ACCURATE LIME RECOMMENDATIONS UNDER SOUTH AFRICAN CONDITIONS

Abstract

In a trial to test the bioavailability of certain heavy metals from slags, twelve liming materials (including different slags) were applied at three different rates to an Acrisol (sandy loam, pH_(Water) of 5.2 and CEC of 4 cmol_c kg⁻¹) from the South African Eastern Highveld. Two Ca(OH)₂ incubations were done on the specific soil—one in a soil to solution ratio of 1:1 before the trial and another in a soil to solution ratio of 1:2.5 on the control treatment soil after the trial. The Calcium Carbonate Equivalents in HCl (CCE) and RH-values (Resin Suspension Method) were determined for each lime before the trial. After an incubation period of three months, the pH_(Water) and pH_(KCl) of each of the four replicates for every treatment was measured. An incubation curve and regression equation was drawn up for each lime using the average pH values. Lime recommendations for each lime to target pH-values of 5.8, 6.8, and 7.8 were modeled using the CCE and RH-values as well as the values from the two Ca(OH)₂ incubations. The soil to solution ratio of 1:2.5 and the RH-value gave a very accurate indication of the lime required for the specified pH targets of 5.8 and 6.8. All the methods underestimated the lime required for the target of 7.8. The CCE value overestimated lime reactivity, especially in the case of courser liming materials. However, the RH-value gave a more accurate indication of the reactivity of the lime, especially through the pH ranges 5.8 to 6.8.

ACKNOWLEDGMENTS

The authors wish to acknowledge H. Pistorius & Group and THRIP (Technology and Human Resources for Industry Programme) for funding the project.