Calcium Water Treatment Residue Reduces Cu Bioavailability In Cu-Contaminated Soils – a Green House Study.

Due to its wide and repeated use in agriculture and horticulture as fertilizers or fungicides copper contamination to agricultural soils has been accelerated, and so has its export potential to water bodies. In this study, a greenhouse study was conducted to test the ability of calcium water treatments residue (Ca-WTR, pH 9.1, containing mainly CaCO₃ and minor CaO) to reduce the toxicity and uptake of Cu by crop plants in Cu-contaminated sandy soils.  Ryegrass (Lolium perenne L.) and lettuce (Lactuca sativa L.) were used as indicator crop plants and grown for eight weeks in the Cu-contaminated soils (Alfisol and Spodosol with and without addition of 1000 mg Cu kg^-1 soil) amended with different levels of Ca-WTR (5 to 100 g kg^-1 soil). The growth of plants was inhibited in the slightly Cu-contaminated soils (~100 mg kg^-1), but no plant survived in the highly Cu-contaminated soils (added with 1000 mg kg^-1). Plant biomass yields increased with Ca-WTR application rates at the low levels (5-20 g kg^-1 for Alfisol, pH 5.45 and 5-50 g kg^-1 for Spodosol, pH 4.66), reached maximum at the moderate level (10-50 g kg^-1), but decreased at the high levels (>20 g kg^-1 for Alfisol and >50 g kg^-1 for Spodosol). Copper concentrations in ryegrass shoots decreased significantly with increasing Ca-WTR application rates and thus improved plant growth as evidenced by a significant increase in plant biomass yield (P<0.01). For lettuce, plant Cu concentration decreased only at the high Ca-WTR rates. In comparison, ryegrass had a higher potential for Cu uptake and translocation than lettuce in both soils. These results indicate that application of Ca-WTR at adequate amounts could effectively increase plant growth and reduce plant Cu uptake which merit attention in the remediation of Cu-contaminated soils.