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) bioavailab ility to corn seedlings (Zea mays L) in an artificial soil mix produce d from alkaline coal fly ash and sewage sludge under greenhouse condit ions. 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 a t either 1:1 or 1:5 (v/v). Both water soluble B (WS-B) and hot water s oluble B (HWS-B) increased with an increase in the fly ash amendment r ate. Plant tissue B contents also increased according to the rate of a sh 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 conten ts than with WS-B, and HWS-B gave a better indication on soil B availa bility. Boron toxicity symptoms in leaf margins were observed in 50% a nd 35% ash-amended sludge at 1:1 soil-mixing ratio, with shoot [B] rea ching 225 mg kg(-1). However, a significant yield reduction was observ ed only at 50% ash-amended sludge at 1:1 v/v, indicating that factors in addition to B might affect plant growth.