The Hydrochar Physiochemical Properties Following Different Aging Methods, and Its Impact on Kale Seed Germination, Plant Growth and Nutrient Elements Accumulation

Abstract

Hydrochar, a product from hydrothermal carbonization (HTC) of biomass waste, has gained considerable attention in agriculture as a potential soil amendment. However, it has been found to exhibit phytotoxicity, which could inhibit plant growth. This study aimed to investigate the effects of three modification methods (water washing, microbial aging, and freezing-thawing aging) on the physicochemical properties of hydrochar derived from coffee grounds. Furthermore, the study evaluated the effects of applying four types of hydrochar with 10% and 20% application rates in growing medium on seed germination and plant growth. The results revealed that the physiochemical properties of hydrochar were significantly (P<0.05) altered by the different hydrochar pre-treatment methods. Moreover, the seed germination experiment showed that microbial aged hydrochar (MHC), water-washed hydrochar (WHC) and freezing-thawing aged hydrochar (FTHC) were effective in promoting germination compared to fresh hydrocar (FHC). The plant growth experiment demonstrated that 10% MHC was the most effective treatment in mitigating plant growth inhibition, despite some inhibitory effects still being observable compared to the control. Further studies should focus on a large-scale field study and investigate the effect of improved hydrochar on soil biology.