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A new approach to soil testing, designed to improve accuracy and usefulness, is being developed. A spherical, mixed‐bed ion‐exchange resin capsule is embedded in saturated‐paste soil samples and allowed to accumulate all nutrients the soil can deliver, as a function of diffusive ion movement. This simulates the action of nutrient movement to plant roots. The approach is called the Phytoavailability Soil Test (PST). Objectives were to determine if nutrient accumulation by the resin capsule was described by diffusion models, and to investigate rate‐limiting diffusion processes. Nutrient‐uptake curves were obtained on Ap horizon samples from 20 Montana agricultural soils by measuring time dependence of K, P, and S accumulation in resin capsules during 15 d. Also, a planar system was used in which both sides of a cylinder of resins accumulated P, K, and S from saturated pastes during 96 h. Fluxes to the resin were compared with nutrient gradients, measured by two other extraction methods, on soil slices from successive distances beyond the resin‐soil interface. The mass of nutrients adsorbed by the resin as a function of time was consistent with a diffusion process, as was the concentration of nutrients in the soil vs. distance from the resin‐soil interface. The process appeared to be that termed film diffusion. Results demonstrated independence of specific nutrient diffusion and resin adsorption. The PST may provide an improved approach to soil testing because it is sensitive to nutrient diffusion, a governing factor in plant availability of most nutrients.

The phytoavailability soil test (PST) is designed to assay plant‐available nutrient quantity as a function of diffusive ion movement to a spherical, mixed‐bed ion‐exchange resin sink. Temperature is known to alter many parameters relating to nutrient availability and plant uptake. This study was conducted to determine PST sensitivity to temperature‐induced changes in availability of NO‐3‐N, NH+4‐N, P, K, and S. Nutrient flux to resin accumulators was measured during 96 h at 25, 35, and 45 °C. Fluxes of P, K, S, and NH+4‐N all increased with increasing temperature, while the flux of NO‐3‐N decreased. The size of the temperature effect was nutrient and soil specific. Nutrient‐accumulation characteristics were significantly represented by quadratic equations, corresponding to diffusion‐controlled processes. Initial flux (0.5 h) of each nutrient to the resin was rapid and highly related to nutrient ion activity in saturated‐paste soil solutions equilibrated for 24 h. The slope of the accumulation curve decreased after the initial rapid flux. This is interpreted to suggest that diffusion characteristics of the soil control, to a large degree, the flux of nutrients to the resin accumulator after an initial rapid phase related to high nutrient activity in the soil solution. These results provide strong evidence that the PST system is diffusion controlled and that it is sensitive to conditions known to influence nutrient availability in soils, such as temperature and nutrient ion activities.

Nitrate is one of the most important chemicals in agricultural and environmental management. Most methods for NO3analysis, however, require expensive equipment or complicated procedures. The objective of this study was to develop a simple, rapid, accurate procedure for NO3analysis that can be conducted in laboratories worldwide, without the need for specialized equipment. We based our studies on a colorimetric method that involves electrophilic aromatic substitution (nitration) between nitronium and salicylate. The simplified procedure was tested for NO3analysis of water, soil, and resin extracts. Only 1 mL of sample containing 0 to 4 mg NO3‐N L‐1is required, and a single solution (TRI solution made as a mixture of sodium salicylate [2‐hydroxybenzoic acid monosodium salt], NaCl, and ammonium sulfamate [sulfamic acid monoammonium salt]) is used for color development. The detection limit is 0.1 µg NO3‐N, with linearity up to 4 µg NO3‐N in a final volume of 11 mL. Evaporation of the sample may be done in several ways to remove water from reactants, as long as the temperature for activiation of nitration is attained. Resin extracts from 2 MHCl required neutralization with 2 MNaOH prior to analysis, and soil extracts from 1 MKCl provided more uniform results than from 2 MKCl. Results from all types of solution samples were highly significantly correlated with those by the automated Cd‐reduction method. This simplified sodium salicylate procedure (SSP) for NO3analysis is simple, reproducible, and it requires only inexpensive equipment.

The toxicities of solutions of 10 mercury compounds to luminescent bacteria were measured using the Microtox Toxicity Bioassay. The aim of this study was to assess the influence that the counter-ions have on the aquatic toxicity of mercury salts. The toxicities of these mercury compounds were very similar, except for mercurous tannate and mercuric salicylate. This can be attributed to differences in the ionization and speciation patterns of these compounds relative to the other compounds tested. In general, the toxicity of the solutions at pH 5 was not significantly different from the toxicity of these solutions at pH 6, but a clear reduction in toxicity was observed when the pH of the solution was adjusted to pH 9. Significant differences were found between the toxicity of Hg(I) and Hg(II) salts of the same anion at pH 9. When cysteine was added to a mercuric nitrate solution (at pH 6), a reduction in the toxicity was observed. This can be explained in terms of the strong binding of mercury to cysteine, thus reducing the concentration of mercury species available to cause an observable toxic effect to the bioluminescent bacteria.