Sulfur mineralization in sphagnum peat

Abstract

Open and closed incubation systems were studied as means of quantifying sulfate fractions in sphagnum peat moss. Sulfate was extracted in the closed system with a 0.15% CaCl₂‐H₂O or a 500 mg P/L extractant. Sulfate was extracted in the open system with 10 mM KC1, 0.15% , CaCl₂‐H₂O, or 500 mg P/L extractant. Extractants were quantified by ion chromatography. Phosphate extractant released more sulfate than CaCl₂, in the closed system. There was a significant increase over time of sulfate released by the CaCl₂ extractant. In the open system, there was no significant difference in release and total amounts leached of sulfate‐S between extractants. The closed system released more sulfate‐S than the open system. Phosphate extractants in both systems mineralized 43% of initial sulfur content     

Estimation of phosphorus availability in composts and compost/peat mixtures by different extraction methods

Abstract

A trial was carried out with compost and compost/peat mixtures to test several extraction methods for the estimation of availability of phosphorus (P). The test plant was Dendranthema grandiflorum All composts had a high pH and salt content. Amounts of P extracted by different extraction methods decreased in the order: Formate < CAL < NH₄‐acetate < CaCl₂/DTPA < CaCl₂. Dilution of compost with peat decreased pH and increased availability of P. The better availability of P caused by dilution with peat was not reflected by the Formate‐, CAL‐, and NH₄‐acetate method. These acid and well‐buffered extraction solutions overestimate P, and are therefore not suited to estimate availability of P in composts and compost/peat mixtures. Weak extraction solutions, like CaCl₂ and CaCl₂/DTPA, gave results which showed a good correlation with P content of plants and P uptake. The advantage of the latter method compared with CaCl₂ is the extraction of amounts of P comparable to amounts taken up by the plants. Therefore of all the extraction methods tested, the CaCl₂/DTPA method showed the best suitability to estimate the availability of P in composts and compost/peat mixtures.     

A method for extracting sulfate from sphagnum peat

Abstract

The efficacy of five solutions for extracting sulfate from a peat‐based medium was investigated. Extracting solutions used were 10 mM LiCl, 10 mM KC1, 100 mg/L P, 500 mg/L P, 0.15% CaCl₂, or distilled water. Equilibration time affected the amount of sulfate extracted with the use of 100 mg/L P or distilled water extractants. Differences in the amount of sulfate extracted were observed at 0.5‐, 4‐, and 12‐hour equilibration times. Extraction effectiveness increased with the increase of equilibration time, up to a maximum of 4 hours. The concentration of sulfate extracted with all extractants levelled off at the 2‐hour equilibration time. CaCl₂ was the most effective solution for the extraction of water‐soluble sulfate. Water‐soluble sulfate plus absorbed sulfate was most efficiently extracted with 500 mg/L P. No relationship was observed between measured sulfate and the pH levels of the extracted solutions.     

Evaluation of soil sulfate extractants and methods of analysis for plant available sulfur

Abstract

A steady decline in sulfur additions to Atlantic Canadian soils has prompted the need for an accurate method of determining their plant available sulfur status. Three soils were extracted with five soil extractants ‐ 0.01M Ca(H2PO₄)₂‐H₂O in 2M HOAc, 0.1M CaCl₂, Bray‐1 and de‐ionized water. The soil extracts were analyzed for sulfur or sulfate using inductively coupled argon plasma emission spectrometry (ICAP), AutoAnalyzer (AAN), anion exchange‐high performance liquid chromatography (HPLC‐CD) or atomic absorption spectroscopy (AAS). Results were compared with plant response of sulfur treatments to red clover, ryegrass, canola and wheat in a growth room. Instrument reproducibility and crop response indicated the ideal method of determining plant available soil sulfur was HPLC‐CD using the extractant Ca(H2PO₄)₂‐H₂O.     

