Sodium bicarbonate as an extractant for soil phosphate,I. Separation of the factors affecting the amount of phosphate displaced from soil from those affecting secondary adsorption

A mathematical procedure was developed to permit the estimation of both the amount of phosphate initially displaced from soil and the amount undergoing secondary adsorption.The proportion of previously added phosphate which was initially displaced by bicarbonate decreased as the period and temperature of prior contact between soil and phosphate increased. The proportion displaced was greater than was displaced by dilute calcium chloride.The amount of secondary adsorption depended on the soil:solution ratio, the level of addition of phosphate, the period of shaking, and the kind of soil. Part of the effect of soil:solution ratio appeared to arise because of adsorption of bicarbonate. As a result, at high soil:solution ratios, the bicarbonate concentration in solution was lower and so competition for re-adsorption was less effective. Bicarbonate was less effective at preventing re-adsorption when the level of prior addition of phosphate was high. This may have occurred because prior adsorption of phosphate had increased the negative charge on the surface. Because of secondary adsorption, there was a curvilinear relationship between the amount of phosphate added to the soil and the amount present in the extract.     

Sodium bicarbonate as an extractant for soil phosphate,II. Effect of varying the conditions of extraction on the amount of phosphate initially displaced and on the secondary adsorption

The effects of varying the period of shaking, the concentration of bicarbonate, the pH, and the dryness of the soil on the phosphate extracted by sodium bicarbonate were investigated. A regression procedure in which the soil: solution ratio was the independent variable was used to separate the effects on the amount of phosphate initially displaced from those on the secondary adsorption.Both the amount initially displaced and the amount of secondary adsorption increased with period of extraction. At small soil:solution ratios the effect on displacement was dominant and the net effect was a continuing increase in the amount of phosphate in the extract. At large soil:solution ratios, secondary adsorption eventually predominated and caused a decrease in the amount of phosphate in the extract.Increasing the bicarbonate concentration from 0.01 M to 1.0 M decreased secondary adsorption but had no significant effect on the initial displacement. The effects of changing the concentration were most marked at low concentrations.Increasing the pH of 0.5 M bicarbonate solutions increased the amount of phosphate initially displaced but had no significant effect on secondary adsorption. In the absence of bicarbonate, the effects of pH differed: increasing the pH decreased secondary adsorption. Secondary adsorption was important when the ratio of soil to solution was large and in these cases the net effect of pH on bicarbonate - as measured by difference - was greatest near the pK₂ of carbonic acid.Drying the soil increased the amount of phosphate displaced from the soil after 30 min extraction but the effect was eliminated by extending the period of extraction to 16 h.     

THREE EFFECTS OF TEMPERATURE ON THE REACTIONS BETWEEN INORGANIC PHOSHATE AND SOIL

Phosphate was added to soil, incubated at a range of periods and of temperatures, and the rate of desorption was measured at several solution: soil ratios at 25°C. One sample was incubated at a high temperature for several days and the rate of desorption was measured at 5, 15, 25 and 38 °C. A regression approach was used to describe the results which were interpreted in terms of a model in which phosphate was present (a) in solution, (b) adsorbed in equilibrium with the solution, and (c) firmly held. When neither adsorption nor desorption occurred, the phosphate concentration in solution increased with temperature. This was interpreted as an effect of temperature on the position of the equilibrium between solution phosphate and adsorbed phosphate. The direction of the effect indicates that adsorption was exothermic. When either adsorption or desorption occurred the rate increased with temperature and to a similar extent. For both reactions, the change in heat content was small. Thus, while temperature affected the rate of interchange between adsorbed and firmly-held forms it should not affect the position of the equilibrium between these forms.     

THE DETERMINATION OF DESORPTION ISOTHERMS FOR SOIL PHOSPHATE USING LOW VOLUMES OF SOLUTION AND AN ANION EXCHANGE RESIN

Phosphate desorption isotherms were determined (a) by shaking 1 g soil with 3 ml 0.01M CaCl₂ solution plus different amounts of an anion exchange resin, and (b) by diluting soil with different volumes of 0.01M CaCl₂ solution. Adsorption isotherms were determined using a soil to solution ratio of 1 g to 3 ml. In soils of intermediate P status adsorption isotherms appeared continuous with desorption by method (a), but not with desorption by method (b), which predicted lower buffer powers than did (a). Method (a) led to increases and (b) to decreases in pH. Additions of dissolved silica had no influence on P desorption by method (b).     

