Effect of the Combined Application of Biochar and Iron-Based Materials on Soil Improvement in Peanut Fields

Iron is an essential micronutrient for crops, and iron oxides play critical roles in the formation and physicochemical properties of soil aggregates. However, whether the combined field application of biochar and Fe-based amendments produces synergistic effects on the improvement of acidified soils in peanut fields remains unclear and requires further verification through field trials.

A two-year field experiment was conducted in an acidified peanut-cropping system, in which biochar was co-applied with either zero-valent iron (BC+Fe⁰) or magnetite (BC+Fe₃O₄). Soil physicochemical properties, microbial community structure, and peanut yield were determined to evaluate the soil amelioration potential of these combined amendments.

The combined treatments significantly increased soil pH from 5.48–5.83 to 5.93–6.37 and total organic carbon content from 8.47–9.11 to 11.35–13.55 g·kg⁻¹. They also promoted the formation of macroaggregates (>0.25 mm) and reduced soil bulk density. The application of Fe-based materials alone increased the contents of free iron oxides, organically complexed iron, and Fe²⁺ by 4.56%–35.09%. Following the combined application of biochar and Fe-based materials, the contents of free and amorphous iron oxides and Fe²⁺ increased further. The Shannon and Chao1 diversity indices also increased, while the relative abundances of the three dominant bacterial phyla increased by 0.75%–1.59%. Among the treatments, BC+Fe₃O₄ resulted in the highest pod yield and 100-pod weight, both of which were strongly associated with improved soil properties and increased plant-available Fe.

The combined application of biochar and Fe-based amendments is an effective strategy for ameliorating acidified soils in peanut fields, improving soil quality, increasing microbial diversity, and enhancing peanut productivity. This study provides a new management strategy and a mechanistic basis for the field-scale application of biochar-Fe systems in agricultural soil amelioration.