Co-amendment of silicate dust and manure improves soil health metrics and crop yield in coarser-textured more than medium-textured soils

Silicate rock dust and manure admixtures are increasingly considered to improve crop growth and soil health. Soil application of silicate rock dust can capture and store atmospheric CO₂ as inorganic carbon but could also have the potential to stabilize manure-derived organic matter when combined. However, synergies between rock dust and manure have been rarely investigated, while identifying the optimal combination rate remains elusive. Here, we set up a field trial in two contrasting kaolinitic soil (coarse-textured sandy loam and medium-textured silt loam) amended with a modest realistic rate of broiler manure (10 Mg ha⁻¹) [100 %], finely ground silicate rock dust (granite) (10 Mg ha⁻¹) [100 %], and a combination of manure (7 Mg ha⁻¹) + rock dust (3 Mg ha⁻¹) [70:30 %], manure (5 Mg ha⁻¹) + rock dust (5 Mg ha⁻¹) [50:50 %] and an un-amended control to investigate their effects on a leafy vegetable plant (Amaranthus cruentus) and metrics of soil health, and an incubation experiment to monitor soil heterotrophic CO₂ emission. Despite a reduction in manure input, the manure-rock dust mixture outperformed sole manure by increasing vegetable fresh herbage yield (by 19 %) and enhancing all soil health metrics, as revealed by the decrease in soil acidity, increased soil EC and soil total C, enhanced N availability and retention, increased bioavailable P, decreased soil dissolved organic C losses, increased soil microbial activity, and improved soil physical properties (viz., soil aggregate, bulk density, porosity, and water infiltration). Soil texture modulates the effects of manure-rock dust, as demonstrated by the better response from coarse-textured sandy loam than medium-textured silt loam soil. Manure-rock dust admixture [50:50] ratio decreased soil CO₂ emissions by 26 % and 54 %, respectively, in sandy loam and silt loam soil texture compared to sole manure. The synergistic performance of manure-rock dust admixture at 70:30 and 50:50 ratios was similar; however, to reduce nutrient limitation in the soil towards a more nutrient-equilibrated system while enhancing soil functioning and mitigating CO₂ emissions, we adjudged the manure-rock dust [70:30] ratio to be optimal.