Effect of sewage sludge application on growth and photosynthetic pigments in vetiver grass (<em>Vetiveria zizanioides</em> L. Nash)

Abstract

The study was conducted to evaluate the effect of sewage sludge application on growth and photosynthetic pigments in vetiver grass. Vetiver plants were grown in poly-ethylene U-V stabilized grow bags (24 X 24 X 40) for a period of three months (90 days), where the soil treated with different sewage sludge concentrations (0, 25, 50 and 75%). Physico-chemical characterization of sewage sludge showed that it was slightly acidic with significant concentrations of heavy metals (Cd, Cr, Cu, Pb and Zn), nutrients and mineral ions. Results showed that there were no apparent symptoms of toxicity on the morphology (leaf color, plant height and number of leaves) of the sludge amended vetiver plants. It has been observed that 25% sludge concentration has a favorable effect on the growth and photosynthetic pigments of plants. But at 50 and 75% sludge concentration, photosynthetic pigments such as chlorophylls and Pheophytin content showed a gradual decline with increase in sludge concentration while the carotenoid content was increased gradually. Even though compared to control plants sludge amendment increased the total wet biomass production in all the experimental plants with a gradual increase with increase in sludge concentration. This study proves that use of sewage sludge as an amendment will improve the growth and biomass production in vetiver plants up to 25% of the total soil. But even at this concentration carotenoid content was high and it may be due to defense mechanisms induced in response to heavy metal stress. The study, therefore, suggests that even though the sewage sludge is highly enriched with various nutrients, considering the heavy metal content, the fertilizer application of sewage sludge is dangerous, because the risk of environmental contamination is very high. The study pointed out that the vetiver plants growing in sludge amended area have potentially developed the defense strategy to combat against heavy metal toxicity. Therefore, the highly tolerant vetiver plants (Vetiveria zizanioides, L. Nash) may be used for phytoremediation purposes.