STUDIES ON SOIL COPPER

A method based on that used by McAuliffe et al. (1948) for phosphorus was developed for determining isotopically exchangeable copper in soils using the radioisotope ⁶⁴Cu. The authors are confident that, with a few exceptions, isotopic equilibrium in soil/solution systems is attained rapidly enough to overcome possible difficulties resulting from the short half-life of this isotope. For the twenty-four soils examined, amounts of isotopically exchangeable copper were found to be between 0.19 and 12-24 μg g^-I and represented between 2 and 21 per cent of the total soil copper. A correlation test and an experiment involving fractionation of labelled soils both demonstrated that the bulk of the isotopically exchangeable copper was located in the organic-bound fraction. Not all copper specifically adsorbed by organic matter was readily exchangeable with ⁶⁴Cu : for one sample of organic material examined only 20 per cent of the adsorbed copper was isotopically exchangeable after 24 hours equilibration. The corresponding figures for clay materials and oxide material were found to be between 75 and 60 per cent.     

Potassium supplying capacity in Argentine soils and plant uptake rate

Abstract

Exchangeable potassium (K) is the readily available form but when this pool is not sufficient, plants must be supplied from less labile forms of this nutrient. In this study, the contribution of nonexchangeable K to plant nutrition and the uptake rate of this nutrient in successive harvests were investigated. A greenhouse experiment was performed sowing annual ryegrass (Lolium multiflorum sp) on four agricultural soils with a wide range in exchangeable K concentration. The soils were a) Acuic Argiudol, b) Entic Hapludol, c) Typic Argiudol (Ordoñez and M. Juarez). Five harvests were conducted resowing after each one. Soil K extractable with 0.01 M CaCl₂, exchangeable and nonexchangeable K was determined. Plant analyses were conducted to asses total K. The highest nonexchangeable K contribution to the total K uptaken by plants (in percentage) was observed in the Acuic Argiudol soil due to its low exchangeable K concentration. For the Typic Argiudol soils, this contribution varied according to exchangeable K concentration (Ordoñez soil) or according to the clay content and the mineralogy (M. Juarez). For all soils, the highest plant uptake rate was for the first harvests corresponding to the uptake of soluble K and the K located in the most labile positions in the exchange complex. This fact is confirmed by the high correlation obtained between the uptake rate and the amount of K extracted with CaCl₂ (p<0.05). For subsequent harvests, a progressive decrease of K uptake rate was observed. In the fifth harvest plant uptake mostly depends on the nonexchangeable K concentration (p<0.05). The Acuic Argiudol soil, presents a special behavior ? given that it reaches the minimum rate in the third harvest due to the low concentration of all K forms of this soil.     

Determination of labile Cu in soils and isotopic exchangeability of colloidal Cu complexes

Measurement of labile (isotopically exchangeable) pools of metals (E values) in soil is required to assess the size of metal pools potentially available to soil organisms, from both a micronutrient deficiency and metal toxicity viewpoint. In this paper, E values of soil Cu were measured by an isotope dilution technique using different solution extracts – water with and without resin purification, water coupled with Donnan dialysis (free ion determination) and 0.01 m CaCl₂. Using these techniques, the isotopic exchangeability of Cu species in water extracts was investigated. The results showed that the specific activity of ⁶⁴Cu in the water‐soluble fraction was less than in the free metal ion fraction or in the fraction that adsorbed to resin. The isotopically non‐exchangeable Cu in water extracts ranged between 4% and 40% of water‐soluble Cu (16% on average), and appeared to be associated with dispersed colloids. The existence of isotopically non‐exchangeable Cu in water extracts led to overestimation (17.7% on average) of isotopically exchangeable Cu in soils when based on the specific activity in water extracts. The method of isotope dilution coupled with resin extraction is recommended for the determination of isotopically exchangeable Cu in soils when water extracts are used.     

