JWSS - Journal of Water and Soil Science

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Twenty-two surface soil samples (0-20 cm) from Fars province were extracted by five extractants (i.e., DTPA, 1.5 M NH₄H2PO₄, 0.1 NH₃PO₄, 0.05 MNa2EDTA, and 1% Na₂EDTA) and used in a 7-week greenhouse experiment which was a 22 × 3 factorial with 22 soils (clay 16-63% pH 7.8-8.2 electrical conductivity 0.32-1.78 dS m^-1 calcium carbonate equivalent 28-63% organic matter 1.1-4.9% cation exchange capacity 9-27 cmol kg^-1 and DTPA-extractable Mn 4-24 mgkg^-1), 3 levels of applied Mn (0, 10, 20 mg Mn kg^-1 as manganese sulfate), 3 replications, and soybean [Glycine max (L.) Merr., cv. Williams]. Application of Mn significantly increased top dry weight by 4 to 104%, averaging to about 12% over the control. But the increase in Mn concentration was not significant. Total Mn uptake also significantly increased but the apparent recovery of the applied Mn was very low (i.e., 0.05%). Soil pH, calcium carbonate equivalent, and clay content were found to be the properties influencing the extractability of Mn. The DTPA-extractable Mn, alone (with a critical level of 13 mg Mn kg^-1) or along with some soil properties, was the only form of Mn that could reasonably predict the plant responses.

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Different Extractants have been proposed to assess available P in different soils. Olsen method is widely used to determine available P in calcareous soils of Iran. However, it has not been compared adequately with other extractants. The main objective of this experiment was to compare this procedure with some other methods. Thirty nine calcareous soil samples from Fars Province with different physico-chemical characteristics were examined for available P by nine extractants. Furthermore, the effects of four P levels (0, 50, 100, 200 µgPg^-1 soil) on growth, P concentration and P uptake by corn were studied in a greenhouse experiment using 20 soil samples. The results indicated that the amount of extractable P decreased in the order, anion-exchange resin > Colwell > Morgan > Olsen > Bray P₁ (1:50) > Soltanpour & Schawb > EDTA > Bray P₁ (1:7) > Water. The amounts of P extracted by all methods, except that by Bray method, showed significant correlation. However, the correlation coefficients between resin, Olsen, Colwell and water were higher than the others. Regression analysis showed that P extracted by all methods, except Bray, was affected by organic matter and native Zn. Moreover, P removed by Bray method was decreased with an increase in calcium carbonate equivalent. Correlation between top dry weight, relative growth and P uptake and P extracted by resin, Colwell, Olsen and water were highly significant. Although the correlation coefficients between growth parameters and P extracted by Morgan and Soltanpour & Schawb were significant, they were of lower magnitude. Plant phosphorus concentration showed significant correlation with P extracted by Olsen and Colwell methods. In general, resin, Olsen and Colwell methods seem to be appropriate extractants for available P in the present study. However, to select the appropriate extractants, more research is needed.

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Evaluation of nutrient status in soil is important from nutritional, environmental and economical aspects. Potassium is a very important plant nutrient not only because of its large demand, but also because of its important physiological and biochemical functions in plant. In order to evaluate K availability and common K extractants in the central region of Isfahan Province, surface soil samples from 26 important soil series were taken, out of which 16 soil samples were selected for further study based on their ammonium acetate extractable K and texture. Available K was extracted from the soil samples by NH₄OAC (4 methods), CaCl₂ (2 methods), NaCl (2 methods), NaOAC, AB-DTPA, Mehlich I, Mehlich III, Morgan-Wolf and HNO₃. A green house experiment using corn (Zea mays L.) variety Single-cross 704 as the test plant with 2 treatments (zero and 150 mg/kg K) and three replications was performed with the 16 selected soils to correlate K uptake with K extracted by different extractants.

