Potassium Release Rate Research Articles

Integrated interaction between Nano, conventional potassium fertilizer and Zeolite on kinetic K-release from calcareous soil

Calcareous soil suffers from deficiency in available of potassium due to its high contain of CaCO3. So, it is important to increase the availability of potassium. Potassium release rate constant is an important indicator for the ability of soil to supply potassium. A field experiments in sulaimani governorate was conducted to evaluate the effect of soil amendment with natural zeolite at rate of (0 and 2 t ha-1), three levels of Nano potassium fertilizer (0, 5 and 10 kg ha-1), three levels of conventional fertilizer K2SO4 (0, 100 and 200 kg ha-1 K2O) and their interactions on kinetic of potassium release within 55 days. Results revealed that there was significant effect of application Zeolite on cumulative K-release that increased by 13.27 % relative to the control treatment. the application Nano, conventional K fertilizer and their interaction with zeolite at level of 5 kg ha-1 Nano, 200 kg ha-1 K2O and 10 kg ha-1 Nano + 100 kg ha-1 K2O amendment with 2 t ha-1 zeolites increased the cumulative K-release from 33.55 to 35.35 and 42.45 mg kg-1 respectively as a compared with control (24.00 mg kg-1). Kinetic data were best described by parabolic diffusion, power function and Elovich models. The cumulative K-release rate constants for parabolic models indicated that all types of fertilizers applied to soil gave high and significant increase in rate of K release compared to the control treatment.

Decomposition Characteristics, Nutrient Release, and Structural Changes of Maize Straw in Dryland Farming under Combined Application of Animal Manure

Straw and animal manure are major organic waste materials from agricultural ecosystems. Different kinds of animal manure combined with straw (AM-S) may have varying effects on the decomposition, nutrient release, and structural changes of maize straw. Using the Humic Cambisols soil as the experimental area, the straw decomposition characteristics under the co-application of animal manure were studied following the nylon net bag landfill method. The experiment involved four treatments: maize straw only (S), maize straw plus ox manure (SO), maize straw plus chicken manure (SC), and maize straw plus pig manure (SP). The treatments with AM-S accelerated the decomposition of straw and increased the release rate of nutrients and organic components (cellulose, hemicellulose, and lignin). During the 240 days of the study, straw decomposition showed a trend of increasing rapidly in the first stages and then increasing slowly in the latter stages in all the treatments. At 240 d, the straw decomposition rates and carbon release rates of the AM-S treatments were 65.25–71.87% and 64.04–69.35%, respectively. At the end of the experiment, the order for the final release rates of nitrogen (N), phosphorus (P), and potassium (K) was K (93.25–96.56%) > P (42.25–55.08%) > N (40.01–52.23%). Moreover, scanning electron microscopy showed that SP treatment had the highest degree of structural changes of the maize straw compared with the other treatments. The purpose of this study was to screen the effective animal manure that can promote straw decomposition and provide a reference for the rational use of straw and animal manure management. In conclusion, the study suggested that the co-application of animal manure and straw should be adopted in agricultural systems, especially SP treatment, as it was more conducive to promoting the decomposition of maize straw and the release of nutrients.

Familial pseudohyperkalemia induces significantly higher levels of extracellular potassium in early storage of red cell concentrates without affecting other standard measures of quality: A case control and allele frequency study

Familial pseudohyperkalemia (FP) is characterized by an increased rate of potassium leakage in refrigerated red cells and is associated with the minor allele of the single nucleotide polymorphism rs148211042 (R723Q) in the ABCB6 gene. The study aims were to obtain the minor allele frequencies of ABCB6 variants and to measure supernatant potassium accumulation, and other red cell storage parameters, in red cell concentrates (RCC) from carriers of variant rs148211042 under standard blood bank conditions. Whole blood units were collected from 6 FP individuals and 11 controls and processed into RCC in additive solution. RCC were sampled and tested over cold storage for full blood count, extracellular potassium, glucose, lactate, microvesicle release, deformability, hemolysis, pH, adenosine triphosphate, and 2,3-diphosphoglycerate. Screening of genotyped cohorts identified that variant rs148211042 is present in 1 in 394 British citizens of European ancestry. FP RCC had significantly higher supernatant potassium at all time points from day 3 onwards (p < .001) and higher mean cell volume (p=.032) than controls. The initial rate of potassium release was higher in FP RCC; supernatant potassium reached 46.0 (23.8-57.6) mmol/L (mean [range]) by day 5, increasing to 68.9 (58.8-73.7) mmol/L by day 35. Other quality parameters were not significantly different between FP RCC and controls. These data suggest that if a blood donor has FP, reducing the RCC shelf-life to 5 days may be insufficient to reduce the risk of hyperkalemia in clinical scenarios such as neonatal large volume transfusion.

