Impact of Biochar, Mineral Phosphorus, and Lime on Dynamics of Phosphorus Fractions and Soil Characteristics in Ethiopian Acidic Soil

In acidic soils, phosphorus (P) fixation onto iron (Fe) and aluminum (Al) oxides significantly reduces its bioavailability, which presents a significant problem for agriculture. In this controlled incubation study (8 weeks), the combined impacts of biochar, mineral phosphorus, and lime on phosphorus fraction dynamics and soil characteristics in acidic Ethiopian soil were examined under laboratory conditions. Three rates of mineral P (0, 62.56, 125.12 kg P ha −1 ), biochar (0, 5, 10 t ha −1 ), and lime (0, 5.40, 8.70, 10.70 t CaCO 3 ha −1 ) in a fully randomized factorial incubation experiment with three replicates were used. The combined application of all three amendments decreased exchangeable Al and oxalate‐extractable Al/Fe and significantly ( p < 0.001) increased soil pH. By reducing the soil’s ability to adsorb phosphorus, this inhibition of P‐sorbing agents increased labile inorganic phosphorus fractions and transferred phosphorus from stable, nonlabile pools to forms that plants could use. While lowering its fixation in Fe‐ and Al‐bound fractions, the incorporation of amendments significantly improved the distribution of phosphorus in readily soluble and moderately labile inorganic pools. In comparison with single or multiple adjustments, the combined treatment also markedly raised the accessible phosphorus and total phosphorus content. As evidenced by significant main effects and synergistic two‐ and three‐way interactions, the integrated application of biochar, lime, and mineral phosphorus effectively mitigated phosphorus fixation through pH amelioration, surface passivation of Al/Fe oxides, and redistribution of P into labile and moderately labile pools. These findings demonstrate mechanistic synergy under controlled conditions; however, field validation and crop response studies are required before extrapolating to agricultural productivity outcomes.