Phytoavailability Soil Test: Development and Verification of Theory

Abstract

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.

Yield response of forage grasses to N fertilizer as related to spring soil nitrate sorbed on anionic exchange membranes

“…This indicates that NO 3 -extracted by AEMs described more adequately soil N availability to forage grasses than NO 3 -extracted by water. These results may be related to the fact that AEMs can act as a sink for NO 3 -submitted to the in situ soil conditions for a defined lapse of time while chemical extraction (i.e., water) only monitor a static concentration in this specific N pool (Yang et al 1991). Our findings support the suggestions of Dahnke and Johnson (1990) who recommended the use of fluxes as indices to soil N-availability to plants in cold-humid environments.…”

Practical applications of ion exchange resins in agricultural and environmental soil research

“…As diffusion-sensitive procedures measure both the rates of release of ions from different soil surfaces and their diffusion through the bulk soil, the systems integrate both chemical and biological transformations as well as diffusion to a sink into the measure of nutrient availability. The theoretical verification of the procedures has been well-documented (Yang et al 1991a, b;Yang and Skogley 1992). Size, exchange capacity, resin type, initial saturation of counterions of the resin, soil moisture content, and soil temperature influence adsorption kinetics in this technique .…”

Integrating knowledge of nutrient forms and dynamics into improved nutrient management practices: Atribute to Régis Simard

“…Although chemical extraction methods have proved useful in estimating the concentration of plant-available nutrients, a major limitation is that they are only an index of true nutrient availability during a growing season (Yang et al 1991;Skogley 1994;Skogley and Dobermann 1996). The chemical extractants may also mobilize fractions that are not plant-available under field conditions, leading to overestimation of nutrient supply.…”

“…Under field conditions, IEMs accumulate nutrients from soils through exchange reactions by a similar mechanism to the soil-root system, which is different from EUF or chemical extraction; therefore, the nutrient supply measured by IEMs is affected by factors that influence nutrient availability to the crop, such as the solution concentration, the ability of the soil to replenish the solution concentration and the mobility of the ion in the soil (Yang et al 1991;Abrams and Jarrel 1992). Both anionic and cationic exchange resins can be used to extract a wide range of nutrients (Qian and Schoenau 2002).…”