Evaluation of Ammonium Bicarbonate–Diethylene Triamine Penta Acetic Acid as a Multinutrient Extractant for Acidic Lowland Rice Soils

Abstract

Simultaneous extraction of nutrients using ammonium bicarbonate–diethylene triamine penta acetic acid (ABDTPA) extractant has been successful for highland soils, but its potential for lowland soils is still uncertain. This study evaluated the suitability of ABDTPA extractant to determine available phosphorus (P), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) in lowland rice soils of Sri Lanka. Available nutrients were analyzed both by conventional and ABDTPA methods, using the original ABDTPA (1∶2 soil–extractant) method as well as a modified (1∶4 soil–extractant) method. Conventional methods tested were Olsen, Bray 1, and FeO strip for available P; neutral NH₄OAc extraction for exchangeable Ca, Na, K, and Mg; and DTPA extraction for available Zn, Cu, Fe, and Mn. Nutrient content and uptake by plants were determined by a pot experiment with rice (Oryza sativa). Nutrients extracted by the conventional methods and ABDTPA methods correlated well, in general, for all nutrients. Highly significant correlations were observed between plant uptake and extractable nutrients by 1∶2 and 1∶4 ABDTPA methods for P (r=0.85***and 0.73***, respectively), K (r=0.79*** and 0.66***, respectively), Na (r=0.86*** and 0.78***, respectively), Zn (r=0.66*** and 0.60***, respectively), Mn (r=0.72*** and 0.84***, respectively), and Fe (r=0.74*** and 0.68***, respectively). Calcium and Mg extracted by ABDTPA showed a poor relationship with their respective plant uptake. The ABDTPA method was as effective as or even better than the conventional methods in evaluating fertility status of lowland rice soils with respect to most nutrients. Replacing the conventional methods by the single ABDTPA multielement extractant will reduce the time and cost of soil analysis.     

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous,gypsiferous, saline and sodic soils

Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO₃ or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO₄ and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na₄EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO₄ in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.     

KC1‐extractable aluminium in highly weathered soils. Is it exchangeable?

Abstract

In a study involving 212 samples of surface and sub‐surface soils derived from basaltic, granitic, and metamorphic parent materials in the high rainfall region of north Queensland, Australia, the Al extracted with 1 M KC1 has been compared with ‘exchangeable aluminium’, defined as the difference between CEC and sum of basic exchangeable cations. It was concluded that for these highly weathered soils KCl‐extractable Al is exchangeable, and therefore that the sum of basic and acidic cations (ECEC) is a reliable measure of CEC at field conditions.     

A comparison of buffered and unbuffered ammonium salts to determine exchangeable base cations in acid soils

Abstract

In soil samples from two study sites in southern Norway, exchangeable cations were determined using two different ammonium (NH₄)‐salts as extractant. As expected, the cation exchange capacity (CEC) determined in 1M ammonium acetate (NH₄OAc), buffered at pH 7.0 was higher than the CEC measured in ammonium nitrate (NH₄NO₃). By contrast, the amount of exchangeable calcium (Ca), magnesium (Mg), and barium (Ba) was lowest in the NH₄OAc extract, in particular in the upper soil horizons high in organic matter (O‐ and E‐horizon). This suggests that NH₄ in 1M NH₄OAc does not compete effectively with multivalent base cations. The relatively high levels of exchangeable base cations in NH₄NO₃ could not be explained by increased weathering. An increase in selectivity of especially divalent cations may explain the relatively low amount of exchangeable base cations extracted by NH₄OAc, as this involves increased deprotonation and thus a higher negative charge.     

