Substituting fertigation with swine liquid manure maintains tomato performance while enhancing dissolved nutrient pools

Synthetic nitrogen (N) fertilization accounts for ~2.1% of global greenhouse gas emissions. Transitioning to a circular nutrient economy requires replacing synthetic inputs with recycled substrates. This study evaluated the agronomic performance of greenhouse tomato (Solanum lycopersicum) fertigated with swine-derived aerobically digested liquid manure (AeD-LM) and tracked the resulting carbon (C)–N stoichiometric trajectories within the soil. A greenhouse pot experiment was conducted under drip fertigation, comparing chemical fertilizer (urea; CF) with various AeD-LM regimes, including raw liquid manure (LM), optimized liquid manure (OL), and biochar co-amendment (OB). Crop growth parameters, fruit quality, and post-harvest soil biogeochemical properties including dissolved organic C (DOC), total dissolved N (TDN), microbial biomass C (MBC), and microbial biomass N (MBN) were quantified. Tomato growth, yield, and qualitative fruit traits exhibited no statistical differences between the CF and AeD-LM treatments, suggesting the potential of AeD-LM as a viable alternative nutrient source. However, soil biochemical analysis revealed a distinct divergence in dissolved organic and microbial biomass pools. Compared to the CF treatment, the application of AeD-LM significantly enriched the dissolved nutrient pools, resulting in 15–42% and 6–20% higher residual DOC and TDN concentrations, respectively. By co-supplying labile C alongside N, AeD-LM alleviated the C limitation typical of synthetic N fertilization, and the stoichiometric shift stimulated microbial activity as evidenced by 17–30% elevated β-glucosidase activity relative to the CF control. In conclusion, substituting conventional mineral fertigation with swine-derived AeD-LM maintains short-term pot-scale tomato productivity without inducing temporal nutrient deficits, while simultaneously enhancing soil biochemical functioning through the stimulation of microbial activity.