Short-term release and fixation of K in calcareous clay soils. Consequence for K buffer power prediction

Non-exchangeable K always contributes to some degree to plant nutrition. To understand this contribution and to deduce a predictive buffer power model the release and fixation of K was studied on a range of 44 calcareous clay soils. Short-term K sorption and desorption experiments (16 h) were followed by the measurement of soil exchangeable K (ammonium acetate extraction). Soil K-Ca exchange properties and the contributions of exchangeable K and non-exchangeable K to K dynamics of the soil-solution system were estimated. The change in the amount of non-exchangeable K during the experiment was generally proportional to the initial constraint imposed to the soil-solution system (ø), i.e. the solution: soil ratio multiplied by the difference between the solution K concentration imposed at the beginning of the experiment and the solution K concentration for which neither sorption nor desorption of K would occur. The proportionality coefficient (β) called the 'soil ability for K release and fixation’ was identical for release and fixation for 36 soils, whereas eight soils showed some difference between their ability for fixation and their ability for release of K. When β was considered identical in the release range and in the fixation range for all soils it was inversely proportional to the initial K saturation ratio of the CEC corrected for the amount of ammonium extractable K which was not in exchange equilibrium with Ca. This quantity of ammonium extractable K which is not in equilibrium with Ca probably contributes only partially to plant nutrition. For the studied soils this quantity contributed a large proportion of exchangeable K (26–65%) especially in soils with a small K content. Due to the contribution of non-exchangeable K to soil-solution K dynamics the buffer power of the system does not only depend on exchange properties but also on soil release and fixation properties. When β was taken into account buffer power was better estimated than when it was deduced from ion exchange alone.     

Potassium behavior and clay mineral composition in the soil with low effectiveness of potassium application

ABSTRACT

Increasing exchangeable potassium (ExK) content in soil to an appropriate level is important to mitigate the transfer of radioactive cesium to crops. We focused on a buckwheat (Fagopyrum esculentum Moench) field with a low ExK content, despite the application of K, in Fukushima Prefecture, Japan (Field A), following the Tokyo Electric Power Company Fukushima Dai-ichi (No. 1) Nuclear Power Plant accident in March 2011. We examined the relationship between K concentration and clay mineral composition in the soil of Field A and compared the findings with another field in Fukushima Prefecture (Field B) to clarify whether K applied to the soil was leached or remaining fixed. Pot experiments showed that K concentration in water seepage from pots following irrigation was significantly lower in pots from Field A than in those from Field B. Soil ExK content after soybean cultivation was lower in soils of Field A than those of Field B. These results indicate that K applied to Field A was fixed in the soil. Analysis of clay mineral composition confirmed the distinctive vermiculitic nature of Field A soils. This clay mineralogy would be associated with the higher K fixation ability of Field A than Field B soils. This study demonstrated that K fixation in vermiculite was a factor preventing the increase in ExK content from K application to Field A.     

施氮和不同品种水稻对紫色水稻土钾素形态的影响

通过盆栽试验研究了施氮水平和不同品种水稻对四川盆地 3种典型紫色水稻土 5种钾形态的影响以及各种土壤钾形态对水稻钾素营养的贡献。结果表明 ,4个紫色水稻土供钾能力均属中下水平 ,全钾含量为 1.29%～2.62% ,其中矿物钾量平均占 96.82% ,速效钾和非交换性钾仅平均占 0.62%和 2.56% ,土壤供钾能力以中性紫色水稻土 石灰性紫色水稻土 酸性紫色水稻土。施氮 (N 0～ 150mg/kg)促进 4个紫色水稻土钾素的释放 ,提高水稻对非交换性钾和矿物钾的吸收利用 ,使矿物钾和非交换性钾的贡献占植株吸钾的 80.3% ,速效钾仅为 19.7%。中性紫色土供试 4个品种水稻的吸钾能力为开优 5号 汕优 63Ⅱ优 6078引佳 1号。施氮后4个品种水稻吸自非交换性钾和矿物钾量平均占植物吸钾量的 66.9% ,以施中氮 (N 150mg/kg)时植株吸钾量最高 ;而低氮或高氮水平都不利于植物对钾的吸收和土壤钾的释放     

