Digestate-based organic amendment substitution improves the red soil quality and pakchoi yield

This study investigated the effect of the partially substituting chemical fertilizers (CF) with digestate-based organic amendment (OA) on the amelioration of red soil and the growth of plant. OA with nitrogen substitution rates ranging from 10 % to 40 % were mixed with CF and applied to red soil in a pot experiment. The results indicated that plant growth was significantly enhanced in the treatment where 20 % of the CF was substituted with the OA (OA20) compared to other treatments (p < 0.05). Specifically, the OA20 treatment increased nutrient use efficiency by 54.76 %-100.42 % compared to the treatment using only CF. Furthermore, all OA treatments improved the quality of red soil, with the nutrient content significantly higher in the OA20 group than in the other treatments (p < 0.05). The parameters of total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), and total potassium (TK) significantly affected the soil quality index and plant growth, serving as reliable indicators of soil quality and plant yield. Microbial analysis revealed that the bacterial Chao index and the abundance of microorganisms involved in C-N nutrient cycling, such as Chryseolinea and norank_f__norank_o__Actinomarinales, were highest in the OA20 group. Significant correlations were observed between soil nutrient content (AN, AP, and TK) and the abundance of norank_f__norank_o__Actinomarinales and Chryseolinea, indicating their close relationship with pakchoi growth. Consequently, digestate-based OA may positively affect plant growth in acidic ecosystems by enhancing soil properties, inducing shifts in microbial community composition, and promoting the enrichment of potentially beneficial bacteria. This study provides valuable insights for the enhancement of low-quality soils and the resource utilization of digestate.