Effect of pH on Zinc Sorption–Desorption by Soils

The objective of this study was to examine the effect of soil pH on zinc (Zn) sorption and desorption for four surface soils from the Canterbury Plains region of New Zealand. Zinc sorption by the soils, adjusted to different pH values, was measured from various initial solution Zn concentrations in the presence of 0.01 M calcium nitrate [Ca(NO₃)₂]. Zinc desorption isotherms were derived from the cumulative Zn desorbed (µg g^?1 soil) after each of 10 desorption periods by sequentially suspending the same soil samples in fresh Zn‐free 0.01 M Ca(NO₃)₂. Zinc sorption and desorption varied widely with soil pH. Desorption of both native and added Zn decreased continuously with rising pH and became very low at pH values greater than 6.5. The proportion of sorbed Zn that could be desorbed back into solution decreased substantially as pH increased to more than 5.5. However, there were differences between soils regarding the extent of the hysteresis effect.     

Effects of humic acid and Ca(NO3)2 on nutrient contents in pepper (Capsicum annuum) seedling under salt stress

This study was carried out in order to determine the effects of calcium nitrate (Ca(NO₃)₂) and humic acid (HA) applications on nutrient uptake of pepper seedling under salt stress in a plant growth room. Before sowing Demre variety of pepper seeds, 60?mM NaCI was added to each 300?cm³ pot. The experiment was ended at eighth week after the sowing. Applications of HA significantly affected K, Ca, Fe, Mn, Zn (p?p?3)₂ applications did not show a significant effect on Fe and Cu contents of pepper seedling. However, Ca(NO₃)₂ applications significantly affected N and P contents (p?<.05) and K, Ca, Mn, and Zn contents (p?相似文献   

Adsorption‐desorption of zinc in mollisols and their relationship with uptake of fertilizer‐applied zinc by rice

Abstract

Zinc (Zn) adsorption in mollisols conformed to the linear form of Freundlich equation. The log K values were positively correlated with silt, clay, and carbonate contents and soil pH, but negatively correlated with sand content. Sequential desorption of adsorbed Zn in 0.05M Ca(NO₃)₂, 0.1M Mg(NO₃)₂, 0.005M DTPA, and 0.1M HCl revealed that weakly and specifically bound fractions of added Zn, which could easily equilibrate with soil solution, were low and decreased with silt and carbonate contents and soil pH. Weakly bound fraction increased with sand content. Strongly bound and complexed fraction of applied Zn was the maximum and increased with clay, soil organic carbon and carbonate contents and specific surface area, but decreased with sand content. The mineral bound fraction of applied Zn was intermediate and increased with silt, clay and carbonate contents, and soil pH and specific surface area. Zinc uptake due to added Zn fertilizer by rice crop (Y) negatively correlated with log K, but positively related to Zn content in the equilibrium soil extract and Zn desorbed in 0.05M Ca(NO₃)₂. Both log K and l/n values together explained 59.5% of the total variation in Y, while Zn content in the equilibrium soil extract, Zn desorbed in 0.05M Ca(NO₃)₂, 0.005M DTPA and 0.1M HCl collectively accounted 79.6% of the total variation in Y.     

Redistribution of cadmium,copper, lead,nickel, and zinc among soil fractions in a contaminated calcareous soil after application of nitrogen fertilizers

This study was conducted to evaluate the redistribution of the heavy metals Cd, Cu, Pb, Ni, and Zn among different soil fractions by N fertilizers. In a lab experiment, soil columns were leached with distilled water, KNO₃, NaNO₃, NH₄NO₃, or Ca(NO₃)₂ · 4H₂O. After leaching, soil samples were sequentially extracted for exchangeable (EXCH), carbonate (CARB), organic‐matter (OM), Mn oxide (MNO), Fe oxide (FEO), and residual (RES) fractions. Distilled water significantly increased the concentrations of Cd and Ni in EXCH fraction, while concentration of Cu and Zn did not change significantly. Application of KNO₃, NaNO₃, NH₄NO₃, or Ca(NO₃)₂ · 4H₂O significantly increased the concentrations of Cd and Zn in EXCH fraction, while concentration of Pb and Ni was decreased. Application of all fertilizers caused an increase of Cu in the OM fraction. Moreover, leaching with these solutions significantly increased Cd [except in Ca(NO₃)₂ · 4H₂O], Cu, and Zn concentrations in the CARB fraction, while Pb and Ni concentrations were decreased. With application of all leaching solutions, Zn in the EXCH, CARB, FEO, and MNO fractions was significantly increased, while Zn in the OM fraction did not change. The mobility index indicated that Ca(NO₃)₂ · 4H₂O increased the mobility of Cd, Cu, and Zn in the soil, whereas NaNO₃ decreased the mobility of Pb and Ni in the soil. The mobility index of Pb decreased by all leaching solutions. Thus, these results suggest that applying N fertilizers may change heavy‐metal fractions in contaminated calcareous soil and possibly enhance metal mobility and that N‐fertilization management therefore may need modification.     

Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chloride

The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH₄NO₃ and 0.5 M NH₄Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl₂) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one‐to‐one. However, for all heavy metals NH₄Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH₄Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl₂) values and/or contents of OC were taken into account. In comparison to NH₄Cl, NH₄NO₃ proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH₄NO₃ is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation‐exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH₄NO₃ method. However, the applicability of the NH₄NO₃ method to other soils still needs to be investigated.     

A comparison of Mehlich I and Mehlich III extractants as predictors of manganese,copper and zinc availability in four Delaware soils

Abstract

The relative effectiveness of Mehlich I (.025N H₂SO₄ + .05N HCl) and Mehlich III (0.2N CH₃COOH + 0.25N NH₄NO₃ +.015N NH₄F + .013N HNO₃ + .001M EDTA) extractants as predictors of Mn, Cu and Zn uptake was assessed in a greenhouse experiment with four Delaware soils. The soils were adjusted to eight pH levels by addition of Ca(OH)₂ or elemental S, and received comparable amounts of Mn, Cu and Zn as either (1) MnSO₄ + CuSO₄ + ZnSO₄ or (2) Poultry Manure. Mehlich 1 and III extractable Mn and Zn, but not Cu, were well correlated in most instances. Excellent correlations were obtained between Mn uptake and Mehlich I and Mehlich III extractable Mn, for all soils and sources. In general, however, neither Zn nor Cu was found to correlate well with plant uptake. Based on this study, conversion to Mehlich III, as a routine soil test extractant for micronutrients, would not result in a significant improvement over the currently used Mehlich I extractant.     

Comparison of Four Different Extraction Methods to Assess Plant Availability of Some Metals in Organic Forest Soil

Abstract

The objective was to find an uncomplicated test giving the best correlation between calcium (Ca), magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn), and lead (Pb) extracted from humic forest soil and the total concentration of the element in some understorey forest plants using well‐known extractants. The elements were selected because Ca, Mg, Mn, Cu, and Zn are essential nutrients to plants and Zn and Pb are potentially harmful heavy metals received over the years in the southern parts of Norway by long‐range atmospheric transport. Extraction of organic podzolic surface soil (Oe and Oa horizon) from 17 different pine forests in central and southern Norway was carried out with four different reagents to evaluate uptake of Ca, Mg, Mn, Cu, Zn, and Pb in the understorey plants Deschampsia flexuosa, Vaccinium myrtillus (leaves and stems), and Vaccinium vitis‐idaea (leaves and stems). The NH₄OAc, NH₄NO₃, HCl, and EDTA solutions used to extract the soil in addition to concentrated HNO₃, demonstrated variability in capacity to extract the different elements from the soil. The extractants yielded significant relations between concentrations of Ca, Mn, and Pb in the Oe or Oa horizon and some of the plants or plant compartments, even though distinct correlation was more dependent on species and plant part than the actual extractant used. In the case of Zn, Cu, and Mg only a few sporadic correlations were observed between the different plant/plant compartments and the element concentrations in the soil extracts. Altogether none of the extractants was shown to be superior to the others in providing the best correlation with the elements concentrations in selected plant/plant compartments. In the case of Ca, Mn, and Pb all the extractants including concentrated HNO₃ provided significant correlations with at least some of the selected plant/plant compartments.     

