Ammonium Bicarbonate‐DTPA and DTPA Extractions of Sludge‐amended Soils

Abstract

AbstractA DTPA (diethylenetriaminepentaacetic acid) solution is typically used to extract sludge‐amended soils to determine the relationship between soil concentration and plant levels of certain trace elements. The objective of this study was to compare the standard DTPA soil test method with the ammonium bicarbonate (NH4HCO3)‐DTPA (AB‐DTPA) procedure for extraction of trace elements, and to correlate extractable levels with elemental concentration in leaf of Swiss chard (Beta vulgaris L., cv. Fordhook Giant) grown in the greenhouse and in the grain and straw of hard red winter wheat (Triticum aestivum L. cv. Vona) grown in the field. For the greenhouse study, sewage sludges containing low (Fort Collins, CO) and high (Chicago, IL) metal conent were added to Nunn clay loam (Aridic Argiustolls, pH = 8.0) and Redfeather loamy sand (Lithic Cryoboralfs, pH = 5.3) at rates ranging from 0 to 120 Mg dry sludge ha−1 in 15 Mg ha−1 increments. For the greenhouse study, coefficients of correlation (r) for the greenhouse study between AB‐DTPA and plant concentrations of Cd, Cu, Ni, and Zn in Swiss chard were > 0.90 for the calcareous soil (Nunn) and > 0.93 (except for Cu) for the acidic soil (Redfeather). Even though DTPA extracted less Cd, Cu, Ni, Pb, and Zn than AB‐DTPA, the r values between these two extractants were > 0.98 for each metal. For the field studies involving addition of a low metal sludge from Littleton/Englewood, CO, to four sets of plots from 1982 to 1985, only the DTPA levels of Zn correlated significantly (r = 0.84) with the associated grain concentration. In contrast, AB‐DTPA provided significant correlations between soil levels and concentrations of Cd (r = 0.57) and P (r = 0.43) in straw and the Ni (r = 0.42), Pb (r = 0.83), Zn (r = 0.82), and P (r = 0.39) in the grain. The field studies indicate that when a low metal sludge is applied at rates consistent with N needs of the crop, levels of AB‐DTPA extractable Zn and possibly Pb should indicate the potential for Zn and Pb uptake into wheat. Because the concentrations of Cd, Cu, and Ni in the sludge applied did not result in plant uptake at levels that were significantly different from those in the untreated control, nonsignificant correlations were found. Also, AB‐DTPA extraction of soils showed that adequate P was present so that no response to the P added with the sludge was expected. For the field study, the r values between AB‐DTPA and DTPA were > 0.95 for each metal. The results indicate that AB‐DTPA is as valid as, if not superior to, DTPA for metal extraction and offers the additional advantage in allowing nutrient analysis if one wants to assess both plant nutrients and trace metals.