Boron availability in ash-sludge mixture and its uptake by corn seedlings (Zea mays L)

A pot experiment was conducted to investigate the boron (B) bioavailability to corn seedlings (Zea mays L) in an artificial soil mix produced from alkaline coal fly ash and sewage sludge under greenhouse conditions. Sludge was amended with ash at an application rate of 0, 5, 10, 35, and 50% (w/w), and each mixture was then mixed with a loamy soil at either 1:1 or 1:5 (v/v). Both water soluble B (WS-B) and hot water soluble B (HWS-B) increased with an increase in the fly ash amendment rate. Plant tissue B contents also increased according to the rate of ash amendment, and at high ash application rates, more than 70% of the tissue B content was accumulated in leaves. Among the plant organs, B contents of young leaves showed a better correlation with HWS-B contents than with WS-B, and HWS-B gave a better indication on soil B availability. Boron toxicity symptoms in leaf margins were observed in 50% and 35% ash-amended sludge at 1:1 soil-mixing ratio, with shoot [B] reaching 225 mg kg^-1. However, a significant yield reduction was observed only at 50% ash-amended sludge at 1:1 v/v, indicating that factors in addition to B might affect plant growth.