Effect of application of different biogas fertilizer on eggplant production: Analysis of fertilizer value and risk assessment

Abstract Anaerobic digestion (AD) is an important technology for manure treatment in livestock farms, but when a large amount of biogas slurry (BS), and biogas residues (BR) from large-scale farms are used as fertilizer, there are usually main ways to utilize the raw digestate (untreated BS, and BR), as a bio-based fertilizer. In this study, the effects of direct application of digestate and bio-based ammonium sulfate (AS) fertilizer obtained by ammonia stripping of BS on the cultivation of eggplant and crop yield were compared. Eggplant growth, nitrogen fertilizer efficiency, crop yield, and heavy metals accumulation were studied under the normal-dose application and double-dose application of digestate. In addition, the fertilizer efficiency and safety risk assessments of bio-based AS liquid fertilizer and bio-based AS solid fertilizer were also discussed. A comprehensive comparison of N-fertilizer efficiency and yield showed that the bio-based AS liquid fertilizer had the best fertilizer efficiency, followed by double-dose digestate, and the bio-based AS solid fertilizer, while the normal-dose digestate had poor efficiency. The application effect of bio-based AS liquid fertilizer was closer to the traditional urea N fertilizer. The results showed that compared with the bio-based AS solid fertilizer, the apparent recovery efficiency of N (ARE N ) of eggplant with bio-based AS liquid fertilizer increased by 2.8 times, and the eggplant yield increased by 24.5%. Moreover, the yield of eggplant with bio-based AS liquid fertilizer was increased by 28% compared to direct application of digestate. Furthermore, no seedling burning and growth inhibition occurred with double application of digestate, but the content of heavy metal (Pb) increased significantly. The results can be used as a reference for understanding the effect of digestate and bio-based AS fertilizer on the cultivation of eggplant and the correlated safety risks assessment.