Rungsun Im-Erb, Noparat Bamroongrugsa, Koji Kawashima, Tomoyuki Amano, and Shigeru Kato

pp. 697 - 708

Abstract

The study on utilization of coal ash to improve acid soil was carried out in a greenhouse at the Land
Development Regional Office 1, Pathum Thani Province, Central Thailand, from January-May 2003. Fly ash
mixture (fly ash plus gypsum and lime at the proportion 5:4:1) and clinker ash mixture (clinker ash plus
gypsum and lime at the proportion 5:4:1) were used as soil amendments at varying rates i.e., 0, 6.25,12.5,
18.75 and 25 t/ha to improve the soil. The aim of this study was to determine the effect of application of coal
ash on acid soil and the growth of a vegetable (Chinese kale). Chinese kale cultivars were planted in a
randomized complete block design with three replications. Pak Chong soil series (Ultisols) was used as the
growth medium. Twenty-day-old seedlings were transplanted in 270 pots (two plants per pot) containing
acid soil with different treatments of coal ash mixture which were as follows: 1) control, 2) fly ash mixture
6.25 t/ha, 3) fly ash mixture 12.5 t/ha, 4) fly ash mixture 18.75 t/ha, 5) fly ash mixture 25 t/ha, 6) clinker ash
mixture 6.25 t/ha, 7) clinker ash mixture 12.5 t/ha, 8) clinker ash mixture 18.75 t/ha and 9) clinker ash mixture
25 t/ha. Chemical fertilizers were applied at the rate of 250 kg/ha using a grade of 15-15-15 of N, P and K,
respectively. Plants were harvested 40 days after transplanting. Among the treatments, application of fly ash
mixture at a rate of 25t/ha (4t/rai) substantially increased soil pH up to 5.7. Fly ash was found more effective than clinker ash in increasing soil pH. The highest yield of Chinese kale was also obtained when fly ash
mixture was applied at a rate of 25 t/ha followed by fly ash mixture at 18.75 t/ha and clinker ash mixture at
18.75 t/ha with an average yield per plant of 4.980, 3.743 and 3.447 grams, respectively. It can be concluded
that the application of coal ash mixture, either fly- or clinker ash, at 18.75-25 t/ha (3-4 t/rai) was the most
effective in terms of plant yield. The use of coal ash mixture increased cation exchange capacity, base saturation percentage and Ca, Mg and S contents in the soil as well as plant uptake of N. The concentrations of
heavy metals in the soil (Cd, As, Co, Cr, Cu, Hg, Ni, Pb and Zn) were found to be within permissible levels
while Cd, Cr and Ni in the plants were at critical levels for health.