Many of the agricultural soils surrounding coal-burning power stations on the South African Highveld are acidic and require liming.  The large volume of fly ash produced as a by-product from the power stations may hold agricultural potential as a liming material.  A factorial field trial was conducted on Beestepan farm near Middelburg, Mpumalanga, to assess the viability of using fly ash as a liming material, and compare its performance to other neutralizing materials that are commonly used, namely agricultural lime and Calmasil®, and additionally observing the interaction of gypsum with these materials.

It was found that liming with fly ash in this field experiment reduced soil acidity and improved soil nutrient status and bean and maize yield for two seasons.  We found that larger quantities of flyash would be required in order to neutralize the soil when compared to lime or Calmasil.  However, if the other nutrient benefits (especially P and K) and if the use of fly ash is encouraged in the localities of power stations this may well be a viable route for both the farmers and Eskom to consider. This is pertinent at a time when input costs are rising and countries are being encouraged to reduce their carbon footprint.

Although fly ash was the least effective in increasing pH and improving soil basic cation levels among the liming materials evaluated, its effects on improvement of bean yield and maize yield was comparable to the other liming materials, and may be as a result of its nutrient content and supply of deficient plant nutrients such as P and K.