The fate of phosphorus during pedogenesis

The beneficial effects of mycorrhizae on plant growth have often been related to the increase in the uptake of immobile nutrients, especially phosphorus (P). In this review the mechanisms for the increase in the uptake of P by mycorrhizae and the sources of soil P for mycorrhizal and non-mycorrhizal plants are examined. Various mechanisms have been suggested for the increase in the uptake of P by mycorrhizal plants. These include: exploration of larger soil volume; faster movement of P into mycorrhizal hyphae; and solubilization of soil phosphorus. Exploration of larger soil volume by mycorrhizal plants is achieved by decreasing the distance that P ions must diffuse to plant roots and by increasing the surface area for absorption. Faster movement of P into mycorrhizal hyphae is achieved by increasing the affinity for P ions and by decreasing the threshold concentration required for absorption of P. Solubilization of soil P is achieved by the release of organic acids and phosphatase enzymes. Mycorrhizal plants have been shown to increase the uptake of poorly soluble P sources, such as iron and aluminium phosphate and rock phosphates. However, studies in which the soil P has been labelled with radioactive 32P indicated that both mycorrhizal and non-mycorrhizal plants utilized the similarly labelled P sources in soil.

A critical review on the role of mycorrhizal fungi in the uptake of phosphorus by plants

The primary mode of interaction of dissolved phosphate with fluvial inorganic suspended particles is via a reversible two-step sorption process. The first step, adsorption/desorption on surfaces, has fast kinetics (minutes-hours). The second step, solid-state diffusion of adsorbed phosphate from the surface into the interior of particles, has slow kinetics (days-months) and is dependent on the time history of the previous surface sorption and the chemistry of the solid diffusional layer. Natural clay particles with a surficial armoring of reactive iron and aluminum hydroxyoxides resulting from chemical weathering of rocks and soils have a high capacity for absorbing phosphate in the second step and for maintaining low “equilibrium phosphate concentrations” in solution. Extrapolation of laboratory sorption and extraction experiments with natural soils and suspended sediments to the environment suggests that the phosphate concentrations of unperturbed turbid rivers (SPM > 50 mg liter I) are controlled near the dynamic equilibrium phosphate concentration of their particles (EPC, = 0.2-l .5 PM) and that fluvial suspended particles “at equilibrium” contain up to 10 pmol-P g-l that is desorbable. Release of this phosphate from particles entering the sea produces the characteristic shape and magnitude of input profiles of dissolved phosphate observed in unperturbed estuaries. On a global scale, fluvial particulates could transport from 1.4 to 14 x 1O’O mol yr-I of reactive phosphate to the sea, some 2-5 times more than that in the dissolved load alone.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1988.33.4part2.0649

Kinetic control of dissolved phosphate in natural rivers and estuaries: A primer on the phosphate buffer mechanism1

Publisher Summary This chapter reviews the mechanism of immobilization and mineralization of organic phosphorus in soil The chapter describes two analytic techniques for the determination of the organic phosphorus content of soils: ignition and extraction In the ignition method, the organic phosphorus is determined by measuring the differences in the acid-extractable phosphorus in soil samples before and after ignition In the extraction method, the organic phosphorus is determined by the difference between the inorganic and total phosphorus in the soil extracts Various factors that affect the organic phosphorus content of soils are rainfall, mean temperature, drainage, soil pH, cultivation, inorganic phosphorus content of the parent material, and sulfur content in areas of low atmospheric returns Investigations have been carried out on the accumulation of organic phosphorus under pasture and the incorporation of added inorganic phosphorus in soil organic matter The chapter also examines the chemical nature of organic phosphorus in soils and summarizes the phosphorus cycle of a native grassland ecosystem

