JWSS - Journal of Water and Soil Science

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  Organic fertilization has been practiced in Iran due to the shortage of soil organic matter. In recent years, attention has been payed to the organic fertilizers because their commercial production has recently started and demands for their application have increased. The objectives of this study were to investigate the effects of organic fertilizer type, rates and times of application on the N mineralization potential (NMP) in a calcareous soil (fine loamy, mixed, thermic, Typic Haplargid) in Isfahan region. The soil samples were collected from a previousely established field experiment. The experiment design was split plot with three replications. Each main plot was split into subplots receiving 1, 2 and 3 annual consecutive applications of cow manure and sewage sludge at the rates of 0, 25 and 100 Mg ha^-1. The soil samples were taken from 0-15 cm depth, 6 months after the third application of the organic fertilizers. Nitrogen mineralization potential was measured by a long-term leaching-incubation procedure. Results indicated that NMP was similarly affected by cow manure and sewage sludge. Nitrogen mineralization potential in the treatments which received 100 Mg ha^-1 organic fertilizers, was 4 and 1.7 times greater than that of control and 25 Mg ha^-1 treatments, respectively. A significant increase was also observed in NMP in the treatments which received different times of application. The NMP in the three-year applied treatments was 5, 2.5 and 2.1 times greater than that of control, two- and one-year applied soils. Significant correlations were observed between NMP and corn yield (r=0.531**) and corn N uptake (r=0.568***). The product of NMP and N mineralization rate constant was also significantly correlated with corn yield (r=0.710***) and corn N uptake (r=0.734***). Different patterns were observed between the responses of total N and NMP in the treated soils.

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  Soil properties play a significant role in phosphorus (P) sorption. Information about P sorption is limited in Hamadan soils. The objectives of this research were to study the P sorption in twelve soils of Hamadan, assess the capability of different kinetics equations describing P sorption and correlate the P sorption characteristics with the soil properties. The soils were fertilized with 200 mg P kg^-1 as KH₂PO₄. Fertilized soil was incubated at 25±1 ˚C for 2520 h. The incubated samples at 1, 2, 4, 8, 24, 48, 72, 96, 120, 144, 168, 240, 336, 504, 672, 840, 1008, 1176, 1344, 1512, 1680, 1848, 2016, 2186, 2352, 2520 hours after P addition were extracted by two extractants. The soil phosphorous was extracted by 0.5 M sodium bicarbonate (Olsen solution) or by AB-DTPA. Zero order, first order, simplified Elovich equation, parabolic diffusion law and power function equations were fitted on the experimental data. The results showed that P sorption was initially rapid followed by a slow phase. The amounts of P sorption after 2520 h, ranged from 162.7 to 253.84 and 193.37 to 235.11 mg kg^-1 for the Olsen and AB-DTPA methods, respectively. Regarding to higher determination coefficient and lower standard error, Elovich and power function equations were suitable to describe P sorption kinetics. Rate constants of the Elovich and power function equations ranged from 0.036 to 0.49 and 0.157 to 0.304 mg kg^-1h^-1 for Olsen and from 0.074 to 0.76 and 0.184 to 0.382 mg kg^-1h^-1 for AB-DTPA. The trend of the data implied a discontinuity in slope at 336 h, as two region models might better satisfy the trend of the data in to two range ( 0 to 336 and 336 to 2500 hr). At the first section, the P sorption could be describe by simplified Elovich, power function and parabolic diffusion law kinetics equations. Rate constants in these equations varied among the soils. At the second section, kinetics equations could not describe the P sorption. The results of this study indicated that P sorption rates varied among the soils and Fe , Al and CaCo₃ affected on P sorption kinetics.