Determination of alkali release during oxyfuel co-combustion of biomass and coal using laser-induced breakdown spectroscopy

The impetus for clean energy utilization has increased acceptance of biomass as a co-fired fuel with coal, since it reduces carbon emissions. This work utilized time-resolved online LIBS measurement to investigate the release of potassium from oxyfuel co-combustion of fuels. A coal-biomass blended particle consisting of 20% biomass (energy basis) is set as a reference fuel, and its results are compared with native biomass and coal particles. As expected, the potassium release rate was highest with 100% biomass and decreased with reducing biomass content in the blend. Therefore, there are trade-offs associated with potassium-related deposition, fouling and corrosion of a boiler’s heat transfer surfaces when biomass and coal are co-fired compared with biomass alone. Analyses of particle size and surface temperature changes suggest that the evolution of potassium in the gas phase can be characterized by temperature evolution. The online measurement for a 20% blend indicates that about 80% of the releasable potassium is volatilized, mainly during the char combustion stage. The release kinetics model developed obeys an Arrhenius expression. The activation energy reported for a 20% fuel blend was 161.9 kJmol−1 K, and was much lower than that of 100% biomass, but higher than that of 100% coal.

Combustion of poultry litter and mixture of poultry litter with woodchips in a fixed bed lab-scale batch reactor

Experiments have been conducted in a batch fixed bed lab-scale reactor to investigate the combustion behaviour of three different biomass fuels, poultry litter (PL), blend of PL with wood chips (PL/WC) and softwood pellets (SP). Analysis of the data gathered after completion of the test runs, provided useful insights about the thermal decomposition behaviour of the fuels, the formation of N gaseous species, the release of ash forming elements and the estimation of aerosol emissions. It was observed that the N gaseous species are mainly produced during the devolatilisation phase. Hydrogen cyanide (HCN) was the predominant compound in the case of SP combustion, whereas ammonia (NH3) displayed the highest concentration during the combustion of PL and blend (PL/WC). With reference to ash forming elements, the release rates of potassium (K) and sodium (Na) range between 15–50% and 20–37% respectively, whereas the release rate of sulphur (S) falls between 54–92%. Chlorine (Cl) presents very high release rate for all tested fuels acquiring values greater than 85%, showing the volatile nature of the specific compound. The maximum potential of aerosol emissions was estimated based on the calculation of ash forming elements. In particular, during PL combustion the maximum aerosol emissions were observed, 2806 mg/Nm3 (dry flue gas, 13 vol% O2), mainly influenced by the release rate of K in the gas phase. Fuel indexes for the pre-evaluation of combustion related challenges such as NOx emissions, potential for aerosols formation, corrosion risk, and ash melting behaviour have also been investigated.

Particle temperature and potassium release during combustion of single pulverized biomass char particles

This work investigated the combustion characteristics of single pulverized biomass-derived char particles. The char particles, in the size range 224–250 µm, were prepared in a drop tube furnace at pyrolysis temperatures of 1273 or 1473 K from four types of biomass particles – wheat straw, grape pomace, kiwi branches and rice husk. Subsequently, the char particles were injected upward into a confined region of hot combustion products produced by flat flames stabilized on a McKenna burner, with mean temperatures of 1460, 1580 and 1670 K and mean O2 concentrations of 4.5, 6.5 and 8.5 vol%. The data reported include particle temperature, obtained using a two-color pyrometry technique, and potassium release rate, measured using a laser-induced photofragmentation fluorescence imaging technique. In addition, particle ignition delay time and burning time, obtained from the temporal evolution of the thermal radiation intensity of the burning char particles, are also reported. The results indicated that ignition of the char particles occurs simultaneously with the starting of the potassium release, then the particle burning intensity increases rapidly until it reaches a maximum, after which both the particle temperature and the potassium release rate remain approximately constant until the end of the char oxidation process. The char ignition process is temperature controlled, and the char oxidation process is oxygen diffusion controlled, with the total potassium release being independent of the oxygen concentration and the temperature of the combustion products. The combustion behavior of the chars studied is more affected by the char type than by the conditions used to prepare them.

