Concentrations of 60 elements in the soil solution as related to the soil acidity

Little is known about solubility and soil solution concentrations of most elements occurring in the solid phase of soils. This study reports changes in solution concentrations of 60 mineral elements following CaCO₃ addition to a moderately acid semi‐natural soil, and possible mechanisms accounting for the differing solubility patterns as related to soil acidity are discussed. Soil solutions were obtained by high‐speed centrifuging and ultrafiltration (0.2 μm) of samples at 60% water‐holding capacity of the A horizon of a Cambisol developed from a shale–gneiss moraine and supplied with CaCO₃ at 20 rates to yield a soil solution pH range of 5.2–7.8. Concentrations of elements were determined in the solutions by ICP‐AES or (for most elements) ICP‐MS. Several distinct patterns of soil solution concentrations as a function of soil solution pH were demonstrated. Positively related to pH and CaCO₃ supply were soil solution concentrations of As, Br, Mo, S, Sb, Se, U, and W, and to a lesser degree, Co, Cr, Hg, Mg, and Sr. Inversely related to pH were concentrations of Al, B, Ba, Bi, Cs, Ce, Eu, Ga, Ge, Fe, Li, K, Rb, Na, Th, and Ti; less distinctly inversely rated were Dy, Er, Gd, Hf, La, Lu, Mn, Nd, Pr, Sm, Sc, Si, Tl, Tm, and Yb. ‘U‐shaped’ relationships to pH were demonstrated for the concentrations of Ag, Cd, Nb, Ni, P, V, and Zr. There were no or irregular relations between pH and concentrations of Be, Cu, Ho, Pb, Ta, and Tb. Differences between elements in their soil solution concentrations as related to total (HNO₃‐digestible) concentrations and the solubility of organic C were also treated. Increasing the pH of a soil by adding CaCO₃ changes the solubility of most mineral elements substantially, the several distinct patterns observed being governed by, for example, ionic properties and charge, affinity for organic compounds, and pH‐dependent formation and solubility of complexes.     

REACTIONS RESPONSIBLE FOR HIGH pH OF Na-SATURATED SOILS AND CLAYS

Hydrolysis, defined as double decomposition between Na-adsorbent and water, occurred to extremely limited extent in suspensions of Na or Na-Ca smectites, soil, or Dowex-50. High pH, near 10 or above, occurred only when CaCO₃ was present. Concentrations of Na were from 1–5 me/l in systems containing CaCO³, With Na or Na-Ca Dowex-5o and CaCO³, in CO²-free water or NaCl solution, pH and concentrations of Na in solution-phase were predictable from Na-Ca exchange coefficients, CaCO³, solubility product, and ionization constants of H²CO³.     

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.     

Sugarcane yield and plant nutrient response to sulfur-amended Everglades histosols

High soil pH causes leaf nutrient deficiencies and reduces sugarcane yield. Soil pH in Florida histosols has been increasing as these soils subside and depth to limestone is decreased. A factorial experiment of four sulfur (S) rates and three added calcium carbonate (CaCO₃) levels in soil was designed to determine S-amendment effectiveness in reducing pH and increasing nutrient availability in sugarcane as calcium (Ca) carbonate levels were increased. Sulfur-amendment and increased CaCO₃ level had limited effects on yield and leaf nutrient concentrations during the growing season. Most leaf nutrients were within optimum range except nitrogen (N), phosphorus (P), iron (Fe), and manganese (Mn). Unexpected increases in Mn concentrations with added CaCO₃ were associated with reducing conditions due to increased soil bulk density. High soil pH caused Mn deficiencies in the plants. Soil pH, P and Mn concentrations were important factors in predicting sugarcane yield.     

