Abstract
This research aimed to evaluate the residual Cu and Zn in tropical soil over 21 years after amendment with industrial waste, lime, and compost. Soil samples were collected from a well-maintained experimental field amended one time with industrial waste high in Cu and Zn set in 1998 at about 1.5–20 years after amendment. Treatments were arranged in a randomized block design with a metal-wares industrial waste at rates 0, 15, and 60 Mg·ha−1, lime at 0 and 5 Mg·ha−1, and compost at 0 and 5 Mg·ha−1. Soil samples were also taken vertically in the exact plot centers at depths of 0–75 cm of plots not amended with lime and compost and also from topsoils (0–15 cm) at 90 points with distances 50 cm between each other in each of the respective plots 21 years after amendment. Significant increases in Cu and Zn caused by waste were observed over 21 years. The increase in soil pH by lime was observed over 10 years but its effect in decreasing Cu and Zn was observed only at 1.5 years, particularly in topsoils. However, the effect of lime in lowering Cu and Zn was observed over 20 years when waste and/or compost were also given. Similarly, the effect of compost was absent over 20 years but significant when waste and/or lime were also given. The relative concentration of Cu and Zn in the 60 Mg waste ha−1 plots decreased over 20 years to 17–53% for Cu and to 12–33% for Zn; their concentrations were, in general, lower with lime and/or compost addition. The relative concentrations of Cu and Zn significantly decreased over 21 years in plots with 15 or 60 Mg·ha−1 and increased in the control plots. Heavy metals moved in soil significantly through soil tillage and erosion and partially by leaching.
Highlights
High concentrations of heavy metals in soils must be properly managed [1,2,3,4,5,6,7,8,9,10,11]
Some significant amounts of Cu and Zn were observed in 30–60 cm layers, in high metal plot (HMP), and insignificant amounts in control plot (CP) and low metal plot (LMP)
When combined with waste or lime, organic compost significantly decreased the soil concentrations of Cu and Zn (Tables 3 and 4, Figures 5 and 6) for some time of observation. e increase in soil pH due to waste or lime treatment (Table 5) may have enhanced the adsorption sites on the remaining organic matter functional groups. is process may have eventually decreased the soil concentrations of Cu and Zn. e significant effect of organic compost was observed after 3, 10, and 20 years when compost was combined with waste and lime (Tables 3 and 4, Figures 5 and 6). e presence of OH− ions at higher soil pH by lime may have detached bonded H on the organic matter functional
Summary
High concentrations of heavy metals in soils must be properly managed [1,2,3,4,5,6,7,8,9,10,11]. Ese mechanisms have been reported to lower the heavy metal labile fractions in the soils [20,21,22]. Previous researches showed that the increase in soil pH by liming and in soil colloid negative charges by organic matter amendment significantly reduced the DTPA-extracted Cu, Cd, and. Some other soil workers reported the reducing effects of lime and/or organic matters on soil heavy metal concentrations [22, 24,25,26,27]. Some soil workers [28, 29] showed the movement of some heavy metals in soils treated with heavy metal containing
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