Mixture of plant functional groups inhibits the release of multiple metallic elements during litter decomposition in alpine timberline ecotone

Mixed litter decomposition is a common phenomenon in nature and is very important for the circulation of material through an ecosystem. Different plant functional groups (PFGs) are likely to interact during decomposition. It is unclear how mixed decomposition influences the release of multiple metallic elements, and the biogeochemical circulation mechanism in the alpine ecosystem remains elusive. In this study, a two-year experiment on decomposition of mixed litter from six dominant PFGs was conducted at two elevations in an alpine timberline ecotone using the litterbag method. First, the results suggested that PFG identity had greater impacts on the release of all metallic elements than elevation. The release rates of potassium (K), calcium (Ca), magnesium (Mg) and copper (Cu) in graminoid, deciduous shrub and forb litter were significantly higher than those in evergreen conifer, evergreen shrub and mixed litter. Second, the release of metallic elements showed non-additive effects during mixed litter decomposition. K, Ca, Mg, sodium (Na), Cu, and aluminium (Al) exhibited antagonistic effects, while Fe exhibited a synergistic effect. The antagonistic effects on Na, K, Ca and Cu release increased with increasing elevation, while the antagonistic effects on Mg, Al and Mn release decreased with increasing elevation. Third, Al and Fe showed high levels of accumulation. The K release rate decreased while Al and Fe accumulation increased with plant litter upward shift. In conclusion, mixtures of PFGs inhibits the release of multiple metallic elements during litter decomposition in the alpine timberline ecotone. We speculate that an upward shift in PFGs in response to climate warming will slow the release of K and accelerate the enrichment of Fe and Al in alpine timberline ecotones.

POPULATION DYNAMICS OF THE MICROBIOTA IN THE LITTER OF TWO TREE SPECIES OF THE ATLANTIC FOREST

This study analyzes microbiota population dynamics as a function of nutrient release rate during litter decomposition. For that, we observed two tree species native to the Atlantic Forest: brazilwood (Paubrasilia echinata) and inga (Inga laurina). To assess nitrogen (N), phosphorus (P), and potassium (K) release rates from the litter, we performed six collections over 365 days. In these collections, we placed polyvinyl bags called ‘litter bags’ below the treetops of the chosen species to collect dry leaves. To identify the groups of litter microorganisms (fungi, bacteria, and actinomycetes), we used the plate culture method to count the number of colony-forming units (CFU), and the fatty acid profile method, through biomarkers, associating nutrient release rate and abiotic factors (temperature and rainfall). Nutrient release rate correlates with litter decomposition at 140 days, and most microorganisms correlate with litter decomposition at 30 days. Nitrogen and phosphorus release rates correlate with rainfall. Fungi correlate with P release rate in inga litter decomposition. The bacteria biomarker 17:1 was the only one that correlated with N and P release rates. In conclusion, rainfall affects nutrient solubilization in the studied species, and microbiota differs between the species. When comparing the two methods to identify these microorganisms, information from one method complements information from the other, since both provide different but interdependent data.

Mulch decomposition and nitrogen, phosphorus and potassium release in vetiver grass at different plant densities

ABSTRACT In order to meet the need for nutrients or soil cover, when plants are used as green manure, it is necessary to determine the ideal plant population, as well as the amount and duration of released nutrients. This study aimed to assess the decomposition and nitrogen (N), phosphorus (P) and potassium (K) release rates of vetiver grass mulch. A split-plot arrangement was used, with the plots consisting of mulch decomposition times after cutting (0, 15, 25, 70 and 125 days) and the subplots of vetiver plant densities (1, 2, 3 and 4 plants m-2). A randomized block design was used, with four replications. The highest release rates for N, P and K were recorded during the first five days. The plant density of 3 plants m-2 exhibited the highest mulch dry weight at 125 days and contained more N, P and K, when compared to the populations of 1, 2 and 4 plants m-2.