Effects of phosphogypsum or calcium sulfate on aluminon reactive aluminum in solutions at varying pH

Abstract

Growing evidence of positive crop responses to gypsum or phosphogypsum (PG) application in acid soils strongly support the use of these amendments as an ameliorant of subsoil acidity. Although gypsum improves Ca availability in subsoils, its role in alleviation of Al toxicity needs careful attention. In the current study, either PG, CaSO₄.2H₂O or CaCl₂.2H₂O was added (to supply 12 mM Ca) to solutions containing 40 μM Al at pH 4.1 + 0.1. Solution pH was gradually raised to 4.5, 4.8 and then to 5.3 at various time intervals during 25 d aging of the solutions at 25 + 1^OC.

Concentration of Al measured by aluminon method without preacidification and preheating, referred to as “reactive Al”; in this paper, was 16 μM in 2 g L^‐1PG solution without added Al. This accounted 38% of total soluble Al in PG solution. Addition of 2 g L^‐1PG to solution containing 40 μM Al, resulted in only 42% of total Al in solution present in forms reactive with aluminon. According to MINTEQ speciation model, Al in solution was present as an entirely complexed form with F^‐. An increase in solution pH up to 5.3 had no effect on measured concentration of reactive Al or predicted distribution of Al species.

Addition of CaSO₄.2H₂O to 40 μMAl solutions had no effect on the concentration of reactive Al within pH 4.1 ‐4.8, however, up to 62% of total Al was in a form complexed with SO₄ ^2‐, as predicted by MINTEQ model. The concentration of reactive Al decreased by 60% at pH 5.3. Addition of CaCl₂.2H₂O also had no effect on the concentration of reactive Al within pH 4.1 ‐ 4.8. Nearly 73 ‐ 94% of total Al was present in Al³⁺form. An increase in pH to 5.3, decreased the concentration of reactive Al by 27%. The results suggest that ion‐pairing of Al with F^‐would appear to be a possible mechanism for alleviation of Al toxicity by PG at pH range 4.1 ‐ 5.3. With regard to CaSO₄.2H₂O, at pH 4.1 ‐ 4.8 ion‐pairing with SO.₄ ^2‐appears to be possible mechanism for the alleviation of Al toxicity. In addition, at pH 5.3 a considerable decrease in reactive Al was evident which would further alleviate Al toxicity.     

Remediation of a Magnesium‐Contaminated Soil by Chemical Amendments and Leaching

The deposition of magnesium (Mg)‐rich dust from magnesite mining activities has resulted in serious land degradation. However, the main factors limiting plant growth in Mg‐contaminated soils are unclear. Moreover, little information is available on the remediation of Mg‐contaminated soils. In this study, remediation of soils contaminated with Mg‐rich dust was investigated in a pot experiment using maize as the indicator plant. There were five treatments: (i) control; (ii) leaching; (iii) application of CaCl₂; (iv) leaching + CaCl₂ application; and (v) application of Ca(H₂PO₄)₂ · H₂O. Soil properties and growth of maize (Zea mays L.) seedlings were measured. Leaching alone significantly decreased soluble Mg concentration. Leaching + CaCl₂ application greatly increased exchangeable Ca concentration and decreased soil pH by 0·3 units. Application of CaCl₂ alone increased soluble Mg concentration sharply, which directly inhibited the germination of maize seeds. Application of Ca(H₂PO₄)₂ · H₂O significantly increased the concentrations of exchangeable Ca and available phosphorus and decreased soil pH by 1·7 units. The biomass of maize seedlings increased in the order of control = leaching < leaching + CaCl₂ < < Ca(H₂PO₄)₂ · H₂O. These results suggested that the plant growth in Mg‐contaminated soils was limited primarily by Ca deficiency and secondarily by high soil pH when exchangeable Ca was sufficient. High soil pH suppressed plant growth probably mainly by inhibiting phosphate uptake from the soil. Applying acid Ca salt with low solubility is an attractive option for the remediation of Mg‐contaminated soils. Copyright © 2015 John Wiley & Sons, Ltd.     