Factors affecting the amount of phosphate extracted from soil by anion exchange resin

In resin—solution systems at equilibrium, solution concentration of phosphate was proportional to the square of the phosphorus sorbed, and inversely proportional to the weight of resin and the volume of solution. The rate of approach to equilibrium was decreased by: enclosing the resin in mesh bags, by increasing the volume of solution, and by decreasing the vigour of shaking.In resin-solution-soil systems, the concentration of phosphate in the solution was important in determining the amount of phosphate extracted from the soil. Consequently, phosphorus extracted increased as volume of water and weight of resin increased, and decreased when the resin was enclosed in mesh bags. Even after long periods of shaking, when the concentration of phosphate in solution had reached low values, appreciable phosphate remained on the soil in equilibrium with this solution phosphate. Equations suggested that, if the solution concentration could be reduced to zero, phosphate sorbed by the resin would be proportional to the phosphorus added to the soil. However, at finite levels of addition of resin, the proportion of added phosphate sorbed by the resin increased as the level of addition of phosphate increased.     

有机肥对土壤磷素吸附的影响

本文研究发现,有机肥可以显著活化土壤本身的磷,并能减少磷的吸附,前者是由于有机肥分解所产生的有机酸,后者是由于有机肥中碳水化合物对吸附位的掩蔽。去除土壤有机质的试验进一步证明了有机质对吸附位的掩蔽作用。有机肥的水提液可以降低土壤对磷的吸附。证明了磷和有机物之间有竞争吸附的存在。     

EFFECTS OF IONIC STRENGTH AND NATURE OF THE CATION ON DESORPTION OF PHOSPHATE FROM SOIL

The effects of cations on desorption of phosphate previously added to soil were studied by mixing phosphated soil with solutions of chloride salts at a range of solutionitoil ratios and for periods which ranged from 1 to 96 h. Phosphate desorbed was then related to the experimental variables by a pair of simultaneous equations. In calcium chloride, the rate of desorption of phosphate was inversely proportional to the calcium concentration. Desorption was faster in 0.01 M magnesium chloride than in 0:01 M calcium chloride, and faster in 0.03 M sodium chloride than in either magnesium or calcium chloride. Addition of a further supply of the cation on an exchange resin increased the rate for both sodium and magnesium but decreased it for calcium. A range of monovalent cations formed a sequence from fastest to slowest of: Li⁺ > Na⁺ > NH₄^?> K ⁺, Rb ⁺ > Cs ⁺. The identity and concentration of the cations had a large effect on the concentration of phosphate when the solution: soil ratio was small. There were also large effects in the amount of phosphate desorbed when the solution: soil ratio was large and the concentration of phosphate approached zero. This suggested that the escaping tendency of the phosphate was decreased when the cations which balanced the negative charge on the adsorbed phosphate were close to the surface.     

EFFECTS OF SOLUTION: SOIL RATIO ON PHOSPHATE SORPTION BY SOILS

Isotherms for the sorption of inorganic phosphate (P) by three contrasting soils during 40 h showed a dependence on solution: soil ratio. Above a final solution P concentration of 0.5 μg ml^?1, more P was sorbed at a solution: soil ratio of 5:1 than at 40:1 for a given level of P in solution. With time up to 146 h, the effect of solution: soil ratio on P sorption was kinetically controlled. Equilibrium solution P concentrations, estimated by extrapolation of the linear relationships between solution P concentration and the reciprocal of time to I/t= o (i.e. t=∞)appeared to be coincident for each solution:soil ratio at high and the low levels of added P. Consequently, sorption isotherms at equilibrium would be coincident, irrespective of the solution soil ratio used. The kinetic control of solution: soil ratio on P sorption is interpreted in terms of the number of P sorbing sites and initial solution P concentration on the rate of P sorption by soils.     

十万大山北坡土壤条件对马尾松高生长影响的初步分析

回归分析结果表明,广西十万大山北坡土壤条件与马尾松高生长间的关系属非线性关系。母岩(母质)、海拔、土壤有机质、土壤质地与马尾松高生长间正相关显著;土壤紧实度与马尾松高生长间负相关显著;而土壤全氮、碱解氮、速效磷、速效钾与马尾松高生长间相关未达到显著水平。各土壤条件对马尾松高生长相关程度的大小顺序为:母岩(母质)>海拔>土壤质地>土壤紧实度>土壤有机质>土壤全氮>土壤速效磷>土壤速效钾>土壤碱解氮。以母岩(母质)、海拔、紧实度、有机质、质地与马尾松平均高所建立的相应一元非线性回归方程,X~2检验无显著差异,对该地区马尾松高生长有较高的预测精度。     

