Saturday, 15 July 2006

Impacts of Long-Term Land Application of Poultry Litter on Metal Status in Soil.

Irenus A. Tazisong1, Zhongqi He2, Zachary N. Senwo1, and Donglin Zhang3. (1) Alabama A&M Univ, Plant and Soil Science, P.O. Box 1208, 4900 Meridian St, Normal, AL 35762, (2) USDA-ARS, New England Plant, Soil, and Water Laboratory, Orono, ME 04469, (3) Univ of Maine, Dept of Plant, Soil and Environmental Sciences, Orono, ME 04469

Poultry Litter (PL) often contains fairly high concentrations of heavy metals due to their uses as growth promoters or biocides in poultry feeds. Whereas some of these elements are micronutrients for plant growth, high concentrations that have accumulated in soils due to long-term PL application could lead to crop toxicities. Thus, in this study, we determined the concentrations of 10 metals (Al, Fe, Cu, Mn, Ni, Zn, Cr, Pb, Cd, and Mo) in pastured soils with various histories of PL application to get insights in their long-term impacts on soil metal status. Samples were collected from three soil depths (0 20, 20-40, and 40-60 cm) of the Hartsells series (fine-loamy, siliceous, subactive, thermic, Typic Hapludults) on a 3-8% slope in the Sand Mountain region of north Alabama. Soils had received annual broiler litter applications for 0, 5, 10, 15, and 20 years at rates of 0, 2.27, 2.27, 3.63, and 1.36 Mg ha-1 yr-1, respectively. Total and diethylenetriaminepentaacetic acid (DTPA)-extractable metal concentrations in these soil samples were determined and analyzed. The Al and Fe concentrations (6000 to 22000 mg/kg soil) in the soils were far greater compared to the other metals tested in this study. PL application increased total concentrations of Al and Fe in all soil depths. Although similar patterns in increase of total concentrations were observed, the patterns in DTPA-extractable concentrations of the two metals were different. PL application increased DTPA-extractable Fe in 0-20 cm soil, with no impact on Fe in 40-60 cm, but indeed reduced the DTPA-extracted amount of Al. These observations demonstrated that these two metals from PL application had been transferred or immobilized in deep soil. The concentrations of Cu and Mn were in the range of 40 to 120 mg/kg soil. PL application increased both total and DTPA-extractable Cu concentrations in an order responding to the cumulative amounts of PL applied. The impact of PL application on Mn concentrations was not significant. PL application affected the status of other trace elements. Total and DTPA-extractable Zn concentrations increased with the increase of cumulative amounts of PL applied, but the extent of the impacts decreased with soil depths. Total Pb concentrations fluctuated over application years and the amplitude of fluctuation decreased with the soil depth. On the other side, the levels of DTPA-extractable Pb were basically unchanged over application years. The total Cd concentrations were lower in most PL-applied soils than unamended soil, but DTPA-extractable Cd concentrations were higher with PL-applied soils. The patterns of increasing DTPA-extractable Cd concentrations seem to complement the decrease in total Cd, suggesting that PL mobilized Cd in soils. The change of Cr status due to PL application was basically similar to that of Fe. Changes in Mo and Ni concentrations were observed, but the standard deviations were so great that these changes were not statistically significant. Our data indicate that the build-up of some metals in soils was significant with long-term PL application, but not for others. However, the extractability, or mobility and bioavailability, were not built up in similar patterns to the total metal concentrations. Furthermore, deciphering the relationships between the build-up and extractability with the cumulative amounts and/or years of PL application would improve the prediction of their long-term impacts on metal behaviors in soils.

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