-coal mining soil. However, a higher dose may be needed to increase N status.