An evaluation of methods for characterizing phosphate sorption in rice soils

Abstract

Two single value methods of indexing P sorption were compared to parameters derived from P adsorption isotherms in a range of waterlogged and dry rice soils. These measures of P sorption capacity correlated closely with one another. However, they did not correlate equally with several other soil properties (pH, extractable Fe and Al). Because relationships between P sorption and soil properties proved to be method dependent, results from different methods must be compared with caution.

It is suggested that the single value method of Bache and Williams² be adopted when the rapid analyses of many samples is required. It is suited to routine analysis of soils with markedly different P sorption capacities, from both waterlogged and dry conditions.

Close correlations between the single value methods and P sorbed at a standard supernatant concentration suggest they may be useful in testing soils for P fertilizer requirements.     

Limitations of the Olsen method to assess plant-available phosphorus in reclaimed marsh soils

The aim was to assess the ability of bicarbonate-extractable P (Olsen P) to estimate total plant-available P (TPAP) in reclaimed marsh soils (Aeric Endoaquepts) which differed widely in P buffering capacity (PBC). Total plant-available P was estimated as the cumulative P uptake for a final concentration of 0.02 mg P/L in the soil solution which is the typical P requirement for field crops. The Olsen P estimated for that concentration was adopted as the critical level for crop production. We found that TPAP was better predicted by anion exchange resin-extractable P (AER-P) (65% of variance accounted for) than by Olsen P, probably because the effectiveness of the AER depends on the soil P buffering capacity, a factor that greatly influences the availability of P to plants. The critical Olsen P level was found to depend on those soil properties affecting the relationship between sorbed P and P in soil solution, viz. the P buffering capacity of soil, the Na/Ca mole ratio in the 1:1 soil:water extract, which explained 63 and 84% of the variance in the critical level, respectively, and the affinity of the sorbing surfaces for P. These properties must be taken into account when using Olsen P as the P index for fertilizer management.     

Transformation of added phosphorus to acid upland soils with different soil properties in Indonesia

Abstract

The transformation of added phosphorus (P) to soil and the effect of soil properties on P transformations were investigated for 15 acid upland soils with different physicochemical properties from Indonesia. Based on oxide-related factor scores (aluminum (Al) plus 1/2 iron (Fe) (by ammonium oxalate), crystalline Al and Fe oxides, cation exchange capacity, and clay content) obtained from previous principal component analyses, soils were divided into two groups, namely Group 1 for soils with positive factor scores and Group 2 for those with negative factor scores. The amounts of soil P in different fractions were determined by: (i) resin strip in bicarbonate form in 30 mL distilled water followed by extraction with 0.5 mol L^?1 HCl (resin-P inorganic (P_i) that is readily available to plant), (ii) 0.5 mol L^?1 NaHCO₃ extracting P_{i and} P organic (P_o) (P which is strongly related to P uptake by plants and microbes and bound to mineral surface or precipitated Ca-P and Mg forms), (iii) 0.1 mol L^?1 NaOH extracting P_i and P_o (P which is more strongly held by chemisorption to Fe and Al components of soil surface) and (iv) 1 mol L^?1 HCl extracting P_i (Ca-P of low solubility). The transformation of added P (300 mg P kg^?1) into other fractions was studied by the recovery of P fractions after 1, 7, 30, and 90 d incubation. After 90 d incubation, most of the added P was transformed into NaOH-P_i fraction for soils of Group 1, while for soils of Group 2, it was transformed into resin-P_i, NaHCO₃-P_i and NaOH-P_i fractions in comparable amounts. The equilibrium of added P transformation was reached in 30 d incubation for soils of Group 1, while for soils of Group 2 it needed a longer time. Oxide-related factor scores were positively correlated with the rate constant (k) of P transformation and the recovery of NaOH-P_i. Additionally, not only the amount of but also the type (kaolinitic) of clay were positively correlated with the k value and P accumulation into NaOH-P_i. Soils developed from andesite and volcanic ash exhibited significantly higher NaOH-P_i than soils developed from granite, volcanic sediments and sedimentary rocks. Soil properties summarized as oxides-related factor, parent material, and clay mineralogy were concluded very important in assessing P transformation and P accumulation in acid upland soils in Indonesia.     

Mobility of metals in Egyptian desert soils subject to inundation by Lake Nasser

Abstract. Extraction and adsorption techniques were used to study the behaviour of Al, Fe, Mn, Co, Ni, Cu and Zn in soils from around Lake Nasser in the Eastern Desert of Egypt, to assess the potential of such areas for agricultural development and the risks of pollution of the lake. Soil metal contents were very variable, either because of particle size sorting by flowing water or through changes in redox resulting from flooding by lake water. Metal availability was low. Extraction using EDTA and oxalate suggested that mobility of copper was controlled by carbonate, whereas Co, Ni and Zn were controlled by Fe and Mn oxides. Adsorption studies confirmed the strong ability of these soils to remove Cu and Zn from solution, and suggested that Cu and Zn concentrations in solution were controlled by carbonate. Some trace metal fertilizers will probably be required for certain crops, but pollution of the lake by leaching of metals from soil is unlikely. The main process by which metals could be lost from the soil to lake water is a lowering of soil redox potential as a result of flooding by lake water.     