Sodium bicarbonate‐DTPA test for macro‐and micronutrient elements in soils

Abstract

Individual soil tests are used to assess plant nutrient element needs. Separate soil tests, however, are time consuming and costly. Our objective was to develop a 0.5M sodium bicarbonate (NaHCO₃) soil phosphorus (P) test in combination with 0.005M diethylenetriaminepentaacetic acid (DTPA) so macronutrient dements: ammonium‐nitrogen (NH₄‐N), nitrate‐nitrogen (NO₃‐N), P, potassium (K), calcium (Ca), and magnesium (Mg); and micronutrients: iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) could be quantified in one extraction. The NaHCO₃‐DTPA extracting solution is a combination of 0.5M NaHCO₃ and 0.005M DTPA and has a pH of 7.60±0.05. Sodium in the solution enhances the NH₄, K, Ca, and Mg extraction; bicarbonate (HCO₃) is for P extraction; DTPA chelates Ca, Mg, and micronutrients; and the water is for NO₃ extraction. Soil samples (0–15 cm depth) came from two sources. The first set was from 12 N x P dryland proso millet (Panicum miliaceum L.) experiments, conducted from 1985 through 1987 in eastern Colorado. These soils were extracted with potassium chloride (KCl), NaHCO₃, ammonium acetate (CH₃‐COONH₄), DTPA, ammonium bicarbonate DTPA (AB‐DTPA), and with the NaHCO₃‐DTPA solutions. The second set included 25 soils from Alabama, Georgia, North Carolina, and South Carolina and were analyzed only for available P with the NaHCO₃ and NaHCO₃‐DTPA methods. Simple linear correlations for macronutrient elements and micronutrients were highly significant. Critical levels for the macronutrient elements: NO₃‐N, P, and K were 27, 11, and 144 mg kg^‐1, respectively; and the critical levels for the micronutrients: Fe, Mn, Zn, and Cu were 3.9, 0.35, 0.97, and 0.24 mg kg^‐1, respectively.     

Mehlich 3 or modified olsen for soil testing in Malawi

Abstract

Soil nutrient extraction methods, which are currently being used in Malawi, are time consuming and require too many resources. The use of a universal soil extractant would greatly reduce resource requirements. The objectives of the study were to (i) compare the universal soil extractants, Mehlich 3 (M3) and Modified Olsen (MO) with ammonium acetate (AA), Bray P1 (BPl), and diethylene triamine penta acetic acid (DTPA) in the amount of nutrients extracted, (ii) determine the relationship among the extractants for the nutrients they extract, and (iii) determine the critical soil‐test levels of phosphorus (P), potassium (K), and zinc (Zn) for a maize crop. Missing nutrient trials involving P, K, and Zn were conducted on thirty sites across Malawi using maize (Zea mays L.). Phosphorus application rates ranged from 40 to 207 kg P₂O₅ ha^‐1. Potassium and Zn were applied at 75 kg K₂O and 10 kg Zn ha^‐1, respectively. Procedures of Cate and Nelson were used to identify soil nutrient critical levels. Results showed that the correlations between M3 and BP1, and MO and BPl were highly significant (r=0.93, 0.94, respectively). Mehlich 3 extractable K and AA extractable K (r=0.90), MO and AA extractable K (r=0.94) were highly significant (P<0.01) and the correlations between M3 and AA and MO and AA extractable calcium (Ca) (r=0.92, 0.90, and 0.94, respectively) were also highly significant (P<0.01). The correlations between M3, MO, and AA extractable magnesium (Mg) (r=0.99) were highly significant (P<0.01). Zinc, copper (Cu), and manganese (Mn) extracted with M3 and DTPA were significantly correlated (r=0.89, 0.87, and 0.95, respectively). Correlations between MO and DTPA extractable Zn, Cu, and Mn were also highly correlated (r=0.89,0.85, and 0.95, respectively). Maize grain yields ranged from 730 to 9,400 kg ha^‐1. Mehlich 3‐P and MO‐P critical levels were 31.5 and 28.0 μg g^‐1, respectively. Mehlich 3 and MO gave a similar critical level of 0.2 cmol kg^‐1 for K while Zn critical levels were 2.5, and 0.8 μg g^‐1 for M3 and MO, respectively. Mehlich 3 and MO were equally effective in separating responsive to none responsive soils for maize in Malawi.     

