Efficiency of Sulfur Application on Soybean in Two Types of Oxisols in Southern Brazil

Modern agricultural techniques have been increasing the yield of soybean (Glycine max (L.) Merr.) while also causing increasing removal of sulfur (S) from the soil. Besides this, the use of concentrated fertilizers with this element and inadequate soil management, with consequent formation of organic matter with low S concentrations, has been causing frequent symptoms of deficiency in the plants. To assess the effect of S on soybean yield and to establish critical levels of sulfur sulfate (S-SO₄^2-) available in the soil, two experiments were conducted over a 2-year period in the Paraná State, Brazil, in fields containing Typic Haplorthox and Typic Eutrorthox soils, located in the Ponta Grossa and Londrina Counties, respectively. The experimental design was randomized blocks with five S rates (0, 25, 50, 75, and 100 kg ha^?1) and four replicates. The source used was elementary S with 98 percent purity. The maximum estimated yields on average for the 2 years were obtained with application of 49.9 and 63.0 kg ha^?1 in the Typic Haplorthox and Typic Eutrorthox soils, for an overall average of 56.4 kg ha^?1, with concentrations of available S-SO₄^2- in the 0- to 20-cm depth of 16.9, 19.3m and 17.1 mg kg^?1, respectively, values greater than the 10 mg kg^?1 indicated as the adequate concentration for soybean plant. In turn, at the 21- to 40-cm depth, the S concentrations were 49.5, 74.2, and 56.4 kg ha^?1. The efficiency of the fertilization diminished with increasing S rates, in both soil types, while the greatest yield efficiency was obtained in the plants grown in the Typic Haplorthox soil.     

Calibration and Categorization of Plant Available Silicon in Rice Soils of South India

ABSTRACT

Calibration of field crop responses to nutrient availability acts as a basis for making fertilizer recommendations from soil and tissue analysis. The purpose of this study was to evaluate and summarize silicon (Si) fertilization of rice in different soils of south India. The experiment consists of four levels of calcium silicate as Si with three replications. Initially, soils were analyzed using eleven different extractants. The grain and straw yield were recorded and analyzed for Si content. The critical levels for plant available Si in the soil ranged from 14 mg kg^?1 (distilled water-1) to 207 mg kg^?1 [0.005 M sulfuric acid (H₂SO₄)]. There was a wide variation in low, medium, and high categories of plant available Si for different extractants calculated based on percent relative yield. The critical level of Si in straw and grain were 2.9 and 1.2%, respectively.     

Evaluation of the sulphur status of some soils from Portugal

Total S, extractable SO₄, and SO₄^? retention capacity were determined in a range of soils covering the dominant soil groups in Portugal which are expected to show S deficiency. Total S was relatively low (83–435 mg S kg^?1) in all soils and KH₂PO₄^? extractable SO₄ was, in general, low for plant growth, ranging from 0.9 to 32.2 mg S kg^?1. SO₄^? retention capacity ranged from ?33.1 to 64.7 mg S kg^?1 and was negative in many (14 out of 20) of the soils. Most of the soils are expected to be S deficient and show extensive leaching of SO₄. Other selected soil properties that may affect the chemistry of SO₄ were determined. A highly significant simple correlation was obtained between SO₄ adsorbed and extractable Al by the Mehra and Jackson method (CDB-Al) (r = 0.74; P < 0.001). A multiple regression which included silt improved the correlation of SO₄ adsorbed with CDB-Al (r = 0.79; P < 0.001).     

Evaluation of Extractants for Boron under the Influence of Organic Matter and Applied Boron in Rhizosphere and Nonrhizosphere Soils Growing Rape (Brassica campestris L.)

