Transport and plant uptake of Zn in an Oxyaquic Haplustalf amended with coal ash and sewage sludge: A field study

Field experiments were conducted to study the movement and uptake of Zn in an Oxyaquic Haplustalf (pH = 5.2) amended with coal ash (pH = 7.5) and sewage sludge (pH = 4.3) at low application rates. The plots received cumulative loadings of sludge (39.5 Mg ha(-1)), ash (78 Mg ha(-1)) and mixture of ash and sludge (1:2 i.e. 19.5:39 Mg ha(-1)) over two years. Irrigated peanut (Arachis hypogaea L.) was the test crop. Irrigations were scheduled at two levels viz. 15% (I-1) and 50% (I-2) maximum allowable depletion (MAD) of available soil water (ASW) in the root zone. Soil samples were collected from 0-15, 15-30, 30-45 and 45-60 cm depths during the experiment and analyzed for pH and water extractable concentration (WEC) of Zn. Pre and post experiment profile soil samples were also analyzed for total Zn concentration. The water extractable concentrations (WEC) of Zn were generally higher in sludge treated plots than the ones receiving mixture and ash. This is in accordance to the order of Zn loading by the amendments. Cyclic variation in WEC of Zn was perceptible within the top 15 cm layer of the soil compared to that at higher depths in all sampling periods across the treatments; but was more distinct in the case of plots treated with only sludge. The increase in WEC of Zn below 15 cm layer in sludge treated plots indicated the possibility of leaching. Noticeable increases in total Zn concentrations in the surface layers of sludge and mixture treated plots were observed. The total Zn concentration in the profile soil from sludge applied plots indicated significant movement of Zn within 15-30 cm and thereafter a marginal increase up to 45cm signifying the possibility of Zn movement at lower depths. Plant accumulation of Zn was the highest in sludge treated plots (150 mg kg(-1)) followed by the ones treated with mixture (99 mg kg(-1)) and coal ash (56 mg kg(-1)) as compared to the control (25 mg kg(-1)). On the other hand, the ratio of concentrations of Zn in the plant to its total in surface soil followed the order -: control < ash < mixture < sludge indicating that the plant accumulation is governed by its loading rates.