Biochar from Co-pyrolysis of Sewage Sludge Improves Plant Eco-physiology in Degraded Soils?

A pot experiment was conducted under greenhouse conditions using a completely randomized design in a 3 × 4 + 1 factorial arrangement. Three organic residue sources were evaluated: sewage sludge (SS), a mixture of sewage sludge and cashew pruning residues (SSCP), and the co-pyrolyzed biochar derived from these materials (BSSCP), applied at four phosphorus-equivalent rates, in addition to an untreated control. Mimosa caesalpiniifolia Benth. was used as the model plant species. A pot experiment was conducted in a greenhouse in a completely randomized design (3 × 4 + 1 factorial), with three organic residue sources: sewage sludge (SS), a sludge–cashew pruning mixture (SSCP), and their co-pyrolysis biochar (BSSCP) at four phosphorus-equivalent doses, plus a control. BSSCP at moderate doses (5 and 10 Mg ha⁻¹) enhanced photosynthetic efficiency and water use, while non-carbonized residues promoted greater biomass accumulation, likely due to faster nutrient release. BSSCP raised soil pH and stabilized carbon but reduced short-term nitrogen availability. BSSCP is a potential alternative for degraded soil management and improving plant ecophysiology, provided application rates are properly adjusted.