Comparison of calcium ameliorants and coal ash in alleviating the effects of subsoil acidity on maize root development near Middelburg, Mpumalanga

[摘要] ENGLISH ABSTRACT: Acidic soils are a major limitation to agriculture worldwide. The Highveld in SouthAfrica has many acidic soils and several coal burning power stations. These coalburning power stations generate alkaline fly ash as a waste material and it can thusserve as an ameliorant to the surrounding acidic soils.A two year field trial was undertaken to compare fly ash and other calciumameliorants to alleviate the effects of subsoil acidity on maize root development. Thefield trail was established on Beestepan Farm in Middelburg, Mpumalanga. Itconsisted of 24 treatments, each done in triplicate, rendering a total of 72 plots.The materials used were unweathered fly ash (CCE 10%), calcitic lime (CCE 77%)and Calmasil (a calcium silicate slag, CCE 99%). Calmasil and lime were applied atrates of 0-, 1-, 2-, and 4t/ha, while fly ash was applied at 0-, 7-, 14- and 28t/ha. Thesetreatments were applied to an acidic sandy loam soils in the presence or absence of4t/ha gypsum.Beans were harvested after the first season following the application of amendmentsand maize was harvested in the second season. Yield, root length, leaf and soilanalysis was undertaken to evaluate the effectiveness of the different limingmaterials. The effect of the treatments on fertility indicators such as pH, exchangeableacidity, Ca and Mg was investigated.Results indicated that all liming materials increased topsoil pH, soil nutrient and basestatus and crop yield in both seasons. Calmasil was the superior liming material in allrespects.Fly ash increased pH minimally but reduced exchangeable acidity by 12% and 24% inthe first and second seasons, respectively. Fly ash increased topsoil Ca levels from 74to 102mg/kg and subsoil Ca from 61 to 114mg/kg. Topsoil Mg levels were increasedfrom 7.3 to 16mg/kg and subsoil Mg was increased from 9.4 to 13mg/kg. Theconsequence of these increased nutrients was the subsequent increased foliar uptakeof Ca and Mg. The substantial increase in bean yield from 958 to 1724kg/ha andmaize yield from 5569 to 7553kg/ha following ash application compared well withresults obtained from lime and Calmasil application. This may partly be due to thepresence of additional plant nutrients such as P and K in the fly ash. Dissolutionbehaviour of fly ash indicates that upon exposure to acidity the release of micronutrients like B, Co, Cu, Fe, Mo, Mn and Zn occurs, and preliminary data showsthat there is comparatively little concern regarding heavy metal accumulation incrops.The application of 4t/ha gypsum had no effect on pH and decreased subsoil acidityonly minimally however, subsoil Ca status and acid saturation levels wereconsiderably improved which would possibly account for the overall beneficial effecton maize yield, increasing by an average of 1071kg/ha.It was not possible to make any conclusions relating treatment application and maizeroot length.This field trial has confirmed that fly ash can be used as an efficient liming materialand that it compares well with traditional liming materials.

[发布机构] Stellenbosch University