Suitability of Extractants for Predicting Available Sulfur in Natural Grassland in the Inner Mongolia Steppe of China

Abstract

It was the objective of this study to compare the suitability of different extractants for predicting the availability of sulfur (S) in natural grassland in a sulfur response trial on three different soil types in the Inner Mongolia steppe of China. For soil analysis, seven different extractants have been employed. The inorganic SO₄–S concentration was determined by ion chromatography. Additionally, in the Ca(H₂PO₄)₂ extract the total soluble S was determined employing turbidimetry. Weak salt solutions (0.15% CaCl₂, Ca(H₂PO₄)₂, and KH₂PO₄) extracted similar amounts of SO₄–S. Extraction with 0.025 M KCl provided the lowest SO₄–S values. Deionized water dissolved significantly more SO₄–S in the control plots than most weak salt extractants. The concentration of soluble organic S decreased in the control plots after 100 days of plant growth, indicating that the organic S pool contributed significantly to the S nutrition of the forage crops. Significant relationships among the SO₄–S in the soil determined in different extracts and crop yield, sulfur content in the forage, and total sulfur uptake were only found for the Ca(H₂PO₄)₂ extract. In general, the correlation coefficients proved to be unsatisfactory for field experimentation.     

Comparison of water,DTPA, and nitric acid as extractants to assess the availability of copper in peat substrates

Abstract

An experiment was conducted to assess the suitability of three extractants, water (H₂O), 0.005M DTPA, and 0.4M nitric acid (HNO₃) for determining plant available copper (Cu) in peat substrates. Cucumber was used as a test crop. Four levels of Cu were compared in two peat substrates, each at two pH levels. There was good correlation between Cu extractable in H₂O, DTPA, and HN0₃ and the Cu content of cucumber leaves, the correlations being 0.88, 0.87, and 0.89, respectively. These correlation coefficients did not differ significantly. It was concluded that all three extractants are suitable for estimating Cu availability in peat substrates.     

Growth of bedding plants and poinsettias in mineral wool and mineral wool/peat substrates

Abstract

Studies were conducted to ascertain the suitability of mineral wool (MW), either alone or in combination with sphagnum peat moss, as a substrate for potted greenhouse plants. Two types of hydrophyllic mineral wools, cleaned mineral wool (CMW) and uncleaned mineral wool (UMW), were used. Unamended CMW had a low bulk density, excellent water holding capacity, good aeration, but a high pH. Once peat moss was added to the CMW, bulk density remained low, water holding capacity remained good, and the pH dropped to a more suitable level. Unamended UMW had a high bulk density, good water holding capacity, poor aeration, and a high pH. Once peat moss was added to UMW, bulk density decreased, water holding capacity remained good, aeration increased, and the pH decreased to a more optimal level. CMW and UMW, were used unamended, as well as amended with 25%, 50%, and 75% peat moss. Two bedding plants, Impatiens walleriana ’Dazzler Violet’ and Begonia semperflorens ’Whiskey’ were grown for six and nine weeks respectively, and Euphorbia pulcherrima ’Glory’ was grown for 20 weeks, in nine different substrates. Plants grown in unamended CMW and UMW were generally smaller in size and lower in fresh weight than plants grown in 50% MW/50% peat moss. The plants grown in MW with either 25% or 75% peat moss were similar in size and weight to plants grown in 50% MW/50% peat moss. Plant tissue analysis showed that generally plants were receiving adequate nutrition.     