 From XRD analysis, the dominant clay mineral was found to be Illite. Based on the amount of potassium extracted by these extractants from the soils the extractants used in this research may be divided into three groups: relatively weak extractants including CaCl₂, Mehlich I and Morgan-Wolf relatively strong extractants including NH₄OAC, NaCl (2N), Mehlich III, AB-DTPA, NaOAC and NaCl (1N), the strongest and weakest extractants in this group were NH₄OAC and NaCl (1N), respectively and finally, a very strong extractant which includes only HNO₃. In each group, the quantities of extracted K showed high correlation with each other. A high and significant correlation was observed between the quantities of K extracted by NH₄OAC, AB-DTPA and HNO₃. The amount of K extracted by 2N NaCl, 1N NaOAC, 1N NH₄OAC, and AB-DTPA was significantly correlated with K taken up by plant and its K concentration. 2N NaCl and 1N NaOAC were selected as the most suitable extractants for K based on their high correlation coefficients with plant uptake (0.79** and 0.72**, respectively) and K concentration in plant (0.86** and 0.85**, respectively). Yield, relative yield and plant response were not significantly correlated with K extracted by different extractants indicating that available K of the selected soils was not a limiting factor for corn growth therefore, it was impossible to determine the critical level of K for corn by the selected extractant.

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Nitrogen is usually the most limiting nutrient for crop production. Thus, N fertilizer is widely used by farmers. Moreover, Mn deficiency in some calcareous soils of Iran with high pH has been reported. Therefore, the addition of nitrogen and manganese to achieve the optimum yield is necessary. The objective of this study was to evaluate the effect of N and Mn applications on the availability of some soil nutrients under wheat (Triticum aestivum L.), corn (Zea mays L.), and spinach (Spinacia oleracea L.) plants in greenhouse conditions. In a factorial test, five levels of N (0, 50, 100, 200 and 400 mg/kg soil as NH₄NO₃) and three levels of Mn (0, 15 and 30 mg/kg soil as MnSO₄) in a completely randomized design with four replication were applied. Corn, wheat and spinach varieties were sc₇₀₄ Falat and Spinacea spp., respectively. After eight weeks, total N content and DTPA-extractable Mn, Fe, Zn and Cu of soil were measured.

 The results indicated that N and Mn applications increased Mn-extractable of soil in three cultures but didn’t affect the soil total N. Nitrogen application in corn increased available Fe in soil. Mn application decreased extractable Zn and Cu of soil in wheat and soil extractable Cu in corn.

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Iron oxide-coated strips (P_i) can serve as a sink to continuously remove P from solution. In this way, probably, P extraction is analogous to P absorption by plant root. The objective of this study was to evaluate the iron oxide-coated paper strips to estimate the availability of soil P of corn (Zea mays) grown under greenhouse conditions in some soils of Hamadan Province. Sixteen soil samples with different physico-chemical properties were examined for available P by Olsen, Colwell, Mehlich1, 0.01 M CaCl₂, AB-DTPA, 0.1 M HCl methods and two (P_i1, P_i2) P_i methods. Furthermore, the effects of two P levels ( 0 and 250 mg P Kg^-1 soil) on the plant responses (P uptake, P concentration, and relative yield) were studied in the greenhouse experiment using 12 soil samples. The results showed that the amount of extractable P decreased in the order: 0.01 M Cacl₂ < P_i2 < AB-DTPA < P_i1 < Olsen

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Garlic (Allium Sativum) is a major crop in Hamadan Province. However, adequete information on K status in this region is not available and no suitable extracting solution can yet be introduced. This experiment was carried out to determine the available K level in 10 soils from Hamadan region. The treatments included two K levels (0 and 200 mg K /kg soil as K₂SO₄) and 10 Soils in a factorial experiment in a randomized block design with three replications. The results indicated that K application increased yield, K concentration and K uptake of garlic. On the basis of K extracted, the extractants were classified in 4 groups, and the correlation between extractants in each group was significantly high. The correlation studies showed that NH₄OAC, AB-DTPA and boiling 1 M HNO₃ can not be used as an available K extractant. The correlation of other extractants with relative yield, plant response and additional uptake were significant. Therefore, these extracting solutions can be used as available K extractant. Potassium critical levels by extractants were also determined using Cate-Nelson method. Potassium critical levels for 90 percent relative yield were 131, 50, 46, 184, 163,203, 202, 41, 50 and 31 mg kg^-1 for Mehlich 1, 0.002 M SrCl₂, 0.01 M CaCl₂, 0.1 M BaCl₂, SrCl₂ + Citric acid, Sodium acetate, 0.1 M HCl, 0.05 M HCl, 0.025 M H₂SO₄ and distilled water, respectively.

