The surface horizons of two arid‐zone field soils that had received amendments of either liquid or dried, anaerobically digested sewage sludge for 4 years were sampled to determine the forms of selected trace metals in the solid phase. The soils had been amended with sludge twice annually at rates of 0, 22.5, 45.0, or 90.0 tons · ha−1 · year−1. Barley and sorghum had been grown on the soils in randomized experimental plots. The soil samples were analyzed for total Ni, Cu, Zn, Cd, and Pb and were fractionated by sequential extraction to estimate the quantities of these metals in “exchangeable,” “sorbed,” “organic,” “carbonate,” and “sulfide” forms.The total contents of the five metals in the two field soils were governed by the total content of the metals in the sludges applied and by the rate of sludge application. The accumulation of metals in the surface horizons of field plots receiving liquid sludge was less than that in the plots receiving composted sludge, possibly because of a lesser reduction in soil bulk density resulting from sludge applications. The percentage of the total metal content in exchangeable and sorbed forms was very low, averaging between 1.1 and 3.7% for all of the metals regardless of the type of soil, the form of sludge applied, or the sludge application rate. The application of sludge tended to reduce the sulfide fraction and to increase the organic and carbonate fractions of all five trace metals. At the highest rate of sludge application, the predominant forms of the metals were: Ni, sulfide; Cu, organic; and Zn, Cd, and Pb, carbonate.

Fly ash from a coal‐fired power generating plant was mixed with five California soils at rates of 0, 2.5, 5.0, 10.0, 25.0, and 50.0% by volume. The physical properties related to the agronomic use of fly ash‐amended soils were characterized by determining water‐holding capacity, bulk density, hydraulic conductivity, and modulus of rupture on laboratory compacted soil cores. The moisture release characteristics of each mixture were also determined. Results indicated that a small amount of fly ash added to soils does appear to affect some measured physical properties of soils. At application rates > 25%, there was a consistent increase in water‐holding capacity (except a Domino loam soil), and a decrease in bulk density and modulus of rupture in all soils tested. The hydraulic conductivity increased with small amounts of fly ash, but declined rapidly as fly ash volume increased. Although fly ash application increased the water‐holding capacity of soils, the amount of water available to the plant did not change significantly. At a low applicant rate, fly ash amendment appeared useful in improving certain agronomic properties of soils.

A sequential extraction procedure was used to fractionate Cd, Cu, Ni, and Zn in sludge‐treated soils into the designated forms of exchangeable, adsorbed, organically bound, carbonate, and residual. Samples were obtained from a soil column study where anaerobically digested sewage sludge in either liquid or air‐dried form was mixed into the top 15 cm of three reconstructed soil profiles and leached for 25 months with Colorado River water. The applied sewage sludge and uncontaminated soil samples were also sequentially extracted. The metals added into the soil had not moved out of the sludge‐soil layers during the course of leaching. The chemical forms present in the sludge‐soil layers at the termination of the leaching process were compared with those initially present in the soil and sludge. Most of each of the metals studied in the columns were found in the organically bound, carbonate, or residual forms, with the relative distribution among these forms depending on whether samples were taken in or below the sludge‐soil layer. Less than 36% of each metal in the sewage sludge was in the residual form, while, except for Cd, the soils contained > 65% of each metal studied in this form. It appeared that Cd, Ni, and Zn were all shifting to the residual form. The chemical forms of Cu had not changed significantly during the study. The occurrence of metals in the stable organically bound, carbonate, and residual forms in the sludge, coupled with a shift toward the more stable form (residual) after soil incorporation, contributed to the lack of metal movement in the soil profiles.

The accumulation of Cd, Cr, Cu, Ni, Pb, and Zn in sewage sludge‐treated soils was studied after 6 y of continued annual sludge application at a cropland disposal site. Soil samples were taken at 15‐cm depth increments from Greenfield sandy loam (coarse‐loamy, mixed, thermic, Typic Haploxeralf) and Domino loam (fine‐loamy, mixed, thermic Xerollic Calciothid) that received 0 (control), 22.5, 45, and 90 Mg ha−1 y−1 of composted sludges or 0 (control), 3.75, 7.5, and 15 cm y−1 of liquid sudges since 1976. Samples were also obtained from areas where liquid sludge treatment was terminated after 1978. Heavy metals in soils were extracted by 4M HNO3 and analyzed by atomic absorption spectroscopy. Over 90% of the deposited heavy metals were found in the 0‐ to 15‐cm soil depth where sludges were incorporated; no statistically significant increase in heavy metal contents of the soil was detected below the surface 30 cm of the soil profile. Although crop absorption of heavy metals has increased with the sludge application rates, the total uptake amounted to < 1% of the metal introduced through sludge application. Through a material balance calculation, it was found that recovered heavy metals were low relative to amounts added due to incomplete extraction of metals from soils by 4M HNO3 and changes in soil bulk density.

A statistical modeling approach is presented that predicts spatial soil salinity patterns from aboveground electromagnetic induction (EM) readings. In this approach, EM readings are obtained from a field sampled on a uniform (centric systematic) grid. A small number of these sample sites are chosen for soil sampling, based on the observed EM field pattern. The salinity levels for these soil samples are determined and then the remaining nonsampled salinity values are predicted from the corresponding EM readings through a multiple linear regression equation. Experimental results suggest that this approach will work well in fields having low to moderate levels of soil textural variability. For example, 95% of the spatial variability in soil salinity within typical 16.2‐ha (40‐acre) cotton (Gossypium hirsutum L.) fields could be accounted for with only 36 soil samples, as opposed to the 200 to 300 soil samples typically required if no EM readings were available. This approach makes EM readings a more practical and cost‐effective tool by substantially reducing the number of soil samples needed for accurate mapping of spatial salinity patterns at the field scale.