Effect of soil pH on cation and anion solubility

Abstract

The effect of soil pH on the exchangeability and solubility of soil cations (Ca, Mg, Na, K, and NH₄‐N) and anions (NO₃‐N, Cl, and P) was investigated for 80 soils, spanning a wide range in physical and chemical properties and taxonomic groups. This information is needed from environmental and agronomic standpoints to estimate the effect of changes in soil pH on leachability and plant availability of soil nutrients. Soils were incubated with varying amounts of acid (H₂SO₄) and base (CaCO₃) for up to 30 days. Although acid and base amendments had no consistent effect on cation exchangeability (as determined by neutral NH₄OAc), amounts of water‐soluble Ca, Mg, Na, K, NH₄‐N, and P decreased, while NO₃‐N and Cl increased with an increase in soil pH. The increase in cation solubility was attributed to an increase in the negative charge of the soil surface associated with the base addition. The change in surface electrostatic potential had the opposite effect on amounts of NO₃‐N and Cl in solution, with increases in N mineralization with increasing soil pH also contributing to the greater amount of NO₃‐N in solution. The decrease in P solubility was attributed to changes in the solubility of Fe‐, A1‐, and Ca‐P complexes. The logarithm of the amount of water‐soluble cation or anion was a linear function of soil pH. The slope of this relationship was closely related (R² = = 0.90 ‐ 0.96) to clay content, initial soil pH, and size of the cation or anion pool maintaining solution concentration. Although the degree in soil pH buffering increased with length of incubation, no effect of time on the relationship between cation or anion solubility and pH was observed except for NO₃‐N, due to N mineralization. A change in soil pH brought about by acid rain, fertilizer, and lime inputs, thus, affects cation and anion solubility. The impact of these changes on cation and anion leachability and plant availability may be assessed using the regression equations developed.     

Evaluation of coal combustion byproducts as soil liming materials: their influence on soil pH and enzyme activities

There is considerable interest in the use of coal combustion byproducts as soil liming materials in agricultural production, but there is concern that such use may be detrimental to the quality of agricultural soils. To evaluate these byproducts as liming materials and address issues related to soil quality, we compared the influence of different amounts of four combustion byproducts [fly ash and bed ash from a fluidized bed combustion furnace, lime-injected multistage burner residue, and spray dryer residue] and CaCO₃ on soil pH and activities of urease, phosphatase, arylsulfatase, and dehydrogenase in an acidic soil. Studies comparing the influence of the combustion byproducts and CaCO₃ on soil pH showed that on a weight basis of application, substantial differences were observed in the ability of these materials to influence soil pH but that such differences decreased markedly after the data were transformed to a CaCO₃ equivalent basis of application. Analysis of covariance for these transformed data indicated that whereas the liming abilities of fly ash and CaCO₃ were not significantly different when compared on the CaCO₃ equivalent basis, those of bed ash, multistage burner residue, and spray dryer residue were less than that of CaCO₃. Studies comparing the influence of the byproducts and CaCO₃ on soil enzyme activities showed that the effect of these liming materials on the enzyme activities studied was largely due to their influence on soil pH. The relationships obtained between soil pH and enzyme activities in soil amended with the liming materials generally demonstrated the marked similarities in the influence of the combustion byproducts and CaCO₃ on these activities when observed within the domain of soil pH. These studies showed that the combustion byproducts tested functioned as soil liming materials in a manner similar to that of CaCO₃ and seemed to have little adverse effect on soil quality.     

Amelioration of Cadmium Polluted Paddy Soils by Porous Hydrated Calcium Silicate

Porous hydrated calcium silicate (PS) is a by-product of autoclave light weight concrete and is being used as a silicon fertilizer in Japan. The impacts of this amendment on the yield and cadmium content of rice (Orzya sativa L. var. Kokoromachi), soil pH and the extractability of soil cadmium assessed by 1 M NH₄OAc were compared with those of silica gel and CaCO₃ by pot experiments. The application of PS at the rate of 2.0% and silica gel at the rate of 1.0% in Andosol and PS at the rate of 0.75% in Alluvial soil significantly increased the grain weight of rice. PS and CaCO₃ treatment significantly increased soil pH, decreased the 1 M NH₄OAc extractability of cadmium and reduced cadmium content in straw and brown rice in the two soils. However, cadmium content of rice of PS treatments was not significantly different from that of CaCO₃ treatments in Andosol, while was significantly lower than that of CaCO₃ treatments in Alluvial soil. Soil analysis showed that it was less effective in increasing soil pH and decreasing the extractability of cadmium by 1 M NH₄OAc than CaCO₃ at the same application rate in Andosol. Soil pH and 1 M NH₄OAc extractability of cadmium were not significantly different between 2.0% of PS and CaCO₃ treatments in Alluvial soil. The application of silica gel did not improve soil pH nor decrease the extractability of soil cadmium, but resulted in a significant decline of cadmium content in brown rice. These results demonstrate that the supply of silicon together with an increase in soil pH, as obtained by PS application, shows potential to reduce the cadmium content of rice.     

