Application of activated carbon from biomass waste as slow-release fertilizer for horticultural plants

Rice straw is the remaining post-harvest waste from rice plants. The availability of rice straw in Indonesia is very abundant because every year rice farming can be carried out three times a year to meet national food needs. Increasing the use value of rice straw biomass waste can be done by converting it into active carbon. In this research, activated carbon was made in three stages. The first stage is carbonation of rice husks and rice straw using a batch reactor at a temperature of 300°C for 2 hours to obtain bio-char and the second stage is to make adsorbents from bio-char of rice straw and rice husks using chemical methods with KOH. Mass ratios of bio-char and KOH 4:1, 3:1, and 2:1 were left for 24 hours and then heated to a temperature of 300°C for 2 hours in a batch reactor. In the third stage, the activated carbon is soaked with NPK fertilizer for 24 hours and ready to be applied to horticultural plants. This research shows that activated carbon with a 2:1 ratio has the lowest ash content, the highest fixed carbon and the highest volatile matter. the value of fixed carbon is inversely proportional to the value of ash content and volatile matter. This fixed carbon is what really influences soil improvement. Carbon can bind the nutrients needed in plants and increase the nutrients in the soil to be good. The carbon in rice straw has porous properties so it is good for use as a slow release fertilizer medium for plantsApart from that, at this ratio it can absorb the highest N and P, this is due to the large pore size. The results of the N and P analysis are directly proportional to the results of fixed carbon on activated carbon.