Rice husk ash (RHA), palm oil mill effluent (POME) sludge and decanter cake can be utilized together in compost production to minimize the environmental pollution. This study aims to evaluate the role of different composition of RHA in enhancing the physicochemical properties of palm oil-based compost. The composts were prepared by mixing different composition of RHA, in the range of 0% to 30%, with 1:1 (wt/wt) weight ratio of POME sludge and decanter cake. The moisture content, water holding capacity, pH, nitrogen (N), phosphorus (P), potassium (K), silica (Si) contents, and C:N ratio of raw materials were analyzed by using CHNS and WDXRF analyzers. The composting process was conducted in compost containers for 60 days, in which the temperature and pH of the composts were monitored daily. The finished composts were analyzed for physicochemical properties as same as raw materials. For physical properties of finished composts, RHA30 had the highest moisture content and water holding capacity which was 1.9 to 23.8% (wt/wt) and 4.2 to 26.8% higher compared to other finished composts, respectively. For chemical properties, the highest N and P contents were recorded by control compost. However, for K and Si content, the elements were found to be higher in RHA10 and RHA30, respectively, compared to other finished composts. Overall, RHA, POME sludge and decanter cake combination in compost production can create a well-balanced condition for the compost to perform effectively as an organic fertilizer. The addition of 5% to 10% RHA in compost formulation made from palm oil mill wastes is suggested to achieve the desirable condition.

Rice husk ash (RHA), palm oil mill effluent (POME) sludge, and decanter cake can be utilized as compost to reduce environmental pollution. This research attempted to investigate the effect of RHA addition to palm oil-based compost in boosting the nitrogen (N) uptake and the growth of Brassica oleracea var. <i>alboglabra</i> L. (Chinese kale plant). Two categories of compost treatment were prepared in this study: Treatment 1 (control) and Treatment 2 [consisting of 10% (wt/wt) of RHA]. Both treatments were composted for 60 days until it was matured. The temperature and pH of the composts were recorded daily throughout the study. The treatments were analyzed for moisture, water-holding capacity, and nutrient content. The Chinese kale plant was grown in growing media and applied with Treatment 1 and Treatment 2 composts. The progress of plant growth was tracked every week. Based on the analysis, Treatment 2 exhibited a higher temperature and pH profile than Treatment 1. Meanwhile, the contents of N, P, and K were higher in Treatment 1 compost. However, Treatment 2 compost had higher silicon (Si) content, moisture content, and water-holding capacity. Based on the field test study carried out on the Chinese kale plant, the N uptake, and the growth of the plant, were found to be significantly higher when applied with Treatment 2 compost compared to Treatment 1 by 19% to 31% and 13% to 53%, respectively. It was proven that the addition of 10% RHA managed to provide an adequate amount of Si, moisture content, and water-holding capacity in Treatment 2 compost that can enhance the N uptake and improve the growth of the Chinese kale plant in this study.