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  Phosphorus (P) after nitrogen limits agricultural production in most region of the world. Information about P release rate is limited in Hamadan soils. The objective of this research was to study P release in 10 soils from Hamadan province by successive extraction with 0.5 M NaHCO over a period of 1752 h and the correlation of P release characteristics with soil properties and corn plant (Zea mays) indices. The results showed that soil P release began with a fast initial reaction, followed by a slow secondary reaction until 1752 h. The amounts of soil P released after 1752 h ranged from 309 to 586 mg kg^-1. The cumulative P release was evaluated by six kinetics equations. Statistical analysis showed that phosphorus release kinetics were described by parabolic diffusion law, first order and power function equations. The correlation study indicated that soil P release coefficients such as rate constant of first order, parabolic diffusion law, power function equations, P released after 168 and 1752 h were significantly correlated with some soil properties such as Olsen-P, calcium carbonate equivalent, sand and silt. The correlation studies between plant indices and constants of kinetics equation showed that rate constant of first order equation was not significantly correlated with plant indices. Equation constants of parabolic diffusion law, power function and P release after 1752 h were significantly correlated with plant indices. The results of this research indicated that release rate of P is different in soils and is an important factor in supplying available P to plants.

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In Iran, no research has yet been performed on potassium release from feldspar in comparison with that from muscovite. The objective of this research was to compare potassium release kinetics of these minerals as influenced by organic and inorganic extractants using successive extraction method. The experiment was carried out in a completely randomized design with a factorial combination. Treatments consisted of three kinds of K-bearing minerals (Muscovite, and Yazd and Ward feldspars), three extractants including CaCl2, oxalic and citric acids of 0.01 M concentration and 6 times of extraction (1, 2, 8, 24 and 48 hours). The results indicated that the potassium release from muscovite was 6-8 times higher than that from feldspars. The type of extractant significantly affected potassium release. Potassium release by organic extractants was 2.5-3 times higher than that by CaCl2 as an inorganic extractant. Different kinetic equations showed that power function, parabolic diffusion and first order equations adequately described K release whereas Elovich equation did not. Among the three equations, power function equation was selected as the best model describing K release from the minerals. Based on the selected kinetic equations, it seems that potassium release from K-bearing minerals is controlled by diffusion process.

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Rate of nonexchangeable K release can significantly influence K availability. Kinetics of K+ release was studied by extraction using 0.01 M CaCl2 in 12 surface calcareous soils of Kohgilouye Province. Results showed that cumulative K release ranged from 89.9 to 460.9 mg kg-1(Average 195.4 mg kg-1). Calcium carbonate, nonexchangeable K, cation exchange capacity and mica showed a significant correlation with K release. Maximum of potassium release was observed in Alfisols, probably because of high amount of clay content and the clay mineral of mica. The amount of K release was in the following order: Alfisols> Entisols> Inceptisols. Elovich, parabulic diffusion and power function equations could reasonably describe the K release kinetics. Fitting the data to these equations indicated that release of K is controlled by diffusion process.

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The aim of this study was to assess the kinetics of nonexcheangable potassium release in surface and subsurface soil horizons, using organic and inorganic extractions, in Kohgilouye-va-Boyerahmad Province. Kinetics of K⁺ release was studied by successive extractions of K from 64 selective surface and subsurface soil samples, using 0.01 M CaCl₂ and 0.01 M oxalic acid, for 1948 h, with two replicates. Nonexchangeable K⁺ release was fitted by Elovich, Pseudo-first order, Power function and Parabolic equations. Result showed that the average nonexchangeable K⁺ released (extracted by 1M HNO₃) was 356 mg/kg, while those extracted by CaCl₂ and oxalic acid after 1948 h were only 58% and 52% of the total amount of nonexchangeable K⁺ of the soils, respectively. In all soil samples, nonexchangeable K⁺ released by oxalic acid was less than that released by CaCl2, due to the high buffering capacity resulting from high carbonates in the soils. Potassium release rate in Elovich and Parabolic equations were significantly correlated with non-exchangeable potassium and some physical and chemical characteristics.  Based on high Coefficients of determination (r²) and low Standard errors (SE), Elovich, Power function, First order and Parabolic equations were selected as the best equations for prediction of K⁺ release from the soils.

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