Residue and Biochar-based Amendments from Maize and Sorghum Cultivars Regulate CO2 Emissions and Nutrient Mineralization

Abstract

Abstract Soil fertility decline and climate change threaten sustainable crop production, creating a need for residue-based strategies that enhance nutrient cycling and soil carbon stabilization. This study investigated how feedstock and biochar produced from different maize and sorghum cultivars influence CO 2 emissions, nitrogen (N) and phosphorus (P) mineralization, and soil pH. An incubation experiment was conducted using feedstock (raw residues) and biochar derived from two maize (R201, SC701) and two sorghum (AS8, PAN8816) cultivars pyrolyzed at 350 °C and 650 °C. Amendments were applied to 100 g soil at 10 t C ha − 1 , with a soil-only control. CO 2 emissions were trapped in NaOH and quantified over 120 days. A parallel destructive sampling experiment was set up to assess NH 4 + -N, NO 3 − -N, extractable P, and soil pH at multiple time intervals. CO 2 -C emissions increased rapidly at the beginning of the incubation, peaking between 21 and 42 days and declined thereafter. Feedstocks produced higher CO 2 -C emissions than biochars for all cultivars, with PAN8816 feedstock showing the greatest increase (205% above the control). Biochar emissions decreased with increasing pyrolysis temperature. Nitrogen and phosphorus mineralization, as well as soil pH, also varied significantly among cultivars and pyrolysis temperatures. Relative to the unamended control, SC701-B650 increased soil NO 3 − -N by 17%, while PAN8816-B350 increased both NH 4 + -N and NO 3 − -N concentrations. Extractable P was highest in R201-B650 (maize) and AS8-B650 (sorghum). Soil pH generally increased in the order feedstock< B350 < B650. Cultivar-specific differences and pyrolysis temperature had stronger effects on CO 2 -C emissions, nutrient mineralization, and soil pH than crop type. Biochars, particularly those produced at 650 °C, showed greater stability and lower CO 2 -C emissions while enhancing nutrient availability. These findings demonstrate that selecting suitable cultivars and pyrolysis temperatures can improve soil fertility, support carbon sequestration, and contribute to sustainable residue management.