Extraction of water‐soluble organic matter from mineral horizons of forest soils

Dissolved organic matter (DOM) is involved in many important biogeochemical processes in soil. As its collection is laborious, very often water‐soluble organic matter (WSOM) obtained by extracting organic or mineral soil horizons with a dilute salt solution has been used as a substitute of DOM. We extracted WSOM (measured as water‐soluble organic C, WSOC) from seven mineral horizons of three forest soils from North‐Rhine Westphalia, Germany, with demineralized H₂O, 0.01 M CaCl₂, and 0.5 M K₂SO₄. We investigated the quantitative and qualitative effects of the extractants on WSOM and compared it with DOM collected with ceramic suction cups from the same horizons. The amounts of WSOC extracted differed significantly between both the extractants and the horizons. With two exceptions, K₂SO₄ extracted the largest amounts of WSOC (up to 126 mg C kg^–1) followed by H₂O followed by CaCl₂. The H₂O extracts revealed by far the highest molar UV absorptivities at 254 nm (up to 5834 L mol^–1 cm^–1) compared to the salt solutions which is attributed to solubilization of highly aromatic compounds. The amounts of WSOC extracted did not depend on the amounts of Fe and Al oxides as well as on soil organic C and pH. Water‐soluble organic matter extracted by K₂SO₄ bore the largest similarity to DOM due to relatively analogue molar absorptivities. Therefore, we recommend to use this extractant when trying to obtain a substitute for DOM, but as WSOM extraction is a rate‐limited process, the suitability of extraction procedures to obtain a surrogate of DOM remains ambiguous.     

Characterization of sulfur retained by soils exposed to sulfur dioxide

Abstract

Soils have substantial capacity for sorption of sulfur dioxide (SO₂) but little is known about the nature of the sorbed S. Three surface soils varying in pH, organic matter, CaCO₃ equivalent and surface area were exposed to air containing 5% SO₂ and subsequently analyzed by ten different procedures to characterize the sorbed S. Most of the sulfur retained by soils after exposure to SO₂ could be recovered as CaCl₂‐extractable S, Ca(H₂PO₄)₂‐extractable S, or S released as H₂S by hydriodic acid (HI). Only small amounts of sulfur could be recovered as tetrachloromercurate (TCM)‐extractable S, S released as SO₂ by HCl, or S released as H₂S by HCl + Zn, HCl + Sn, or Raney Ni and NaOH. However, large amounts of S released as SO₂ by HCl were recovered from the air‐dry Webster and the moist Storden soils indicating that SO₂ sorption is influenced by organic matter in air‐dry soils and by CaCO₃ in moist soils.     

Salinity effects on annual bedding plants in a peat‐perlite medium and solution culture

Annual vinca (Catharanthus roseus (L.) G. Don ‘Pink Carpet'), geranium (Pelargonium x hortorum L. H. Bailey ‘Jackpot'), and marigold (Tagetes erecta L. ‘First Lady') were grown in a sphagnum peat moss and perlite medium. Plants were irrigated with solutions of different salinity by the addition of 0.0, 1.0, 2.0, 4.0, and 8.0 g/1 of a NaCl and CaCl₂ mixture resulting in solution electrical conductivity (EC) values of about 1.3, 3.0, 4.5, 7.9, and 13.9 ds/m, respectively. In another experiment marigold and geranium were grown in solution culture containing the same salt mixture at 0.0, 1.0, 4.0, and 8.0 g/1 with EC values of 1.4, 3.0, 7.4, and 12.5 ds/m, respectively. All species showed some salinity tolerance up to 2.0 g/1 in peat‐perlite and 1.0 g/1 in solution culture as growth reductions were below 10% and no foliar injury occurred. Foliar injury occurred on marigold and geranium, but not annual vinca, at 4.0 and 8.0 g/1 in both growing media. On a concentration basis, recently mature leaves sampled from marigold grown in peat‐perlite contained more chloride (Cl) but less sodium (Na) than geranium and annual vinca. However results of the solution culture experiment showed that, with the exception of 1.0 g/1 treatment, geranium and marigold plants absorbed the same amount of Cl and Na when content was expressed on a mg/g dry weight basis. The low Na concentration in marigold leaves was a reflection of restricted translocation of Na from the roots to the shoots.     

