A Keratin-Ash Biocomposite Mitigates Boron Toxicity by Regulating Boron Uptake in Maize and Subsequently Grown Sorghum in Soils with Varying Native Boron Levels

Boron (B) toxicity limits crop production in arid and semi-arid soils. This study evaluated a sheep wool-poultry litter ash biocomposite (WASH) for mitigating B toxicity in maize and a subsequent sorghum crop. A pot experiment was conducted using four soils collected from different sites with contrasting plant-available B concentrations (1.2, 3.1, 6.1, and 9.3 mg kg− 1), to which WASH was applied at rates of 0, 1, 2, and 4 g kg− 1. Dry matter production, plant B, N, and P concentrations, and post-harvest soil plant-available B and P were determined. WASH application significantly increased biomass across all soils, with the greatest relative improvements observed in soils with moderate (6.1 mg kg− 1 B) to high B levels (9.3 mg kg− 1 B). Optimal maize growth was generally achieved at the 2 and 4 g kg− 1 rate of WASH application rate, while biomass in the highest-B soil increased progressively with increasing WASH application. Plant B concentrations in both crops increased with soil B content but were substantially reduced by WASH application in soils containing 6.1 and 9.3 mg kg− 1 B, indicating effective regulation of B uptake. Sorghum grown subsequently exhibited clear residual benefits of WASH, with dry weight responses varying according to soil-B level and application rate. Post-harvest soil analyses showed no consistent trend for plant-available B, while plant-available P increased significantly with increasing WASH rates after both cropping cycles. The WASH biocomposite effectively mitigated B toxicity by regulating plant B uptake and enhancing nutrient availability and crop productivity, demonstrating its potential as a sustainable, waste-derived amendment for B-affected soils.