Factors influencing the variation of some properties of soils in relation to their suitability for direct drilling

Soils from fifteen field experiments in the United Kingdom and one in France that compared direct drilling with mouldboard ploughing were examined with respect to their composition and physical properties. Indices of the stability and shrinkage of soil aggregates were obtained by measurement and an index of compactability was derived from an established relationship. It was hypothesized that these properties were possible determinants of soil responses to zero-tillage.Aggregate stability and shrinkage were correlated with organic carbon and clay content, respectively. Organic matter contents were greater at the surface of direct-drilled soils than in the complete topsoil layer after direct drilling or ploughing. In some cases the increase in organic matter significantly improved the physical properties of the soils.The three indices, of stability, shrinkage and compactability, were each ranked in high intermediate or low groups, and the soils classified according to their ratings in these groups. The resulting classification broadly agreed with a previous one of soil suitability for sequential direct drilling mainly based on experimental agronomy.     

Effective diffusion coefficient of cations as influenced by physical and chemical properties of selected Indiana soils

Abstract

Ion diffusion through the soil matrix is dependent upon both the physical and chemical properties of the soil. Cation (K, Na, Ca and Mg) diffusion coefficients De, were determined for seven Indiana soils by using the ion diffuison flux to a hydrogen resin paper technique. Volumetric moisture, clay content exchange and solution phase ionic concentrations, buffer capacity and organic C content were variously related to the determined De values. The larger the diffusion coefficient of K, Ca, and Mg, the lower the clay content, and exchange capacity of soils, and the higher the concentration of these cations in the solution phase. From the present study, it was concluded that the De of these cations was affected by one or more soil physical and chemical property which must be considered if De is to be used to estimate supply rate of these ions to growing roots in soil systems.     

Potassium additions on ionic equilibria,selectivity and diffusion of cations in soils

Abstract

In a soil system variation in the concentration of any one ion as induced by external addition might bring changes in the ionic‐equilibria, diffusion rate and strength of adsorption of all the ions involved. In four Indiana soils the changes in ionic equilibria, selectivity coefficient and rate of diffusion coefficient for K, Na, Ca and Mg were investigated at 5 levels of added K. The experiments were carried out under controlled laboratory conditions by incubating soils for 3 weeks at 25C. All soils had a greater fraction of Ca and Mg on the exchange phase than in solution, whereas with K and Na the reverse occurred. Potassium adsorption isotherms for all the soils differed indicating the difference in the nature of soil materials involved. Chalmers soil with high clay content with high exchange capacity had high differential buffer value for K. In all the soils, K was adsorbed preferentially to Na at all the levels of K addition, Calcium was adsorbed preferentially to Mg on the Zanesville and Toronto soils. However, in Chalmers and Raub soils, reverse was observed when the level of K addition was exceeded 1.0 and 0.5 me K/100g soil, respectively. This difference in Mg for Ca is attributed to smaller proportion of Mg saturation on the exchange surface. Divalent cations were preferentially adsorbed over monvalent ions. Increasing levels of K addition increased the diffusion rates of all the ions under consideration. The rate of diffusion for K and Ca were governed by concentrations of these ions on the exchange and solution phase.     

Band-applied elemental sulfur to enhance the phytoavailability of phosphorus in alkaline calcareous soils

Summary Applications of elemental sulfur (S°) increase the phytoavailability of P in alkaline high-Ca soils through the production of H₂SO₄ which is induced by microbial oxidation of S. Concentrated S bands, allowing time release acidity, may aid in maintaining the phytoavailability of both residual and fertilizer P. Greenhouse and field studies were therefore conducted to determine the effectiveness of band-applied S° for increasing the phytoavailability of residual and fertilizer P for spring wheat (Triticum aestivum L.) and corn (Zea mays L.). We also used inoculation of S° with Thiobacillus thioparus to determine whether it is necessary or helpful in alkaline soils to initiate acidification. Treatments were inoculation, S°, S° + inoculation, triple superphosphate, triple superphosphate + S°, triple superphosphate + inoculation, and triple superphosphate + S° + inoculation applied to three alkaline soils: Typic Argiborolls, Borollic Calciorthids, and Ustollic Haplargids. P availability was determined by plant uptake of P, NaHCO₃-extractable P, dry-matter yield, grain yield and grain-protein production, and on available-P index (NaHCO₃-extractable P, post-harvest, + plant uptake of P). Application of S° with triple superphosphate gave a significantly higher available-P index than triple superphosphate alone on all three soils. Inoculation of S° with T. thioparus increased soil acidity; however, in some cases this treatment eliminated the beneficial effect of S°. Grain yields of wheat increased with S° applications at one of two field sites. These results suggest that applying S° with triple superphosphate may be an effective means of increasing soil P availability and the efficiency of superphosphate fertilizers on alkaline high-Ca soils.     

