Year: 2008
Type: dissertation
Abstract: Soil acidity is one of the greatest limitations to crop production in most soils of the \nworld. The increasing high costs of conventional liming materials have made it \nnecessary to explore the possibilities of using cheaper substitutes. In South Africa, 16 \nmillion hectares of land are naturally acid while on the other hand, the country’s coalfired \npower plants generate 28 million tons of mostly alkaline coal ash per year, \ndisposal of which is increasingly becoming difficult. The use of coal ash as an \nagricultural soil amendment while solving the liming needs of local farmers, may also \npresent a safe and more economical disposal option. This study was carried out to \nevaluate the effectiveness of coal ash as an agricultural liming material. A greenhouse \nexperiment was conducted using maize as test crop. A field experiment was also \nestablished on Beestepan Farm in Middelburg, Mpumalanga Province using dry beans \nas test crop for the first season. In both experiments, fresh unweathered coal ash from \nDuvha power station (CCE 10%), dolomitic lime (CCE 77%) and calmasil (calcium \nsilicate slag, CCE 99%) were applied to acidic sandy loam soils in the presence or \nabsence of gypsum. Both calmasil and dolomitic lime were applied at equivalent rates \nof 0, 1, 2, and 4 tons/ha, and rates of 0, 7, 14 and 28 tons/ha were used for ash. \nGypsum was applied at a rate of 4 tons/ha. All treatments were applied in three \nreplications. Results showed that liming increased soil pH, improved soil nutrient \nstatus and plant uptake of base cations, and enhanced yield. In the greenhouse, coal \nash decreased exchangeable acidity from 13.0 mmolc/kg to 6.67 mmolc/kg, increased \nCa levels from 200 mg/kg to 379 mg/kg, and increased Mg levels from 25.9 mg/kg to \n42.0 mg/kg. Nitrate levels were also raised from 4.4 mg/kg to 14.8 mg/kg \nhypothetically as a result of the increase in the activity of nitrifying bacteria following \na decrease in soil acidity after ash application. Maize yield in the greenhouse was not \nsignificantly affected by ash or by other liming materials, and the sufficient watering \nand consequent elimination of aluminium-induced drought stress is put forward as \nhaving masked crop responses to acidity. In the field, coal ash reduced exchangeable \nacidity from 10.0 mmolc/kg to 5.88 mmolc/kg, increased Ca levels from 71 mg/kg to \n132 mg/kg, and increased Mg levels from 7.3 mg/kg to 17 mg/kg. The increase in \nbean yield from 958 kg/ha to 1724 kg/ha by ash was similar to that realized by \ndolomitic lime and calmasil. Gypsum had little effect on soil acidity, but it \nsubstantially 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 \nmaterial, and underscores the need for a cost-benefit assessment of ash use \nnecessitated by the relatively higher rates of ash required to obtain significant soil and \nplant responses.
Author: Ikenna Mbakwe
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W769412093