Soil science
Z. Sokhanvar Mahani; N. Boroomand; M. Sarcheshmeh Pour
Abstract
IntroductionPhosphorus (P) is one of the most important elements necessary for plant growth and production of agricultural products. In calcareous soils, phosphorus deficiency is a general issue due to high pH, high soil calcium carbonate content, lack of organic matter and moisture. Phosphorus absorption ...
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IntroductionPhosphorus (P) is one of the most important elements necessary for plant growth and production of agricultural products. In calcareous soils, phosphorus deficiency is a general issue due to high pH, high soil calcium carbonate content, lack of organic matter and moisture. Phosphorus absorption capacity depends on different soil reactions such as: adsorption, sedimentation, stabilization and release. The speed and amount of plant available P depends on the soil reactions. Studying the kinetics of P release from soil is a good indicator to check the status of P uptake by plant. The kinetics of P release in soils is a subject of importance in soil and environmental sciences. The aim of this research was to investigate the kinetics of P release and derive the most suitable equation to describe the release of P from a calcareous soil when subjected to the acidification of rock phosphate and the addition of vermicompost. Materials and MethodsIn order to investigate the ability of acidified rock phosphate and vermicompost in P release, an experiment was conducted with 2 replications on a light-textured soil with low OC and Olsen-P (1.2 mg/kg). One hundred grams air dried calcareous soil was transferred into special containers and 5 treatments including: 1- control (soil), 2- rock phosphate, 3- acidified rock phosphate (20 CC nitric acid 0.1 N and 5 g rock phosphate), 4- vermicompost, and 5- acidified vermicompost (20 CC nitric acid 0.1 N and 5 g vermicompost) were applied. The treatments incubated two weeks in 20±2℃ temperature. The Kinetics of P release was studied by adding 20 mL of 0.5N NaHCO3 to, one gram of air dried treatments. Extraction times were considered to be 0.25 h to 256 h (in 11 times) based on the time of adding the NaHCO3 extractant until filtering. After adding the extractant, the samples were shaken and centrifuged. After filtering, the concentration of released P in samples were determined by spectrophotometer (Model: CE 292 Series2, ultraviolet). For higher accuracy in the measurements, acid-washed containers were adjusted based on the amount of soil moisture which was dried in the oven (105℃). Finally, the P release data were fitted to different kinetic equations. The effect of different fertilizer treatments on P release in specified times and then kinetics parameters were investigated and compared with the control. Results and DiscussionAddition of acidified and non acidified rock phosphate and vermicompost increased the amount and speed of P release in the calcareous soil. Six kinetic equations were fitted to describe the release of P in the period of 0.25 h to 256 h from the soil to evaluate the effect of the treatments. The highest release of P was in vermicompost and acidified rock phosphate treatment, which were an organic fertilizer and a source for preparing phosphate fertilizers. To describe the release rate, kinetic equations were used. The best equations were chosen by highest coefficient of determination (R2) and the least of standard error (SE). The zero, first, second order equations could not describe the release of P in the studied calcareous soil. The R2 value decreased from the zero to second order equation. The simplified Elovich equation described well the release of P from the soil with the average R2 of 0.79 and with the average SE of 0.4. Comparison of the average effect of the studied treatments with the control showed that the acidifed vermicompost and rock phosphate treatments increased the capacity and speed of P release compared to the control. On the other hand, acid addition has increased the capacity and speed of P release in the calcareous soil. ConclusionThe findings indicated an initial rapid release of P, which then decreased over time. Notably, the application of vermicompost and the acidification of the soil with rock phosphate resulted in a pronounced and accelerated release of P. Generally, organic fertilizer treatments exhibited a higher release of P compared to chemical fertilizer treatments. This observation is in accordnce with the findings of the data presented by Ghorbanzadeh et al. (2009), who explored the P release potential of bone meal. Their data demonstrated that the acidification of bone meal accelerated and enhanced P release. To further enhance the practical relevance of these results, it is recommended to conduct this research in the presence of plants.
sanaz ashrafi saeidlou; Mirhasan Rasouli-Sadaghiani; Abbas Samadi; mohsen barin; ebrahim sepehr
Abstract
Introduction: Potassium is one of essential nutrients for plants and its importance in agriculture is well known. Non-exchangeable potassium that is mainly placed with in layers of K-bearing minerals, such as K-feldspar and mica, is considered as an important source of potassium for plant growth in most ...