THE DESCRIPTION OF DESORPTION OF PHOSPHATE FROM SOIL

After incubation with soil, phosphate was desorbed in dilute calcium chloride solutions. After short periods of incubation, the amount of phosphate desorbed increased rapidly at first but then net re-adsorption occurred. After long periods of incubation, desorption was slower and there was no net re-adsorption with prolonged desorption. Desorption was described in terms of two limiting values: the amount of phosphate (K) which would be desorbed as the concentration of phosphate approached zero, and the solution concentration of phosphate (C_o) at which no desorption occurred. Both values decreased as the period of incubation increased. The value of K increased during the desorption phase, but the value of C_o decreased. The decrease in C_o during desorption was most marked after short periods of incubation and was important in describing the trend for re-adsorption of phosphate.     

Sodium bicarbonate as an extractant for soil phosphate III. Effects of the buffering capacity of a soil for phosphate

An index of the buffering capacity for phosphate of a group of soils was obtained by measuring adsorption of phosphate from dilute solutions of calcium chloride. The effect of buffering capacity on the amount of phosphate initially displaced by solutions of sodium bicarbonate and on the amount of secondary adsorption from bicarbonate was then studied. These two effects were separated using a regression procedure in which the soil: solution ratio was the independent variable.As buffering capacity increased the amount of phosphorus initially displaced decreased and the amount of secondary adsorption increased. Both these changes resulted in a decrease in the amount of phosphate in the extract. The effect of buffering capacity was greater with the Olsen method (soil : solution ratio 1 : 20; 30 min) than with the Colwell method (soil : solution ratio 1 : 100; 16 h). The relation between phosphorus extracted and buffering capacity was of a similar shape to that between effectiveness of fertilizer and buffering capacity. However, the first relation depends on the conditions of extraction and the second on the kind of plant grown and on the conditions of growth. Hence the two relations do not necessarily coincide.The effect of buffering capacity on the proportion of added phosphate initially displaced from the soil became more marked as the period of incubation prior to extraction was increased. Bicarbonate soil tests would therefore indicate that, on soils of low buffering capacity, the decrease with time in availability of applied phosphate would be smaller than on soils of high buffering capacity. This effect differs from that observed with plants.     

滤纸法测定非饱和土壤离子吸附等温线的初步研究

滤纸法对非饱和土壤溶液离子浓度的变化有较高的敏感性和较好的重现性 ,能够用于非饱和土壤离子吸附等温线的测定。滤纸法和乙醇浸提法、离心法有很好的一致性。滤纸法测定的非饱和土壤NH 4 、K 离子吸附等温线具有一般吸附等温线的共性 ,可用Freundlich方程描述 ,且达极显著相关水平。在土壤溶液浓度相同的情况下 ,液土比增大 ,离子固相吸附量增大 ,Freundlich方程的k值 ,n值增大 ,说明液土比增大有利于非饱和土壤离子吸附反应进行     

多种有机酸共存对可变电荷土壤吸附磷的影响

研究了２种或３种有机酸在不同浓度组合时对可变电荷土壤吸附磷酸根离子的影响,结果表明:（１）有机酸的种类、各自的浓度及总浓度对土壤吸附磷有显著影响;（２）土壤组成及表面性质不同时,有机酸与磷的竞争效果也不大相同;（３）多种有机酸混存对土壤吸附磷量的影响不等于各单一有机酸贡献的简单加和。因此,根际环境中有机酸、磷在土壤表面的相互作用还有许多待探讨的问题。     

石灰性土壤与磷酸盐的反应及吸持态磷的同位素交换性

本文研究了种石灰性土壤（Ｌｏｕ土）与磷酸盐的反应动态过程，短期反应的等温吸附研究表明，在低磷浓度下，以吸附反应机制为主，吸持态磷的同位素交换性随着吸持量的增加而增加；在高磷浓度下，以形成磷酸盐的沉淀反应机制为主，吸持态磷的同位素交换性随着反应时间的延长和吸持量磷数量的增加而了降低。认为在低施磷水平下，土壤中铁，铝氧化物对磷的吸持起重要作用。本文还探讨了在长期（２６０天）恒温恒湿培养过程中，土壤可溶     

The effect of pH on zinc adsorption by a lateritic soil in the presence of citrate and oxalate

