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TECHNICAL REPORTS

Waste Management

The Disposal of a Lime Water Treatment Residue on Soil and Spoil Material from a Coalmine

A Glasshouse Investigation

^a Soil Science, School of Environmental Sciences, Univ. of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, South Africa
^b Agricultural Research Council, c/o Univ. of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, South Africa
^c College of Agriculture, Engineering and Science, Univ. of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, South Africa

^* Corresponding author (hughesj{at}ukzn.ac.za)

Received for publication July 10, 2006. Eragrostis tef (Zucc.), Cenchrus ciliaris L., and Digitaria eriantha Steud. were grown in a soil (Psammentic Haplustalf) and spoil material from a coalmine both treated with a lime water treatment residue (WTR) at rates of 0, 50, 100, 200, and 400 g kg^–1. The yield of the grasses, from the sum of the three harvests, and concentrations of B, Ca, Cu, K, Fe, Mg, Mn, N, Na, P, and Zn in foliage from the second harvest were determined. The yield of grasses grown in the soil decreased exponentially as WTR application increased. The yields of C. ciliaris, D. eriantha, and E. tef (in the 400 g kg^–1 WTR treated soil) decreased by 74.4, 78.7, and 59.8%, respectively, when compared with the control treatments. In the spoil, the yield of E. tef and D. eriantha decreased by 13.6% and and D. eriantha by 23.9%, while an increase was observed for C. ciliaris (45.4%), at the highest WTR application rate. No relationship existed between yield of E. tef and WTR application rate when grown in the spoil, while a weak negative linear relationship (p < 0.05) was found for D. eriantha and a positive linear relationship existed for C. ciliaris. Magnesium concentrations of the grasses were positively correlated to WTR application rate. Grasses grown in the soil had higher Na concentrations, while those grown in the spoil typically had higher B, N, and Zn concentrations. The decreases in yield were attributed to nutrient deficiencies (notably Zn), induced by high WTR application rates that led to high substrate pH. Disposal of high rates of WTR on the mine materials was not recommended.

Abbreviations: ANOVA, analysis of variance • CCE, calcium carbonate equivalence • CEC, cation exchange capacity • DAE, days after establishment • EC, electrical conductivity • OC, organic carbon • RDA, redundancy analysis • WTR, water treatment residue