Field experiments during 2006–07 and 2007–08 were conducted in an Aeric Endoaquept to evaluate extractants suitable for boron (B) under the influence of organic matter and B in both rhizosphere (R) and nonrhizosphere (NR) soils with rape (Brassica campestris L.) as a test crop. The results reveal that the average B content in Mehlich 3 (MH-3) B was greatest (0.791 mg kg^?1) in NR soil, while that of the same in R soil was greatest (0.785 mg kg^?1) with Mannitol–calcium chloride (CaCl₂) (MCC) followed by hot -CaCl₂ (HCC, 0.750 mg kg^?1) in the treatment T₄ where NPK (80:40:40), B at 0.5 kg ha^?1, and farmyard manure (FYM) at 5 t ha^?1 were applied together. Based on linear regressions and correlations between different extractants and yield responses, the MH-3 extractant gave the greatest value of co-efficient of determination (R² = 0.36**, r = 0.598**) and has proved to be a superior extracting solution for B in NR in an Aeric Endoaquept. The results further suggested that the extractability of B with these three extractants did not have any control over rhizosphere soil zone.     

Evaluation of Some Chelates in Estimating Available Zn for Soybean in Calcareous Soils

Six fertilizer trials on calcareous soils in Saudi Arabia were conducted for the prediction of Zn deficiency in soybean (Glycine max L., var Merr). Zinc level before planting was tested by using 3 different extractants, i.e. DTPA, AB-DTPA and EDTA. Zinc was applied in the form of ZnSO₄ · 7H₂O at 0, 5, 10, 15, 20 and 40 kg Zn ha^?1. Plant samples were taken at early bloom and tissue was analysed for Zn. Two methods were used to judge the critical deficiency level of Zn: Cate-Nelson and chisquare models. The critical level estimated according to the Cate-Nelson method for DTPA extractable soil Zn was 0.43 mg kg^?1 in the growing season 1991. EDTA gave a much higher level (1.80 mg kg^?1) and AB-DTPA gave an intermediate level (0.68 mg kg^?1). Chi-square statistical procedure gave a very similar critical level of 0.66 mg kg^?1 for AB-DTPA but lower for either DTPA (0.38 mg kg^?1) or EDTA (1.32 mg kg^?1). The critical level based for three growing seasons ranged from 0.25 to 0.68, 0.32 to 0.82 and 1.12 to 3.4 mg Zn kg^?1 for DTPA, AB-DTPA and EDTA extractants, respectively. The values obtained by the linear regression equation with soybean leaf concentration were 0.45 and 0.70 mg Zn kg^?1 for DTPA and AB-DTPA, respectively. Such values are very close to those determined by using the Cate-Nelson method. On the other hand, the value obtained for EDTA (1.15 mg Zn kg^?1) was comparatively lower than that calculated by applying the Cate-Nelson method.     

Assessing a suitable extractant and critical limits of nickel in soil and plant for predicting the response of barley (Hordeum vulgare L.) to nickel grown in Inceptisols

ABSTRACT

Nickel (Ni) is an essential element for plants. Abundant information exists on Ni toxicity in soil–plant system but not much is available on its critical level of deficiency (CLD) in soils and plants. Five chemical extractants were evaluated to find a suitable extractant for Ni in Inceptisol. Twenty-one soils having low to high levels of Ni were used to grow barley (Hordeum vulgare L). The amount of Ni extracted was correlated with Ni concentration and uptake by barley. The diethylene triamine penta acetic acid-calcium chloride (0.005 M DTPA-CaC1₂) was identified as the most promising soil extractant for Ni. The CLD of Ni for 0.005 M DTPA-CaC1₂ in soil was 0.22 mg kg^?1 whereas in barley plant it was 2.14 mg kg^?1. Application of 7.5 mg kg^?1 Ni in soil caused a significant increase in Ni concentration in the shoot of barley in all the soils irrespective of the initial Ni status.     