Soil Organic Phosphorus

Nine different organic and inorganic soil phosphorus fractions were obtained by a sequential extraction of samples from 168 USDASCS benchmark soils, representing eight soil orders of the Soil Taxonomy The distribution of P across the different fractions (resin, bicarbonate, hydroxide, sonification-2nd hydroxide, acid, and acidperoxide digest fractions with separate organic and inorganic P determinations) and their relationships to other soil chemical properties were used to evaluate the effects of different soil development on phosphorus composition Correlation and regression analyses of P distribution and chemical analyses confirmed the partial dependence of organic matter accumulation on available forms of P Weathering indicators such as base saturation were related to the formation of secondary P forms The relative proportions of available and stable as well as organic and inorganic P forms were dependent upon soil chemical properties and related to soil taxonomy Path analysis of relationships between labile and stable P forms showed that in Mollisols much of the labile resin extractable P was derived from inorganic bicarbonate and hydroxide extractable P forms In more weathered Ultisols, 80% of the variability in labile P was accounted for by organic P forms, suggesting that mineralization of organic P may be a major determinant of P fertility in these soils Additional Index Words: organic phosphorus, inorganic phosphates, sequential phosphorus extraction, soil taxonomy, path-analysis View complete article To view this complete article, insert Disc 4 then click button8

Pathways of Phosphorus Transformations in Soils of Differing Pedogenesis

A modified version of the phosphate fractionation procedure of Chang and Jackson (1957) included the determination of "residual inorg. P" and introduced a revised nomenclature for the other fractions. Added phosphate sorbed during the fluoride extraction was usually completely recovered in the succeeding sodium hydroxide extraction; this enabled mutually compensating corrections to be applied to NFLjF-P and 1st NaOH-P values. A second acid treatment increased the amount of Ca-P extracted. Further modifications simplified the colorimetric determinations of inorganic phosphate in several of the extracts. A measure of the reproducibility of fractionation results was also obtained. Additional

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Fractionation of soil inorganic phosphate by a modification of Chang and Jackson's procedure

Apatite inclusions have been identified in several primary minerals, and their abundance and morphology have been described. A comparison of several methods used for the determination of total P in soils showed that Na2CO3 fusion is the most reliable method for samples which contain apatite inclusions and that the effectiveness of extraction was usually in the order: Na2CO3 fusion > HF digestion > HC1O4 digestion > N H,SO4 extraction following ignition. Included apatite was identified using a petrological microscope in residues after digestion with 60% HC1O4. This form was also extracted much more slowly by 0.5./V HC1 than was nonincluded apatite. Included apatite resistant to attack by 1]V HQ was determined as "residual inorganic P" in fractionation studies on weakly weathered materials, and the influence of fineness of grinding on the ratio of "acid-extractable Ca-P" to residual inorganic P indicated the likely dimensions of the inclusions in different minerals. Additional

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The significance of apatite inclusions in soil phosphorus studies

a Comparison of Methods for the Determination of Soil Organic Phosphorus

The amounts of total P extracted by Na2CO3 fusion and by HF and HClO4 digestion procedures from selected New Zealand soils and parent materials were compared. It is suggested that Na2CO3 fusion is the most reliable procedure. Digestion with HClO4 gave low results with strongly weathered materials and with samples which contained apatite inclusions within constituent primary minerals; whereas digestion with HF gave slightly low results only with samples which contained included apatite. Incomplete extraction of P by HClO4 and HF digestion procedures from samples which contained apatite inclusions was ascribed to the partial resistance to attack of the host minerals. Because of occlusion within highly crystalline iron and aluminium oxides, secondary inorganic P in strongly weathered soils was less readily extracted by HClO4 digestion than by Na2CO3 fusion or HF digestion.

The determination of total phosphorus in soils and parent materials

A method for the direct introduction of 35S isotope into different soil depths under field conditions to study the uptake of sulphur by pasture plants is described This method was designed to minimise bias and contamination during the introduction of the isotope It involved the horizontal introduction of the isotope enclosed in water-soluble capsules Recovery of 35S by the pasture plants indicated that when 35S was introduced at a depth of 22 cm the area above ground in which pasture plants were labelled extended little more than 15 cm from the line of placement This lateral spread of 35S in the pasture plants varied according to the soil and the depth of application The results may be explained in terms of the extent and nature of root development in the soil profile

T. W. Walker

Papers

Fractionation of soil inorganic phosphate by a modification of Chang and Jackson's procedure

The significance of apatite inclusions in soil phosphorus studies

a Comparison of Methods for the Determination of Soil Organic Phosphorus

The determination of total phosphorus in soils and parent materials

Isotopic studies on the uptake of sulphur by pasture plants