Competitive Effect of Copper,Zinc, Cadmium and Nickel on Ion Adsorption and Desorption by Soil Clays

This study evaluated the effect of competing copper, zinc, cadmium and nickel ions in 0.01 M Ca(NO₃)₂ on heavy metal sorption and desorption by soil clay fractions. Initial Cu addition levels varied from 99 mg kg^-1 to 900 mg kg^-1 and Zn, Cd and Ni levels were 94, 131 and 99 mg kg^-1, respectively. Sorption of Cu conformed to a Freundlich equation. The amounts of metals not displaced by successive 48 h desorption cycles with 0.01 M Ca(NO₃)₂ were considered ‘specifically adsorbed’. Total sorption of Zn and Cd generally decreased in the order: Vertisol > Gleyic Acrisol > Planosol clay. More than 70% of the copper was specifically sorbed. Specific sorption of Zn was depressed by competition with Cu in the three clays investigated. At surface coverages higher than 200 mg Cu per kg of soil clay, zinc sorption in the Planosol and Gleyic Acrisol clays took place at low affinity sites. The exchangeable component of sorbed cadmium accounted for >:60% of the sorption in the Vertisol clay, >70% in the Gleyic Acrisol clay and was almost 100% in the Planosol clay. Nickel was not retained by the Planosol and Gleyic Acrisol clays and was ionexchangeably adsorbed by the Vertisol clay. At the conditions studied, Ni and Cd remain a ready source of pollution hazard.     

The effect of EDTA on the extractability of Zinc (Zn), Cadmium (Cd) and Nickel (Ni) in Vertisol and Alluvial soils

Ethylendiamintetraacetic acid (EDTA) is persistent in the environment. The presence of EDTA in soil may alter the mobility and transport of Zn, Cd and Ni in soils because of the formation of water soluble chelates, thus increasing the potential for metal pollution of natural waters. Mobility of metals is related to their extractability. To investigate metal extractability affected by EDTA, Zn, Cd and Ni were added to Vertisol and Alluvial soil at rates of 50, 2 and 5 mg kg^-1, respectively. Both natural and metal amended soils were treated with Na₂EDTA at rates of 0; 0.2 and 0.5 mg kg^-1. After five months of incubation soil samples were extracted with 0.1 N HCl, 0.005 M DTPA + 0.01 M CaCl₂ + 0.1 M TEA (0.005 M Diethylenetriaminepentaacetic acid + 0.01 M Calcium cloride + 0.1 M Triethanolamine) and 1 M Mg(NO₃)₂, the latter of which extracts the exchangeable from of metald (Zn, Cd and Ni).

According to experiment results, Zn, Cd and Ni in all extraction increased with increasing rates of EDTA in the natural and metal amended soils.     

Comparison of mehlich 1 and mehlich 3 extractants for P,K, Ca,Mg, Mn,Cu and Zn in atlantic coastal plain soils

Abstract

The Mehlich 3 (M3) extractant was introduced in 1981 to improve the efficiency of soil testing laboratories by eliminating the need for multiple extractants for P, K, Ca, Mg, Mn, Cu and Zn. The M3 was also intended to be suitable for a wide range of soils, perhaps to serve as a “universal”; soil test extractant. At present, regional soil testing committees throughout the U.S. are investigating the M3 in this regard.

Development of a field calibration data base for a new soil testing extractant is an essential, but expensive and time‐consuming process. An interim measure is the use of conversion equations between new and current extractant(s). These equations allow for use of the new extractant with existing field calibration data. The objectives of this study were (i) to develop conversion equations for the Mehlich 1 (M1) and M3 extractants for Atlantic Coastal Plain soils, and (ii) to determine the influence of soil pH and organic matter content on the relative extractability of P, K, Ca, Mg, Mn and Zn by Ml and M3.

Four hundred soil samples, obtained from field plots and commercial crop samples submitted to the University of Delaware Soil Testing Laboratory were analyzed for P, K, Ca, Mg, Mn, Cu and Zn by M1 and M3. Highly significant correlations between M3 and M1 were found for all nutrients (r=0.92*** to 0.97***) and, except for Cu and Mn, soil pH and OM did not markedly improve the linear regression equations developed for conversion between M3 and M1. Inclusion of OM in a multiple regression equation between M3 and M1 extractable Cu increased R² from 0.46** to 0.71***; R² for Mn+(pH+OM) was 0.48***, relative to 0.35*** for extractable Mn alone. Critical values for M3 P, K, Ca, and Mg, based on conversion equations restricted to soils testing less than high with the M1 extractant, were 41, 49, 295 and 45 mg.dm^‐3, respectively. For Mn and Zn, at a pH of 6.2, M3 critical values were 9.5 and 0.6 mg.dm^‐3, while for Cu, the M3 critical value ranged from 0.5 to 1.1 mgdm^‐3 for soil OM of 2 to 8%.     