Genese und Klassifikation von Organomarschen der Wesermarsch

Formation and classification of humus-rich marshland soils of the Weser marshland, Germany The formation and classification of marshland soils are still controversial. To improve the knowledge on the formation of humus-rich marshland soils 11 soil profiles have been investigated. The soils mostly showed Phragmitis in the subsoil. The Gr-horizons began at low depths (40–60 cm). The clay content was often about 60% and the C_org content up to 480 g kg^?1. The amount of total sulfur was up to 29.6 g kg^?1, that of exchangeable sulfate up to 4608 mg kg^?1 and that of sulfate in the saturation extract 51.2 mg l^?1. With pH (H₂O) values between 2.0 and 7.4, Carbonate/S ratios < 3 and total sulfur contents > 7.5 g kg^?1 some soils showed “Actual Acid Sulfate Soil” (AASS) properties. The pH(per) values varied between 2.4 and 7.1, thus some profiles showed “Potential Acid Sulfate Soils” (PASS) properties. Brakish as well as marine environments with an intensive sulfur dynamics and carbonate leaching are likely within the geogenetic phase of soil development. Via the control of the water regime the pedogenetic phase is mainly of anthropogenic influence. We propose to classify humus-rich marshland soils into “Organomarsch” and “Thiomarsch” on the soil type level of the German systematics.     

Evaluation of Extractants and Quantity–Intensity Relationship for Estimation of Available Potassium in Some Calcareous Soils of Western Iran

Accurate estimation of the available potassium (K⁺) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K⁺, determined by ammonium acetate (NH₄OAc), might not be the best predictor of the soil K⁺ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K⁺ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K⁺. The following methods extracted increasingly higher average amounts of soil K⁺: 0.025 M H₂SO₄ (45 mg K⁺ kg^?1), 1 M NaCl (92 mg K⁺ kg^?1), 0.01 M CaCl₂ (104 mg K⁺ kg^?1), 0.1 M BaCl₂ (126 mg K⁺ kg^?1), and 1 M NH₄OAc (312 mg K⁺ kg^?1). Potassium extracted by 0.01 M CaCl₂, 1 M NaCl, 0.1 M BaCl₂, and 0.025 M H₂SO₄ showed higher correlation with K⁺ uptake by the crop (P < 0.01) than did NH₄OAc (P < 0.05), which is used to extract K⁺ in the soils of the studied area. There were significant correlations among exchangeable K⁺ adsorbed on the planar surfaces of soils (labile K⁺) and K⁺ plant uptake and K⁺ extracted by all extractants. It would appear that both 0.01 M CaCl₂ and 1 M NaCl extractants and labile K⁺ may provide the most useful prediction of K⁺ uptake by plants in these calcareous soils containing micaceous minerals.     

Different Fractions of Soil Potassium,Olsen Phosphorus,and Available Sulfur Status of Intensively Cultivated Berpura Soil Series of India and Nutrient Indexing of Rice Crop

Berpura alluvial soil series of the Indo‐Gangetic Plains is situated in the Ambala District of the Haryana State of India. Soils of this series had medium concentrations of both potassium (K) and phosphorus (P) and large concentrations of sulfur (S) before 1970. To study different fractions of K, Olsen P, and 0.15% calcium chloride (CaCl₂)–extractable (available) S of soils of the Berpura series and to create nutrient indexing of rice crops growing on this series, surface soil samples were collected from 100 farmers' fields after the harvest of the wheat crop in 2005. During kharif season of same year, samples of upper two leaves at anthesis growth stage of rice crop were also collected from the same 100 farmers' fields that had earlier been sampled for soil analysis. Analysis of soil samples showed more K depletion in soils of this series, of which 86% of farmers' fields were deficient in ammonium acetate (NH₄OAc) K (available K). Thirty and 62% of leaf samples of the rice crop growing on the 100 fields of this series were extremely and moderately deficient in K, respectively. The mean values of water‐soluble, exchangeable, nonexchangeable, lattice, and total K were 10.6, 30.3, 390.0, 8204, and 8635 mg kg^?1, respectively. In soils of this series, 0.123, 0.351, 4.517, and 95.009% of total K were found in water‐soluble, exchangeable, nonexchangeable, and lattice K forms, respectively. On the other hand, long‐term farmers' practice of more application of P fertilizer in wheat crop has resulted in P buildup in the soils of the Berpura series. Olsen P in soils of farmers' fields of this series ranged from 9.0 to 153.0 mg kg^?1, with the mean value of 41.8 mg kg^?1. Eighty‐two percent of leaf samples of rice crops grown on this series without application of P fertilizer were sufficient in P. The analysis of soil and rice crops for P and K proved the suitability of 0.5 M sodium bicarbonate (NaHCO₃) and 1 N NH₄OAc for extracting available P and K, respectively, in alluvial soils of the Indo‐Gangetic Plains. The 0.15% CaCl₂–extractable S in this soil ranged from 9.6 to 307 mg kg^?1 with a mean value of 34.6 mg kg^?1. Four and 26% of soil samples had low and medium, respectively, in 0.15% CaCl₂–extractable S. S deficiency was recorded in rice crops, as 29% of the leaf samples were extremely deficient in S and 58% were moderately deficient in S. This indicated the unsuitability of the 0.15% CaCl₂ to extract available S from the Udic ustochrept utilized for cultivation of rice crops.     

