Abstract
Contamination of agricultural and industrial lands by environmentally dangerous metals (heavy metals) such as Cd, Pb, Cu, and Zn poses a major threat to food security, ecosystem balance, and the agrobiological capability of soils in the arid regions of Kazakhstan. This research thoroughly assessed the efficiency of the combined application of electrokinetic (EK) remediation and pyrolyzed organic matter (biochar) across three distinct soil types - Light gray soil, Light Chestnut Soil, and chernozem (black) soil. The fundamental soil characteristics (pH, trace elements, organic matter, macronutrients, cation exchange capacity, exchangeable cations, particle size distribution) were identified per international guidelines. The remediation process was divided into two phases: (1) EK treatment (30 V, 12 h, 0.01 M citric acid), and (2) biochar augmentation (0, 15, 25, 35 t/ha). Findings indicated that the EK treatment alone diminished the mobile fractions of heavy metals by approximately 20–60%, whereas the combination of EK + biochar enhanced this effectiveness to 60–95%. The most significant immobilization was recorded for Cu and Zn: in Light gray soil and chernozem soils, the decline in the mobile form of Zn reached 76–80%, and for Cu — 61–95%. Pb and Cd also demonstrated substantial reductions, being immobilized within the range of 65–80%. Differences between soil types were revealed: in chernozem soils, biochar bound heavy metals most intensely, leading to a sharp decrease in mobile forms; whereas in Light gray soil and Light Chestnut soils, the immobilization efficiency increased proportionally with the dose applied. A multifactorial ANOVA revealed a substantial impact of biochar dosage, soil type, and pollution severity on all assessed parameters ( p < 0.001; η² ranged from 0.75 to 0.93). Tukey’s Honestly Significant Difference (HSD) test further confirmed that all tested biochar doses (0, 15, 25, and 35 t/ha) produced statistically significant variations. Phytomeliorant yields showed a considerable enhancement across all soil types, with plant numbers rising 3 to 10-fold, plant heights increasing 2 to 5-fold, and productivity index (PI) peaking at approximately 7000 to 7500 in chernozem soils. This indicates that biochar reduces the phytotoxicity of heavy metals. Overall, EK + biochar technology is a highly effective, synergistic approach for restoring soils contaminated with heavy metals to an environmentally safe condition and for recovering their agrobiological productivity under various natural-regional conditions of Kazakhstan.