A dispersion method has been developed for the determination of aromatics in the presence of paraffinic and naphthenic hydrocarbons. The method has been applied to selected cuts obtained by fractionation of Turner Valley crudes. The percentages of benzene, toluene, and the xylenes occurring in a series of Turner Valley crudes have been determined.
Abstract The competitiveness of 19 selected Bradyrhizobium japonicum strains in the midwestern USA was evaluated in field studies during 1984 and 1985. Of the 11 selected strains evaluated in 1984, a range in nodule occupancy of 0.3 to 15.7% was observed across three locations in Illinois and Wisconsin. During the second year of the study, 7 of 12 strains showed nodule occupancy averaging between 14.8 to 26.6% for eight locations in Illinois, Michigan, South Dakota, and Wisconsin. Strain An‐11 exhibited an average nodule occupancy of 15.7% in 1984 and 26.6% in 1985 which was significantly greater than any of the other 18 strains tested. Estimates of biologically‐fixed N via non‐nodulating isolines of soybean ( Glycine max L.) showed a significant difference between one inoculum treatment (strain An‐14) and the noninoculated control for only one location (Plainfield, WI) during the second year of the study. No significant differences in grain yield were observed in either year of the study. The data suggests that selected strains of B. japonicum can be more successfully introduced into midwestern USA soils if they are adapted for the soils and cultivars in that geographic region.
Abstract Laboratory incubation experiments were conducted to evaluate the ability of the urease inhibitor phenylphosphorodiamidate (PPD) to reduce NH 3 volatilization and immobilization of urea (100 mg N kg −1 of soil). Application of 20 mg PPD kg −1 of soil effectively inhibited urea hydrolysis for approximately 4 d in both soil and oat straw‐amended soil systems. This delayed urea hydrolysis reduced NH 3 losses after 7 d from 82 to 19% in the straw‐amended soil, and from 26 to 14% in the soil system. When urea was applied to soil incubated in closed vessels, only 80% of the applied urea could be recovered as inorganic N after 3 d of incubation. This apparent immobilization of N was prevented for 7 d by application of PPD. Immobilization of N in the straw‐amended soil exceeded 40% within 7 d, but the onset of these losses was delayed for at least 3 d by PPD. These results demonstrate that losses of surface‐applied urea via both NH 3 volatilization and immobilization can be prevented by application of an effective urease inhibitor.
Abstract Metal adsorption characteristics obtained using conventional batch equilibration methods are often of limited use for predicting the behavior of trace metals under natural conditions due to inadequate control of the composition and pH of the equilibrium solution. Much of the existing adsorption data has also been obtained using unrealistically high metal concentrations and in response to total soluble metals rather than unassociated metal ions. These limitations were overcome via the use of chelating resin to establish and maintain constant pH and metal activity in a solution of constant ionic strength and composition. The Cd/Ca ratio of the resin was varied to provide a range of Cd activities (0–1.5 µ M ) consistent with normal soil solution concentrations when equilibrated with 0.01 M Ca(NO 3 ) 2 . A series of these prepared resin systems were equilibrated with an Fe gel, a muck, and an intact soil to obtain Cd adsorption data in response to Cd activities as low as 10 −8 M . These resin systems can also be used to describe metal adsorption as a function of ionic metal concentrations in systems containing soluble complexing agents. The resins can provide ionic metal concentrations below the sensitivity of flameless atomic absorption spectrophotometry, and the activity of several trace metals can be maintained by the same resin, thus enabling evaluation of metal competition for adsorption sites. In some cases, the resin system may eliminate the requirement for a complete adsorption isotherm, since metal adsorption can be determined in response to one or more predetermined metal activities.
Abstract A method is presented to differentiate between free and complexed trace metals in solution at concentrations at or below the sensitivity of flameless atomic absorption spectrophotometry using a pH and solution composition consistent with natural systems. The method utilizes a pH‐adjusted chelating resin saturated with Ca and selected trace metals that maintains pH and solution metal activities essentially constant when equilibrated with a Ca(NO 3 ) 2 solution. Equilibration of this solid‐phase buffer with a Ca(NO 3 ) 2 solution containing a soluble complexing agent results in a soluble metal concentration in excess of that obtained when equilibrated with Ca(NO 3 ) 2 alone. The increase in the soluble metal concentration is attributed to the formation of soluble metal complexes. The resin method was verified by evaluating Cd, Zn, and Ca complexation by EDTA (ethylenediaminetetraacetic acid). Relative selectivity coefficients were consistent with published values, and the concentration of EDTA added to the system was accurately determined. Solution Cd concentrations were also increased by Cl ‐ addition to an extent consistent with published formation constants. The ability of the method to evaluate complexation of several metals simultaneously may make it more attractive than existing methods for characterizing simple monofunctional complexing agents. The method was also used to characterize soluble complexing agents extracted from a sludge‐amended soil. The results indicated that a portion of the ligands had approximately 10 5.5 times greater affinity for Cd and Zn than for Ca. This marked selectivity for Cd and Zn is much greater than existing selectivity data for similar systems obtained under conditions of low pH and/or unrealistically high metal levels and is likely attributable to the much greater Ca to metal ratios maintained by the resin system.