Relationship Between Extractable Metals in Acid Soils and Metals Taken Up by Tea Plants

Abstract

The accumulation of heavy metals in plants is related to concentrations andchemical fractions of the metals in soils. Understanding chemical fractions and availabilities of the metals in soils is necessary for management of the soils. In this study, the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn) in tea leaves were compared with the total and extractable contents of these heavy metals in 32 surface soil samples collected from different tea plantations in Zhejiang province, China. The five chemical fractions (exchangeable, carbonate‐bound, organic matter‐bound, oxides‐bound, and residual forms) of the metals in the soils were characterized. Five different extraction methods were also used to extract soil labile metals. Total heavy metal contents of the soils ranged from 17.0 to 84.0 mgCukg^?1, 0.03 to 1.09 mg Cd kg^?1, 3.43 to 31.2 mg Pb kg^?1, and 31.0 to 132.0 mg Zn kg^?1. The concentrations of exchangeable and carbonate‐bound fractions of the metals depended mainly on the pH, and those of organic matter‐bound, oxides‐bound, and residual forms of the metals were clearly controlled by their total concentrations in the soils. Extractable fractions may be preferable to total metal content as a predictor of bioconcentrations of the metals in both old and mature tea leaves. The metals in the tea leaves appeared to be mostly from the exchangeable fractions. The amount of available metals extracted by 0.01 mol L^?1 CaCl₂, NH₄OAc, and DTPA‐TEA is appropriate extractants for the prediction of metals uptake into tea plants. The results indicate that long‐term plantation of tea can cause sol acidification and elevated concentrations of bioavailable heavy metals in the soil and, hence, aggravate the risk of heavy metals to tea plants.     

Determination of Zinc Phytoavailability in Soil by Diffusive Gradients in Thin Films

Assessment of zinc (Zn) phytoavailability by the newly developed technique of diffusive gradients in thin films (DGT) has started gaining more importance because of some advantages over routine soil extractants. A greenhouse study was conducted to determine Zn phytotoxicity thresholds and the phytoavailability of Zn to sorghum sudan (Sorghum vulgare var. sudanese) grass by DGT, compared with calcium chloride (CaCl₂) extraction. Treatments were five Zn levels and two soil pH (6.5 and 6). To obtain various amounts of Zn phytoavailability, soils having two different pH values were amended with zinc sulfate (ZnSO₄) at rates of 0, 150, 300, 600, and 1200 mg Zn kg^?1. Control soil (pH = 6.5) was treated with predetermined elemental sulfur to create different soil pH values (6). Shoot and root Zn concentrations ranged from 27 to 827 mg kg^?1 and 101 to 2858 mg kg^?1, respectively. In general, the Zn concentrations in shoots and roots were increased by increasing Zn concentrations and soil pH. Increasing applied Zn to soil decreased the plant biomass yield and increased adsorption of Zn by DGT. Calcium (Ca) to Zn ratios for all treatments except controls were <26 for shoots and <13 for roots. The CaCl₂‐extractable Zn and effective concentration (C_E) correlated well with plant Zn concentration. A critical shoot Zn concentration for 90% of the control yield was chosen as an indicator of Zn toxicity. The performance of DGT, CaCl₂ extraction, Ca/Zn ratio and plant Zn concentrations were similar for assessing Zn phytoavailability.     

