Comparative study on EUF and other methods of soil analysis for the determination of available potassium in soils from Northern Greece

Summary Twenty-one representative soils from Northern Greece could be grouped into three categories based on the EUF-K curves which displayed marked differences in the magnitude of K release by the soils employed. The cumulative K desorption by EUF within 35 min and the cumulative K-uptake values of ryegrass (10 cuts) were found to be correlated (r=0.87***). Although this correlation is rather close, the K dynamics of a soil can be better characterized by the course of the K-desorption curves. Because the quotient EUF-K-80°C/EUF-K-20°C can give information on the course of K desorption it is therefore sufficient in routine investigations to know the EUF-K-20°C contents and the numerical values of the quotients EUF-K-80°C/EUF-K-20°C.The EUF procedure does not only indicate the close relationship between K extracted and K uptake by plants, but it can also provide information on other nutrients in the same soil sample. With this extra information it was possible to explain why in some of the analysed soils K uptake was low despite high K availability, the reason being that P availability was not optimal in one of the experimental soils and that the Mn concentration of the soil solution was too high in another. At equal K availability the K uptake was also dependent on the amount of EUF-extractable N.     

Rice yield in relation to electroultrafiltration extractable soil potassium

Summary Potassium in wetland rice soils from five different locations in the Philippines was analyzed using the electroultrafiltration (EUF) technique and by extraction withN NH₄ acetate (pH 7). The soils contained low exchangeable K and responded to K application. The K soil test values were calibrated against the rice response to K application under field conditions. EUF extractable soil K correlated highly significantly with the rice yield response to K fertilizer, whereas the NH₄ acetate extractable K (exchangeable K) did not. Under limiting K supply in soils, rice yield depends more on the EUF-K than on the exchangeable K. Maximum grain yields were obtained when the EUF-K values after harvest and before wetland preparation were above 30 ppm K.     

Evaluation of the electro-ultrafiltration technique (EUF) as a measure of the K supplying power of Quebec soils

The electro-ultrafiltration (EUF) method has been used to evaluate the short-term and long-term supplying power of soils for many essential plant nutrients. The objective of this study was to compare the capacity of EUF with other extraction techniques to predict the plant availability of soil K and K fertilizer responsiveness by 10 cuts of alfalfa (Medicago sativa L.) growing over a 366-day period. Increasingly higher average concentrations of soil K were extracted by EUF at 50 V and 20°C (29 mg kg^-1), EUF at 200 V and 20°C (48 mg kg^-1), 0.002 M SrCl₂ (55 mg kg^-1), EUF at 200 V and 80°C (85 mg kg^-1), 0.1 M HCl (105 mg kg^-1), Mehlich 3 (119 mg kg^-1), 1 M NH₄OAc (120 mg kg^-1) and boiling 1 M HNO₃ (601 mg kg^-1). The large content of vermiculitic minerals in the silt and clay fractions is responsible for EUF desorbing more K in 55 minutes than NH₄OAc in 29 out of 30 soils. The total amount of K desorbed by EUF at 80°C was as effective as Mehlich 3-extractable K in predicting K uptake for the first three cuts and was best among the extracting procedures after boiling 1 M HNO₃ in predicting the long-term K supply, the uptake of K from non-exchangeable sources and the relative yield of alfalfa over 10 cuts. The desorption of soil K with EUF provides a better evaluation of the K-supplying power of Quebec soils than the extractants currently used, especially on a long-term basis.Contribution no. 396.     

A comparison of electro-ultrafiltration and quantity/intensity measurements of soil potassium with its uptake by ryegrass in Scottish soils

Summary Electro-ultrafiltration (EUF) and quantity/intensity (Q/I) parameters of soil K were compared for 14 soils from each of three soil series. The K desorbed by EUF during the first 10 min (K₁₀) was closely correlated with the equilibrium activity ratio (AR₀) for soils of the same series, but differences between series reflected the soil K-buffering capacity, indicating that K₁₀ includes loosely held exchangeable K and is not strictly an intensity measurement. EUF values were compared with conventional soil test methods for predicting K-uptake and dry-matter yield of ryegrass grown in the glasshouse. Correlation coefficients between K uptake at the first cut were 0.80 for K₁₀, 0.88 for K_a (the initially labile K derived from the Q/I curve), 0.92 for K₃₅ (desorbed by EUF in 35 min) and 0.97 for K_ex (1.0M ammonium acetate extraction).     

