Irrigation water pH regulates cadmium accumulation, growth performance, and forage quality trade-offs in Sorghum (Sorghum bicolor L.).

BACKGROUND: Cadmium (Cd) contamination is a serious challenge to agricultural sustainability, threatening soil health, crop productivity, and the safety of food and feed chains globally. Irrigation water chemistry can significantly alter Cd mobility, plant uptake, and forage quality in arid and semi-arid regions. Sorghum (Sorghum bicolor L.) is an important forage valued for its high biomass production and stress tolerance. However, the role of irrigation water pH in regulating Cd accumulation, soil chemistry, and forage quality in sorghum remains poorly understood. METHODS: A pot experiment was conducted in which sorghum cv. 'Master BMR' was grown in soil contaminated with 10 mg kg⁻¹ Cd (cadmium sulfate, 3CdSO₄·8 H₂O). Irrigation water was adjusted to pH levels of 5.0, 6.0, 7.0, 8.0, and 9.0 using HCl/NaOH over a 120-day season. Cadmium concentrations in plant tissues, morphological traits, soil chemical properties, forage quality parameters, translocation factors (TF), and bioconcentration factors (BCF) were evaluated to determine the effects of irrigation water pH on Cd behavior and plant performance. RESULTS: Increasing irrigation water pH reduced Cd concentrations in roots, stems, leaves, and panicles. Root BCF was highest under acidic irrigation and lowest at pH 9. Alkaline irrigation was associated with lower tissue Cd concentration but higher ADF and NDF values and lower crude protein content. Better plant growth and biomass production were observed under moderately acidic to neutral irrigation conditions (pH 6-7). Multivariate analyses revealed strong interactions among Cd accumulation, soil chemistry, forage quality, and growth-related traits across the pH gradient. CONCLUSIONS: Irrigation water pH strongly influenced Cd behavior and forage quality in sorghum. Alkaline irrigation water lowered Cd concentrations in plant tissues but reduced forage nutritional value by increasing fiber fractions and decreasing crude protein. Considering Cd accumulation, plant growth, and forage quality together, pH 6-7 represented the most favorable overall compromise under the present pot-experiment conditions, although some aboveground Cd concentrations remained relatively high at pH 6. These results indicate that a near-neutral pH in irrigation water could mitigate heavy-metal risks in Cd-contaminated forage production systems. Nonetheless, further validation across various soils, sorghum varieties, levels of Cd contamination, and field conditions is necessary prior to making broad management recommendations.