Phosphorus availability to corn from wood ash-amended soils

Wood ash is a residual material produced during biomass burning. In the northeastern United States up to 80 % of the ash is spread on agricultural lands as a liming amendment with the remainder being disposed of in landfills. As well as raising soil pH, wood ash also adds plant nutrients to soil. This study is an examination of the plant availability of the P in 8 different soils amended with one wood ash. Plant availability was assessed by measuring the biomass and P concentration of corn (Zea mays) L.) plants grown in the greenhouse for 28 d in soil amended with either CaCO₃ (control), wood ash to supply 200 mg kg^?1 total P, or monocalcium phosphate (MCP) to supply 200 mg kg^?1 total P and CaCO₃. Both corn growth and P uptake were highest in the MCP treatments, intermediate in the wood ash treatments, and lowest in the controls for all soil types. The soil property which seemed to have the greatest influence on P availability was pH buffer capacity. The soils with the greatest capacity to buffer OH additions also tended to exhibit the greatest absolute P uptake from wood ash-amended soils and the greatest P uptake relative to that from MCP-amended soils. The ability of soil test extractants to predict uptake of P in the three soil treatments was examined. A buffered ammonium acetate extradant overestimated P availability in the ash-amended soils relative to the MCP-amended soils. An unbuffered, acid, fluoride-containing extract provided a measure of P levels that was consistent with P uptake from all soil treatments. In this study the predictive relationship was as follows: P uptake = 0.017× (Bray P, mg kg^?1) + 1.19; r = 0.81.     

Determination of DTNB-reactive sulphhydryl groups in soil humic acids: their enrichment in humic acids from volcanic acid soils

Thirteen acid soils were collected from typical volcanic regions in Japan (S content: 0.9–4.1, mean = 2.2g kg^?1; pH (H₂O): 2.81–3.93, mean = 3.33), as well as nine reference soils (S: 0.6–1.7, mean= 1.1 gkg^?1; pH(H₂O): 4.10–4.74, mean = 4.47). Humic acids were extracted from the soils separately with 0.1 M NaOH and precipitated by acidification (pH = 2, HCl). After purification, the humic acids were subjected to colorimetric analysis using a DTNB reagent [5,5′-dithiobis(2–nitrobenzoic acid] for the active -SH group. Since humic acids have significant absorption at 4I2 nm, the coloured compound (5–mercapto-2–nitrobenzoic acid) was separated from the humic acids by ultrafiltration or solvent extraction prior to the colorimetric measurement. Humic acids also caused discoloration of the coloured compound when they coexisted in the reaction solutions. Thus, the reproducible determination of -SH was accomplished by employing a standard addition technique (-SH standard: cysteine). Although -SH contents obtained by the ultrafiltration method were considerably higher than those by the solvent-extraction method, probably due to the denaturation of humic acids by the higher buffer concentration used in the ultrafiltration method, they correlated well with each other. The humic acids from acid soils contained apparently higher concentrations of -SH (120–510, mean = 270mg S kg^?1 by the ultrafiltration method; 8–110, mean = 38mg S kg^?1 by the solvent-extraction method) compared to those from reference soils [20–260, mean = 90mg S kg^?1 by the former; not detectable (<5)-34, mean = 11 mg S kg^?1 by the latter]. This -SH enrichment in the humic acids from acid soils may result from the degradation and subsequent humification of S-rich debris of plants and micro-organisms and/or direct incorporation of volcanic acid gas (H₂S) into the humic acids.     

Effects of glucose and rhizodeposits (with or without cysteine-S) on immobilized-35S, microbial biomass-35S and arylsulphatase activity in a calcareous and an acid brown soil

Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass‐S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose‐C and artificial rhizodeposit‐C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg^?1 soil) to the two soils and then incubated with Na₂³⁵SO₄ for 1 week prior to analysis. The percentages of ³⁵S immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine‐containing rhizodeposit, the percentages of ³⁵S immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine‐containing rhizodeposit additions showed no significant correlation between immobilized‐³⁵S and microbial biomass‐³⁵S, suggesting that microorganisms immobilized cysteine‐S preferentially instead of ³⁵S from the tracer (Na₂³⁵SO₄). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass‐³⁵S (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit‐C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p‐nitrophenol kg^?1 soil hour^?1 in the calcareous soil and of 27.0 mg p‐nitrophenol kg^?1 soil hour^?1 in the acid brown soil.     