Key soil and topographic properties to delineate potential management classes for precision agriculture in the European loess area

Recent advances in on-the-go soil sensing, terrain modelling and yield mapping have made available large quantities of information about the within-field variability of soil and crop properties. But the selection of the key variables for an identification of management zones, required for precision agriculture, is not straightforward. To investigate a procedure for this selection, an 8 ha agricultural field in the Loess belt of Belgium was considered for this study. The available information consisted of: (i) top- and subsoil samples taken at 110 locations, on which soil properties: textural fractions, organic carbon (OC), CaCO₃ and pH were analysed, (ii) soil apparent electrical conductivity (EC_a) obtained through an electromagnetic induction based sensor, and (iii) wetness index, stream power index and steepest slope angle derived from a detailed digital elevation model (DEM). A principal component analysis, involving 12 soil and topographic properties and two EC_a variables, identified three components explaining 67.4% of the total variability. These three components were best represented by pH, EC_a that strongly associated with texture and OC. However, OC was closely related to some more readily obtainable topographic properties, and therefore elevation was preferred. A fuzzy k-means classification of these three variables produced four potential management classes. Three-year average standardized yield maps of grain and straw showed productivity differences across these classes, but mainly linked to their landscape position. In the loess area with complex soil-landscape interactions pH, EC_a and elevation can be considered as key properties to delineate potential management classes.     

THE HIGH- AND LOW-ENERGY PHOSPHATE ADSORBING SURFACES IN CALCAREOUS SOILS

The two-surface Langmuir equation was used to study P adsorption by 24 calcareous soils (pH 7.2-7.6; 0.8-24.2 per cent CaCO₃) from the Sherborne soil series, which are derived from Jurassic limestone. High-energy P adsorption capacities (x″_m) ranged from 140–345 μg P/g and were most closely correlated with dithionite-soluble Fe. Hydrous oxides therefore appear to provide the principal sites, even in calcareous soils, on which P is strongly adsorbed (x″_m 6–51 ml/μg P). The low-energy adsorption capacities (x″_m) ranged from 400–663 μg P/g and were correlated with organic matter contents and the total surface areas of CaCO₃ but not with per cent CaCO₃, pH, or dithionite-soluble Fe. Total surface areas of CaCO₃ in the soils ranged from 4.0 to 8.5 m²/g soil. Low-energy P adsorption capacities agree reasonably with values (100 pg P/m²) for the sorption of phosphate on Jurassic limestones but phosphate was bonded much less strongly by soil carbonates (k″= 0.08–0.45 ml/μg P) than by limestones (k～10.0 ml/μg P). Low-energy P adsorption in these soils is tentatively ascribed to adsorption on sites already occupied by organic anions (and probably also by bicarbonate and silicate ions) which lessen the bonding energy of co-adsorbed P.     