A change in the pH of the rhizosphere may alter the effect that organic ligands have on the concentration of Zn in the soil solution. To assess this effect, Zn adsorption by a lateritic soil was measured in the presence of 0, 1 and 3 mM of citrate and oxalate at nine values of pH ranging from pH 2 to 8. The concentrations of Zn and the ligands remaining in the solution were determined after 17 h shaking with the soil at soil:liquid ratio of 1:5. Subsequently, Zn speciation was calculated. The effectiveness of an organic ligand (L) in changing Zn adsorption was influenced by the sign of the charge of the Zn-L complex, the point of zero salt effect (PZSE) of the soil, the pH of the soil solution and the quantity of the complex formed. When the pH was above the PZSE of the soil, citrate decreased Zn adsorption by up to 38% whereas it increased Zn adsorption by as much as 51 % when the pH was below the PZSE. Oxalate had a similar but smaller effect than citrate under the conditions of the experiment. Zn adsorption was correlated with the concentration of zinc citrate in both pH regions (r2>0.98) and with oxalate above pH 2.7. The increase in Zn adsorption at low pH could have been caused by the adsorption of negatively charged Zn-L complexes.     

Extraction of active aluminum from acid soils in Japan with different reagents

The paper deals with methods of determining active aluminum in acid soils. Extraction reagents examined were 4 acids, 4 salts, and 11 compounds of chelating agents. The effects of different conditions, such as pH, temperature, shaking time and the ratio of solution to soil were observed. Barium salicylate solutions, in which the normal concentration of barium and the molar concentration of salicylate were 1.0 and 0.1 respectively, were found promising as extractants. Initial pH of the solution, shaking time and the ratio of solution to soil were set at 7.0, 2 hours and 50:1, respectively. Ammonium salicylate and ammonium EDTA also extracted active aluminum but amounts varied according to different conditions. The most promising procedure was applied to a few kinds of soils and to soil treated with either lime or phosphate. The amounts of aluminum extracted from soils high in humus were larger than those from soils low in humus. Liming or phosphate application decreased the amounts of aluminum extracted.     

AGEING OF PHOSPHATE ADDED TO SOIL

The ageing of phosphate added to suspensions of a calcareous soil was measured in terms of the solubility of the phosphate and the amount of isotopically exchangeable phosphate (E value). These both showed a decrease in reactivity of the added phosphate during a period of 5 months. A constant ratio of E values after 24 and 500 hours showed that no redistribution within different fractions of labile phosphate occurred.     

离子强度和磷酸盐对铁铝矿物及土壤吸附As（V）的影响

选用针铁矿、赤铁矿、水铁矿、水铝矿4种铁铝矿物以及性质差异较大的黑土、紫色土和红壤3种土壤,研究离子强度和磷酸盐对其吸附As（V）的影响。结果表明,在0．01、0．1、1mol·L^-13种离子强度下,矿物和土壤对As（V）的吸附量无明显差异或随离子强度增大而增大,其对砷的吸附以专性吸附为主。磷酸盐对矿物和土壤吸附砷的影响与其添加顺序及摩尔浓度比有关。水铝矿和水铁矿在这3种添加顺序下的砷吸附量无明显差异,仅在P／As摩尔比较大时表现出下降趋势;而在针铁矿和赤铁矿两种矿物上,先添加砷时的砷吸附量高于先添加磷时或两者同时添加时,且砷吸附量随WAs摩尔比的增加而逐渐下降。在黑土、紫色土和红壤上,先添加砷比先添加磷或两者同时添加时的砷吸附量均要高,尤其是在紫色土上。随P／As摩尔比升高,土壤对砷的吸附量表现出下降趋势。     

SOIL FLUORINE

The development of techniques for measuring soluble and labile soil fluoride using a specific-ion fluoride electrode are described. The methods evolved were used to assess the fluoride status of numerous agricultural soil samples in addition soils which had received known fluoride additions. Two soil profiles were analysed with respect to distribution with depth of soluble and labile fluoride. The equilibrium-fluoride concentration was determined after shaking the soil with a 0.01 M CaCl, solution. Isotopically exchangeable (labile) soil fluoride was determined by use of the radioactive fluorine isotope ¹⁸F. These labile fluoride values were well correlated with the amount of soil fluoride extracted by an anionexchange resin, and the latter method was consequently adopted for further determinations of labile soil fluoride. Nearly half the 1OO agricultural soil samples examined gave fluoride concentrations < 0.2 ppm in 0.01 M CaCl, extracts whereas labile fluoride values were evenly distributed around a mean of 20 ppm. For any given pH value, there appeared be an upper limit to the solubility of soil fluoride. Application to soil of superphosphate (in the field) or of fertilizer containing fluoride (in the laboratory) brought about increases in soluble soil fluoride.