Predicting potassium fertilizer requirement using exchange isotherm approach in relation to soil characteristics

Determining potassium (K) fertilizer requirement using sorption isotherms is considered more accurate than conventional soil K tests. A total of 59 surface soil samples were used to establish K exchange isotherm. To evaluate K requirement sorption test, a glasshouse experiment using perennial ryegrass (Lolium perenne, cv. Roper) was carried out on 10 soil samples. The experiment was laid out as a completely randomized design with four replications and four K levels (K₀, K₂₀, K₄₀, K₈₀). Concentrations of K in solution established by adding K in the pots estimated from the sorption curve ranged from 20 to 80 mg K l^?1 including check treatment (no K). Dry matter yield of ryegrass in most soils approached maximum as adjusted K levels were increased to 20 mg K l^?1. The amounts of K required to bring the soils to 20 mg l^?1 in soil solution varied among soils and ranged from 99 to 399 mg kg^?1, on average 205 mg kg^?1 soil. It was found that a useful regression model for the prediction of standard K requirement (K₂₀) included the combination of plant available K extracted by NH₄OAc (Av-K) and clay content: K₂₀ = ?41 ? 0.63 Av-K + 9.0 Clay (R² = 0.61, p < 0.001, n = 59).     

Determination of silver in soils by atomic absorption spectrometry

A method for the determination of Ag in soils using atomic absorption spectrometry is described. The method involves the extraction of Ag from soil by boiling with 6 M HC1 followed by separation of the extracted Ag into methylisobutylketone (MIBK) using sodium N, N-diethyldithiocarbamate (DDTC) as a complexing agent. Silver is determined in the MIBK by direct aspiration into a flame atomic absorption spectrophotometer. The detection limit (S/N=2) for this method is 0.0001 mg L^?1 for aqueous solution and 0.002 mg kg^?1 for soil. The Ag content of even unpolluted soils can be determined by this method. The determination of Ag using this method was shown to be unaffected by the presence of various ions in the soil. The method was able to recover nearly 100% of Ag added to soil and approximately the same amounts of soil Ag were determined using this method as with HF-H₂SO₄ decomposition. For 3 reference soils of the Canadian Certified Reference Materials Project (CCRMP), the Ag values obtained by this method were the same as the values determined by Ebarvia et al. (1988). The amounts of Ag in the soils sampled in the Ichi River basin and the Ichi River sediments were determined using this method. This area has been polluted by Cd, Cu, Pb, and Zn discharged from the Ikuno Mine and Smelter. The Ag values ranged from 0.27 to 6.89 mg kg^?1 which were much higher than the values of the unpolluted soils.     

Geochemistry of Manganese in Neutral to Alkaline Soils of Punjab,Northwest India and Its Availability to Wheat and Rice Plants

Manganese (Mn) release in 18 soil–water suspensions after their equilibration for 24 and 240 h periods at 25°C was studied in a laboratory experiment. Total dissolved Mn released into the soil solution was observed to increase from a range of 0.03–0.41 mg L^?1 (mean = 0.13 mg L^?1) to a range of 0.45–44.44 mg L^?1 (mean = 22.40 mg L^?1) with the increase in incubation periods from 24 to 240 h, respectively. The increase in Mn released was observed to be related with the redox potential (pe) induced by incubation conditions. After 24 h of equilibration period, pe of soil–water suspension ranged from ?1.75 to 0.77 (mean = ?0.24). Increasing the incubation period to 240 h, pe of soil–water suspensions declined in the range of ?4.49 to ?2.74 (mean = ?3.29). Laboratory results of redox pe and corresponding dissolved manganese concentrations of some soil–water equilibrated systems were compared with the leaf Mn content in wheat and rice plants grown in the fields, from where soil samples were collected for laboratory experiment. These results demonstrated that decline in pe due to longer equilibration period (240 h) of soil–water systems in the laboratory experiment or keeping standing water for a couple of weeks in the fields for cultivation of rice crop results in higher release of Mn and eventually its higher uptake in rice than in wheat plants. Leaf manganese content in rice ranged from 94 to 185 mg kg^?1, which was markedly higher than its range from 25 to 62 mg kg^?1 found in the wheat grown at 10 different sites. Pourbaix diagrams were drawn for different soil–water systems containing carbonate, phosphate, or sulfate along with manganese. The presence of carbonate and phosphate anions along with manganese oxides minerals in the soil–water systems of all soils results in its precipitation as MnCO₃ and MnHPO₄, respectively, in both oxidized and reduced soil field environment. In Punjab, wheat and rice crops are generally cultivated on soils heavily fertilized with P fertilizers. The presence of phosphate anion with manganese oxides minerals in the soil–water systems of all soils results in the precipitation MnHPO₄ in both oxidized and reduced soil field environment. Thus, in P-fertilized soil, MnHPO₄ compound is even more predominant than aqueous Mn²⁺ and its solubility actually controlled the availability of Mn²⁺ to plants.     