Effects of biochar application on soil potassium dynamics and crop uptake

Biochar has been suggested as a possible means for enhancing soil fertility, including soil potassium (K). However, understanding of the effects of biochar on soil K dynamics remains limited. In this study, a pot trial was conducted to investigate the influence of biochar application (0, 5, 10, and 25 g kg^?1 soil) on soil K dynamics and crop K uptake under a winter wheat–maize rotation in two types of soil (an Alfisol, which contained a high initial available K and an Entisol, which contained a high abundance of 2 : 1 K‐bearing minerals). Changes in soil K in various forms following biochar application and cropping were determined, and their contributions to plant K uptake were evaluated. Soil microbial activity, especially the development of K‐dissolving bacteria (KDB), was evaluated to obtain insights into its effects on the weathering of K‐bearing minerals in the soils. During the wheat growth period, crop K uptake was more enhanced (13.6–40.5% higher) in the Alfisol than in the Entisol due to the higher availability of water‐soluble and exchangeable K, while K fixation occurred in the Entisol because of the higher content of 2 : 1 K‐bearing minerals. During the maize period, crop K uptake was generally higher in the Entisol soil due to the release of non‐exchangeable K. In addition, biochar application enhanced the growth of KDB in both soils, which was associated with changes in soil pH and water‐soluble K. However, improved mineral K release was observed only in the Entisol. It is concluded that biochar application could be a feasible soil amendment to improve soil K availability, but crop K uptake responses may vary depending on soil types. Soils abundant in 2 : 1 K‐bearing minerals tend to prolong biochar effects on crop K uptake. Biochar application enhanced the growth of KDB, which may facilitate mineral K weathering in soils with abundant K‐bearing minerals.     

Differential potassium buffer behavior of individual soils related to potassium corrective treatments

Abstract

Although the basic chemistry and behavior of potassium in the soil is well understood, little of this knowledge is used in soil testing and practical soil fertility mangement. In this study the K buffer behavior of three individual soils (Hagerstown silt loam (Typic Hapludalf), Gatesburg sand (Entic Haplorthod) and Gilpin channery silt loam (Typic Hapludult)) was investigated. The buffer relationships determined indicated very different K behavior for these soils even though exchangeable K soil tests indicated similar K levels. It was also determined that for these soils the buffer relationship was apparently independent of previous K management, indicating that the K buffer behavior could be included as part of soil characterization data.

The role of nonexchangeable K in determining K buffer behavior was also investigated. It was found that the levels of solution K where the release of nonexchangeable K becomes measurable (0.27 ‐ 0.83 × 10^‐4 M) are similar to solution K levels reportedly required for crop growth (0.02 ‐ 0.95 × 10^‐4 M). It was also found that these soils were capable of maintaining a relatively high level of exchangeable K even after extraction of significant amounts of nonexchangeable K with sodium tetraphenyl boron.

It was concluded that K buffering behavior of individual soils could and should be included in K management decisions involving corrective soil treatments and/or crop removal estimation. Otherwise, based on current soil tests, soils with very different K buffer behavior will be treated similarly.     

Effect of NaCl-induced saline sodicity on the interpretation of soil potassium dynamics

Excess of exchangeable sodium (Na) in salt-affected soils causes ion toxicity and decrease in nutrient uptake by plants, particularly potassium (K). A number of studies have been conducted to investigate the effect of K-fertilization on plant growth under sodic and saline-sodic conditions but the results are much diverse to process for concrete recommendations. To explore the possible reasons, it was hypothesized that Na applied as NaCl to produce salinity/sodicity in the soil may release non-exchangeable K, minimizing the effect of K-fertilization. Incubation studies were conducted for 2, 4 and 6 days in the light (sandy loam) and heavy (clay loam) textured soils producing two saline/sodic levels, i.e. 20 and 30 sodium adsorption ratio (SAR) along with control (SAR 3). Potassium fertilizer applied was calculated according to 40 (general recommendations based on soil-nutrient status), 80 and 160 kg K ha^?1. Interestingly, it was observed that addition of NaCl possibly released non-exchangeable K from the soil minerals and increased the K concentration in soil solution. Total K release was more in heavy textured soil but initial release was more in light textured soil. This release may eliminate the effect of K-fertilization applied under salt stress induced by NaCl. Therefore, it is suggested that while studying Na–K interaction in salt-affected soils, NaCl should be avoided to produce salinity, and naturally occurring saline-sodic soils may be used. Soil Na–K interaction studies including ameliorating effect of K under sodic or saline-sodic conditions should be conducted carefully considering the above-stated argument.     