Evaluation of universal extractants for determining plant available potassium in intensively cultivated soils

Abstract

Eighteen soils from northwestern Switzerland were used to study the value of seven universal extractants (CaCl₂; DB‐DTPA; Mehlich 1, 2, and 3; Morgan‐Wolf; and NH₄OAc‐EDTA) for predicting plant available potassium (K) as compared to a bioassay (a modified Neubauer test with winter rye). These extractants were evaluated on the basis of K uptake by the bioassay test and the soil K status. In order to create the sufficiency level of exchangeable K for plant growth, soils were treated with 0, 20, 40, 80, and 160 mg K/kg of soil. The range of K uptake by the bioassay tests was between 89.2 and 403.0 mg/kg of soil for the control pots, and 136.6 to 495.8 for the K treatments with optimal conditions for plant growth. The average amounts of K extracted by the seven universal extractants, in ascending order, were: CaCl₂ < Morgan‐Wolf < Mehlich 1 < Mehlich 2 < NH₄OAc‐EDTA < Mehlich 3 < DB‐DTPA. The highest simple correlation with K uptake versus the bioassay test was obtained with the DB‐DTPA (r = 0.89) extractant and the lowest with the Mehlich 1 (r = 0.53) extractant. The DP‐DTPA, NH₄OAc‐EDTA and Mehlich 3‐K procedures showed an advantage over K procedures based on water soluble and exchangeable K pools in the investigated soils in order to predict the amount of plant‐available K. A simple regression and the Cate‐Nelson graphic method offer the possibility of assessing the soil‐K status using K values obtained by these universal extractants and to calibrate them against K forms as follows: exchangeable, water soluble, and non‐exchangeable.     

Distribution and bioavailability of selenium fractions in some seleniferous soils of Punjab,India

Soil-solid phase associations of Se in seleniferous soils of Punjab were investigated by following sequential extraction procedures involving multiple extractions with 0.2 M K2SO4 (2 times), 0.1 M Na2SeO3 (4 times), 0.05 M NH4OH (4 times), 6 M HCl (2 times) and 9 M HNO3 (2 times) vis-a-vis single extractions with 0.25 M KCl, 0.1 M KH2PO4, 4 M HCl and concentrated HCl. Soil samples were equilibrated with 75Se (as Na2SSeO3) @ 9.25 kBq g - 1 soil by incubating at field capacity moisture regime and subjecting to alternate wetting and drying cycles. Following multiple extraction procedure, out of total 75Se added, 8.8 - 26.1% was present in readily available form (0.2 M K2SO4 extractable); 27.6 - 49.0% as isotopically exchangeable (0.1M Na2SeO3 extractable) and 5.3 - 12.0% as organic Se (0.05 M NH4OH extractable). Selenium extractable in K2SO4 was significantly correlated with free iron (r = - 0.774, p < 0.05) and CaCO3 (r = 0.670, p <0.10) content of the soils. Negative relationship was observed between Se uptake by maize (Zea mays L.) and ammonium hydroxide extractable (r = - 0.752, p <0.05) as well as residual Se (r = - 0.726, p <0.05) in soils. Highly positive coefficients of correlation between isotopically exchangeable Se and Se content (r = 0.851, p <0.01) as well as its uptake by maize (r = 0.841, p <0.01) indicated that the isotopically exchangeable form of Se may be considered as an index of bioavailable Se in seleniferous soils of Punjab. None of the fractions defined by following single extraction procedure was correlated with either the soil characteristics or Se uptake by maize plants. Multiple extraction procedure could, thus, better explain the distribution of Se in different fractions and uptake by plants.     

用63Ni示踪技术研究土壤－植物系统的Ni的转化

A study was carried out on the transfer of native and added Ni towards plant both in different soils and at different time by using ⁶³Ni tracer technique. The transfer of added Ni in soil was greater than native Ni and declined as time increased. The mobility was greater for soluble plus exchangeable fraction of soil Ni but very smaller for residual and Fe/Mn oxide bound fractions. These indicated that Ni was more mobile and more harmful in soils with a low pH and/or low content of Fe/Mn oxides.     