Sequencing Zerovalent Iron Treatment with Carbon Amendments to Remediate Agrichemical-Contaminated Soil

Agrichemical spills and discharges to soil can cause point-source contamination of surface and ground waters. When high contaminant concentrations inhibit natural attenuation in soils, chemical treatments can be used to promote degradation and allow application of treated soils to agricultural lands. This approach was used to remediate soil containing >650 mg atrazine, >170 mg metolachlor and >18,000 mg nitrate kg^?1. Results indicated a decrease in metolachlor concentration to <1 mg kg^?1 within 95 days of chemical treatment with zerovalent iron (Fe⁰, 5% w/w) and aluminum sulfate (Al₂(SO₄)₃, 2% w/w) but after one year >150 mg atrazine and >7000 mg nitrate kg^?1 remained. Laboratory experiments confirmed that subsequent additions of sucrose (table sugar) to the chemically pretreated soil promoted further reductions in atrazine and nitrate concentrations. Field-scale results showed that adding 5% (w/w) sucrose to windrowed and pretreated soil significantly reduced atrazine (<38 mg kg^?1) and nitrate (<2,100 mg kg^?1) concentrations and allowed for land application of the treated soil. These results provide evidence that zerovalent iron in combination with Al₂(SO₄)₃ and sucrose can be used for on-site, field-scale treatment of pesticide- and nitrate-contaminated soil.     

Laboratory Assessment of Nostoc 9v (Cyanobacteria) Effects on N2 Fixation and Chemical Fertility of Degraded African Soils

The potential of Nostoc 9v for improving the nitrogen (N)₂–fixing capacity and nutrient status of semi‐arid soils from Tanzania, Zimbabwe, and South Africa was studied in a laboratory experiment. Nostoc 9v was inoculated on nonsterilized and sterilized soils. Inoculum rates were 2.5 mg dry biomass g^?1 soil and 5 mg dry biomass g^?1 soil. The soils were incubated for 3 months at 27 °C under 22 W m² illumination with a photoperiod of 16 h light and 8 h dark. The moisture was maintained at 60% of field capacity. In all soils, Nostoc 9v proliferated and colonized the soil surfaces very quickly and was tolerant to acidity and low nutrient availability. Cyanobacteria promoted soil N₂ fixation and had a pronounced effect on total soil organic carbon (SOC), which increased by 30–100%. Total N also increased, but the enrichment was, in most soils, comparatively lower than for carbon (C). Nitrate and ammonium concentrations, in contrast, decreased in all the soils studied. Increases in the concentration of available macronutrients were produced in most soils and treatments, ranging from 3 to 20 mg phosphorus (P) kg^?1 soil, from 5 to 58 mg potassium (K) kg^?1 soil, from 4 to 285 mg calcium (Ca) kg^?1, and from 12 to 90 mg magnesium (Mg) kg^?1 soil. Positive effects on the levels of available manganese (Mn) and zinc (Zn) were also observed.     

Potassium fixation of some calcareous soils after short term extraction with different solutions

This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl₂, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl₂ and HCl (137 vs. 111 and 113 mg kg^?1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg^?1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution.