Alkali–thermal treatment of waste activated sludge (WAS) can produce a liquid fertilizer (LF) rich in plant nutrients and biostimulants. However, studies on its actual effects on plant growth and soil quality during field application remain limited. This study employed pot experiments to investigate the impacts of LF substitution (0%, 50%, 100%) for urea on pakchoi cabbage yield, soil physicochemical properties, and microbial communities. The results demonstrated that the LF100 treatment (complete substitution) exhibited the most favorable performance in terms of both plant yield and soil quality enhancement. Compared to the CK, LF0, and LF50 treatments, the LF100 treatment increased various growth and soil parameters: fresh and dry weights of pakchoi cabbage by 50.31–110.61% and 52.48–72.00%, respectively; total soil nitrogen by 1.54–9.09%; total soil phosphorus by 13.89–54.56%; soil available phosphorus by 37.51–116.88%; as well as soil urease, invertase, and protease activities by 2.73–9.41%, 17.11–32.52%, and 7.14–36.36%, respectively. Meanwhile, soil microbial diversity in all fertilized groups was higher than in CK, and it increased with the rising LF substitution ratios. Furthermore, the dominant phyla of LF100 soil microbial community included Actinobacteriota, Proteobacteria, Acidobacteriota, and Crenarchaeota, encompassing multiple bacterial genera involved in carbon/nitrogen cycling and nitrogen fixation. Thus, this liquid fertilizer carries resource utilization potential as a urea substitute, offering valuable insights for sustainable agricultural development.
Li et al. (Fri,) studied this question.