土壤性质对土壤–水稻系统中硒迁移的影响

采集浙江省北部水稻种植区成熟期水稻和对应的土壤样品,分析土壤中硒(Se)总量和7种形态Se的含量以及水稻根、茎、叶、谷各部位的Se含量。结果表明:研究区土壤Se平均含量0.344 mg/kg,达到中Se土壤水平,并且与土壤有机质含量呈显著正相关。7种Se形态中,强有机结合态和腐植酸结合态是主要的两种形态,占Se全量的75.92%;离子交换态、水溶态的含量在1.7%左右;碳酸盐结合态为3.2%。水稻根部富集了大部分的Se(73%),其各部位中Se含量随根、叶、茎、谷的顺序依次减少。将土壤按有机质和p H的大小进行分区分析后发现,当有机质含量小于25 g/kg时,土壤铁锰氧化物结合态Se与水稻根部Se呈显著正相关;当有机质含量大于35 g/kg时,土壤铁锰氧化物结合态Se与谷Se呈显著正相关;当p H7时,碳酸盐态Se与谷Se呈显著负相关。水溶态Se和离子交换态Se与水稻各部位Se含量之间并未呈现明显的相关性。水稻各器官Se含量受土壤p H、有机质含量、各形态Se含量等土壤性质的交互作用影响。     

Effect of phosphate fertilization on crop yield and soil phosphorus status

To evaluate the effect of three phosphorus (P) fertilization regimes (no P, P input equivalent to P off‐take by crops, P input higher than P off‐take) on crop yield, P uptake, and soil P availability, seven field experiments (six in crop rotations, one under permanent grassland) were conducted in Switzerland during nine years (six trials) or 27 years (one trial). Soil total P (Pt), inorganic P (Pi), organic P (Po), and the amount of isotopically exchangeable soil P were measured in the 0–20 cm and 30–50 cm layers of the arable soils and in the 0–10 cm layer of the permanent grassland soil. Omitting P fertilization resulted in significant yield decreases only in one field crop trial as the amount of P isotopically exchangeable within one minute (E_1min) reached values lower than 5 mg P (kg soil)^–1. In the absence of P fertilization Pi decreased on average from 470 to 410 mg P (kg soil)^–1 in the upper horizon of 6 sites while Po decreased only at two sites (from 510 to 466 mg P (kg soil)^–1 on average). In all the treatments of the trials started in 1989 the E_1min values of the upper horizon decreased on average from 15.6 to 7.4 mg P (kg soil)^–1 between 1989 and 1998. These decreases were also observed when P inputs were higher than crops needs, showing that in these soils the highest P inputs were not sufficient to maintain the high initial available P levels. Finally for the six arable trials the values of the isotopic exchange kinetics parameters (R/r₁, n, C_P) and P exchangeable within 1 minute (E_1min) at the end of the experiment could be estimated from the values measured at the beginning of trial and the cumulated P balance.     

磷对富硒赤红壤与红壤上小白菜硒吸收及土壤硒形态的影响

采用土培盆栽试验方法,研究了广西两种主要富硒土壤施入不同水平磷对小白菜硒吸收积累的影响及土壤硒形态转化规律,旨在为提高土壤有效形态硒含量及植物硒含量提供理论依据。试验采集广西具有代表性的富硒赤红壤(贵港市桂平市)和富硒红壤(桂林市永福县),设置4个磷梯度盆栽试验。结果表明:相同的磷处理在不同土壤上对小白菜硒吸收效果不同。在富硒赤红壤上低磷处理(P50,50 mg/kg)有利于小白菜地上部和地下部对硒的吸收;在富硒红壤上中磷处理(P110,110 mg/kg)小白菜地上部硒含量最高,地下部施入磷则硒含量均显著低于对照。同时,磷的施入对硒在小白菜体内的转运在两种土壤上也存在差异。在富硒赤红壤上当磷施入量在80 mg/kg以下时,磷的施入会抑制硒从地下部向地上部的转运;在富硒红壤上磷的施入则均能促进硒的转运;但二者均在中磷处理时达到峰值。植株体内硒含量间的差异取决于土壤有效形态硒含量。研究结果显示磷的施入均显著增加了土壤中水溶态和交换态硒的含量,且小白菜硒的含量与土壤中水溶态硒规律一致。研究还发现在两种土壤上不同磷处理对土壤硒形态转化规律不同,这为进一步研究磷与土壤硒间的互作关系提供了参考。     

Die Veränderung der Phosphatintensität der Bodenlösung eines Pelosol-Pseudogleys nach Grünlandumbruch