Release of Al by hydroxy-interlayered vermiculite and hydroxy-interlayered smectite during determination of cation exchange capacity in fine earth and rock fragments fractions

The fine earth (<2 mm) and rock fragments (>2 mm) fractions of two soils derived from Oligocene sandstone have been examined to assess the origin of the discrepancies between cation exchange capacity (CEC) and effective CEC (ECEC). The soils differ in terms of acidity: soil A is more acid than soil B. When the A samples are treated with BaCl₂, the solution became sufficiently acid (pH < 4·5) to dissolve and to maintain Al in solution. From these samples more Al is released than base cations. Aluminium was continuously replenished even after 192 h, so that the ECEC was always larger than the CEC. Samples from soil B contain less H and Al ions, and the BaCl₂ solution could not lower the pH below 5·0. In these samples little Al is released, and the base cations dominate the exchangeable pool of ions. This Al can be considered to be exchangeable, and a good agreement exists between the ECEC and the CEC. The source of non-exchangeable Al in the A samples is the OH-Al polymers of the hydroxy-interlayered vermiculite (HIV) and hydroxy-interlayered smectite (HIS) that tend to dissolve during the BaCl₂ treatments. In the less acid B samples the Al polymers are not affected by BaCl₂ treatment. Different results were obtained when the clays, extracted from an Na-dispersed suspension, were treated with BaCl₂ solution. Because the clays are no longer acid, no H⁺ is released, and the OH-Al polymers are not dissolved. Therefore, the saturating ions play an important role in the dissolution of the OH-Al polymers and cause differences between the CEC and ECEC. We discount organic matter and specifically Al-organo complexes as a source of non-exchangeable Al. Both A and B soils contain very similar pyrophosphate-extractable Al, but show substantial differences in the amount of exchangeable Al.     

Changes since 1950 of mineral pools in the upper C-horizon of Swedish deciduous forest soils

Soils from the C-horizon of deciduous forests in southern Sweden, originally sampled in 1947-52, were resampled in 1988. Air-dried soil from both periods were extracted in 1991 using M NH₄Ac, pH 4.8, and 0.2 M HNO₃ for analysis of exchangeable and acid soluble pools of Na, Mn, Ca, Mg, K, Sr, Zn, Fe, S, P, and Al. Using acid NH₄Ac as extractant nine elements had changed significantly (p<0.05) over 40 yr. In particular, the pools of exchangeable base cations and Mn had decreased, whereas those of Al, S, and Fe had increased. The HNO₃ extraction showed the same tendency as NH₄Ac for most elements, but the relative changes were always smaller. The largest decrease was measured in Na with both extractants (only 10 to 30% remaining in 1988). Of K, Mg, Ca, and Sr, about 40 to 60% remained with NH₄Ac and about 70% with HNO₃. The NH₄Ac exchangeable pool of Al, on the contrary, was twice as high in 1988 as in 1947–52. Amounts obtained with the two extractants were usually positively correlated (r>0.90 for Na, K, Mg, and Sr), but with the exception of S, values for HNO₃ were higher or much higher. It is concluded that a decided decrease of the exchangeable pools of base cations and an equally decided increase of exchangeable Al has occurred even in the C-horizon, well below the main rhizosphere. That also the acid soluble pools of base cations have decreased indicates mineralogical changes which may counteract a complete reversibility of the current soil acidification.     

Zur Bestimmung austauschbarer Kationen in sauren Waldböden

On the determination of exchangeable cations in acid forest soils Different samples from acid forest soils were percolated with large amounts of H₂O. Significant amounts of anions, especially sulfate, were found in the percolates mainly accompanied by Na. K, Ca and Mg (M_b-cations). The dissolution of Al-Sulfates and subsequent exchange of M_b-cations by Al as dominant mechanism is proposed. Thus the common method for determination of the cation exchange capacity (CEC) of acid forest soils, the percolation with NH₄Cl may overestimate the CEC. The overestimation may be related to the sulfate content of the soil and also influences the calculation of relative CEC proportions of individual cations.     