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Introduction: Potassium is one of essential nutrients for plants and its importance in agriculture is well known. Non-exchangeable potassium that is mainly placed with in layers of K-bearing minerals, such as K-feldspar and mica, is considered as an important source of potassium for plant growth in most soils. Regarding that low molecular weight acids (LMW) play an important role in improving the bioavailability of soil nutrients such as non-exchangeable K (NEK), and the release rate of NEK plays a significant role in supplying necessary K for plants, the purpose of this study was comparison of potassium release kinetic from K-bearing including feldspar, illite as well as phlogopite minerals and choose the best kinetic equation describing potassium release process, influenced by organic as well as mineral extractants.
Material and Methods: The experiment carried out in a completely randomized design with three replications. Experiment factors were including extractant type (0.01 mol l-1 oxalic acid, 0.01 mol l-1 calcium chloride, control (deionized water)), potassium mineral type (feldspar, illite and phlogopite) and incubation time (1, 2, 4, 8, 12, 16, 24, 32, 48, and 64 hours). Elemental composition of minerals identified by Fluorescence spectroscopy device (S4 Pioneer). Used minerals in the experiment including feldspar, phlogopite and illite were ground and filtered through a 230 mesh sieve. In order to remove exchangeable K, samples were saturated by calcium chloride solution (with a ratio of 2:1), after washing with HCl, samples were dried at 105 °C for 48 hours. 100 mg of washed minerals, was weighed carefully and transferred to centrifuge tubes. Then 20 ml of each of extractants (oxalic acid and calcium chloride 0.01M) was added to the tubes. After 15 minutes shaking, tubes containing a mixture of minerals-extractants was carried out in a controlled incubation chamber for periods of 1, 2, 4, 8, 12, 16, 24, 32, 48 and 64 hours at 25 °C. After each period, samples were centrifuged at 3000 rpm for 10 minutes and filtered using Whatman paper (No. 41). pH and potassium concentration of samples were measured by pH meter and flame photometer, respectively. Data related to potassium release was fitted by zero order, first order, second order, power function, parabolic diffusion and ellovich equations.
Results and Discussion: Results showed that the effect of extractant type was significant on kinetic of potassium release, so that potassium release amount in samples extracted with oxalic acid was 1.48 and 2.35 times higher than samples extracted with calcium chloride and control (deionized water), respectively. Also, different minerals released various amounts of potassium. K release from phlogopite was 1.99 and 2.95 times higher than feldspar and illite, respectively. The maximum potassium concentration (440 mg kg-1) was seen in phlogopite which was extracted with oxalic acid. So that, amount of potassium in this treatment was 3.15 times higher than control one. Furthermore, the effect of extraction time on K release was significant. So that, at the beginning of incubation period the release of potassium by different extractants was more, but its amount decreased over time and finally continued with a constant speed. Kinetic equation fitting showed that zero order, first order, power function, parabolic diffusion and ellovich equations are able to describe potassium release but second order model cannot justify it. Among these five equation, the power function and parabolic diffusion equations with the maximum coefficient of determination (R2) and the least standard error of estimate (SE), could reasonably describe the K release kinetics, so they are introduced as the best models for data fitting. The slope (b) and interception (a) of ellovich equation indicate interlayer and initial K release, respectively. Oxalic acid and phlogopite had the most amount of interception, it means that the impact of oxalic acid on initial and interlayer release rate of K in phlogopite, is more effective than calcium chloride.
Conclusions: It is concluded that different factors like mineral and extractant type influence kinetic of potassium release and organic extractant have more ability in extracting non-exchangeable potassium from minerals structure. Also, the adjustment of the results of this study with first order, parabolic diffusion and power function equations suggest that nonexchangeable potassium release from minerals can be affected by diffusion process from the surface of the study minerals, indicating that NEK release rate is controlled by K diffusion out of the mineral interlayer.
