Thesis (MScAgric (Soil Science))--Stellenbosch University, 2005. / Soil acidity is one of the greatest limitations to crop production in most soils of the
world. The increasing high costs of conventional liming materials have made it
necessary to explore the possibilities of using cheaper substitutes. In South Africa, 16
million hectares of land are naturally acid while on the other hand, the country’s coalfired
power plants generate 28 million tons of mostly alkaline coal ash per year,
disposal of which is increasingly becoming difficult. The use of coal ash as an
agricultural soil amendment while solving the liming needs of local farmers, may also
present a safe and more economical disposal option. This study was carried out to
evaluate the effectiveness of coal ash as an agricultural liming material. A greenhouse
experiment was conducted using maize as test crop. A field experiment was also
established on Beestepan Farm in Middelburg, Mpumalanga Province using dry beans
as test crop for the first season. In both experiments, fresh unweathered coal ash from
Duvha power station (CCE 10%), dolomitic lime (CCE 77%) and calmasil (calcium
silicate slag, CCE 99%) were applied to acidic sandy loam soils in the presence or
absence of gypsum. Both calmasil and dolomitic lime were applied at equivalent rates
of 0, 1, 2, and 4 tons/ha, and rates of 0, 7, 14 and 28 tons/ha were used for ash.
Gypsum was applied at a rate of 4 tons/ha. All treatments were applied in three
replications. Results showed that liming increased soil pH, improved soil nutrient
status and plant uptake of base cations, and enhanced yield. In the greenhouse, coal
ash decreased exchangeable acidity from 13.0 mmolc/kg to 6.67 mmolc/kg, increased
Ca levels from 200 mg/kg to 379 mg/kg, and increased Mg levels from 25.9 mg/kg to
42.0 mg/kg. Nitrate levels were also raised from 4.4 mg/kg to 14.8 mg/kg
hypothetically as a result of the increase in the activity of nitrifying bacteria following
a decrease in soil acidity after ash application. Maize yield in the greenhouse was not
significantly affected by ash or by other liming materials, and the sufficient watering
and consequent elimination of aluminium-induced drought stress is put forward as
having masked crop responses to acidity. In the field, coal ash reduced exchangeable
acidity from 10.0 mmolc/kg to 5.88 mmolc/kg, increased Ca levels from 71 mg/kg to
132 mg/kg, and increased Mg levels from 7.3 mg/kg to 17 mg/kg. The increase in
bean yield from 958 kg/ha to 1724 kg/ha by ash was similar to that realized by
dolomitic lime and calmasil. Gypsum had little effect on soil acidity, but it
substantially improved soil Ca and sulfate levels, and enhanced bean yield in the field experiment. The study demonstrated that coal ash could be effective as a liming
material, and underscores the need for a cost-benefit assessment of ash use
necessitated by the relatively higher rates of ash required to obtain significant soil and
plant responses.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1976 |
| Date | 12 1900 |
| Creators | Mbakwe, Ikenna |
| Contributors | Fey, M. V., Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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