Different methods have been used to quantify the amount of sealing or crusting that takes place. These Soil sealing is a severe problem worldwide. Increased runoff and include measuring infiltration rates, using pocket and decreased seedling emergence cause on-and off-site problems affecting farmers and communities. One possible soil sealing control mea-needle penetrometers, and percent seedling emergence. sure is the application of polyacrylamide (PAM). Little is known Infiltration rate measures the amount of water passing about the interaction of specific PAMs with soils of differing characterthrough the soil and is an indication of the total available istics. This study was conducted to examine the relationship between pore space and pore conductivity. At the beginning of different PAMs and soils of varying characteristics. We examined a storm event, infiltration rates of well-aggregated soil PAM charge densities (CD) of 20, 30, and 40% hydrolysis with molecare relatively high. As rain impacts the soil and slaking ular weights (MW) of 6, 12, and 18 Mg mol Ϫ1. The soils used were and dispersion occur, structural and depositional seals Heiden clay (fine, smectitic, thermic Udic Haplustert), Cecil sandy develop, decreasing the amount of pore space. As the loam (clayey, kaolinitic, thermic Typic Kanhapludult), and Fincastle amount of pore space decreases, the infiltration rate silt loam (fine-silty, mixed, mesic Aeric Epiaqualf). Polyacrylamide decreases until the steady state infiltration of the sealed (20 kg ha Ϫ1) was sprayed onto the soil in liquid form. Soil material was exposed to rainfall simulation in the laboratory. Infiltration rate soil is reached, which will be less than that from reducwas used as an indicator of soil surface sealing. Polyacrylamide in-tion in soil water gradient alone (Levin et al., 1991). creased infiltration rates on all three soils relative to the control. Hence, we can quantify surface sealing using infiltration Twenty and 30% CD PAMs performed best in maintaining high measurements (Norton, 1987). Measuring the infiltrainfiltration rates on Heiden clay. The 12 Mg mol Ϫ1 MW formulations tion rate has the advantage of being able to monitor worked best for Cecil sandy loam. Fincastle silt loam showed no the sealing process through time. preference for a particular PAM formulation. Polyacrylamide in-Polyacrylamide (PAM) stabilizes soil structure but creased final infiltration rate by as much as 3-to 5-fold for these does not remediate poor soil structure (Cook and Nelsoils. Different PAM formulations provided differing degrees of soil son, 1986). In the arid and Mediterranean climates of protection, varying between soils. Understanding the interaction of the world, anionic PAM of high molecular weight (MW; different soils with various PAM formulations will enable PAM users to select the best PAM product for their soil conditions.

Predicting the irreversible interactions between aromatic amines and soil is essential for assessing mobility, bioavailability and subsequent remediation of aromatic aminecontaminated sites. The kinetics of irreversible binding and/ or transformation of a series of para-substituted anilines and R-naphthylamine were studied on several surface soils for a one-to two-month equilibration period. To estimate reaction rates, a heterogeneous reactivity model was developed assuming that irreversible reactions are firstorder with respect to the amine solution concentration; activation energies vary linearly as a function of reacted sites; and available soil reactive sites change over time but remain more numerous than sites consumed. The validity of the latter assumption was demonstrated for the experimental variables in these studies. The observed change in reaction rates with time was best described using a biphasic approach where apparent rate constants (k app ) and the relationship between activation energies and reacted sites (R) were independently estimated for contact times e 20 h and > 20 h. For both operationally defined time frames, inverse log-linear relationships are observed between k app values and both Hammett constants and half-wave oxidation potentials (E 1/2 ), which are indicators of the intrinsic solute reactivity. Dimerization was only evident for amines with reactivity greater than methylaniline or with E 1/2 < 0.54 V. Reaction complexity and site heterogeneity resulted in a lack of correlation with soil properties. However, preliminary results showing an increase in exchangeable Mn 2+ from soils after irreversible reactions with amines were allowed to occur demonstrated that manganese oxides in whole soils play a significant role in causing radical amine cation formation and subsequent coupling.

The covalent binding of two aromatic amines, 1‐naphthylamine and 4‐methylaniline, to substituted quinones in aqueous solutions has been studied as a model for the covalent binding of amines to humic acids. An inline compound was the only type of product identified for the reactions between 1‐naphthylamine and selected quinones. Reactions of 4‐methylaniline with the same quinones gave a 1,4‐ addition product in addition to the imine compound, although only the imine product was formed when the quinone had bulky substituents at the 2‐ and 6‐ positions. These results provide additional insight into the reactions of aromatic amines with humic acid quinones.

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Vacuum displacement, a modification of traditional column displacement utilizing 75‐g soil samples and a mechanical vacuum extractor, was compared to centrifugation as a method for obtaining unaltered soil solution for comprehensive analysis. Soil solutions were displaced by the two procedures from field‐moist Lily (Typic Hapludults), Memphis (Typic Paleudalfs), and Etowah (Typic Paleudults) soil samples having varied chemical and physical properties. Solutions obtained were analyzed for volume of solution recovered, pH, EC, Ca, Mg, Mn, K, Na, NH4, Cl, NO3, SO4, P, and percent ion difference. Vacuum displacement was more efficient than centrifugation in terms of man‐hour requirements and sample turn‐around time. Smaller volumes of soil solution (usually <5 mL) were obtained by vacuum displacement compared to centrifugation, necessitating analytical techniques adapted to uL‐volumes of solution. For the most part, both methods resulted in analate concentrations with coefficients of variation <5% and ion differences <12%. Exceptions were NH4, K, and Na, which were sometimes present at concentrations approaching the limits of detection for the procedures employed. Although significant differences in analate concentrations between the two methods were observed, few of the measured differences would lead to interpretive difficulties for the solution components and soils considered.