APPLICATION OF INCREASING LEVELS OF ZINC TO SOIL REDUCED ACCUMULATION OF CADMIUM IN LUPIN GRAIN

Yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (L. angustifolius L.) are grown as grain legumes in rotation with spring wheat (Triticum aestivum L.) on acidic sandy soils of south-western Australia. Yellow lupin can accumulate significantly larger cadmium (Cd) concentrations in grain than narrow-leafed lupin. A glasshouse experiment was undertaken to test whether adding increasing zinc (Zn) levels to soil increased Zn uptake by yellow lupin reducing accumulation of Cd in yellow lupin grain. Two cultivars of yellow lupin (cv. ‘Motiv’ and ‘Teo’) and 1 cultivar of narrow-leafed lupin (cv. ‘Gungurru’) were used. The soil was Zn deficient for grain production of both yellow and narrow-leafed lupin, but had low levels of native soil Cd (total Cd <0.05 mg kg^?1) so 1.6 mg Cd pot^?1, as a solution of cadmium chloride (CdCl₂·H₂O), was added and mixed through the soil. Eight Zn levels (0–3.2 mg Zn pot^?1), as solutions of zinc sulfate (ZnSO₄·7H₂O), were added and evenly mixed through the soil. Yellow lupin accumulated 0.16 mg Cd kg^?1 in grain when no Zn was applied, which decreased as increasing Zn levels were applied to soil, with ～0.06 mg Cd kg^?1 in grain when the largest level of Zn (3.2 mg Zn pot^?1) was applied. Low Cd concentrations (<0.016 mg Cd kg^?1) were measured in narrow-leafed lupin grain regardless of the Zn treatment. When no Zn was applied, yellow lupin produced ～2.3 times more grain than narrow-leafed lupin, indicating yellow lupin was better at acquiring and using indigenous Zn from soil for grain production. Yellow lupin required about half as much applied Zn as narrow-leafed lupin to produce 90% of the maximum grain yield, ～0.8 mg pot^?1 Zn compared with ～1.5 mg Zn pot^?1. Zn concentration in whole shoots of young plants (eight leaf growth stage) related to 90% of the maximum grain yield (critical prognostic concentration) was (mg Zn kg^?1) 25 for both yellow lupin cultivars and 19 for the narrow-leafed lupin cultivar. Critical Zn concentration in grain related to 90% of maximum grain yield was (mg Zn kg^?1) 24 for both yellow lupin cultivars compared with 20 for the narrow-leafed lupin cultivar.     

Risks of Boron Toxicity in Canola and Lupin by Forms of Boron Application in Acid Sands of South-Western Australia

Boron (B) deficiency frequently occurs on soils that are low in organic carbon (C) (<1.0% organic C), pH (soil pH_Ca <5.0), and clay content (<5% clay). Acid sands with these soil properties are common in south-western Australia (SWA). Moreover, hot calcium chloride (CaCl₂) extractable B levels are commonly marginal in the acid sands of SWA. This study examined the effects of soluble and slow release soil-applied B fertilizer and foliar B sprays on crops most likely to respond to B fertilizer on these soils, canola (oil-seed rape, Brassica napus L.) and lupin (Lupinus angustifolius L.).

At 25 sites over three years, canola was grown with (0.34 kg ha-¹) or without B applied as borax [sodium tetraborate decahydrate (Na₂B₄O₇·10H₂O) 11% B], and this was followed by nine experiments with B rates [0, 0.55, 1.1 kg ha^?1, applied as borax or calcium borate (ulexite, NaCaB₅O₆(OH)₆·5(H₂O), 13% B] and foliar sprays (0.1% solution of solubor, 23% B) in 2000–2001. A further five sites of B rates and sources experiments were carried out with lupin in 2000–2001. Finally, foliar B sprays (5% B w/v as a phenolic complex) at flowering were tested on seven sites in farmers’ canola crops for seed yield increases. No seed yield increases to soil-applied B were found while foliar B application at flowering increased canola seed yield in only one season across seven locations. By contrast, borax fertilizer drilled with the seed at sowing decreased canola seed yield in nine of 34-farm sites, and decreased lupin yield in two of five trials. Toxicity from drilled boron fertilizer decreased yield could be explained by decreases in plant density (by 22–40%) to values lower than required for optimum seed yield. Seedling emergence was decreased by borax applied at sowing but less so by calcium borate. Foliar B spray application never reduced seed yield due to toxicity effects.

Boron fertilizer drilled with the seed increased the B concentration in plant dry matter at early to mid-flowering. Boron application decreased the oil concentration of grain of canola at four sites. The oil yield of canola was significantly decreased at seven sites.