Ammonium Chloride Solution as an Alternative Laboratory Procedure for Exchangeable Cations in Southern Brazilian Soils

Most Brazilian soil-testing laboratories use Mehlich 1 and 1.0 M potassium chloride (KCl) solutions as extractants for the determination of phosphorus (P), potassium (K), and sodium (Na) and for exchangeable calcium (Ca), magnesium (Mg), manganese (Mn), and aluminum (Al) in agricultural soil samples. Other laboratories use a combination of exchangeable ionic resin and KCl procedures. With recent adoption of the inductively coupled plasma (ICP-OES) in routine soil-testing laboratories, soil extraction with 1.0 M ammonium chloride (NH₄Cl) became an alternative due to the possibility of determining all exchangeable elements in one run (Ca, Mg, K, Mn, Na, and Al), leaving determination of phosphorus (P) with Mehlich 1 or exchangeable ionic resin. To evaluate the performance of the NH₄Cl solution, an experiment was carried out with thirty-seven samples of soils representative of the southernmost state of Brazil, Rio Grande do Sul. Four extraction solutions [Mehlich 1 at soil/solution ratio of 1:10 and 1.0 M ammonium acetate (NH₄OAc), 1.0 M KCl, and 1.0 M NH₄Cl at soil/solution ratio 1:20] were used with three different shaking times (5, 30, and 60 min). Correlation coefficients among all methods were high. Mehlich 1 did not perform well against NH₄OAc and NH₄Cl, despite the high correlation coefficients, with values consistently lower for K, even when the time of extraction was increased from 5 to 30 or 60 min. However, for concentrations less than 0.30 cmol kg^?1 (i.e., in the range of K deficiency), both solutions performed similarly. Calcium and Mg increased with time of shaking. Comparable values of exchangeable Ca, Mg, and K, as well as of Al and Mn, were obtained with 1.0 M NH₄Cl with 60 min shaking and the standard procedures of 1.0 M NH₄OAc and 1.0 M KCl. The determination of Al by traditional titration/back-titration of the 1.0 M KCl solution gave slightly greater results compared to ICP-OES obtained using extraction with 1.0 M NH₄Cl. The results indicate that for Ca, Mg, Mn, and Al, it is possible to replace the traditional 1.0 M KCl extraction with 1.0 M NH₄Cl solution, with 60 min shaking time and a soil/solution ratio of 1:20.     

Exchangeable cations in rock fractions and fine earth in soil profiles of different genesis

Data on accumulated exchangeable H, Al, Fe and Mn (M_a) cations in rock fractions in German soil profiles are scarce. The objective of this study was to describe the sum of accumulated M_a cations of fine earth and rock fragments in 11 deep soil profiles of varying genesis. Soil profiles were laid out at the sites Solling, Eifel, Harz mountains and the Erzgebirge and the parent materials included sandstones, siltstones, quartzite, slate, greywacke, diabase, gneiss and quartz porphyry. Exchangeable cations in the fine earth and rock fragments were measured in depths down to 6 m. Additionally, effective porosity and specific surface of rock fragments were determined. The effective porosity of the different rock fragments ranged from 4 to 28% (v/v), indicating that the rocks were accessible to solutions. For most samples, the cation exchange capacities (CEC) of the fine earth fractions were larger than those of the rock fragments, and the CEC (fine earth)/CEC (rock) ratios decreased with depth. All 11 profiles had small (<40%) amounts of exchangeable Na, K, Mg and Ca (M_b) cations in the fine earth fraction. Exchangeable M_a and M_b cations in the rock fragments changed similarly with depth as in the fine earth fractions for all profiles. Cumulative (rock + fine earth) M_a cations from 0—200 cm ranged from 474 to 1592 kmol_c ha⁻¹. The contribution of the rock fraction to the cumulative exchangeable M_a cations accounted for 13 to 85% of the total. The sum of exchangeable M_a cations was much higher than the cumulative acid deposition in western Germany since the beginning of industrialization, suggesting that carbonic acid and organic acids contributed largely to soil acidification. The rocks contribute significantly to buffering the acidity of the seepage water by silicate weathering and cation exchange. Therefore, acidification models which consider the fine earth fraction only, may lead to an overestimation of the rate of soil and groundwater acidification.     

