Utilization of Palm Oil Midrib Biochar as Soil Amendment with a Newly Isolated Bacillus sp. SM11 for Growth Enhancement and Nitrate Reduction in Romaine Lettuce (Lactuca sativa L. var. longifolia)

Abstract

Biochar is a carbon-rich material that enhances nutrient availability, soil quality, and microbial activity, improving plant growth and crop productivity. In this study, the palm oil midrib biochar (POMB) was used as a soil conditioner to improve the growth of romaine lettuce (Lactuca sativa L. var. longifolia), together with a biofertilizer containing a newly isolated bacterial strain SM11. The newly isolated SM11 was closely related to Bacillus siamensis, with 99.77% similarity based on 16s rRNA gene sequence analysis. POMB treatment improved the fresh weight of romaine lettuce by up to 181.33 ± 1.15 g plant−1, which is equivalent to 160.27% growth enhancement compared to the control without POMB. By comparison, POMB treatment with a biofertilizer containing SM11 increased fresh weight to 275.67 ± 11.59 g plant−1 with a growth enhancement of 295.68%. The addition of SM11 biofertilizer also protected against disease during cultivation. The addition of POMB reduced nitrate accumulation in romaine lettuce from 631.38 ± 0.36 to 223.31 ± 0.20 mg kg−1 by 59.08% compared to the control. This study suggests a way to manage agricultural waste from local palm oil plantations, thereby reducing waste accumulation and adding value to palm oil waste by-products for agricultural benefit through a biotechnological process.