Notwithstanding the marginal B levels on acid sands of the SWA region, care needs to be taken on use of borax fertilizer as toxicity was induced in canola and lupin; with 0.34 to 1 kg B ha^?1(3-10 kg borax ha^?1) at sowing depressing seed yield, mostly by decreasing plant density. Rather than making general recommendation for B fertilizer application based on 0.01M CaCl₂ soil extractable B, soil and plant analysis should be used to diagnose B deficiency and B fertilizer use limited to calcium borate or foliar borax rather than soil-applied borax on low B sands.     

Soil properties related to phosphate buffering in calcareous soils

Abstract

In a group of 24 related calcareous soils, derived from Jurassic oolitic limestone, there was marked variability (13‐fold) in phosphate buffering when expressed as the maximum buffer capacity. This variability was most closely related to the iron content and pH of the soils, and these together accounted for 72% of the variance. This percentage was not increased by including CaC0₃ content or organic matter, which were also correlated with the maximum buffer capacity. A high correlation with specific surface area of CaCO₃ was probably an indirect effect due to the high correlation between this variable and the Fe and pH of the soils.

The equilibrium buffer capacity, which is the traditional measure of phosphate buffering, was less variable but quite unrelated to all the soil properties measured except the soil surface area. However the maximum buffer capacity and quantity of adsorbed P together accounted for 63% of the variance in this parameter.     

Soil hydrophobicity: a contribution of diuron sorption experiments

Retention processes play a major role in the fate and impact of organic contaminants in soils. The main goal of this study was to determine the influence of soil hydrophobic properties on the retention of diuron by using plots of a long‐term experiment in Versailles. We selected seven plots with pH 3.4 to 8.2 and low organic content. Sorption isotherms were obtained on soil slurries and kinetic measurements of diuron sorption were performed on undisturbed soil samples. The results showed that the Freundlich coefficient k_f decreased as pH increased and that the K_oc coefficient, k_f/TOC, was linearly related to the contact angle measured on the clay fraction over a wide range of pH. A low initial adsorption rate and low adsorption equilibrium were observed for the plot treated with NaNO₃. In this case, the structure in micro‐aggregates was assumed to limit the accessibility of adsorption sites. The CaCO₃ and CaO treated plots had similar organic matter contents, pHs, CECs and bulk densities, although their < 2 μm:C ratio differed. The higher retention of diuron in the CaCO₃ plot is attributed to the higher hydrophobicity of the < 2 μm fraction, probably masking part of the permanent clay negative charges. Thus, in addition to the different treatments, organic matter composition and distribution should also be included as specific soil properties. We conclude that the sorption properties of pesticides such as diuron can be a good tool to obtain greater understanding of soil properties and the degree of soil hydrophobicity/hydrophilicity in particular.     

Increases in pH and soluble salts influence the effect that additions of organic residues have on concentrations of exchangeable and soil solution aluminium

It has been suggested that additions of organic residues to acid soils can ameliorate Al toxicity. For this reason the effects of additions of four organic residues to an acid soil on pH and exchangeable and soil solution Al were investigated. The residues were grass, household compost, filter cake (a waste product from sugar mills) and poultry manure, and they were added at rates equivalent to 10 and 20 t ha^?1. Additions of residues increased soil pH measured in KCl (pH_(KCl)) and decreased exchangeable Al³⁺ in the order poultry manure > filter cake > household compost > grass. The mechanism responsible for the increase in pH differed for the different residues. Poultry manure treatment resulted in lower soil pH measured in water (pH_(water)) and larger concentrations of total (Al_T) and monomeric (Al_mono) Al in soil solution than did filter cake. This was attributed to a soluble salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al³⁺ and H⁺ back into soil solution. The considerably larger concentrations of soluble C in soil solution originating from the poultry manure may also have maintained greater concentrations of Al in soluble complexed form. There was a significant negative correlation (r = ?0.94) between pH_(KCl) and exchangeable Al. Concentrations of Al_T and Al_mono in soil solution were not closely related with pH or exchangeable Al. The results suggest that although additions of organic residues can increase soil pH and decrease Al solubility, increases in soluble salt and soluble C concentrations in soil solution can substantially modify these effects.     

