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.