Quantitative imaging of potassium release from single burning pulverized biomass char particles

The release of potassium from single burning pulverized wheat straw char particles was quantitatively measured using laser-induced photofragmentation fluorescence (LIPF). The char particles were prepared in a drop tube furnace at 1000 °C from wheat straw particles with sizes in the range 224–250 µm. Subsequently, the char particles were injected upward into a hot flue gas flow produced by a premixed CH4/air flame anchored on a McKenna burner. The flue gas had a mean temperature of 1580 K and a mean O2 concentration of 6.5 vol%. The 193 nm laser beam from an ArF Excimer laser was formed into a collimated laser sheet to photodissociate potassium hydroxide (KOH) and potassium chloride (KCl) around the burning char particles, and the signal of the produced fluorescence was captured by a camera. The measurements were conducted for char particles during residence times in the flue gas between 10 and 70 ms. Quantitative data was obtained from a direct calibration of the LIPF signal in hot gas products doped with known amounts of KOH and KCl. The maximum potassium concentration measured surrounding the burning char particles was over 40 ppm. During the oxidation period until 70 ms, the measured potassium release rate remained almost constant at around 0.5 µg/s, with more than 60% of the potassium being released in the form of KOH. The results indicate that the LIPF imaging method can be used to study the potassium release from burning biomass fuels.

The characteristics of decomposition and nutrient release of Vicia villosa under different fertilization treatments.

The effects of three fertilization treatments (no fertilizer, nitrogen fertilizer, and lime) on the characteristics of Vicia villosa decomposition and nutrient release were studied using the nylon bag method in the fields. The results showed that the cumulative decomposition rate of V. villosa was 65.3%-72.5% across the three fertilization treatments. V. villosa decomposed rapidly during 0-11 d, then slowed down and tended to be stable. The nutrient release rates across the three treatments were potassium > phosphorus > carbon > nitrogen. At the end of the experiment (148 d), the cumulative release rates of carbon, nitrogen, phosphorus and potassium were 83.6%-84.6%, 78.2%-81.2%, 89.8%-91.4% and 96.3%-97.0%, respectively. During the whole decomposition period, the characteristics of nitrogen release and decomposition of V. villosa were similar. Compared with no fertilizer treatment, lime application promoted decomposition and release of nitrogen, phosphorus and potassium. Nitrogen fertilizer application promoted phosphorus release but inhibited potassium release. Both nitrogen application and lime application had no significant effect on carbon release. The application of nitrogen fertilizer promoted the decomposition of V. villosa and nitrogen release in 0-11 d, but inhibited those processes in 11-148 d. The first-order kinetic reaction equation and logarithmic function equation well fitted the characteristics of V. villosa decomposition and the release of carbon, nitrogen, phosphorus and potassium in the rice fields of South Henan. The characteristic parameters of the equation were significantly correlated with the decomposition rate and nutrient release rate of V. villosa. In summary, lime application was better than nitrogen fertili-zer in promoting decomposition and nutrient release of V. villosa. Moreover, the parameters of the first-order kinetic equation and logarithmic function equation showed a good description of decomposition and nutrient release of V. villosa.

Soybean protein hydrolysate-formaldehyde-urea block copolymer for controlled release fertilizer

ABSTRACTUrea formaldehyde (UF) was modified by the soybean protein hydrolysate (SPH) to adjust the rate of nitrogen, phosphorus, and potassium (NPK) release. The SPH section can copolymerize into the UF molecules. The crystallinity of modified UF fertilizer decreased with increasing SPH content. The surface of SPH-modified UF fertilizer was loose and porous. The nitrogen content of SPH-modified UF fertilizer decreased a little, but the nitrogen, phosphorus and potassium release rate was improved with increasing SPH content in modified fertilizer. The grain number per ear, thousand-grain weight and total yield were improved by the SPH-modified UF fertilizer. Compared to UF and control, protein, starch, fat, soluble sugar and vitamin C in the maize were increased by applying SPH-modified UF fertilizer. The results indicated that the nutrient release behavior can be adjusted by the introduced SPH to match the maize needs.

