EFFECTS OF FLY-ASH ON YIELDS AND ELEMENTAL COMPOSITION OF 2 VEGETABLES, BRASSICA-PARACHINENSIS AND BRASSICA-CHINENSIS

Coal fly ash was applied at rates of 0, 3, 6 and 12% to a sandy soil and a sandy loam to evaluate its effect on yields of two vegetable crops, Brassica parachinensis and B. chinensis. The addition of ash at the highest rate raised the pH of sandy soil and sandy loam from 7.3 and 6.7 to 9.7 and 8.6, respectively. Electrical conductivity also increased from 56 to 2035 μmhos cm-1 for sandy soil and 135 to 341 μmhos cm-1 for sandy loam. Hence, sandy loam had a higher buffering capacity for receiving the ash amendment than sandy soil. As compared with 0% ash treatment, yields were found to be significantly higher for 3% ash-amended sandy soil, while yields at 12% level were significantly lower. For sandy loam, B. chinensis had the highest yield at 3% ash amendment while B. parachinensis showed this at 12% ash amendment. Tissue Fe and Zn contents were consistently decreased with an increase in ash amendment. Accumulation of Mo and Mn were observed consistently with an increase in ash amendment while Cu and Ni did not exhibit any general trend of accumulation. Both accumulation and reduction of metals in plant tissue were significantly correlated with the pH of ash-amended soils. Nevertheless, no plant toxicity symptom was noticed in any of the treatment groups. However, the addition of ash to a level of more than 10% caused significant reduction in growth especially for soil with low buffering capacity such as the sandy soil used in the present experiment. © 1990.