Release of interlayer potassium in Norwegian grassland soils

Potassium (K) release from sources that are not initially exchangeable is attributed to depletion of interlayer K of micas and clay minerals or weathering of feldspars. The aim of the present study was to estimate the K release from interlayer K. Soil samples from 17 field experiments in ley on a range of mineral soils in Norway were used in the study. The change in K‐fixation capacity was used as an estimate of depletion of interlayer K. It was assumed that the increase in K‐fixation capacity during 3 yr of cropping was equivalent to the amount of K depleted from the interlayer positions. Mean K fixation increased in the majority of the soils during 3 yr of grass cropping both with and without K application. The increase in K fixation indicated that without K application, the K uptake from interlayer K amounted to 43%, 28%, and 26% of the K yield for clay soils, high‐K sandy soils, and low‐K sandy soils, respectively. Including K uptake from exchangeable K in the topsoil and from subsoil, the explained K uptake amounted to 79%, 69%, and 81% for the three groups of soil, respectively. Simple linear‐regression analyses showed that the change in K fixation during 3 yr of grass cropping was best explained by the percentage of clay in the soil.     

Changes in potassium availability and other soil properties due to soil ingestion by earthworms

An incubation experiment was conducted to study the changes that occur in potassium availability and other soil properties with ingestion of soil by earthworms. Two soils were used. Raumai soil with high non-exchangeable K and Milson soil with low non-exchangeable K were incubated with two species of earthworm, Aporrectodea caliginosa and Lumbricus rubellus, for 8 weeks. The casts and soil samples were analysed for exchangeable K, Ca, Mg, Na, and H, pH, organic C, and texture. The results indicated that in Raumai soil, the exchangeable K levels of the casts of both earthworm species were significantly higher than for the control soil, the effect being more marked for L. rubellus than for A. caliginosa. In Milson soil, the exchangeable K levels were significantly lower in the casts of both types of earthworm than in the control soil. The nitric acid-extractable K of the soil and casts was not markedly different for either soil type, but available non-exchangeable K values were significantly higher for the casts of L. rubellus from Milson soil than for the noningested Milson soil. In Raumai soil, the exchangeable Ca was higher in the casts of L. rubellus, exchangeable Mg and H were reduced, and exchangeable Na did not change markedly in the cast compared to the control soil. For Milson soil, the casts contained lower exchangeable Ca and H but higher Na and Mg than the control. The casts of both species of earthworm had significantly higher pH values for both soil types. There was no marked difference in the organic C content of the control soil and cast samples for Milson but a reduction in the casts of A. caliginosa for the Raumai soil. Finer fractions increased in the casts of both earthworm species in both soil types.     

不同提取方法土壤非交换性钾释放动力学及其速率的研究

采用Ca2+饱和土壤的 0.50molL-1硝酸、0.0 1molL-1草酸和氢质阳离子交换树脂恒温连续提取法 ,利用Elovich和二级动力学模型 ,结合生物吸钾试验 ,研究探讨了描述土壤非交换性钾释放及其速率较为理想的连续提取法及其动力学模型。研究结果表明 ,氢质树脂提取法的Elovich模型描述非交换性钾释放及其速率的效果较为理想 ,拟合方程的相关系数达极显著水平(r =0.982～ 0.996 ) ;不同时间非交换性钾累积释放量的计算值与实测值的标准差最小 (S =1.335～2.480 ) ;通过速率方程计算的不同时间非交换性钾释放速率与黑麦草吸收的非交换性钾数量的相关性也最为密切 (r =0.944～ 0.963) ,故氢质阳离子交换树脂连续提取法结合Elovich模型是描述土壤非交换性钾释放及其速率较为理想的组合方法。以伊利石为主的 2、3和 8号土壤非交换性钾释放速率明显高于其它以高岭石或蒙脱石为主的供试土壤     