Potassium release kinetics from three invasive algae mixed with different media in leachate column studies

Algae can be an important source of nutrients in agriculture. The objectives of this study were to (1) estimate the potassium (K+) release rate from algae, commercially prepared algal cell walls, and synthetic sources, and (2) better understand effects of polymeric chemistry and potential mechanisms among test materials. Three leachate column studies were conducted for 16 weeks. The experiments consisted of five K+ sources applied at 0, 112, and 336 kg K ha−1. At each leachate collection, half pore volume deionized water was applied and leachate samples were analyzed using a K+ ion selective electrode. Results from these studies showed that the amount of K+ released was significantly higher under synthetic K+ in the first 6 weeks (4100–4200 mg L−1) and sharply declined thereafter. Release of K+ from algal samples was slower in the first 3 weeks and peaked in 8 to 9 weeks (2800–3400 mg L−1). The release of K+ from agar weed Gracilaria salicornia was significantly lower than from carrageenan producer, Eucheuma denticulatum and Kappaphycus alvarezii. Another leachate study was conducted for 6 weeks using agar and carrageenan and found that K+ release from agar columns was significantly lower (10–12%) than from carrageenan. We conclude that the differences in release rate of K+ among dried algae may be explained in part by differences in cell wall composition.

Kinetics of potassium release and fixation in some soils of Ogun State, Southwestern, Nigeria as influenced by organic manure

PurposeThe study investigated the effects of poultry and goat manures on the kinetics of potassium fixation and release in some sandy loam and loamy soils of Ogun State, Nigeria.MethodsThe treatments consisted of poultry and goat manures applied at 25 g and 100 g/5 kg soil set in completely randomized design with three replicates. Potassium fixation and release kinetics were computed from the analytical data.ResultsExperimental soils was sandy, slightly acidic, low in nutrients with 80% fixed potassium. However, manure application resulted in 74% reduction of the amount of K fixed by the soils. Elovich and power functions had the best fit for K released in soils treated with goat manure. The K release pattern in poultry manure-amended soil is best described by the parabolic diffusion, Elovich, and power functions, while the first-order equation described K release in soils treated with cattle manure. The potassium release rate constant correlated positively with K uptake.ConclusionThe ability of the studied soils to fixed K was reduced with the application of organic manures. Potassium fixation decreased with increase in organic manure rates, 100 g/5 kg soil tends to be the optimum rate, and poultry manure had greater effect on the fixing and releasing power of K.

Phosphorus and potassium cycling in a long-term no-till integrated soybean-beef cattle production system under different grazing intensities insubtropics

Long-term integrated crop-livestock system enables constant and more efficient nutrient cycling because animal, pasture and crop residues release nutrients at different rates. Therefore, appropriate management of these systems is needed to maximize benefits from nutrient cycling. The objective of this study was to evaluate how grazing intensity affected the release rates of phosphorus (P) and potassium (K) in pasture, dung and soybean residues in a no-till long-term integrated crop-livestock system. The experiment was established in 2001 on a clayey Oxisol after soybean harvest. Treatments consisted of pasture with sward heights maintained at 1020, 30 and 40 cm by different cattle stocking rates and a non-grazed (NG) treatment. Decomposition and release rates of nutrients in the pasture and dung were determined using litter bags, which were installed at soybean seeding and pasture seeding during two pasture-crop cycles (2009–2011). Lighter grazing intensities resulted in greater P release rate from pasture and dung residues. Pasture and dung residues released K at a very high rate and were not influenced by grazing intensity. The P and K released from soybean residue were not affected by grazing intensity; however, decomposition of soybean leaves was greater than of stems. Greatest rates of total P and K released were from pasture and dung residues under lighter grazing intensities and in the NG areas. Large amounts of P (~25 kg ha−1) and K (~130–180 kg ha−1) were cycled in a complete soybean-beef cattle integrated system and must be considered in the fertilization management.