Influence of extractable iron,aluminium, and manganese on P-sorption in flooded acid sulfate soils

We evaluated the effect of 1 N NH₄OAc and sodium-citrate dithionite extractable forms of soil Fe, Al, and Mn on P-sorption of a flooded acid sulfate soil (Sulfic Tropaquepts) and a non-acid sulfate soil (Typic Tropaquepts) under different soil oxidation-reduction and pH conditions. We used Maha-Phot soil (Sulfic Tropaquepts) and Bangkok soil (Typic Tropaquepts) from the Bangkok Plain, Thailand, and incubated them with 0.2% rice straw under aerobic (O₂ atmosphere) and anaerobic (N₂ atmosphere) conditions at three different levels of pH (4.0, 5.0, and 6.0) for 6 weeks in stirred soil suspensions with a soil to 0.01 M CaCl₂ solution ratio of 1:7. After the incubation period, the soil suspensions in the first treatment (control) were not washed or pretreated with any extractants. For the second treatment (II), the soil suspensions were treated with 1 N NH₄OAc (buffered to pH 4.0) to remove Fe, Al, and Mn in exchangeable form. In the third treatment (III), the soils suspensions were treated with sodium citrate dithionite solution (20%) to remove Fe, Al, and Mn in the form of free oxides. The soil residues were then equilibrated with KH₂PO₄ ranging from 0 to 500 mg P kg^-1 soil. Sorption isotherms were described by the classical Langmuir equation. The P-sorption parameters under study were standard P requirement (SPR), Langmuir maximum sorption capacity (X _m), Langmuir sorption constant (k), and buffering index (BI). Treating soils with 1 N NH₄OAc reduced X _m by 32–55%, SPR by 68–84%, and also decreased the differences in P-sorption due to the effects of pH and oxidation-reduction conditions. Significant correlations between the P-sorption parameters and the amount of free iron oxides indicated the primary role of iron oxides in P-sorption of acid sulfate soils. Aluminium oxides seemed to play a secondary role in P-sorption of these soils. Manganese also showed an important effect on P-sorption, but the mechanism is ambiguous.This is a contribution from the Wetland Biogeochemistry Institute, Louisiana State University, Baton Rouge, LA 70803-7511     

Potential contribution of lysed bacterial cells to phosphorus solubilisation in two rewetted Australian pasture soils

Soil drying renders considerable amounts of phosphorus soluble upon rewetting, which may be partly derived from lysed microbial cells. Using direct bacterial cell counting in water and tetra-sodium pyrophosphate extracts of two Australian pasture soils, we found that almost all extractable cells were lysed following the rewetting of dry soils. The amounts of phosphorus in the lysed cells corresponded closely to the increases in water-extractable phosphorus following soil drying, suggesting that bacterial cell lysis is a major source of the released phosphorus.     

Exploitation of potassium by various crop species from primary minerals in soils rich in micas

We investigated the question of whether exchangeable K⁺ is a reliable factor for K⁺ availability to plants on representative arable soils (Aridisols) rich in K⁺-bearing minerals. Five soils with different textures were collected from different locations in Pakistan and used for pot experiments. The soils were separated into sand, silt, and clay fractions and quartz sand was added to each fraction to bring it to 1 kg per kg whole soil, i.e., for each fraction the quartz sand replaced the weight of the two excluded fractions. On these soil fraction-quartz mixtures wheat, elephant grass, maize, and barley were cultivated in a rotational sequence. Growth on the sand mixture was very poor and except for the elephant grass all species showed severe K⁺-deficiency symptoms. Growth on the mixture with silt and clay fractions was much better than on the sand fraction; there was no major difference in growth and K⁺ supply to plants whether grown on silt or clay, although the clay fraction was rich and the silt fraction poor in exchangeable K⁺. On both these fractions the plant-available K⁺ supply was suboptimal and the plants showed deficiency symptoms except for the elephant grass. This plant species had a relatively low growth rate but it grew similarly on sand, silt, and clay and did not show any K⁺ deficiency symptoms, with the K⁺ concentration in the plant tops indicating a sufficient K⁺ supply regardless of which soil fraction the plants were grown in. The reason for this finding is not yet understood and needs further investigation. It is concluded that on soils rich in mica, exchangeable K⁺ alone is a poor indicator of K⁺ availability to plants and that mica concentrations in the silt and clay fraction are of greater importance in supplying crops with K⁺ than exchangeable K⁺.