Treating fermentative residues as liquid fertilizer and its efficacy on the tomato growth

• Liquid residue (LR) from SSF was analyzed for its biochemical properties.
• Under greenhouse condition, it significantly increased the growth of tomato plants.
• It had positive effects on microbial community of rhizosphere soil.
• The enzyme activity and quality of soil were improved by LR.
• This study showed an example for waste utilization in SSF industry.

Considering the rapid development of bioconversion techniques, recycling organic wastes from fermentation processes for agricultural production and soil restoration is a new field. Chemical and biological analyses indicated that the liquid residue (LR) from lipopeptide biosurfactants production contained large amount of available nutrients and free amino acids, and minimal content of heavy metals and showed low phytotoxicity. The greenhouse experiments showed that 1.0%(v/w) of LR to pot soil was the best proportion for its application as liquid fertilizer with an enhancement of plant height, shoot dry weight root length, root diameter and root dry weight by 67.18, 285.62, 122.26, 13.04 and 204.55%, respectively. The bacteria counts, enzyme activities and available nutrients in rhizosphere soil increased significantly with the increasing rates of LR. LR had better promoting effects on plant growth and soil quality in comparison with chemical fertilizer at the same NPK levels. Our results suggested an effective way to use residues from biosurfactants fermentation at large.