Long-term change in phosphate intensity in a clay soil after turning grassland into arable land In a 7years field experiment on a poorly drained clay (Pelosol-Pseudogley) after turning permanent grassland into arable land, the phosphate concentration in the soil solution (P_l) decreased and P retention (P_s) increased even if as much as 265 kg P ha^?1 was added in excess of plant uptake. Neither loss in organic matter nor disaggregation of the well aggregated grassland soil by soil management seemed to be responsible for this decrease in P_l. Instead, a slight increase in pH within the 7 years and, to a lesser extent, a concomitant increase in exchangeable Ca are assumed to have caused the decrease in P_l. Laboratory experiments in which pH, exchangeable Ca and ionic strength were varied support the field results. A multiple correlation between P_l and pH plus exchangeable Ca explained 89% of the variation of P_l whereas pH and Ca alone explained only 76 and 42%, respectively. Solubility data placed the solutions around the hydroxyapatite (HA) isotherm even when P-fertilizer were added in excess of plant uptake. It seems unlikely, therefore that HA governs P_l in this soil. Instead, the results are in favour of surface P adsorption to determine P_l. The effect of exchangeable Ca and ionic strength is then explained by their effects on the thickness of the electric double layer which in turn influences P adsorption.     

EXCHANGEABLE PHOSPHORUS, ESTIMATES OF IT FROM AMORPHOUS IRON OXIDES, AND SOIL SOLUTION PHOSPHORUS, IN RELATION TO PHOSPHORUS TAKEN UP BY MAIZE

Amounts of phosphorus taken up by maize plants during 23 days from an Entisol, two Alfisols and an Ultisol from Nigeria, each with three histories of management, were related to the concentration of soil phosphorus extracted in 0.01 m CaCl₂; but the relationships differed between kinds of management. Phosphorus in plants 51 days old was not related to concentration. Relationships of plant phosphorus with isotopically exchangeable phosphorus, and with phosphorus extracted from the soils by anion exchange resin, were poor in young plants but were good in the older plants, irrespective of field management. Amounts of phosphorus in the older plants were also well related to estimates of exchangeable phosphorus computed from P in solution and amounts of amorphous iron oxides extracted by ammonium oxalate from the soils, using equations derived in an earlier investigation with a larger group of soils. Thus estimates of exchangeable phosphorus made from simple measurements of the soil constituents that largely control it, and from extraction by resins, are potentially useful to indicate the ability of soils to supply phosphate to crops, and hence to guide fertilizer policies.     

Laboratory study of phosphorus forms and test procedures on soils under aerobic and anaerobic conditions

The inorganic forms of phosphorus in nine samples of surface soils from the Nainital Tarai of India were determined by a series of extractions with different reagents after incubation for 45 days under aerobic or anaerobic conditions. The forms of phosphorus in samples incubated under aerobic conditions and the pH range of 7.2–8.5 indicated that the soils had been subject to slight chemical weathering. Anaerobic incubation to simulate conditions in lowland rice paddies converted part of the inorganic phosphorus into more labile forms, based on changes in amounts of isotopically exchangeable phosphorus. Amounts of the element converted to more labile forms differed among the nine soil samples.A better correlation was found between amounts of phosphorus extracted by 0.5M NaHCO³ (Olsen's method) than by 0.03N NH₄F in 0.25N HCl (Bray's method) and the isotopically exchangeable phosphorus. The better correlation suggests that the bicarbonate extraction would be the better method for estimating “availablelrd phosphorus in soils of lowland rice paddies. Recalibration of the test prior to such use seems desirable to allow for increases in amounts of phosphorus in labile forms after soils have been shifted from aerobic to anaerobic conditions.     

Minimal exchangeable potassium status of fifteen smectitic soils in relation to potassium uptake and plant mobilization rate of soil reserve potassium

Abstract

A greenhouse experiment was conducted to study the minimal exchangeable potassium (minimal K) status of fifteen smectite dominant soils and its relationship with K uptake and plant mobilization rate of soil reserve K. Exchangeable K reached minimal level decreasing about 35% from initial K status after 350 days of continuous cropping. Soils with high clay content and initial K status showed higher minimal exchangeable K. Cumulative K uptake by six successive crops varied from 160 mg kg^‐1 to 823 mg kg^‐1 and plant mobilization of soil reserve K varied from 0.151 mg kg^‐1 day^‐1 to 1.880 mg kg^‐1 day^‐1 among soils. Minimal K explained well the variation in total K uptake (r=0.85) and plant mobilization rate (r=0.83) as compared to initial exchangeable K status of soils (r=0.67 and 0.59, respectively) suggesting that the former is a better index of K supplying capacity of soils than the later.     

