Use of Organic Waste as an Alternative Organic Fertilizer and Synthetic Fertilizer to Ameliorate Acid Soil Productivity

Liquid waste generated in large quantities in the palm oil mill has low pH, and high organic content and its use as an organic amendment could offer an environmentally friendly management strategy. This pot experiment aimed to evaluate the impact of organic waste of the liquid waste from the palm oil mill and synthetic fertilizer on organic carbon and nutrients of an acid soil and soybean yield. The treatments consisted of no synthetic fertilizers, half recommended dose of synthetic fertilizers (0.5R), synthetic fertilizers as recommended 50 kg ha-1 Urea + 200 kg ha-1 SP-36 + 150 kg ha-1 KCl (R) and organic waste with doses of 0, 5, 10, 15 and 20 t ha-1. The experiment was arranged in a completely randomized design with a factorial pattern and three replications. The results demonstrated that there was no significant interaction on soil chemical characteristics by the addition of organic waste and synthetic fertilizers. However, organic waste addition increased soil pH, total organic C, labile organic C, humic acid C, total N, available P, exchangeable K, and cation exchange capacity (CEC), whereas synthetic fertilizer addition only increased available P and exchangeable K. Exchangeable Al was significantly reduced by organic waste while significant effect didn’t occur with synthetic fertilizers. The treatment of organic waste increased total organic C content by 7-24%. A larger sensitivity was indicated by labile organic C compared to total organic C and humid acid C so that labile organic C is a better indicator of alterations of soil organic C owing to organic waste treatment. The treatment of organic waste and synthetic fertilizers showed significant interactions on the dry weight of soybean seed, shoot, and root. The addition of synthetic fertilizers without organic waste increased the dry weight of the soybean seed, shoot and root by 133%, 133% and 140% respectively, while with the addition of 15 t ha-1 organic waste combined with synthetic fertilizer, enhancements by 262%, 261%, and 206% in the dry weight of seed, shoot and root were respectively found.