Assessing the Feasibility of Sewage Sludge Applications for the Cultivation of Brassica Juncea L.: Metal Accumulation, Growth, Biochemical and Yield Responses.

Abstract

The present study was conducted to examine the suitability of sewage sludge amendment in soil for mustard (Brassica juncea var. Alankar) by evaluating the heavy metal accumulation, growth, biochemical and yield responses of plants grown at 0, 5, 10, 20, 40, 70 and 100% sewage sludge amendment (SSA) rates. Sewage sludge amendments modified the properties of soil by decreasing pH and increasing organic carbon, total nitrogen and heavy metals in resulting soil-sludge mixtures. Plants showed significant (p < 0.05) increments in root length, shoot length, plant fresh mass and plant dry mass at 10 to 40% SSA rates as compared to unamended soil, but these parameters decreased significantly at SSA rates ≥ 70% at 60 days after sowing (DAS). Biochemical parameters such as photosynthetic pigment content, proline, cysteine, protein and sugar contents in fresh leaves also showed the same trend. Yield of mustard increased by 18.90, 41.80 and 15.42% at 10, 20 and 40% SSA rates, respectively, when compared to those grown in unamended soil. Concentrations of Cd and Pb in mustard shoots were higher than the Indian safe limits of human consumption (for Cd = 1.5 mg kg-1 and for Pb = 2.5 mg kg-1) at all amendment levels. Values of tolerance index (TI) in present study revealed that the selected cultivar is well adapted to tolerate and accumulate high quantities of heavy metals due to increased level of antioxidant cysteine and various other biochemical parameters in leaves when grown in soil amended with 5 to 40% sewage sludge. Therefore, it could be concluded that the selected cultivar if grown on sewage sludge amended soil, may act as important pathway for transfer of metals to primary plant consumers including humans. Further it may be recommended that proper guidelines should be laid for the recommended dosage of agricultural use of sewage sludge in countries which lack such guidelines.