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Hamadan province is one of the most important alfalfa (Medicago sativa) producing regions in Iran. However, little is known about P status in this region and no suitable extraction method has yet been introduced. This experiment was carried out to determine the available phosphorus by nine chemical extractants in some soils of the Hamadan region. The treatments consisted of 15 soils and 2 P levels (0 and 200 mg P kg^-1 as Ca(H₂PO₄)₂.H₂O ) in a factorial experiment in a randomized design with three replications. Alfalfa plant were harvested in three cutting. The results indicated that the amount of extractable phosphorus decreased in the following order: Collwell>Bray 2>0.1 N HCl>Bray 1>Olsen>AB-DTPA>Mehlich 1>Mehlich 2 > 0.01 M CaCl₂ The amounts of P extracted by all methods except that by 0.01 M CaCl₂ method, showed significant correlation. The results of correlation studies showed that in the first cutting, Collwel method, in the second cutting AB-DTPA, Olsen, Collwel, Bray 1, Bray 2 and Mehlich 2 and in the third cutting, AB-DTPA, Olsen, Collwel, Bray 1, and Mehlich 2 methods seems to be suitable extractants for assessing available P of soils in Hamadan province.

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Sorghum (Sorghum bicolor L. Var. Speedfeed) is a major forage crop in Birjand Region, and phosphorus (P) plays an important role in its nutritional value. During a field campaign, eighty soil samples from the region were collected and analyzed. Among them, 24 samples varying in physico-chemical properties and available P were selected. Five extractants were used for measuring sorghum available P as follows: 1) 0.5 M NaHCO3, pH=8.5, shaken for 30 minutes (Olsen's method), 2) 0.5 M NaHCO3, pH=8.5, shaken for 16 hours (Colwel's method), 3) 0.0025 M Na2-EDTA, pH=7 (EDTA method), 4) 1 M NH4HCO3, 0.005 N DTPA (Soltanpour and Schwab's method), and 5) Water (Paauw's method). A greenhouse experiment using a completely randomized design was carried out with 24 soil samples, two treatments of 0 and 90 mg P/kg soil and three replicates. Results indicated that all five extractants are suitable for prediction of sorghum available phosphorus, but Olson and Paauw's methods are preferable. The results also show ed that the critical levels of soil phosphorus for sorghum by Olsen, Colwel, EDTA, Soltanpour and Schwab and Paauw methods are 17, 24, 14, 7 and 2.5 mg P/kg soil, respectively. Statistical analysis indicated that soil pH, clay percentage and organic carbon significantly affected sorghum available phosphorus.

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Determination of carbohydrates in soil requires prior extraction and numerous extraction methods were suggested for this purpose. Three methods and five extractants were applied in order to extract carbohydrate fraction in three soil types forest, clayey and saline soils. The extraction methods were: 1) shaken in a plane rotary shaking machine for 16 h 2) heated in steam-bath for 2.5 h and 3) heated in oven for 24 h and extractants included 1) 0.5 M HCL, (2) 0.25 M H2SO4, 3) 0.5 M H2SO4, 4) 0.5 M K2SO4 and 5) distilled water. Carbohydrate content in soil was measured by phenol-sulphuric acid method. The addition of phenol to the extracted solution of HCl caused to milky precipitation. Therefore, this extractant can not be used for carbohydrate extraction in the phenol-sulphuric acid spectroscopic method. The results showed that in all soils and in the shaker extraction method, carbohydrate content was lower than in the oven and steam-bath extraction methods. In the forest and saline soils, the extracted carbohydrate content was not significantly different among the oven and steam-bath methods. For the clayey soil, the carbohydrate content was higher in the oven method than that of the steam-bath method. In all soils, the extracted carbohydrate by 0.5 M H2SO4 extractant was greater than those of other extractants. In the forest and saline soils, the extracted carbohydrate by distilled water was lower than those of other extractants. Using steam-bath method (for the forest and saline soils) and oven method (for the clayey soil) with 0.5 M H2SO4 extracted the highest amount of carbohydrates.

