Reclaiming saline soil by using acid-modified pineapple biochar

Abstract

Global food security is increasingly threatened by soil salinization, which reduces agricultural productivity. This study evaluates the potential of biochar derived from pineapple crown waste, modified with different acids and produced by slow pyrolysis, to improve the physicochemical properties of saline sandy loam soil. The objectives were to characterize acid-modified biochar and assess its effects on soil pH, electrical conductivity (EC), and water-holding capacity (WHC). The soils were incubated with sulfuric, nitric, and hydrochloric acid-modified pineapple biochars pyrolyzed at 300°C, 350°C, and 400°C. Changes in pH, EC, and WHC were measured over 10, 20, and 30 days. Biochar functional groups were characterized, and data were analyzed using ANOVA with Tukey’s HSD test. Simple linear regression evaluated WHC–EC relationships over time. FTIR showed that biochar pyrolyzed at 300°C retained more carbonyl and phenolic groups, while higher temperatures favored aromatic structures. Among treatments, nitric acid-modified biochar at 300°C was most effective, reducing pH to 6.04, lowering EC to 2.24 mS cm−1, and increasing WHC to 94.30%. These results demonstrate that acid-modified pineapple biochar provides a sustainable, low-cost strategy for mitigating soil salinity while enhancing soil water retention and management in degraded sandy soils.