一种通用型土壤有效元素高效提取方法及应用

Mehlich 3（M3）方法可同时提取土壤中磷、钾、钙、镁、铝、铁、锌、锰、铜等多种元素的有效态，提高土壤检测的效率；另外，M3法适用于钙质土、火山灰土、高度风化土等各类土壤，可作为一个“通用”型土壤有效元素提取试剂。但是硝酸铵（NH4NO3）由于管制不易获取，应用M3方法测定土壤有效元素含量时受到极大限制。因此，本研究用另一种易获取的惰性电解质氯化铵（NH4Cl）替代硝酸铵（NH4NO3），评价氯化铵替代硝酸铵M3法的适用性。Pearson相关分析结果表明，用氯化铵替代硝酸铵M3法测得的30种土壤有效磷、钾含量与M3法测定结果呈极显著正相关，其决定系数（R2）分别为0.99（P=2.31×10-55，n=60）和0.98（P=1.52×10-49，n=60）。同时，氯化铵替代硝酸铵M3法和M3法测定的有效钙、镁、铝、铁、锌、锰和铜含量极显著相关，R2值分别为0.98，1.00， 0.99，0.96，0.99，0.95和0.94。氯化铵替代硝酸铵M3–P与酸性、中性和碱性土壤的 Bray–P和Olsen–P极显著相关，R2分别为0.97和0.91 （P=1.42×10-15和1.00×10-21，n=20和40）。同时，利用氯化铵替代硝酸铵M3法测定酸性改良土壤有效磷含量，发现其得到显著提高。因此，氯化铵替代硝酸铵M3法可作为测定各种土壤，以及改良土壤中有效磷、钾和其他金属元素有效态含量的通用方法。     

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.     

Effects of Different Lead Compounds on Growth and Heavy Metal Uptake of Wetland Rice

Effects of different lead compounds, PbCl₂, Pb(NO₃)₂ and Pb(OAc)₂, on the rice growth and uptake of lead and some microelements by wetland rice were studied. The results showed that the seed germination, rice seedling growth, chlorophyl content, grain yield and uptake of Pb, Cu, Zn, Fe and Mn by rice plant were affected by the chemical forms of Pb compounds added in soil to a certain degree. The germination rate and the amount of chlorophyl decreased remarkably with increasing Pb concentration, the root extension was restrained obviously by the presence of Pb, and the effect of PbCl₂ was more evident than that of Pb(NO₃)₂ or Pb(OAc)₂.     

Nitrogen rate and source affects leaf elemental concentration and plant growth in muscadine grapes

Leaf concentrations of nitrogen (N), phosphorus (P), potassium (K), iron (Fe), and manganese (Mn) in ‘Sterling’ muscadine grapes (Vitis rotundifolia Michaux) grown for two years in sand culture were not influenced by different N‐fertilizer sources. Leaf zinc (Zn) and copper (Cu) were higher with ammonium nitrate (NH₄NO₃)than ammonium sulfate [(NH₄)₂SO₄]. Shoot growth was greatest with NH₄NO₃. Leaf Ca, Mg, Mn, and Cu content decreased and leaf N increased as N‐fertilizer rates were raised. Plant growth was positively correlated with leaf N, but was negatively correlated with leaf Ca, Mg, Fe, Cu, and Mn content. Percent Mg in the leaves was reduced when N levels, regardless of N source, were raised from the low (1.8 mM) to the middle (5.4 mM) rate. High leaf‐N levels were correlated with lower Ca and Mg in the leaves, indicating a relationship between N fertilization and the late‐season Mg deficiency often observed in muscadine grapes.     

The sorption of Cd,Zn and Ni by soil clay fractions: Procedures for partition of bound forms and their interpretation

