Potassium-supplying power of some northern-Greece soils in relation to clay-mineral composition

The correlation between the content of the clay minerals, mica, montmorillonite or vermiculite, and the logarithmic form $\text{pK-}\text{1}\text{2}\text{p (Ca + Mg)}$ of the activity ratio (K)/√(Ca + Mg) was highly significant for 23 soils from northern Greece. The correlation was negative with mica and positive with montmorillonite and vermiculite. A free-energy term, ΔF¹, necessary to bring the activity ratio of each soil equal to the lowest value encountered, using the concentrations of soluble and exchangeable K and Ca + Mg in the equilibrium systems, was also calculated. The relationship between the content of the three clay minerals and ΔF¹ was the same as when $\text{pK-}\text{1}\text{2}\text{p (Ca + Mg)}$ was used except that the correlation coefficient was greater in all cases, being significant at P_0.001 with each of the clay minerals. The regression of ΔF¹ on each of the clay mineral contents was also much greater than the corresponding ones with $\text{pK-}\text{1}\text{2}\text{p (Ca + Mg)}$.     

Zur Pedogenese und Klassifikation von Marschböden des Unterweserraumes. I. Gesamtnährstoffe,Carbonatgehalt, Kationenbelag und Diatomeenflora als Indikatoren für Sedimentations-Bedingungen und Bodenentwicklung

Development and Classification of Marsh Soils from the Unterweser Region, West Germany. I. Total Nutrients, Carbonate Content, Exchangeable Cations and Diatom Flora as Indicators of the Role of Sedimentation Conditions in Soil Development This study was carried out to see how much sedimentation conditions determine the properties– in particular the Ca/Mg ratio – of marsh soils (fluvaquents of coastel areas). The following results show, that the marsh soils properties are not determined by different sedimentation conditions: – The vertic fluvaquents don't have a higher clay content than the mollic and aeric fluvaquents – The total (t) contents of P, Ca, Mg, K and Na varied because of different soil development – The Ca_t/Mg_t ratio in soils with CaCO₃ was higher than in soils without CaCO₃, and – related to the Ca_a/Mg_a ratio – it can also be used as a classification characteristic (a = exchangeable) – The Ca_a/Mg_a ratio varied greatly because of differences in exchangeable Ca content. Vertic fluvaquents sometimes, but not often, have a higher content of exchangeable Mg than the mollic and aeric fluvaquents. Comparing maps of the Weser area as it appeared at various times in the Holocene with the soil map, shows that the sedimentation pattern is invariably brackish-marine. This is further confirmed by the diotom flora of the soils tested. Thus the properties of marsh soils, long believed to be dependent on sedimentation conditions, are the product of different continuance and intensity of soil development.     

DOWNWARD MOVEMENT OF DOLOMITE,KIESERITE OR A MIXTURE OF CaCO3 AND KIESERITE THROUGH THE UPPER LAYERS OF AN ACID FOREST SOIL

Liming and fertilization are important tools for improving the chemical status of acid, base poor forest soils. The downward movement of dolomite, kieserite and a mixture of CaCO₃ and kieserite was investigated by monitoring the leachates and exchangeable cation composition from single and combined horizon columns, reconstructed from an acid brown forest soil profile (0–15 cm). Upon entering the soil, Mg ions from kieserite displaced base cations and acidity (H and Al ions) from exchange sites, which subsequently moved down with the mobile SO₄ ^2- anions. Total leaching during the initial SO₄ ^2- pulse was similar with the CaCO₃ + kieserite mixture. Compared to the single kieserite treatment, the joint application of CaCO₃ greatly increased the proportion of Ca in the leachates from all horizons. It also decreased the leaching of acidity from the surface Oe horizon and prevented pH from dropping under this layer. With both treatments, the redistribution of magnesium with SO₄ ^2- anions resulted in a rapid increase in exchangeable Mg contents throughout the studied columns. Due to the important charge increase in the Oe horizon and to kinetic restraints imposed on dissolution, downward movement of Ca and Mg ions from dolomite was very limited. Mg was however much more mobile than Ca. In the CaCO₃ + kieserite and dolomite treatments, the migration of alkalinity and base cations with time was associated with a decrease in exchangeable acidity and an increase in ECEC in the two upper soil layers. By the end of the monitoring period, overall net Mg retention in the 0–15 cm columns increased in the order kieserite < CaCO₃ + kieserite << dolomite with respectively 20, 35 and 85% of cumulated inputs remaining in the columns. The corresponding net Ca retention amounted to 82 and 96% of cumulated inputs for the CaCO₃ + kieserite and dolomite treatments, respectively. Results from this study complement those obtained in the field by clearly demonstrating the mechanisms involved in the downward movement of some fertilizers commonly used to increase the base saturation of acid forest soils.     

Yield,Nutrient Uptake,and Changes in Soil Chemical Properties as Influenced by Liming and Iron Application in Common Bean in a No-Tillage System

Soil acidity is the principal limiting factor in crop production in Oxisols, and deficiency of micronutrients has increased in recent years because of intensive cropping. A field experiment was conducted over three consecutive years to assess response of common bean (Phaseolus vulgaris L.) to lime and iron (Fe) applications on an Oxisol in a no-tillage system. Changes in selected soil chemical properties in the soil profile (0- to 10- and 10- to 20-cm depths) with liming were also determined. Lime rates used were 0, 12, and 24 Mg ha^–1, and Fe application rates were 0, 50, 100, 150 200, and 400 kg ha^–1. Both lime and Fe were applied as broadcast and incorporated in the soil. Grain yields of common bean were significantly increased with the application of lime. Iron application, however, did not influence bean yield. There were significant changes in soil profile (0- to 10-cm and 10- to 20-cm depths) in pH, calcium (Ca²⁺), magnesium (Mg²⁺), hydrogen + aluminum (H⁺ + Al³⁺), base saturation, acidity saturation, cation exchange capacity (CEC), Ca²⁺ saturation, Mg²⁺ saturation, potassium (K⁺) saturation, and ratios of Ca/Mg, Ca/K, and Mg/K. These soil chemical properties had significant positive association with common bean grain yield. Averaged across two depths and three crops, common bean produced maximum grain yield at pH_w 6.3, Ca²⁺ 3.8 cmol_c kg^–1, Mg²⁺ 1.1 cmol_c kg^–1, 3.5 H⁺ + Al³⁺ cmol_c kg^–1, acidity saturation 41.8%, CEC 7.5 cmol_c kg^–1, base saturation 57.4%, Ca saturation 45.2%, Mg saturation 14.2%, K saturation 9.1%, Ca/Mg ratio 3.1, Ca/K ratio 22.6, and Mg/K ratio 6.7.     

Yield,Nutrient Uptake,and Soil Chemical Properties as Influenced by Liming and Boron Application in Common Bean in a No‐Tillage System

Abstract

In Oxisols, acidity is the principal limiting factor for crop production. In recent years, because of intensive cropping on these soils, deficiency of micronutrients is increasing. A field experiment was conducted on an Oxisol during three consecutive years to assess the response of common bean (Phaseolus vulgaris L.) under a no‐tillage system to varying rates of lime (0, 12, and 24 Mg ha^?1) and boron (0, 2, 4, 8, 12, 16, and 24 kg ha^?1) application. Both time and boron (B) were applied as broadcast and incorporated into the soil at the beginning of the study. Changes in selected soil chemical properties in the soil profile (0- to 10‐ and 10- to 20‐cm depths) with liming were also determined. During all three years, gain yields increased significantly with the application of lime. However, B application significantly increased common bean yield in only the first crop. Only lime application significantly affected the soil chemical properties [pH; calcium (Ca²⁺); magnesium (Mg²⁺); hydrogen (H⁺)+ aluminum (Al³⁺); base saturation; acidity saturation; cation exchange capacity (CEC); percent saturation of Ca²⁺, Mg²⁺, and potassium (K⁺); and ratios of exchangeable Ca/Mg, Ca/K, and Mg/K] at both soil depths (0–10 cm and 10–20 cm). A positive significant association was observed between grain yield and soil chemical properties. Averaged across two depths and three crops, common bean produced maximum grain yield at soil pH_w of 6.7, exchangeable (cmol_c kg^?1) of Ca²⁺ 4.9, Mg²⁺ 2.2, H⁺+Al³⁺ 2.6, acidity saturation of 27.6%, CEC of 4.1 cmol_c kg^?1, base saturation of 72%, Ca saturation of 53.2%, Mg saturation of 17.6%, K saturation of 2.7%, Ca/Mg ratio of 2.8, Ca/K ratio of 25.7, and Mg/K ratio of 8.6. Soil organic matter did not change significantly with addition of lime.     

Effect of excess MgSO4 or Mg(HCO3)2 in irrigation water on corn growth

Abstract

Some irrigation waters have a high Mg/Ca ratio. The objective of the experiment reported herein was to compare the effect of high Mg in combination with different anions and different EC levels on the growth of corn (Zea mays L.). Corn was grown in the greenhouse in a calcareous soil equilibrated and irrigated with the following waters: 1) tap water (check, EC = 0.078 dS/m, SAR = 0.1); 2) Mg(HCO₃)₂, EC=1 dS/m; 3) Mg(HCO₃)₂, EC = 3; 4) MgSO₄₎ EC=1; 5) MgSO₄, EC=3; 6) MgSO₄, EC = 6; and 7) and 8) mixed salts (Ec = 3 & 6 dS/m, SAR = 5, Ca: Mg = 3: 1, Cl: SO₄ = 2: 1). Yield depressions of top growth caused by mixed‐salt waters (EC = 3 & 6) were 17 and 26%, respectively, compared to yields obtained with tap water. Single‐salt MgSO₄ waters (EC = 1, 3 & 6) reduced corn tops 19, 38, and 59%, respectively, more than the mixed‐salt solutions at equivalent soil salinity levels probably due to Mg‐induced Ca deficiency. The Mg(HCO₃)₂ waters (EC = 1 & 3) reduced top growth 45 and 87% more than the mixed salt solutions. Thus Mg (HCO₃)₂ was more than twice as depressive on corn top growth as MgSO₄. Corn root growth depression was similar to top growth depression. Leaf Ca: Mg ratio was related to their ratio in the soil solution. The leaf Ca and Mg concentrations were almost the same for plants irrigated with Mg(HCO₃)₂ or MgSO₄ at EC = 1. Therefore, Mg: Ca ratio of leaves did not explain the yield differences between the two Mg salts. Nutrient imbalances and a high pH of 9 were possibly responsible for the lower yields in the presence of Mg(HCO₃)₂.     

Simulated effects of acid deposition on podzolic soils: Consequences of process and parameter aggregation

Solution cation concentrations and base cation leaching were simulated for a homogenous soil block and a soil showing five horizons of a podzolic forest soil. The dynamic model ACIDIC simulated water flow, nutrient uptake for tree growth, and cation exchange between H⁺, Al³⁺, Ca²⁺, Mg²⁺ and K⁺ in forest soil. In the multi-layer simulations exchangeable base cation concentrations changed most in the O horizon. The subsoil had a decisive effect on the pH of the runoff and base cation leaching from the soil. The one-layer model underestimated Ca and Mg leaching and overestimated H⁺ and Al concentrations in the runoff. In the eluvial and the top of illuvial horizon the solution Al / (Ca + Mg) ratio exceeded that in one-layer structure more than 10-fold. Cases with the horizon-specific cation exchange coefficient values and mean coefficient values for all layers showed only minor differences in Al / (Ca + Mg) ratio. The vertical variation in the soil chemical properties should be accounted for even if some details of processes and parameters were unavailable.     

ON THE POSSIBILITY OF CHARACTERIZING CALCIUM PHOSPHATES IN CALCAREOUS SOILS BY ISOTOPIC EXCHANGE

Characterization of calcium phosphates depended upon the nature and the amount of phosphate used to react with reagent-grade CaCO₃. Formation of octa-calcium phosphate (OCP) was inferred from the solubility equilibria after reacting CaCO₃ with KH₂PO₄ solutions. Isotopic exchange measurements confirmed the presence of OCP, when the amount of P retained exceeded 44 μrnoles/g CaCO₃. The determined surface-Ca to surface-P molar ratios were close to the theoretical Ca/P ratio of 1.33 in OCP. As P retained on CaCO₃ decreased the surface Ca/P ratio markedly increased because of interference from surface Ca of the CaCO₃. When CaCO₃ was reacted with monocalcium phosphate (MCP), solubility equilibria indicated the formation of dicalcium phosphate dihydrate (DCPD). Isotopic exchange measurements, however, showed an average Ca/P ratio of only 0.375. This value corresponds to the composition of the metastable triple point solution (MTPS) formed on MCP dissolution rather than to the Ca/P ratio in DCPD. MCP application decreased the measured surface-Ca (exchangeable Ca) either for soil or Ca-resin, because of blocking of the exchange sites by the MCP reaction products and, consequently, a lower rate of isotopic exchange. Surface phosphorus of the two investigated calcareous soils proved to be proportional to the lowering in pH initiated by MCP application. Characterization of MCP reaction products in calcareous soils may thus prove infeasible, in view of the unexpected reduction in surface-Ca and the pH dependency of surface P.     

Lime and Cattle Manure in Soil Fertility and Soybean Grain Yield Cultivated in Tropical Soil

Most tropical soils have high acidity and low natural fertility. The appropriate application of lime and cattle manure corrects acidity, improves physical and biological properties, increases soil fertility, and reduces the use of chemical and/or synthetic fertilizers by crops, such as soybean, the main agricultural export product of Brazil. This study aimed to assess the effects of the combination of the application of dolomite limestone (0, 5, and 10 Mg ha^?1) and cattle manure (0, 40, and 80 Mg ha^?1) on grain yield and the chemical properties of an Oxisol (Red Latosol) cultivated with soybean for two consecutive years. The maximum grain yield was obtained with the application of 10 Mg ha^?1 of lime and 80 Mg ha^?1 of cattle manure. Liming significantly increased pH index, the concentrations of calcium (Ca²⁺) and exchangeable magnesium (Mg²⁺), and cation exchange capacity (CEC) of soil and reduced potential acidity (H⁺ + Al³⁺), while the application of cattle manure increased pH level; the concentrations of potassium (K⁺), Ca²⁺, and exchangeable Mg²⁺; and CEC of the soil. During the 2 years of assessment, the greatest grain yields were obtained with saturation of K⁺, Ca²⁺, and Mg²⁺ in CEC at the 4.4, 40.4, and 17.5 levels, respectively. The results indicated that the ratios of soil exchangeable Ca/Mg, Ca/K, K/Mg, and K/(Ca+Mg) can be modified to increase the yield of soybean grains.     

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.     

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.     

Plant Availability of Cadmium in Soils: II. Factors Related to the Extractability and Plant Uptake of Cadmium in Cultivated Soils

Abstract

Eighty four soil samples collected from southeastern Norway were analyzed for Cd by extraction with NH₄OAc, DTPA, NH₄OAc-EDTA, NH₄NO₃, HCl and CaCl₂. The total Cd, pH, exchangeable K and Ca, dithionite-extractable Mn, available P and fine sand (0.2–0.02 mm) contents were the principal factors related to the extractable Cd, with some inter-extractant variations. Cadmium extracted by NH₄NO₃, NH₄OAc, HCl and CaCl₂ decreased with increasing soil pH, but the Cd extracted by all the extractants increased with increasing total Cd, exchangeable K and Ca, available P, and Mn-oxide contents in the soils. The Cd concentrations in plants were significantly related to the extractable Cd, exchangeable Ca and Mg, pH, Mn-oxides and organic matter content.     

REACTIONS OF AMMONIA WITH SOIL. I

Heats of adsorption and adsorption isotherms of ammonia gas were measured at 300 K (27 °C) on outgassed soil saturated with Na⁺, K⁺, NH₄⁺, Ca²⁺, or Mg²⁺ ions. The Ca and Mg soils adsorbed apparently one more NH₂ molecule per exchangeable ion than the Na and K soils, mostly in the relative pressure range o to 0.005, but not much more than the NH₄ soil. The initial heat of adsorption was c. 75 kJ mol^-1 on the Ca and Mg soils and c. 60 kJ mol^-1 on the other soils. The results suggest that most NH, is sorbed on these soils through reactions not involving exchangeable cations.     

Effect of ammonium fertilizer on NH3 loss and Ca,Mg, ammonium and nitrate content in a calcareous soil solution

Summary This study examined the effects of NH _inf4 ⁺ fertilizers [(NH₄)₂SO₄, (NH₄)₂HPO₄, CO(NH₂)₂, NH₄OH, and NH₄NO₃] on NH₃ loss and the quantity of Ca + Mg, NH _inf4 ⁺ and NO _inf3 ^sup– in the solution of a calcareous soil (Harkey sicl, Typic Torrifluvent). Various NH₄ fertilizers applied at a depth of 5 cm in the soil produced differing NH₃ loss characteristics. Applying (NH₄)₂SO₄ (AS) resulted in high volatile NH₃ losses as compared with NH₄OH (AH) and (NH₄)₂CO₃ (AC). The AS treatment formed an equal molar amount of CaSO₄, which increased the mobility of ammonium, while AH and AC treatments caused Ca precipitation and decreased ammonium mobility. Leaching the AS system before NH₃ loss could occur resulted in the most rapid nitrification rate. Lower nitrification rates were found with AH and AC than AS under the same conditions. Surface placement of NH₄ fertilizers resulted in variable leachate contents of Ca + Mg. Ammonium sulfate reacted with CaCO₃ either to solubilize some Ca + Mg or simply to replace exchangeable Ca + Mg with NH₄, while AH, AC, and (NH₄)₂HPO₄ (DAP) precipitated essentially an equivalent molar amount of soluble and adsorbed Ca + Mg. Use of NH₄NO₃, which does not form an insoluble calcium precipitate, resulted in the leaching of an equivalent molar amount of exchangeable Ca + Mg from the Harkey soil.The authors are Professor and former laboratory technician, respectively, at Texas A&M Research Center at El Paso, 1380 A&M Circle, El Paso, TX 79927, USA     

Impact of Varying Ca/Mg Waters on Ionic Balance,Dispersion, and Clay Flocculation of Salt-Affected Soils

Inceptisols and Vertisols are two dominant soil orders that support major agricultural production in India. These soils often exist in semi-arid and arid regions. Low precipitation and high evaporation demand leads to salt accumulation in these areas. The problem of salt accumulation is further compounded by the presence of saline/alkaline groundwaters. We evaluated the effect of modified Ca/Mg waters on ionic composition, dispersion, and clay flocculation of sodic Inceptisols, saline-sodic Inceptisols, and normal Vertisols from different parts of India. A completely randomized factorial design with three replications of individual soils were sequentially leached with five pore volumes of deionized, saline water of 60 and 120 me L^?1 total electrolyte concentration (TEC) at a fixed SAR of 5.0 mmol^1/2 L^?1/2 and Ca:Mg ratio of 2:1, 1:1 and 1:2. Application of saline waters decreased pH and increased EC of the soil leachates after leaching five pore volumes of three Ca/Mg ratios of 60 and 120 me L^?1 solutions in sodic Inceptisols and normal Vertisols. In saline-sodic Inceptisols, application of saline waters decreased both pH and electrical conductivity (EC) of the soil leachates. Preferential Ca²⁺ holding in soil was only noticed in sodic Inceptisols when leaching process was performed with independent saline waters, but Mg²⁺ has a tendency to hold in soil upon application of independent saline waters for all soils except sodic Inceptisols. Periodic application of deionized water could increase soil dispersion and decreased flocculation of clay particles. Mg²⁺ ion had less flocculating vis-à-vis high-dispersion effect on soil clays than the Ca²⁺ ion.     

不同磷水平对红壤溶液中锰、铝、镁和钙浓度变化以及小麦生长的影响

为了探明不同磷水平对红壤中土壤溶液主要金属离子变化的影响以及小麦对磷的响应,确定红壤中小麦适宜的施磷水平,采用原位提取土壤溶液和比较生物量的方法,监测了短期内红壤溶液中主要金属离子浓度变化及小麦生物量的变化。结果表明:碳酸钙的加入可以显著升高酸性红壤的p H,土壤溶液中铝、锰和镁浓度显著低于未加碳酸钙处理;800 mg/kg磷处理后铝、锰、镁和钙的浓度要比未加磷处理分别至少降低47%、44%、37%和33%。随着施磷量的增加,小麦在200 mg/kg磷处理时积累的生物量最大,随后磷增加,小麦生物量反而降低。而加碳酸钙处理小麦地下部生物量随着施磷量增加则降低。结果表明碳酸钙不仅可以有效升高土壤p H,降低土壤溶液铝浓度,还降低土壤溶液中锰的浓度。磷的加入同样可以降低锰和铝的浓度,缓解铝和锰毒害。红壤中生长小麦的适宜施磷量为200 mg/kg。     

Leaching of metals from a spruce forest soil as influenced by experimental acidification

Acidified (H₂SO₄+HNO₃, 3:1) throughfall waters (pH 3.16 and 3.40 as volume weighted means or control (untreated throughfall water, pH 3.72) were applied for 3.5 yr by an automatic irrigation device to lysimeters containing podzolized spruce forest soils of 0–5, 0–15 and 0–35 cm soil depth. The total volume of the leachates was measured together with their pH and total content of DOC, Na, K, Ca, Mg, Fe, Mn, Al, Cu, Zn, Cd and Pb and the initial amounts of metals and H in the soil. The main part of H⁺ added with the throughfall waters was retained within the soil. Concentrations and fluxes of Mg, Ca, Mn, Zn and Cd in the soil were significantly increased by addition of acidified throughfall waters; K was less affected. As a consequence of lowered flux of DOC in the A horizon as acid input increased, Fe, Al, Cu, and Pb fluxes also decreased. The mobility of these metals in the A horizon was shown to be regulated mainly by the formation of watersoluble organic compounds rather than directly by pH variations. Compared to the control, the additional annual loss of Mg from the soil profile in the most acid treatment was c. 10% of the currently exchangeable amount.     