The classification and mapping of potassium reserves in soils of England and Wales

Potassium was extracted from samples of 21 surface soils and nine subsoils using a calcium-saturated cation exchange resin and concentrated HCI under reflux. Most of the important arable soils of England and Wales were represented in the samples. The two methods permitted determination of the amounts and rates of release of exchangeable K, K fixed in the weathered periphery of vermiculitic and illitic minerals, and K in the unweathered core of mica minerals. Potassium reserves in the soils were classified as High, Medium or Low according to the rate of release of fixed K and the amount and rate of release of mica K. The K reserves of soils in England and Wales could be mapped by soil series using this method of classification. Such mapping would provide data on the extent and availability of reserves in both the short term (i.e. to a crop over a growing season) and long term.     

共施磷酸二氢钙和硫酸铵对土壤中钾形态转化的影响

Soil potassium (K) deficiency has been increasing over recent decades as a result of higher inputs of N and P fertilizers concomitant with lower inputs of K fertilizers in China; however, the effects of interactions between N, P, and K of fertilizers on K status in soils have not been thoroughly investigated for optimizing N, P, and K fertilizer use effciency. The influence of ammonium sulfate (AS), monocalcium phosphate (MCP), and potassium chloride application on K fractions in three typical soils of China was evaluated during 90-d laboratory soil incubation. The presence of AS significantly altered the distribution of native and added K in soils, while addition of MCP did not significantly affected K equilibrium in most cases. Addition of AS significantly increased water-soluble K (WSK), decreased exchangeable K (EK) in almost all the soils except the paddy soil that contained considerable amounts of 2:1 type clay minerals with K added, retarded the formation of fixed K in the soils with K added, and suppressed the release of fixed K in the three soils without K added. These interactions might be expected to influence the K availability to plants when the soil was fertilized with AS. To improve K fertilizer use effciency, whether combined application of AS and K was to be recommended or avoided should depend on K status of the soil, soil properties, and cropping systems.     

Potassium release on drying of soil samples from a variety of weathering regimes and c clay mineralogy in China

Thirty two soil samples from China were analyzed for exchangeable K before and after drying. Most soil samples were higher in exchangeable K after air-drying and ovendrying (60°C) than when wet. Soil clay minerals, especially clay-size mica, affected K released in air-dry and oven-dry samples. According to composition of clay minerals of air-dried samples, five classes were recognized. Soil samples with high mica and montmorillonite have the highest exchangeable K. Samples that contained higher kaolinite than mica had lower exchangeable K. Samples with higher kaolinite than quartz and mica had still lower exchangeable K. Samples of sandy soils contained very low exchangeable K. When quartz was the main mineral, the samples that had kaolinite and gibbsite as the main clay minerals had very low exchangeable K. The degree of weathering (weathering mean) bore an inverse relationship to the amount of K released on drying in air or at 60°C. Udults and Udalfs (Red Earths) of southeastern China, because of their high K release on being dried, are inferred to have received fine mica from the Western Desert dust rainout, reported to Liu et al. (1981).     

Potassium release and fixation in Ferralsols (Oxisols) from Southern Togo

Potassium release and fixation were studied on Ferralsols (typic Eutrustox) of Southern Togo both by isotopic exchange with ⁴²K+ ions and by exchange with 1 M ammonium acetate. Experiments were conducted on soil samples taken from surface (0–30 cm) and subsoil (80–100 cm) layers of four plots. These plats, with the same soil type, were subjected to various kinds of use: forest and crops, with or without fertilizers. A single wetting and drying of the soil samples increased the amounts of exchangeable K. This exchangeable K release could stem from clay protonation during drying. However, the K release is insufficient to allow permanent intensive agriculture without K fertilizer addition. Soil samples were therefore treated with KCI in order to study K fixation. About 20% of the applied K was fixed and the percentage increased with wetting and drying. The fixation can be explained by the presence of about 2% of interstratified clay minerals in these kaolinitic soils. Comparison of the kinetic characteristics of the isotopically exchangeable K with the amounts of ammonium exchangeable K revealed the existence of several kinds of exchange site for K ions.     