Nutrient Availability Response to Sulfur Amendment in Histosols having Variable Calcium Carbonates

High soil pH and excessive calcium carbonate (CaCO₃) in the Everglades Agricultural Area of south Florida reduce the availability of phosphorus and micronutrients to crops. Sulfur (S) amendment is recommended to reduce soil pH and enhance nutrient supply. The study’s objective was to determine the sulfur amendment effectiveness on soil pH and nutrient availability in organic soil as CaCO₃ content increases in soil. An experiment of four S rates (0, 90,224, and 448 kg ha^?1) and three added CaCO₃ (0%, 12.5%, and 50% by volume) in organic soil was established. Sulfur application had limited effects on soil pH reduction as CaCO₃ level increased and therefore failed to enhance nutrient availability; however, it increased sulfate concentration in soils, which could be at risk for export from the field. Unexpected increases in manganese concentration with added CaCO₃ was associated with reducing conditions due to increased soil bulk density, which changed the soil physical properties.     

Response of Corn to Banded Zinc Sulfate Fertilizer in Fields with Variable Soil pH

Abstract

There are soil series that contain free calcium carbonate (CaCO₃) within fields where the surrounding pHs of the soil series are slightly acid. The objective was to study corn (Zea mays L.) grain yield response to zinc (Zn) fertilizer on different soil series within fields. The study was conducted at 12 sites between 1998 and 2000. Treatments were 0 and 5.6 kg Zn ha^?1 applied in bands to field‐length strips of corn and replicated four times. Multiple soil series were identified at each site, and treatment pairs were located within them. Grain yields, whole plant (V6 to V10 growth stage), and grain Zn content and uptake were measured. The most common result was no response to Zn application. However, significant yield decreases occurred on some soils as a result of Zn application in two situations: on soils with high soil‐test Zn or on soils with low soil‐test Zn and high pH.     

Utilization of fluidized bed material as a calcium and sulfur source for apples

Abstract

Fluidized bed material (FBM), a dry, high Ca, alkaline waste product which results from combining coal and limestone, was used as a Ca or S source or lime substitute in an established apple orchard (Malus domestica Borkh., cv. ‘York Imperial') over a four year period. Treatment comparisons were made between FBM applied at one or two times (1x or 2x) the soil lime requirement and CaCO, applied at the lime requirement (lx). Additionally, FBM lx was compared to a combination treatment consisting of CaCO₃ plus gypsum to apply similar amounts of Ca and S. All treatments were also compared to an untreated control.

No significant treatment comparisons were noted on leaf Ca levels however leaf Mg significantly decreased when FBM applied at the 1x or 2x level compared to CaCO₃ 1x. When FBM was compared with CaCO. plus gypsum there was a significant decrease in leaf Ca with FBM but no difference in leaf Mg. These effects were probably due to either a solubility difference between nutrients or to actual amount of Mg applied by the different sources. Leaf S levels were unaffected by treatments. Yields, fresh fruit weight and the incidence of cork spot were little affected by treatments.

Soil extractable Mg, 1N NH₄Ac, was not a good prediction of leaf Mg content or Mg added to the soil. Only soil Al was significantly reduced, compared to the control, by the treatments among the metals studied (Zn, Mn, Cu, Cd, Pb and Al). FBM applied at twice the lime requirement (wt. basis) resulted in similar soil pH to CaCO₃ applied at the lime requirement.     

Liming effects on soil pH and crop yield depend on lime material type,application method and rate,and crop species: a global meta-analysis

Purpose

The aim of this meta-analysis was to investigate the interactive effects of environmental and managerial factors on soil pH and crop yield related to liming across different cropping systems on a global scale.

Materials and methods

This study examined the effects of liming rate, lime application method, and liming material type on various soil chemical properties and crop yield based on data collected from 175 published studies worldwide since 1980.