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Information about potassium (K) release characteristics in the Chaharmahal-va-bakhtiari soils is limited. In this study, K release kinetics of fifteen calcareous soils was investigated. Soil samples were extracted using successive extractions with 0.01 M CaCl2 and citric acid solutions for 2-2017 h at 25±1 0C. Moreover, soil K was determined using 6 chemical extraction methods. The results showed that released K ranged from 111 to 411 mg kg-1in calcium chloride solution and from 177 to 1199 mg kg-1 in citric acid solution for 2017 h. Amounts of extracted K using any extraction methods were different. Result of kinetics study and chemical methods indicates that K supplying power of the soils is different. A plot of cumulative amounts of released K shows a discontinuity in slope at 168 h. Thus, two equations were applied to the total reaction time (2 to 168 and 168 to 2017 h). Moreover, results showed that release kinetics of K conformed fairly well to parabolic diffusion, simplified Elovich and power function models in two segments in 0.01 M CaCl2 and citric acid. In addition, results showed that correlation between released K by using 0.01 M calcium chloride and citric acid and extracted K using chemical methods was significant. The results of this research showed that kinetic studies and soil testing could be used for evaluating K fertility status of studied soils.

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Rhizosphere is a small zone and has quite different chemical, physical, and biological properties from bulk soil. This research was performed to study the available Zn and its fractions in the wheat rhizosphere and bulk soils by using rhizobox at greenhouse conditions. Total organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and available Zn using 7 chemical procedures and Zn-fractions were determined in the rhizosphere and bulk soils. The results indicated that TOC, DOC and MBC in the rhizosphere were increased significantly (P<0.01). Zn extracted using several chemical extractants (except 0.01 M CaCl2) in the rhizosphere were significantly (p<0.05) higher than in the bulk soils. Also, concentrations of Zn-fractions (except carbonate-associated) in the rhizosphere were significantly (p<0.05) different from concentrations of Zn-fractions in the bulk soils. Results indicated that correlation between uptake index and extracted Zn using DTPA-TEA and Mehlich 3 were significant (p<0.05). Moreover, significant correlation (p<0.05) between uptake index and exchangeable Zn and Zn associated with iron-manganese in the wheat rhizosphere and bulk soils were found. The results of this research illustrated that available Zn and its fractions in the rhizosphere soils are different from the bulk soils. Therefore, application of the rhizosphere soil would be recommended in the study on these properties after planting.

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The ability of different soil tests in predicting soil phosphorus (P) is important in soils amended with municipal sewage sludge. The objective of the present study was to evaluate several chemical extractants to estimate available P for bean growing in 10 calcareous soils amended with municipal sewage sludge from Chaharmahal-Va-Bakhtiari province under the greenhouse conditions. For this purpose, the soil samples were incubated with sludge at a rate of 39-ton sludge ha–1. The amount of available P of the soil samples was determined by Olsen, Colwell, ammonium bicarbonate-DTPA, 0.01 M calcium chloride, BrayІ, ІІ, Mehlich І and ІІ methods. A pot experiment in a completely randomized design was conducted to evaluate the bean plant indices. The results showed that the amount of extractable P with the above methods decreased in the following order: Colwell> Bray ІІ> Mehlich ІІ> Olsen> Ammonium bicarbonate DTPA> Mehlich І> Bray І> 0.01M chloride calcium. The extractable P with 0.01M chloride calcium, Mehlich І, ІІ Colwell and Olsen methods correlated significantly with plant indices (P concentration and P uptake). Thus, mentioned methods could be used to estimate plant-available P in the soils amended with sewage sludge.

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