Effect of magnesium on crop yields within maize–green manure–T. aman rice cropping pattern on acid soil

An experiment was conducted to study the response of maize to magnesium (Mg) and to find out the residual effect of Mg and green manure (GM) on transplanted aman (T. aman) rice in the maize–GM–T. aman cropping pattern. There were six treatments: T₁ (recommended dose of fertilizer (RDF) + 0 kg Mg + 2 t CaCO₃ ha^?1), T₂ (RDF + 10 kg Mg + 2 t CaCO₃ ha^?1), T₃ (RDF + 20 kg Mg +2 t CaCO₃ ha^?1), T₄ (RDF + 30 kg Mg + 2 t CaCO₃ ha^?1), T₅ (RDF) and T₆ (2 t CaCO₃ ha^?1). The response of maize to Mg was quadratic and the optimum dose of Mg was found to be 19 kg ha^?1, which resulted in maximum yield of 10,507 kg ha^?1. The residual effect of Mg along with GM and reduced dose of chemical fertilizer resulted in significant increase of grain yield of rice. Thus, N₂₅₀P₆₀K₁₀₀Mg₁₉S₄₀Zn₅B₂ kg ha^?1 for maize, only 20 kg N ha^?1 for GM (Sesbania) and N₆₀P₉K₃₃S₁₀Zn₁B₁ kg ha^?1 for T. aman appeared as the best combination for maximizing the productivity and may be recommended for this pattern at non-calcareous light-textured soils of Bangladesh. Application of lime increased soil pH, and this together with fertilizer and GM tended to improve soil fertility and thus may be recommended for soil amelioration.     

Evaluation of two coal-derived organic products in ameliorating surface and subsurface soil acidity

Acidity in the soil surface and subsurface is of major concern in horticulture, cropping and pasture production systems in southern Australia. Broadcast applications of lime to the surface have proved to be ineffective in ameliorating subsurface acidity in the short term. Two calcium-saturated coal-derived organic products, an ‘oxi-product’ (OXPR) and an ‘oxi-fulvate’ (OXFU), were evaluated for use as liming materials with specific consideration given to amelioration of subsurface acidity. The effects of these two organic products and of lime on the chemical composition of the A₁ and A₂ horizons of an acid red podzol were investigated in leaching columns, 20 cm long. OXPR and OXFU supplying 80 or 160 g Ca m^?2 were compared to 160 g Ca m^?2 applied as CaCO₃ and a control receiving no amendments. The effects of CaCO₃ on exchangeable Al and pH were limited to the surface 2 cm. In contrast, the two organic amendments were effective in decreasing exchangeable Al and increasing pH and exchangeable Ca to depth, the extent being a function of amendment and rate applied. The formation of inorganic and organic complexes were assumed to be responsible for the movement of Al out of the column in the leachate, although significant quantities of Al were precipitated in the column. Significant linear regressions were observed between the ionic strength and Al in the leachate. Significant quantities of Mg and K were displaced by Ca and leached from the column; consequently, this loss must be considered against the benefits of decreased exchangeable Al when assessing fertility for plant production.     

Effects of aluminium on growth and nutrition in birch seedlings under magnesium- or calcium-limiting growth conditions

Growth and nutrition of birch seedlings (Betula pendula Roth) with and without 0.5 mM Al³⁺ were studied. The seedlings were cultivated at growth-limiting Mg- or Ca-conditions by adding one of these elements at relative addition rates (R_Mg, R_Ca) of 0.15 day^?1. The concentration of Ca²⁺ in the Mg-limited treatments was 0.01.0.1 or 1 mM and Mg²⁺ was given in equal molarities in the Ca-limited treatments. The relative growth rates, R_G, of the plants and plant parts attained values close to R_Mg or R_Ca and were not affected by the concentration of Ca²⁺, Mg²⁺ or Al³⁺ in the culture solution. Uptake of Ca, at Ca-limitation, increased significantly in the roots after addition of Al, and decreased in all plant parts when the Mg concentration of the culture solution was raised. Less clear effects were found on Mg uptake at Mg-limitation. The inhibitory effect of Al on Mg uptake decreased with time as a result of the growth technique. The root mass fraction was significantly larger in plants limited in Ca (24%) than in plants limited in Mg (20%). The usefulness in using the balance between Ca and Al or ratios between Ca, Mg, K and Al as diagnostic tools for assessing the nutritional status of trees is discussed.