Isotope methods for assessing plant available phosphorus in acid tropical soils

Use of isotope methods to measure the availability of phosphorus (P) in soils that are well supplied with P is well established. We have evaluated such methods for acid tropical soils with very small P contents, which are less well studied. The isotopically exchangeable P in soil suspensions (E value) and that in plant growth experiments (L value) were measured in soils that had received varying amounts of P fertilizer in two field experiments in Colombia. We determined the E values over 4–5 weeks of equilibration allowing for the kinetics of isotope exchange. The decrease in radioactivity in the soil solution at a particular time, t, divided by that at the start (r_t/R) was described by three parameters (r₁/R, r_∞/R, and a coefficient n) derived from the time course of isotopic exchange over 100 minutes. Values of E_t were calculated either from measured values of r_t/R or those extrapolated until 12 weeks. Agrostis capillaris was grown on the same soils labelled with carrier‐free ³³P‐orthophosphate ions to obtain L values. Agreement between E values derived from measured and extrapolated values of r_t/R was satisfactory, but errors in n and r_∞/R limited the precision with which we could estimate E values. For most soils, the P concentrations in the soil solution were greater than the detection limit of the malachite green method (0.9 µg l^?1) but smaller than its quantification limit (3.6 µg l^?1). In the soils with the least available P, the P content of the seed limited the determination of the L value. The E values were strongly correlated, but not identical, with the L values measured for the same time of isotopic exchange. We conclude that these approaches are not precise enough to detect in these soils the ability of a plant to access slowly exchangeable forms of P or to quantify the mineralization of organic P. However, these isotope techniques can be used to estimate the total fraction of added fertilizer P that remains available to the plants.     

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     

Effect of organic matter on the distribution, extractability and uptake of cadmium in soils

Distribution and plant uptake of soil Cd as influenced by organic matter and soil type were investigated in a greenhouse experiment. Three soils (a sand, sandy loam and clay loam) were used. The rates of organic matter in its moist state added were 0,20,40, 80, 160 and 320 g kg^-1 of the air-dried soil on mass basis. Ryegrass (Lolium multörum L.) was used as a test crop. Soil Cd was analysed by a sequential extraction technique and by extraction with 1 M NH₄NO₃ and 0.005 M DTPA. The exchangeable fraction of Cd as determined by 1 M MgCl₂ in the sequential extraction procedure increased, whereas the Fe-Mn oxidebound fraction decreased, with increasing levels of organic matter addition in all three soils. The dry matter yields of ryegrass were not affected by the addition of organic matter, but the Cd concentrations in both cuts of ryegrass decreased with increasing amounts of organic matter added. The plant Cd was highly but negatively correlated to soil CEC. At any level of organic matter addition, the decrease in Cd concentration of ryegrass was in the order: sand > sandy loam > clay loam.     

Differential influence of four invasive plant species on soil physicochemical properties in a pot experiment

Purpose

This study compared the effects of four invasive plants, namely Impatiens glandulifera, Reynoutria japonica, Rudbeckia laciniata, and Solidago gigantea, as well as two native species—Artemisia vulgaris, Phalaris arundinacea, and their mixture on soil physicochemical properties in a pot experiment.

Materials and methods

Plants were planted in pots in two loamy sand soils. The soils were collected from fallows located outside (fallow soil) and within river valley (valley soil) under native plant communities. Aboveground plant biomass, cover, and soil physicochemical properties such as nutrient concentrations, pH, and water holding capacity (WHC) were measured after two growing seasons. Discriminant analysis (DA) was used to identify soil variables responsible for the discrimination between plant treatments. Identified variables were further compared between treatments using one-way ANOVA followed by Tukey’s HSD test.

Results and discussion

Plant biomass, cover, and soil parameters depended on species and soil type. DA effectively separated soils under different plant species. DA on fallow soil data separated R. laciniata from all other treatments, especially I. glandulifera, native species and bare soil, along axis 1 (related mainly to exchangeable K, N-NH₄, total P, N-NO_3, and WHC). Large differences were found between R. laciniata and S. gigantea as indicated by axis 2 (S-SO₄, exchangeable Mg, total P, exchangeable Ca, and total Mg). DA on valley soil data separated R. japonica from all other treatments, particularly S. gigantea, R. laciniata, and native mixture, along axis 1 (N-NO₃, total N, S-SO₄, total P, pH). Along axis 2 (N-NO₃, N-NH₄, Olsen P, exchangeable K, WHC), large differences were observed between I. glandulifera and all other invaders.

