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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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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