EFFECT OF SOIL pH AND ORGANIC MATTER ON LABILE ALUMINIUM IN SOILS UNDER PERMANENT GRASS

The rates of extraction of Na, K, Mg, Ca, and Al with 1M NH₄ NO₃ from the mineral-and organic-rich layers of some Park Grass (Rothamsted) soils were measured at the pH of the soil. Below pH 3.7 exchangeable Al, derived from the kinetics curve, increases with decreasing soil pH and is less in the organic-rich layer. The sum of the basic exchangeable cations, ∑(Na + K + Mg + Ca), increases with increasing soil pH and is more in the organic-rich layer. The extraction of exchangeable Al obeys first order kinetics, the rate constant being similar for all the soils (mean value 36 ± 7 × 10^?6|s^?1), which implies that exchangeable Al is released from surfaces with similar properties for the adsorption of Al, and that the rate is not affected by soil pH and organic matter. The rate of extraction of non-exchangeable Al is the same in the mineral-and organic-rich layers of each soil, and is maximal at about pH 3.7, decreasing sharply at more and less acid pH values.     

Cation exchange capacity measurements

Abstract

Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc)₂ (pH 7.0) saturation with Mg(OAc)₂ (pH 7.0) displacement of Ca²⁺; (3) N NH₄OAc (pH 7.0) saturation with NaCl displacement of NH₄ ⁺; (4) N MgCl₂ saturation with N KCl displacement of Mg²⁺; (5) compulsive exchange of Mg²⁺ for Ba²⁺; and (6) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC component to a greater degree than the buffered methods. The compulsive exchange and the summation of N NH₄OAc exchangeable cations plus N KCl exchangeable Al procedures gave CEC estimates of the same magnitude that reflect differences in soil pH and texture. The buffered procedures, particularly the summation of N NH₄OAc exchangeable cations plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity, indicated inflated CEC values for these acid Ultisols that are seldom limed above pH 6.5. Exchangeable soil Ca and Mg levels determined from extraction with 0.1 M BaCl₂ were consistently greater than values for the N NH₄Oac (pH 7.0) extractions. The Ba²⁺ ion is apparently a more efficient displacing agent than the NH₄ ⁺ ion. Also, the potential for dissolving unreacted limestone is greater for the Ba₂ ⁺ procedures than in the NH₄ ⁺ extraction.     

Modelling of sorption experiments and seepage data of an Amazonian Ultisol subsoil under cropping fallow

The results of physico-chemical investigations of an Ultisol subsoil under a 2-year old fallow in eastern Amazonia are presented. Subsoil chemistry was studied using 4 different approaches: i) concentrations of H, Na, K, Ca, Mg, Mn, Al, and Fe in seepage water were measured under field conditions, ii) the equilibrium soil chemistry was studied in sequential batch experiments where the soil was treated with different solutions, iii) results of batch experiments were simulated with a chemical equilibrium model, and iv) the seepage data were calculated using selectivity coefficients obtained by modelling the batch experiments. The model included multiple cation exchange, precipitation/dissolution of Al(OH)₃ and inorganic complexation. Cation selectivity coefficients were pK_x/Ca^sel: X = Na: 0.3, K: 0.8, Mg: ?0.1, and Al: 0.4. The amount of cations sorbed ranged from ?0.2 to 2.0 (K), ?0.7 to 2.3 (Mg), ?1.6 to 1.8 (Ca), ?4.8 to 3.6 (Al) and 0.0 to 8.5 (Na) mmol_c kg^?1. The model predictions were good with values lying within 0.3 pH units (for the pH range 3.7 to 7.2), and 3% of CEC for individual cations. The most important proton buffer reaction seemed to be the dissolution of gibbsite and a large release of Al into the soil solution. When selectivity coefficients obtained by the modelling procedure were used to predict the field data for cation concentrations in the seepage water, they decreased in the following order: Na > K > Ca > Mg > Al. These calculated values were similar to the measured order: Na > Ca > K ≈ Mg > Al. Thus the options for managing these soils should be carefully chosen to avoid soil acidification which may result from inappropriate use of fertilizer during the cropping period.     

Effects of acid rain on ion leaching in a danish forest soil

The mobility of major cations (H⁺, ammonium, Al, Ca, Na, Mg, K, Fe), heavy metals (Mn, Zn, Ni, Cd) and anions (chloride, sulphate and nitrate) was studied in the laboratory in an acidified brown soil from a Norway spruce forest. Lysimeters containing undisturbed soil columns of the A-horizon and the A- plus B-horizon were watered with 540 mm of throughfall precipitation collected in situ, either directly (pH 3.6) or adjusted to pH 3.3 or 2.8. The pH 3.3 treatment increased leaching of Mn and Cd from the B-horizon. The pH 2.8 treatment increased leaching of ammonium, Na, Ca, Mg, K, Mn, Zn and Cd from the A-horizon and ammonium, Al, Na, Ca, Mg, K, Mn, Zn and Cd from the B-horizon. Fe leaching from the A-horizon was decreased by both acidic treatments, and the pH of the leachates was not significantly affected. Sulphate retention was 138-161 meq m^?2 yr^?1 by all treatments. Due to experimental conditions nitrate leaching was observed in all lysimeters.     

Exchangeable cations and CEC determinations of some highly weathered soils

Abstract

Eight methods to determine exchangeable cations and cation exchange capacity (CEC) were compared for some highly weathered benchmark soils of Alabama. The methods were: (1) 1N NH₄OAc at pH 7.0 by replacement (for CEC only), (2) 1N NH₄OAc at pH 7.0 (summation of basic cations plus 1N KCl extractable Al), (3) 1N NH₄OAc at pH 7.0 (summation of basic cations plus exchangeable H⁺), (4) 0.1M BaCl₂ (summation of basic cations plus exchangeable Mn, Fe and Al), (5) Mehlich 1 (summation of basic cations plus 1N KCl extractable Al), (6) Mehlich 1 (summation of basic cations plus exchangeable H⁺), (7) Mehlich 3 (summation of basic cations plus 1N KCl extractable Al), and (8) Mehlich 3 (summation of basic cations plus exchangeable H⁺). The 0.1M BaCl₂ was chosen as the standard method for the highly weathered soils and the other methods compared to it. The results indicated that the 1N NH₄OAc replacement method gave significantly higher CEC values compared to the summation methods. This was probably due to the overestimation of the field CEC caused by measurement of pH dependent cation exchange sites in these soils. There was, however, close agreement between the BaCl₂ method and the summation methods that included extractable Al. The generally good agreement between these summation methods suggests that the Mehlich 1 and Mehlich 3 extractants, commonly used to determine available nutrients in the southeastem USA, may also be used to measure effective CEC of some acid‐rich sesquioxide benchmark soils of Alabama. However, 1N KCl extractable Al as opposed to exchangeable H⁺ should be included in the computation.     

Evaluation of Universal Extractants for Determination of Some Macronutrients from Soil

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. The objective of this work was to find out the most suitable universal extractant for determination of available phosphorus (P) and nitrate (NO₃-) and exchangeable potassium (K), calcium (Ca), and magnesium (Mg) from soils using 0.01 M calcium chloride (CaCl₂), 0.01 M barium chloride (BaCl₂), 0.1 M BaCl₂, 0.02 M strontium chloride (SrCl₂), Mehlich 3, and ammonium bicarbonate diethylene triamine penta acetic acid (AB-DTPA) extractants. Composite surface soil samples (0–20 cm) were collected from the Eastern Harage Zone (Babile and Haramaya Districts), Wolaita Zone (Damot Sore, Boloso Bombe, Damot Pulasa, and Humbo Districts), and Dire Dawa Administrative Council by purposive sampling. The experiment was carried out in a completely randomized design (CRD) with three replications. Results indicated that the greatest correlations were found between Mehlich 3 and Olsen method and also between 0.02 M SrCl₂ and Olsen method for available P. The amount of NO₃^– extracted by 0.02 M SrCl₂ was significantly correlated to the amount determined by 0.5 M potassium sulfate (K₂SO₄). The amounts of exchangeable K, Ca, and Mg determined by ammonium acetate (NH₄OAc) method were significantly correlated to the amount determined by universal extractants tested. In general, both 0.02 M SrCl₂ and Mehlich 3 can serve as universal extractants for the macronutrients considered in this study with the former being more economical when NO₃^– is included.     

Comparison of extractants for the determination of available phosphorus,potassium, calcium,magnesium and sodium in some Ethiopian and German soils

Abstract

A study was conducted with the purpose of comparing the efficiency of Mehlich 1, Mehlich 3, and calcium acetate lactate (CAL) extractants for the deter‐ mination of available phosphorus (P) and exchangeable cations [potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)] on 22 Ethiopian and 10 German agricultural soils. The Olsen and NH₄OAc extractants were used as standards against which P and exchangeable cations values were compared. Results showed that, in general, highly significant correlations were found between all of the methods for available P and exchangeable cations determination on the Ethiopian soils. The highest correlation was, however, found with the Mehlich 3 extractant. On the ten soils from Germany, the Olsen method did not give significant cor‐ relation with the CAL method for P determination. The CAL and Mehlich 3 extrac‐ tants were also not good indicators of Na availability when compared with the NH₄OAc method. It can be generalized that the Mehlich 3 is a suitable extractant for P, K, Ca, Mg, and Na in Ethiopian soils, but further study is recommended to confirm these findings under field conditions.     

Acidification of Solid and Solution Phases at Greater Depths (> 150 cm) at Solling Spruce Site

The acidification of the soil and percolation water at soildepths from 150 to 500 cm was studied at the Solling spruce sitefrom 1991 to 1996. NH₄Cl exchangeable cations of the fineearth and bedrock fractions were obtained from different depthsand the soil solution composition was monitored at 150, 200,300, 400 and 500 cm depths using seven suction lysimeters at each depth.In the seepage water collected from 150 and 200 cm depth, pHvalues decreased in the period 1991 to 1996, but no significantchanges were observed in solutions collected below 200 cm depth.Element budgets of Al and M_b (Na, K, Mg, Ca) cationsindicated that buffering by exchange of Al with M_b cationsoccurred mainly in surface 200 cm soil depth. High variabilities in concentrations of SO₄ (at 150 cm) andM_a (Al, Mn, H, Fe) cations (at 300 and 500 cm) wereobserved. High variabilities in M_a cations could beassigned to one of the lysimeters at each depththat extracted low pH solutions. The amount of exchangeablecations in the fine earth and the bedrock fractions indicatedthat the acidification front (exchangeable M_b cations < 80equivalent percent) had occurred to soil depth of more than 360cm, but the extent of acidification that might have occurred inthe preindustrial period is not known. In both fine earth andbedrock fractions, depthwise changes of exchangeable M_a andM_b cations were quite similar, suggesting that rockfractions have contributed to proton buffering not only bysilicate weathering but also by cation exchange.     

Relationship between water soluble and exchangeable soil cations for estimating plant uptake and leaching potential