Results and discussion

The most important variables that drive changes in soil pH and crop yield were liming rate and crop species, respectively. Soil conditions, such as initial soil organic matter and soil pH, were more important for increasing soil pH in field-based experiments, while lime material type and application method were more important for improving crop yield. To effectively neutralize soil acidity, the optimum liming duration, rate, and material type were?<?3 years, 3–6 Mg ha^?1, and Ca (OH)₂, respectively. Averaged across different crop species, the application of CaO, CaCO₃, Ca (OH)₂, and CaMg (CO₃)₂ increased yield by 13.2, 34.3, 29.2, and 66.5%, respectively.

Conclusions

This meta-analysis will help design liming management strategies to ameliorate soil acidity and thus improve crop yield in agroecosystems.

     

Influence of pH on the redox chemistry of metal (hydr)oxides and organic matter in paddy soils

Purpose

The primary purpose of this study was to determine how flooding and draining cycles affect the redox chemistry of metal (hydr)oxides and organic matter in paddy soils and how the pH influences these processes. Our secondary purpose was to determine to what extent a geochemical thermodynamic equilibrium model can be used to predict the solubility of Mn and Fe during flooding and draining cycles in paddy soils.

Material and methods

We performed a carefully designed column experiment with two paddy soils with similar soil properties but contrasting pH. We monitored the redox potential (Eh) continuously and took soil solution samples regularly at four depths along the soil profile during two successive flooding and drainage cycles. To determine dominant mineral phases of Mn and Fe under equilibrium conditions, stability diagrams of Mn and Fe were constructed as a function of Eh and pH. Geochemical equilibrium model calculations were performed to identify Mn and Fe solubility-controlling minerals and to compare predicted total dissolved concentrations with their measured values.

Results and discussion

Flooding led to strong Eh gradients in the columns of both soils. In the acidic soil, pH increased with decreasing Eh and vice versa, whereas pH in the alkaline soil was buffered by CaCO₃. In the acidic soil, Mn and Fe solubility increased during flooding due to reductive dissolution of their (hydr)oxides and decreased during drainage because of re-oxidation. In the alkaline soil, Mn and Fe solubility did not increase during flooding due to Mn(II) and Fe(II) precipitation as MnCO₃, FeCO₃, and FeS. The predicted levels of soluble Mn and Fe in the acidic soil were much higher than their measured values, but predictions and measurements were rather similar in the alkaline soil. This difference is likely due to kinetically limited reductive dissolution of Mn and Fe (hydr)oxides in the acidic soil. During flooding, the solubility of dissolved organic matter increased in both soils, probably because of reductive dissolution of Fe (hydr)oxides and the observed increase in pH.

Conclusions

Under alternating flooding and draining conditions, the pH greatly affected Mn and Fe solubility via influencing either reductive dissolution or carbonate formation. Comparison between measurements and geochemical equilibrium model predictions revealed that reductive dissolution of Mn and Fe (hydr)oxides was kinetically limited in the acidic soil. Therefore, when applying such models to systems with changing redox conditions, such rate-limiting reactions should be parameterized and implemented to enable more accurate predictions of Mn and Fe solubility.     

Effect of pH and calcium content of soil on earthworm cast production in the laboratory

The relative importance of pH and Ca content of soil in determining cast production by Allolobophora caliginosa (Savigny) was evaluated by a mini-frame technique using soil to which increasing amounts of four inorganic Ca salts were added. Whereas soil pH increased with the addition of increasing amounts of CaCO₃ and Ca(OH)₂, it remained constant with increasing amounts of CaSO₄ and Ca(NO₃)₂. Over the range of values studied, cast production increased with increasing pH and Ca level but did not increase with increasing Ca when soil pH was constant. Decreases in cast production were obtained above pH 7.3 with CaCO₃ and above 6.7 with Ca(OH)₂. Separate studies suggested that a high osmotic pressure of the soil solution resulting from the addition of high levels of soluble Ca(NO₃)₂ was responsible for the dramatic decrease in cast production obtained with this salt. The present study has provided useful methods for related studies of the effect of a range of fertilizer materials on earthworm activity.