Soil pH,extractable aluminum and tree growth on acid minesoils

Abstract

Paper birch and hybrid poplar were grown in acid minesoils amended with different rates and types of lime. Growth of the trees was correlated with soil pH, Ca, Mg, K, P and three measures of extractable Al ‐ 1 N KCl, 0.01 M CaCl₂ and H₂O extractable Al. Correlations between soil pH and extractable Al and between the three measures of extractable Al were also determined. Soil pH accounted for the largest share of the total variation in root and shoot growth of both species over all soils. Correlations between tree growth and extractable Al for all soils combined were low and generally non‐significant. Significant correlations were obtained between soil pH and extractable Al and between the three measures of extractable Al, however, the relationships varied among soils.     

Lime Rate Affects Substrate pH and Container-grown Birch Trees

Nursery production of birch (Betula nigra L.) trees commonly occurs in containers using a soilless substrate such as pine bark or peat moss. Birch trees have been reported to suffer from pH-induced micronutrient deficiencies in landscapes; thus, they are recommended to be planted in low-pH soils (<6.5). Little research has addressed the influence of substrate pH on birch trees during container production. Therefore, the objective of this research was to determine if substrate pH influences birch tree growth and development. Birch (Betula nigra ‘NBMTF’) liners were transplanted into 11.4 L plastic nursery containers filled with an 80 pine bark: 20 sphagnum peat moss (v:v) amended with either 0.6 kg.m^?3 of elemental sulfur (S) or 0, 1.8, 3.5, or 7.1 kg.m^?3 dolomitic lime. Substrate pH ranged from 4.8 to 7.3. There were only a few and minor differences in leaf chlorophyll content and no differences in plant growth. Differences in leachate and plant tissue nutrient concentration occurred for some elements, although these differences were not enough to affect plant growth. Container-grown birch trees can be grown over a wide range of substrate pH (4.8 to 7.3) with little or no effect on their growth.     

Comparison of soil zinc extractants for detection of applied zinc and prediction of leaf zinc concentration

Abstract

Many soil extractants have been developed for determination of zinc (Zn) availability to plants. The optimum soil Zn extractant should be useful not only for prediction of plant Zn concentration but also for detection of applied Zn levels. The objectives of this study were: i) to compare soil Zn extradants for detecting applied Zn and for predicting peanut leaf Zn over a range of soil pH levels, and ii) to correlate other soil‐extractable Zn levels with Mehlich‐1. Soil and peanut leaf samples were taken from a field study testing pH levels as the main plots and Zn application rates in the sub‐plots. Extractable Zn was determined on soil samples using Mehlich‐1, Mehlich‐3, DTPA, MgNO₃, and many dilute salt extradants of varied strength and pH. Correlation of extractable soil Zn to cumulative applied Zn levels revealed Mehlich‐1, Mehlich‐3, DTPA, and AlCl₃ extradants to be among the best indicators of applied Zn. Leaf Zn concentration was best correlated with soil Zn extracted by dilute salts, such as KCl, CaCl₂, NH₄Cl, CaSO₄, and MgCl₂. Including soil pH as an independent variable in the regression to predict leaf Zn considerably improved R‐square values. The DTPA‐extractable soil Zn levels were very well correlated with Mehlich‐1‐extractable Zn. Mehlich‐3 extracted about 20% more soil Zn than Mehlich‐1, but Mehlich‐3 soil Zn was not as well correlated to Mehlich‐1 soil Zn as DTPA soil Zn. Lower pH solutions extracted more of the applied Zn, but more neutral solutions extracted Zn amounts which were better correlated with Zn uptake. On the other hand, Mehlich‐1, which had a lower pH, had better correlations with both applied Zn and leaf Zn than did Mehlich‐3. Shortening the DTPA extraction time to 30 minutes resulted in better correlations than the standard two hour extraction time. Chloride (Cl) was the best anion tested in relation to soil applied Zn recovery in combination with potassium (K), calcium (Ca), and aluminum (Al), and Cl optimized leaf Zn correlations for ammonium (NH₄), K, Ca, and magnesium (Mg). The larger the valence of the cation, the better the correlation with applied Zn and the poorer the correlation with leaf Zn.     