Conclusions

Plant influence on soil differed both among invasive species and between invasive and native species. Impatiens glandulifera had a relatively weak effect and its soil was similar to both native and bare soils. Multidirectional effects of different invaders resulted in a considerable divergence in soil characteristics. Invasion-driven changes in the soil environment may trigger feedbacks that stabilize or accelerate invasion and hinder re-colonization by native vegetation, which has implications for the restoration of invaded habitats.

     

Retention of added copper by two soils as affected by organic matter,CaCO3, and exchangeable ions

The effects of addition and removal of organic matter and CaCO₃ and of saturating a loam and a loamy sand soil with hydrogen (HCl treated), with calcium and with sodium on the retention of added copper were studied. Removal of organic matter reduced the copper-retaining capacity in soils, while addition of 1 to 4% humic acid to H₂O₂-treated soils increased the retention. Soil organic matter had higher specific copper retaining as well as fixing capacity than the added humic acid. Humic acid fixed about 62 and 49% of the copper it retained, while soil organic matter fixed about 65 and 61% in the loam and loamy sand respectively, which could not be extracted with 0.1 N HCl. About 30% extra copper retained by the added humic acid was exchangeable. Saturating the soils with hydrogen (HCl treatment) decreased the retention of added copper considerably but addition of CaCO₃ up to 8% increased the retention by increasing the pH of the soil system. The CaCO₃ induced retention was lower than caused by humic acid additions. The specific copper retention by native CaCO₃ was slightly higher than that of added CaCO₃. However, other changes associated with the pre-treatment of the soil may have caused those differences in specif is copper retention. Although CaCO₃ had as high a copper fixing capacity as organic matter its contribution towards exchangeable copper was negligible.     

Plant Availability Index by Potassium Exchange Isotherms in Selected Rice Soils of Lesser Himalayas

Potassium (K) exchange isotherms (quantity–intensity technique, Q/I) and K values derived from the Q/I relationship provide information about soil K availability. This investigation was conducted to study Q/I parameters of K, available K extracted by 1 N ammonium acetate (NH₄AOc) (exchangeable K plus solution K), K saturation percentage (K index, %), and the properties of 10 different agricultural soils. In addition, the relationship of mustard plant yield response to the K requirement test based on K exchange isotherms was investigated. The Q/I parameters included readily exchangeable K (ΔK₀), specific K sites (K_X), linear potential buffering capacity (PBC^K), and energy of exchange of K (E_K). The results of x-ray diffraction analysis of the oriented clay fractions indicated that some mixed clay minerals, illite clay minerals, along with chlorite/hydroxy interlayered vermiculite and kaolinite were present in the soils. The soil solution K activity ratio at equilibrium (AR₀) ranged from 8.0 × 10^?4 to 3.1 × 10^?3 (mol L^?1)^0.5. The readily exchangeable K (ΔK₀) was between 0.105 to 0.325 cmol_ckg^?1 soil, which represented an average of 88% of the exchangeable K (K_ex). The soils showed high capacities to maintain the potential of K against depletion, as they represented high linear potential buffering capacities (PBC^K) [13.8 to 50.1 cmol_c kg^?1/(mol L^?1)^0.5. The E_K values for the soils ranged from ?3420 to ?4220 calories M^?1. The percentage of K saturation (K index) ranged from 0.7% to 2.2%. Analysis of variance of the dry matter (DM), K concentrations, and K uptake of mustard plants indicated that there were no significant differences among the adjusted levels of K as determined by the exchange-isotherm curve.     

Study on Transfer of Ni in Soil—Plant System Using ^63Ni Tracer Method

A study was carried out on the transfer of native and added Ni towards plant both in different soils and at different time by using ^63 Ni tracer technique.The transfer of added Ni in soil was greater than native Ni and declined as time increased.The mobility was greater for soluble plus exchangeable fraction of soil Ni but very smaller for residual and Fe/Mn oxide bound fractions.These indicated that Ni was more mobile and more harmful in soils with a low pH and /or low content of Fe/Mn oxides.