Microbial degradation of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine (hydroxyatrazine) was investigated in three Oregon soils. Hydrolysis of atrazine was determined by the presence of14C-hydroxyatrazine in methanol extracts. Respired14CO2from the14C-ethyl side chain of atrazine represented less than 10% of the added14C in the soils after 28 days. Degradation was dependent on soil type, atrazine concentration, and moisture content. The isopropyl and ring constituents of atrazine were subject to minimal attack. The hydroxyatrazine ring was attacked more readily than the atrazine ring. Hydroxyatrazine accounted for approximately 10% of the extracted14C from14C-atrazine-treated Parkdale-A, Parkdale-C, and Coker soils and 40% from the Woodburn soil. Hydrolysis was the dominant pathway of detoxification in the Woodburn soil, whereas detoxification of atrazine in Parkdale-A, Parkdale-C, and Coker soils was a combination of chemical hydrolysis and slow microbial degradation byN-dealkylation of the ethyl side chain constituent.

Soil microbial respiration was measured on five soils after treatment with metal salt additions (0.0–50 mmol kg−1 metal to dry wt soil) to evaluate the effect of metal toxicity. After 45 d incubation at 20°C, most lower level metal treatments (0.05 and 0.5 mmol kg−1) had little effect on soil microbial respiration, whereas the higher levels (5 and 50 mmol kg−1) sharply inhibited respiration, suggesting a general threshold for metal toxicity between the 0.5 and 5 mmol kg−1 metal.GEOCHEM, an equilibrium thermodynamic computer model, was used to simulate the chemical speciation of Cu and Cd in two soils. Values for the simulated concentration of the “free” Cd2+ species at which 5–10% inhibition of soil respiration occurred (10 µM) were comparable with those measured in pure bacterial culture fluids. Because of adsorption and complexation by the organic soil, more total Cd was required to achieve an equivalent Cd2+ concentration value in the simulated soil solution. The model of simulated Cd species distribution was supported by the fact that equal Cd amendments to both soils resulted in less growth inhibition in the organic soil. When Cd contamination of the two soils was near the toxic threshold level, relatively small increases in soil acidity could markedly increase Cd2+ concentration in the soil solution.Simulated Cu species distribution for the organic soil correlated with inhibition of respiration. Dissolved Cu was predicted to inhibit microbial respiration when the free ion acidity reached a value of 0.01–0.1 µM in the soil solution.

Fluoride sorption and desorption reactions in 10 soils were investigated. Fluoride sorption kinetic data were obtained by equilibrating 1.0 mmol/L NaF solutions with four soils for periods from 1 h to 77 d. Fluoride sorption reactions with respect to soil properties were examined by equilibrating 0.0 to 2.5 mmol/L NaF solutions with 10 soils for 24 h. Fluoride sorption was rapid in all soils, with 90% of the sorption occurring within 24 h. Increasing sorption equilibration time decreased the amount of F that could be desorbed from the soil in 24 h. Fluoride sorption conformed to the Langmuir sorption isotherm for all soils over limited concentration ranges. The Freundlich sorption isotherm was applicable over the entire initial F concentration range (0.0–2.5 mmol/L) for all soils. Simple and multiple regression techniques allowed various F sorption parameters to be predicted from selected soil properties. Oxalate‐extractable Fe and Al, dithionite‐extractable Al and soil pH correlated most highly with both Langmuir b and Freundlich K values in a simple regression model. A multiple regression equation including oxalate‐extractable Al, clay, and oxalate‐extractable Fe predicted 90% of the variation in Langmuir b values. Fluoride desorption also conformed to the Freundlich isotherm for all soils. Fluoride desorption was hysteretic in 7 of 10 soils, but hysteresis could not be explained by differences in measured soil properties.

Sewage sludge application rates on grasses are mainly determined by N availability and concentration of toxic metals in sludge. The exact availability of N in sludge is difficult to predict. A 3-yr study was conducted to determine which sludge rates would give yields of tall rescue (Festuca arundinacea Shreb. 'Alta') comparable to yields obtained from inorganic N application. Sludge and NH4NO3 were surface applied at annual rates of 0, 110, 220, 440, and 880 (sludge only) kg N/ha. Dry matter yield of tall rescue from sludge-treated soils was 36, 56, and 50% of that on NH4NO3-treated soils for 1976, 1977, and 1978, respectively. Sludge was 27, 41, and 44% as effective as NH,NO3 as a source of available N in 1976, 1977, and 1978, respectively. Ammonium-N in the sewage sludge apparently provided most of the available N for fescue growth. Concentrations of Zn, Cd, and Cu were higher and Mn lower in tall fescue grown on sludge-treated soil with NH~NO3 and usually increased toward the end of the growing season. However, plant concentrations of these heavy metals never reached toxic levels at any time. Sewage sludge was an effective and safe nutrient source for tall fescue. Additional index words:Nitrogen availability, Tall fescue, Festuca arundinacea Shreb., Nutrient source. Kiemnec, G.L., T.L. Jackson, D.D. Hemphill, Jr., and V.V. Volk. 1987. Relative effectiveness of sewage sludge as a nitrogen fertilizer for tall fescue. J. Environ. Qual. 16:353-356.