Study on the Threshold Values of Soil Potassium Parameters for Release and Fixation: A Prognostic Approach to Improve the Use Efficiency of Soil and Fertilizer Potassium

The reserve of nonexchangeable potassium (K), threshold levels for release and fixation of intermediate K, and the Gapon exchange selectivity coefficient for K to calcium (Ca) and magnesium (Mg) exchange were studied in soils of widely varying properties, with a view to optimize the efficiency of native as well as added fertilizer K for plant uptake. The illite-dominated soils recorded greater reserve of nonexchangeable K and showed greater cumulative K release. The threshold values of soil K parameters for release and fixation of intermediate K were found to vary with the change in background electrolyte concentration. The soils dominated by illite were found to possess greater K threshold release and fixation values. In general, the fixation threshold level was greater than release threshold level. The Gapon exchange selectivity coefficient for K to Ca exchange revealed that K ions were more tightly held in the specific sites than in planar sites.     

钾和碳氮比对铵态土壤转化过程的影响

Two soils, one consisting of 1：1 clay minerals at pH 4.5 and the other containing 2：1 clay minerals at pH 7.0, were used to estimate the conversion of added NH4^＋ under different C/N ratios （glucose as the C source） and the addition of potassium. Under lower C/N ratios （0：1 and 5：1）, a large part of the added NH4^＋ in the acid soil was held in the forms of either exchangeable or water soluble NH4^＋ for a relatively long time and under higher C/N ratio （50：1）, a large amount of the added NH4^＋ was directly immobilized by microorganisms. In the second soil containing appreciable 2：1 type clay minerals a large part of the added NH4^＋ at first quickly entered the interlayer of the minerals under both lower and higher C/N ratios. In second condition, however, owing to microbial assimilation stimulated by glucose the newly fixed NH4^＋ could be completely released in further incubation because of a large concentration gradient between external NH4^＋ and fixed NH4^＋ in the mineral interlayer caused by heterotrophic microorganisms, which imply the fixed NH4^＋ to be available to plants. The results also showed that if a large amount of K＋ with carbon source together was added to soil, the higher K＋ concentration of soil solution could impede the release of fixed NH4^＋, even if there was a lot of carbon source.     

Influence of soil solution Ca concentration on short-term K release and fixation of a loamy soil

The Ca concentration of the soil solution influences K plant nutrition by its influence on K concentration of the soil solution and on soil buffer power through ion exchange and K release or fixation. The effects of the imposed solution Ca concentration on the estimates of these parameters and on these two phenomena were studied on a loamy soil. Potassium sorption and desorption experiments were conducted for 16 h at five initial Ca concentrations (from 0 to 10^?1 M) and followed by the measurement of soil exchangeable K (ammonium acetate extraction). Soil K-Ca exchange properties and the contributions of exchangeable K and non-exchangeable K to K dynamics of the soil-solution system were estimated. The‘Ratio Law’ applied for the medium range of Ca concentrations, i.e. 10^?1 M to 10^?3 M. But, it failed for some experiments at small initial Ca concentrations (0 M and 10^?4 M). This failure went with a decrease of the number of sites of great affinity for K in K-Ca ion exchange and/or a decrease of the amount of K not in exchange equilibrium with Ca but extracted by M ammonium acetate. Release of K increased and fixation of K decreased when Ca concentration increased. The relation between the change in the amount of non-exchangeable K during the experiment and the initial constraint (ø) was curvilinear on the large range of ø investigated. But, this relation was independent of Ca concentration. The K concentration of the solution for which neither sorption of K by the soil nor desorption of K from the soil occurred decreased and the slope of the sorption-desorption curve at this K concentration increased when the solution Ca concentration decreased. These two parameters can be considered the K concentration of the soil solution of the soil and the buffer power of the soil, respectively, only if the initial Ca concentration imposed during the sorption-desorption experiments is close to the Ca concentration of the soil solution of the soil. A predictive model of the soil buffer power based on ion exchange and release-fixation properties is proposed. Despite some discrepancies at very low Ca concentrations (<0·5 mM Ca) when‘Ratio Law’did not apply the agreement between calculated and observed values was good. The model permits the correction of the experimentally obtained buffer power for the bias related to the great solution volume: soil weight ratio commonly used during the sorption-desorption experiments.     