Preparation and Application of a Potassium-Substituted Calcium Phosphate Sheet as a Dental Material for Treating Dentin Hypersensitivity

Potassium-substituted calcium phosphate free standing sheet for the treatment of dentin hypersensitivity was prepared and evaluated. The appropriate annealing condition for the target of pulsed laser deposition to prepare the potassium-substituted amorphous calcium phosphate (PS-ACP) sheet was investigated. The target annealed at 1000 °C was used to deposit the PS-ACP sheet. The annealing condition for the potassium-substituted hydroxyapatite (PS-HAp) sheet was evaluated by XRD and EDX. The potassium release rate from PS-ACP sheet in PBS, evaluated by ICP-MS, was 2.5 times larger than that of PS-HAp sheet. The robustness of the PS-ACP sheet was proved by the brushing test of the PS-ACP sheet affixed on a bovine dentin. The dentin tubules on the dentin surface was occluded by the PS-ACP sheet and which confirmed by SEM observations.

Dynamics of multiple metallic elements during foliar litter decomposition in an alpine forest river

Compared with previously reported data, we found that plant litter decomposes faster in river ecosystem than on forest floor in a comparable period, but the dynamics of metallic elements during litter decomposition in river are likely to share common patterns with the corresponding ones in decomposing litter on forest floor. Litter decomposition in terrestrial lotic ecosystem is one of the most important pathways for metallic elements cycling, while little information is currently available about the dynamics of metallic elements in the decomposing litter of lotic ecosystems. The concentrations and release rates of potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and aluminium (Al) were investigated in the decomposing foliar litter of four dominant species in an alpine forest river. Over a 1-year period of decomposition, K, Ca, and Mg were released from virtually all types of litter, whereas Na, Fe, Mn, Zn, Cu, and Al were released from willow litter but accumulated in azalea, cypress, and larch litters during litter decomposition. Litter species, decomposition period, and river water characteristics (e.g., temperature, pH, flow velocity, and nutrient availability) were significantly related to the dynamics of these metallic elements in decomposing litter. Our results suggested that the similarity between the dynamics of metallic elements in the decomposing litter of lotic ecosystems reported here and previously for forest floors indicates a general pattern for the cycling of metallic element across different ecosystem types, and the net accumulation patterns for elements such as Zn, Cu, and Al during litter decomposition suggested that some litter species may act as efficient “cleaner” for metal purification in future ecological engineering.

Extraction of potassium from biotite by Ba2+/K+ ion exchange and the structural transformation

Potassium has been extracted successfully from biotite by Ba2+/K+ ion exchange. The potassium release rate increased along S-curve versus reaction time. The maximum of potassium release rate was about 96 %. Powder X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy were used to characterize the obtained samples to reveal the exchanging behavior and structural transformation. The results showed that after treated with Ba(NO3)2 four times the original biotite transformed to vermiculite-type hydrated Ba-mica. The (001) basal plane was expanded from 1.000 nm of biotite to 1.221 nm of hydrated Ba-mica. Because of the “vacancy effect,” the Ba2+ has two different statuses, causing the structural water vibration of vermiculite-type hydrated Ba-mica split. The edge of vermiculite-type hydrated Ba-mica was crimped compared with the flat edge of original biotite. The (001) basal plane of dehydrated Ba-mica was also split, supporting the “vacancy effect.”

Determination of Nitrogen, Phosphorus, and Potassium Release Rates of Slow- and Controlled-Release Fertilizers: Single-Laboratory Validation, First Action 2015.15.

A previously validated method for the determination of nitrogen release patterns of slow- and controlled-release fertilizers (SRFs and CRFs, respectively) was submitted to the Expert Review Panel (ERP) for Fertilizers for consideration of First Action Official Method(SM) status. The ERP evaluated the single-laboratory validation results and recommended the method for First Action Official Method status and provided recommendations for achieving Final Action. The 180 day soil incubation-column leaching technique was demonstrated to be a robust and reliable method for characterizing N release patterns from SRFs and CRFs. The method was reproducible, and the results were only slightly affected by variations in environmental factors such as microbial activity, soil moisture, temperature, and texture. The release of P and K were also studied, but at fewer replications than for N. Optimization experiments on the accelerated 74 h extraction method indicated that temperature was the only factor found to substantially influence nutrient-release rates from the materials studied, and an optimized extraction profile was established as follows: 2 h at 25°C, 2 h at 50°C, 20 h at 55°C, and 50 h at 60°C.

Kinetics of Nonexchangeable Potassium Release in Surface and Subsurface Horizons of Predominant Soil Series in Kohgilouye-va-Boyerahmad Province

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 (r 2 ) 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.