Growth and lead accumulation by the grasses Vetiveria zizanioides and Thysanolaena maxima in lead-contaminated soil amended with pig manure and fertilizer: a glasshouse study

Bo Ngam lead mine soils contain high concentrations of lead (up 1% total Pb) and low amounts of organic matter and major nutrients (N, P, K). A glasshouse study was conducted to compare growth performance, metal tolerance and metal uptake by two grasses, Thysanolaena maxima (Roxb.) O. Kuntze and four ecotypes of Vetiveria zizanioides (L.) Nash, syn. Chrysopogon zizanioides (L.) Roberty (three from Thailand: Surat Thani, Songkhla and Kamphaeng Phet, and one from Sri Lanka) and to study the effects of pig manure (20% and 40% w/w) and inorganic fertilizer (75 and 150 mg kg(-1)) amendments to this lead mine soil. The results showed that both T. maxima and V. zizanioides (Surat Thani and Songkhla) could tolerate high Pb concentrations in soil (10750 mg kg(-1)) and had very good growth performance. Application of pig manure increased electrical conductivity (EC) and reduced DTPA-extractable Pb concentration in the soils. Pig manure application improved the growth of vetiver, especially at 20%, application dosage. Vetiver had the highest biomass. T. maxima could not tolerate high EC values. The uptake by roots and transport of Pb to shoots of both species was reduced when soils were amended with pig manure. Application of inorganic fertilizer did not improve growth of vetiver but did improve that of T. maxima. Fertilizer application did not have any great influence on the Pb uptake in vetiver while T. maxima took up more Pb as a result of the fertilizer enhancing its biomass yield. Both species transported low Pb concentrations to shoots (8.3-179 mg kg(-1)) and accumulated higher concentrations in roots (107-911 mg kg(-1)). In summary, both species may be species well suited for phytostabilization in tropical lead mine areas.