华北与西北地区典型土壤固钾能力差异研究

试验在我国华北和西北小麦玉米种植地区进行,研究了几种典型土壤在连续13年的K肥施用及小麦秸秆还田条件下耕层土对外源K素的固定能力差异.结果表明:相比常年只施NP肥处理,连续施用K肥或秸秆还田可显著降低土壤对外源K素的固定量,土壤固K量随环境溶液中K素浓度的增加而增加,但固定率下降.随土层变深,各定位点土壤固K量和固K率均随之增加,华北两定位点相对明显.轮作地区各处理0 ～ 20 cm土层土壤对外源K素的固定量(率)均远高于原始土壤,而单作区土壤的固K量(率)稍高或低于原始土.土壤固K能力表现出地带性规律,整体看取自华北两个定位点的土壤对外源K的固定能力强于取自西北两个定位点的土壤.     

Distribution of four major forms of potassium in soils of Galicia (N.W. Spain)

Abstract

The potassium (K) status of a group of Galician natural soils was evaluated, and the equilibria between the four main K forms were examined. The results indicated that the Galician soils studied contained a large mineral K fraction (97% of total K), and a smaller fraction of labile K forms, composed of non‐exchangeable (2%), exchangeable K and solution K (1%). For these soils, the exchangeable K was 38% of the non‐exchangeable K, which was consistent with the moderate development of these soils. The equilibrium between solution K and exchangeable K was displaced towards solution K.     

Plant uptake of exchangeable and non-exchangeable potassium. II. Influence of soil type on uptake by onion roots

Measurements and predictions of uptake of non-exchangeable K have been made for three soils. Exchangeable K is important in controlling the extent to which non-exchangeable K is used; rate of diffusion of exchangeable K seems less important. Rate of release of non-exchangeable K did not vary much between soils, but critical release concentrations in solution varied from 33 to 85 μM with little obvious effect on the extent of use of non-exchangeable K.     

Distribution of potassium fractions in sweet potato (Ipomoea batatas) garden soils in the Central Highlands of Papua New Guinea and management implications

Previous studies indicated that potassium (K) deficiency is an important soil‐related factor for yield decline of the sweet potato gardens in the Central Highlands of Papua New Guinea, where sweet potato is an important staple food crop. An effort was made to characterize various fractions of K in the diverse soils of this region under sweet potato, to ascertain the probable reasons behind the observed K deficiency and its relationship to decreasing yield trends. Soils from two depths (0–10 cm) and (10–20 cm) in two types of gardens (old and new gardens) were assessed for different fractions of soil potassium in volcanic and non‐volcanic soil groups. Volcanic soils (Hydrandepts and Andaquepts) were significantly lower (P < 0.05) in exchangeable K than the non‐volcanic soils (Dystropepts, Tropoqualfs and Eutropepts). Mean exchangeable K content of the non‐volcanic soils was 95.5 mg/kg, whereas that of volcanic soils was 72.4 mg/kg. Similarly, new gardens had an average exchangeable K content of 94.1 mg/kg, which was significantly greater than 71.6 mg/kg soil of older gardens. Non‐exchangeable K content differed significantly (P < 0.001) between the soil types; mean K content was 85.9 mg/kg for the volcanic soils, whereas in non‐volcanic soils, it was 184.9 mg/kg. Garden types also differed significantly (P < 0.05) with respect to non‐exchangeable K content; new gardens registering higher average values (by almost 20%) than the older gardens. Multiple regression analysis showed that variability in the tuber yield was as a result of variability of water soluble and exchangeable K (up to 22%), non‐exchangeable K (2%), mineral K (4%) and leaf K concentrations (10%). Older gardens, which are in volcanic soil groupings, are more susceptible to the K depletion problem because of continuous sweet potato cultivation, possibly owing to their lower K reserves. Such gardens should be managed either with sufficient fallow periods for regeneration of soil fertility or with suitable application of mineral K fertilizers to enhance productivity.