Plant Growth-promoting Potential of Oil Palm Boiler Ash-based Organomineral Fertilizer for Green Mustard Cultivation Under Reduced Urea Dose in Ultisols

This study aims to demonstrate the capability of Oil Palm Boiler Ash (OPBA)-based organomineral fertilizer (OMF) to maintain the growth, green biomass yield, and N uptake of green mustard under a reduced N application rate. This research was carried out from March to May 2021 in a research area in Bengkulu City with a Randomly Complete Block Design scheme and three replications. The treatment consisted of P0 = control (without OMF or urea), P1 = 200 kg urea ha−1, P2 = 325 kg OMF ha−−1 + 50 kg urea ha−−1, P3 = 650 kg OMF ha−−1 + 50 kg urea ha−−1, P4 = 975 kg OMF ha−−1 + 50 kg urea ha−−1, and P5 = 1300 kg OMF ha−−1 + 50 kg urea ha−−1. The results showed that the growth and green biomass yield increased as the application rate of OMF increased. Treatment of P5 produced the highest growth, green biomass yield, and N uptake, equivalent to P2 treatment. The green biomass yield at P5 was 161% higher than that at P0. Therefore, OMF has the potential to promote the agronomic performances of green mustard under 50% reduced N dose in Ultisols. Keywords: slow release fertilizer, nutrient management, oil palm waste, organic pellet fertilizer, green mustard