This work is the first of several projects concerned with the study of higher-affinity reactions of Cd, Zn and Ni ions with soil clay fractions. Procedures for the separation of sorbed metals into fractions of lower and higher affinity for soil surfaces are described and evaluated.Various concentrations of Cd, Zn and Ni were allowed to react in the presence of 0.01 M Ca(NO₃)₂ with soil clays for 1 week after stabilization of suspension pH. The adsorbed metals were partitioned by a brief extraction with 0.01 M Ca(NO₃)₂ and the resultant fractions, called specifically and non-specifically sorbed metals, were measured by radioisotopic procedures.Measured separation factors showed that the fraction of sorbed metals that was desorbed by a rapid Ca(NO₃)₂ extraction still had a preference, sometimes marked, over Ca on the soil clay fraction. Separation of fractions of sorbed metals on the basis of affinity was reproducible, but the boundary conditions defined by separation factors vary appreciably between adsorbents, with values in the range 3–20 for amounts sorbed equivalent to ≦ 0.05% of cation exchange capacity and for pH values < 7.The proportions of Cd, Zn and Ni bound at high-affinity sites were strongly dependent on experimental conditions of pH, equilibrium time and surface saturation in relation to each soil clay. Hence, comparisons of affinities of trace metals for soils by reliance on measures of total sorption only, without assessing the contribution of lower-affinity forms, may prejudice conclusions and predictions arising from studies of the possible retention of metal pollutants in soils and fixation of micronutrients from fertilizers.     

CHARACTERIZATION OF MANGANESE TOXICITY IN TWO SPECIES OF ANNUAL MEDICS

There is interest in the development of cultivars of Medicago spp. tolerant to soil acidity, where manganese (Mn) can be a major constraint to plant growth. We evaluated the response of several ecotypes of M. polymorpha and M. murex to a high level of Mn (50 mg Mn kg^?1 soil), and its impact on biological N₂ fixation and mineral composition. Plant growth in pots was decreased by Mn toxicity, whether plants were dependent on N₂ fixation or provided with fertilizer nitrogen (N). Plant growth was impaired by high levels of Mn to a greater extent than was N₂ fixation. Tolerance to high levels of Mn differed between the ecotypes, with accession 66 of M. polymorpha and 194 of M. murex being the most tolerant. A 500 μM concentration of Mn in nutrient solution led to decreased concentration of zinc (Zn) in the whole plant, and to modifications in the partition of iron (Fe), potassium (K), and calcium (Ca) between roots and shoots. Tolerance to Mn was negatively correlated with the concentrations of Mn and Zn in the roots.     

Investigation of Heavy Metals using Various Extraction Methods in Livestock Manures

The use of animal waste for a soil amendment is a viable option for waste management. For safe and sustainable management of waste, it is important to assess the concentrations of heavy metals (HM). An experiment was conducted to compare metals [copper (Cu), zinc (Zn), and manganese (Mn)] in cow manure (CM), duck litter (DL), poultry litter (PL), and poultry litter ash (PLA) using eight extraction solutions. Extractability of HM was highly dependent upon the type of waste as well as extracting agent. Manures differed for the release of HM in the order of PL > DL > CM. Marked decreases in extractable trace elements were observed after ashing of PL irrespective of extraction method. Except for water, extractions released HM in the order of Mn > Cu > Zn. For Zn and Mn, the amount extracted varied in the order 1 M nitric acid (HNO₃) > 0.1 M HNO₃ > 0.01 M HNO₃ ≈ ethylenediaminetetraacetic acid (EDTA) > ammonium nitrate (NH₄NO₃) > calcium chloride (CaCl₂) > ammonium acetate (NH₄OAc) > H₂O in PL and PLA. Peak concentration of Cu was achieved in 1 M HNO₃ solution and the lowest Cu was found in NH₄OAc solution. On the basis of these results, the low extractability of HM in ash could suggest that the use of burned PL would be less of a water-pollution problem in the fields.     

Spatial and Fractal Characterization of Soil Chemical Properties and Nutrients across Depths in a Clay-Loam Soil

Researchers assessed the spatial distribution of soil chemical properties and nutrients at four depths in a clay loam soil cropped to corn and soybean at Freeman farm of Lincoln University. Soil samples were taken at depths of 0–10, 10–20, 20–40, and 40–60 cm in a 4.05-ha field and analyzed for acidity or basicity (pH), cation exchange capacity (CEC), total carbon (TC), organic matter (OM), base saturations on the CEC, ammonium (NH₄⁺), nitrate (NO₃^?), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), sodium (Na), manganese (Mn), copper (Cu), iron (Fe), and zinc (Zn). Results showed that coefficients of variation (CV) ranged between 5 and 30%, except for TC, NO₃^?, and Zn, which had greater CVs. Soil chemical properties and nutrients responded to exponential, linear, Gaussian, and spherical variogram models with nugget-to-sill ratios ≤ 1.0 and effective ranges from 4 to 56 m. Fractal analysis showed that CEC in all depths belonged to the 1.99 ≥ D3 ≥ 1.90 group, which suggests great disorder and antipersistence in the spatial structure.