A simple bioassay for the diagnosis of aluminium toxicity in soils

Abstract

A bioassay procedure is described for diagnosing aluminium toxicity in soils using short term root growth in extracted soil solution. Soil solution is extracted from moist soil which has been incubated at “field capacity”; for 4 days. Soil solution extracted is divided into two portions, each of which is treated with CaCl₂ and H₃BO₃ to ensure that neither Ca nor B is limiting root growth. One portion is adjusted to pH 5.5 (pH adjusted treatment) with saturated Ca(OH)₂ solution. Aliquots (11 ml) of each portion are separately dispensed into each of five polypropylene tubes. Seedlings (in our experiment Glycine max cv. Forrest) of uniform root length are inserted into each tube (one per tube) and grown for 48 h. The increase in root length during the 48 h growth period (root elongation) in the unadjusted solutions is expressed as a percentage of that in the pH adjusted solutions to derive relative root elongation (RRE) ‐ an index of aluminium toxicity.

For 24 acidic surface soils, RRE using this soil solution bioassay was linearly correlated (r² = 0.96) with RRE obtained from a soil bioassay (with unamended, CaSO₄ and CaCO₃ treatments). The latter is commonly used to obtain an index of aluminium toxicity. The proposed procedure is less time consuming and tedious than the soil bioassay, and interpretation of the result is unambiguous.     

Testing for calcium,magnesium, and potassium in soilless potting media: Differences and similarities between extractants

Abstract

Interpretation guidelines for the availability of calcium (Ca), magnesium (Mg), and potassium (K) in soilless media have been developed through plant growth studies and comparisons amongst extractants. The extractants used were 70% ethanol (EtOH), water, DTPA, ammonium acetate (NH₄OAc) and silver thiourea (AgTu). Ethanol, which removes ions in pore water, extracted only 4.5, 13, and 26% of the Ca, Mg, and K, respectively, that could be extracted by AgTu from Pinus radiata bark of pH 5.66 and CEC of 11.2 cmol⁺/L. Acidification to pH 4.62 increased these proportions to 22, 40, and 38%. Correlations between water and DTPA for 39 media were excellent for both individual elements and the ratios Ca/Mg, K/Mg, and Ca, Mg, and K/(the sums of their concentrations in the extractants) (r² = 0.88–0.98). Correlations between these extractants and AgTu and NH₄OAc were poor for individual elements (r² = 0.37–0.75) but high for ratios (r² = 0.71–0.96). For Petunia ’Celebrity Salmon’ growing in peat media of similar pH but widely different Ca, Mg, and K proportions, the ratios of these elements in the shoots were highly correlated with their ratios in 2 mM DTPA extracts of the media. Similarly high correlations were obtained between the Ca/Mg ratios of the shoots of three Asplenium species growing in pinebark media and this ratio for DTPA, NH₄OAc, and AgTu extracts of the media. The results indicate that the ratios of Ca, Mg, and K to one another in water and DTPA extracts of soilless media are good indicators of the availability of these elements to plants. Healthy specimens of the test plants grew in media whose DTPA extracts had a minimum Ca/Mg mole ratio of 1 or 2, depending on the Ca requirements of the species. The upper limit for good growth was deduced to be about 6. Limits for NH₄OAc and AgTu extracts were similar to those found for crop plants in soils, at 1.6 or 3 to about 9. Minimum amounts of Ca, Mg, and K extracted by water and DTPA that were adequate for short‐term growth in the absence of further inputs were about 9,2.5, and 5 cmol⁺/L medium, respectively, at pH 6.0. The effect of pH on cations removed by water and DTPA raises the minima to about 19, 5, and 7.5 cmol⁺/L at pH 5.0.     

