The co-pyrolysis of sewage sludge with plant biomass for biochar production is a promising strategy for the safe use of nutrients in sludge and sustainable waste management. However, the effects of such biochar on the ecophysiological responses of plants for revegetating degraded soils remain poorly understood. We hypothesized that, compared to raw, uncarbonized materials, biochar—although more recalcitrant—would improve soil chemical properties and plant ecophysiological performance, depending on the dose applied. 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. Thus, BSSCP is a potential alternative for degraded soil management and improving plant ecophysiology, provided application rates are properly adjusted.