Integrated crop-livestock farms have higher topsoil nitrogen and carbon than crop-only farms in Chilean Mediterranean climate volcanic soils

Context: Crop-livestock reintegration could reduce the environmental footprint of decoupled crop and livestock production related to biogeochemical cycles. Previous experiments showed that replacing fallow periods in annual crop rotations with grazed cover crops increases total nitrogen (N) and organic carbon (SOC), based on topsoil sampling and stocks compared by equivalent soil depth. Stock comparisons based on topsoil sampling or equivalent soil depth, rather than whole-profile sampling or equivalent soil mass, can erroneously report stock gains that have not occurred. Evidence of crop-livestock integration effects on commercial farms is needed. Objective: This study assessed on-farm if winter grass forages and beef cattle grazing in annual crop rotations lead to greater soil total N and SOC to a soil depth of 1 m. Methods: We sampled soil at eight paired commercial fields, four integrated crop-livestock (ICL) fields with grazed or ungrazed winter forage (annual ryegrass, oat) in the crop rotation (cereals, grain legumes, industrial crops), and four neighboring fields with winter fallow in the rotation, in volcanic soils in Ñuble Region, central-southern Chile, in fall 2022 and 2023. In each field, 10 soil cores were sampled from a 1 ha plot and separated into four depth layers (0–15 cm, 15–30 cm, 30–60 cm, and 60–100 cm). We quantified soil total N and SOC concentrations and stocks, on an equivalent soil mass basis, and soil texture throughout the soil profile. Results and conclusions: ICL sites had 10 % higher total N (+0.05 % N) and 8 % higher SOC concentrations (+0.5 % SOC) compared to paired non-ICL sites in the top 15 cm soil layer. The topsoil layer at ICL sites had 11 % higher N (+0.37 Mg N ha⁻¹) and 9 % higher SOC (+3.9 Mg SOC ha⁻¹) stocks, based on an equivalent soil mass. Cumulative stocks below 15 cm to a depth of 1 m were similar between ICL and non-ICL sites. Across the 1 m soil profile, 52 % and 53 % of N and SOC stocks were below 30 cm depth. Significance: We provided on-farm evidence suggesting that integrating non-leguminous winter forages and grazing into annual crop rotations can retain N and store SOC in topsoil, with relevance to land managers and decision-makers who seek to build soil fertility and health through biodiversity and reduce N fertilizer use, though further research is recommended. Sampling soil to at least 60 cm depth can help capture management effects on N and SOC and quantify deeper N retention and SOC storage.