Influence of sulfur and nitrogen fertilzer on the uptake of iron,manganese, and zinc by corn plants grown in calcareous soil

Abstract

A pot experiment was conducted with a coarse‐textured calcareous soil (pH‐H₂O 8.3) to study the effect of single and combined application of N and S fertilizers on soil pH, Fe, Mn, Zn, and P mobilization, and on growth and micronutrient uptake by com (Zea mays L.). Increasing amounts of elemental sulfur were mixed with the soil. To stimulate S oxidation, the treated soils were incubated for six weeks at field capacity. Nitrogen was applied as NH₄NO₃ (100, 200, and 400 mg N/kg). After six weeks, dry matter yields were recorded and shoots were analyzed for Fe, Mn, Zn, and P. At the end of the experiment, soil pH and the DTPA‐extractable micronutrients were determined. The results showed that: a. Soil pH was decreased by 0.2, 0.5, and 0.9 unit as a result of increasing S applications.

b. Applied sulfur and N fertilizer had increased the availability of micronutrients to following crops.

c. Application of N and/or S resulted in increased dry matter yields.

d. Manganese uptake tended to be higher as amounts of N applied increased; this was most evident at the higher S application rates. This effect was, however, reversed for Fe, Zn, and P uptake.

e. Under our experimental conditions, promising results were achieved on improving micronutrient availability and uptake when 400 mg N/kg was combined with 3 g S/kg.

     

Effects of phosphate,nitrate and chloride on calcium,magnesium and manganese content of cigar‐wrapper tobacco

Abstract

Nutrient solutions containing three levels of phosphate, nitrate, and chloride were applied to cigar‐wrapper tobacco (Nicotiana tabacum L.) plants growing in sand culture for a period of 18 days. Concentrations of other nutrient elements in the nutrient solutions were held constant and the solutions were applied to pots as needed to maintain favorable moisture conditions for plant growth. Plants were in the two leaf stage when transplanted and were maintained on a single nutrient solution for 38 days before treatments were started. At the end of an eight weeks growing period, plant leaves were harvested and analyzed for Ca, Mg, and Mn. Dry matter yield was significantly (P=0.01) increased when 2 mM/1 of Ca(NO₃)₂ replaced an equivalent amount of Ca(H₂PO₄)₂ or CaCl₂ in the nutrient solution. Nitrate significantly (P=0.05) increased Ca and Mg content and decreased Mn concentration in leaf tissue in comparison to chloride. Calcium and Mg content were significantly (P=0.05) decreased and Mn content of tobacco leaves was increased by phosphate in comparison to nitrate and chloride.     

Predicting Liming Needs of Soybean Using Soil pH,Aluminum, and Manganese Soil Tests

Abstract

Whether a tropical soil should be limed or not for a particular crop is strongly dependent on the levels of soil aluminum (Al) which can be determined with soil tests. Soil pH is used to predict whether lime is needed in less‐weathered soils, although some evidence indicates a soil Al test would be more accurate. The objectives of this study were to determine and to compare the accuracies of four soil tests to separate soils requiring lime from those that do not, and to determine the cause of acid‐soil injury to soybean [Glycine max (L.) Merr.]. Soybean was grown in the greenhouse on four surface soils representing the major land resource areas of Louisiana and were amended with eight rates of lime, yields determined, and soils analyzed for soil pH, extractable Al, CaCl₂‐extractable Al, CaCl₂‐extractable manganese (Mn), and Al saturation. Acid‐soil injury in soybean grown on the Litro clay and Stough fsl was probably caused by soil‐Al effects while low soil calcium (Ca) and high soil Mn was likely responsible for lower yields from the Mahan fsl. Leaf Ca from the limed Mahan‐soil treatment was 5‐fold greater and leaf‐Mn 7‐fold less than control levels. Regression analyses’ R² values were similar for all soil tests except for CaCl₂‐extractable Mn, which was lower. Soil tests were compared across soil type by selecting treatments that had the same 85% relative yield. Using this data subset, there was no difference in the soil pH among the four soils, while there were significant differences among soils for all other soil test measurements indicating the superiority of soil pH for identifying acid‐soil injury. Critical test values were 5.1 soil pH, 30 mg kg^‐1 extractable Al, 7% Al saturation, 0.7 mg‐kg^‐1 CaCl₂‐extractable Al, and 9 mg‐kg^‐1 CaCl₂‐extractable Mn.