Abstract

The relationship between water soluble and exchangeable cations (Ca, Mg, Na, and K) was investigated for surface horizons of 195 soils including many taxonomic categories and a wide range in physical and chemical properties from around the world. This will provide information on exchangeable soil cation solubility for use in estimating plant uptake and leaching potential. Amounts of water soluble and exchangeable cations were not consistently related (r² of 0.50, 0.08, 0.77, and 0.49 for Ca, Mg, Na, and K). High correlations were biased by high water soluble and exchangeable cation levels of a few soils that had 3.8‐ and 2.5‐fold greater mean than median values. The ratio of exchangeable to water soluble cations was closely related to cation saturation (r² of 0.87, 0.95, 0.95, and 0.93 for Ca, Mg, Na, and K, respectively). As the degree of saturation of the exchange complex by a certain cation increased, solubility Increased. A change in saturation had less effect on K than on Na, Mg, and Ca solubility. Only exchangeable soil cations (NH₄OAc extractable) are routinely measured and reported in soil survey reports, thus, water soluble levels may be determined from cation saturation. This will allow estimation of the amounts of cation that can potentially move in solution through the soil or be taken up by plants. Use of cation saturation, in addition to exchangeable content, will better characterize soil cation availability by representing quantity, intensity, and buffer factors.     

Influence of Lime and Gypsum on Yield and Yield Components of Soybean and Changes in Soil Chemical Properties

Soybean is one of the most important legume crops in the world. Two greenhouse experiments were conducted to determine the influence of liming and gypsum application on yield and yield components of soybean and changes in soil chemical properties of an Oxisol. Lime rates used were 0, 0.71, 1.42, 2.14, 2.85, and 4.28 g kg^?1 soil. Gypsum rates applied were 0, 0.28, 0.57, 1.14, 1.71, and 2.28 g kg^?1 soil. Lime as well as gypsum significantly increased grain yield in a quadratic fashion. Maximum grain yield was achieved with the application of 1.57 g lime per kg soil, whereas the gypsum requirement for maximum grain yield was 1.43 g per kg of soil. Lime significantly improved soil pH, exchangeable soil calcium (Ca) and magnesium (Mg) contents, base saturation, and effective cation exchange capacity (ECEC). However, lime application significantly decreased total acidity [hydrogen (H) + aluminum (Al)], zinc (Zn), and iron (Fe) contents of the soil. The decrease in these soil properties was associated with increase in soil pH. Gypsum application significantly increased exchangeable soil Ca, base saturation, and ECEC. However, gypsum did not change pH and total acidity (H + Al) significantly. Adequate soil acidity indices established for maximum grain yield with the application of lime were pH 5.5, Ca 1.8 cmol_c kg^?1, Mg 0.66 cmol_c kg^?1, base saturation 53%, Ca saturation 35%, and Mg saturation 13%. Soybean plants tolerated acidity (H + Al) up to 2.26 cmol_c kg^?1 soil. In the case of gypsum, maximum grain yield was obtained at exchangeable Ca content of 2.12 cmol_c kg^?1, base saturation of 56%, and Ca saturation of 41%.     

Application of High Copper and Zinc Compost and Its Effects on Soil Properties and Growth of Barley

Abstract

A compost of high copper (Cu) and zinc (Zn) content was added to soil, and the growth of barley (Hordeum vulgare L.) was evaluated. Four treatments were established, based on the addition of increasing quantities of compost (0, 2, 5, and 10% w/w). Germination, plant growth, biomass production, and element [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), iron (Fe), Cu, manganese (Mn), and Zn] contents of soil and barley were determined following a 16‐week growing period. Following harvesting of the barley, analysis of the different mixtures of soil and compost was performed. Micronutrient contents in soils as affected by compost additions were determined with diethylene–triamine–pentaacetic acid (DTPA) (Cu, Mn, Fe, and Zn) or ammonium acetate [Ca, Na, Mg, K, cation exchange capacity (CEC)] extractions, and soils levels were compared to plant uptake where appropriate. Increasing rates of compost had no affect on Ca, Mg, or K concentration in barley. Levels of Cu, Zn, Mn, and Na, however, increased with compost application. High correlations were found for DTPA‐extractable Cu and Zn with barley head and shoot content and for Mn‐DTPA and shoot Mn content. Ammonium acetate–extractable Na was highly correlated with Na content in the shoot. High levels of electrical conductivity (EC), Cu, Zn, and Na may limit utilization of the compost.