Pyrolysis of different organic feedstock combinations as soil amendments enhances the reclamation of saline-sodic soil

Utilizing agricultural wastes (e.g., straw, bagasse, manure) as amendments to remediate saline-sodic soils can be beneficial for improving soil quality and better waste management. In this study, we investigated the impact of raw and pyrolyzed feedstocks on salt leaching potential and physical and chemical properties in a saline-sodic silt loam soil. Utilizing a column experiment within a completely randomized design, we evaluated five feedstock combinations (i.e., rice husk, pine wood, cow manure, sugarcane bagasse) as amendments (69 Mg ha–1), including variations of raw feedstock and feedstock pyrolyzed at 300 and 500 °C, alongside a control (CT). For both the amended soil and the leachate, we measured electrical conductivity (EC), sodium adsorption ratio (SAR), pH and cations. Soil saturated hydraulic conductivity (K S) and bulk density (BD) were also measured. The BWR treatment (i.e., sugarcane bagasse, pine wood, and rice husk) exhibited notable improvements in soil physical quality (i.e., decreased BD and enhanced K S). Raw feedstock significantly (p < 0.01) increased soil leachate EC SAR, except for WM (i.e., pine wood and cow manure). The BWR treatments expedited the reduction of soil salinity and sodicity, evident in lower SAR/SARmax and EC/ECmax ratios, indicative of increased leaching potential. The amendments consistently demonstrated a trend of reducing soil SAR compared to the control, with raw feedstock exhibiting a more pronounced effect. Soil ECe decreased after amending with feedstock pyrolyzed at 500 °C compared to raw feedstock and pyrolyzed at 300 °C. Feedstock pyrolyzed at 300 °C did not significantly alter soil pH after leaching, and there was a decrease in the soil Na+/K+ ratio, especially with pyrolyzed feedstock. After leaching, the pyrolyzed feedstock treatments showed better soil aggregate stability (Mg2+/Ca2+<1) compared to raw feedstock. Based on the aggregated amelioration score for each amendment combination, BWR treatments consistently outperformed other combinations, with BWR300 being the most favorable option due to its lower production cost compared to BWR500. This study highlights BWR pyrolyzed at 300 °C as a suitable amendment for improving soil conditions, reducing salinity and sodicity, and increasing leaching potential.