Determination of K forms in K-fertilized soils by electro-ultrafiltration

We confirmed the suitability of electro-ultrafiltration (EUF) for (a) determination of the distribution of potassium fertilizer among the various forms of potassium in soils with a predominance of micaceous minerals in their clay fraction, and (b) investigated the effects of the degree of openness of the dominant micaceous mineral and of incubation time on the kinetics of the EUF extraction of K from these soils.Samples of illitic, mixed-layer and vermiculitic soils from Galicia (N.W. Spain) were incubated at field capacity for 450 days with 0 (blank), 5,15 or 25 mg K (as KCl) per 100 g dry soil. After 1, 30, 150 and 450 days, subsamples were removed and repeatedly extracted using electro-ultrafiltration at low (20° C/200 V) and then high (80° C/400 V) temperature/voltage (6 and 10 five-minute extractions, respectively). Five different pools of K were identified: solution K (K_s), surface and internal K (collectively, K_p), slowly exchangeable K (K_e) and non-exchangeable K (K_i). The effects of increasing the incubation time depended on the dominant clay mineralogy: after 450 days, the K added to illitic soils was mostly solution K, whereas that added to vermiculitic soils was mostly internal K.For both low and high temperature/voltage EUF experiments, the extraction-time data were best fitted by the Elovich equation (extracted K=a+b ln t). The kinetic coefficient b depended on the incubation time and dominant clay mineral, and for given soil and incubation time increased linearly with the dose of added K.Abbreviations EUF Electroultrafiltration - K_s Solution potassium - K_p Easily exchangeable (surface + internal) potassium - K_e Slowly exchangeable potassium - K_i Non-exchangeable potassium     

The relationship between EUF-K and soil-K fractions of different K selectivity

Summary The fraction of K released during EUF 30-35 min, 80°C, 400 V (EUF₃) and various other soil-K parameters were compared for 24 soils that range widely in clay mineral composition, clay content and percentage K saturation. When EUF₃ was compared with fractions of soil-K containing increasing amounts of non-exchangeable K (=selectively adsorbed K), the R² values decreased with increasing quantities of non-exchangeable K. This indicates that EUF₃ is a function of the exchangeable pool of K, although some initially non-exchangeable K is also involved.     

K desorption in an external electric field as related to clay content

Summary The EUF method differs from other soil testing methods in that it not only yields extractable quantities of nutrients but also provides information on the rates with which these quantities are desorbed when an external force is applied. The K desorption can be described by a second-order rate equation. The constants in these equations (maximum desorbable quantity D; halftime t_0.5) are characteristic for a given K-soil system. The K desorption rate depends on clay content and on the buffer power of a soil.     

Influence of soil type and potassium and magnesium fertilization on the release of potassium and magnesium by electro-ultrafiltration and ammonium acetate-lactate extraction

Summary The effect of increasing potassium and magnesium fertilization during 15 years on the amounts of K and Mg extracted by AL-solution and desorbed by Electro-Ultrafiltration (EUF) was determined in four Swedish soils. In all soils, with increasing potassium fertilization the amounts of K extracted by AL and desorbed by EUF increased, and the amounts of Mg-AL and Mg-EUF decreased. Magnesium fertilization had no significant effect on the K values but increased both Mg-AL and Mg-EUF. The EUF-values were lower than the corresponding AL-values, but the ratio of EUF-desorbed to AL-extracted amounts of K and Mg varied depending on soil type as well as on fertilization rate. The ratio of K-EUF to K-AL increased and the ratio of Mg-EUF to Mg-AL decreased with increasing potassium fertilization, whereas magnesium fertilization decreased the ratio of Mg-EUF to Mg-AL.     

Test of the electro-ultrafiltration method's applicability in soil analysis. Reproducibility of the method

Summary The applicability of the Electro-Ultra-Filtration (EUF) method in soil analyses was studied. The reproducibilities of the amounts of soil extracts, of ion concentrations in the extracts and of the distribution of cations and anions over the cathode and anode extracts by use of fully automatic EUF equipment were tested. The degree of variability among replicates was expressed as coefficient of variation (CV) and as the highest percentual divergence of an individual analytical measurement from the mean (L). The extraction volumes of five replicates of six different soils were found to vary between 1.1–7.1% with an average of 3.8%, as CV and between 1.5–11.3% as L. The reproducibility of desorbed P in the anode extract varied between 2.7–31.7% with an average of 8.7%, as CV and between 3.2–37.9% as L. Corresponding values for CV and L of K desorbed varied between 1.3–13.9% and 1.6–23.8%, respectively. Variations among replicates of desorbed P were especially high in the first 1–2 sub-fractions of a total of seven fractions in a single extraction run. Low K concentrations in the extract had a slightly negative influence on the reproducibility of K desorption. Furthermore, it was found that a portion of the cations is collected in the anode extract and a portion of the anions in the cathode extract, especially at the beginning of an extraction run. Pooling of anode and cathode extracts before analysis is therefore recommended.     

The effect of P source on P desorption by electro-ultrafiltration (EUF) on two different soils

Summary P desorption by the EUF method—when carried out with constant field strength—could be described either by zero- or second-order rate equations. In a calcareous soil, different forms of P resulted in different desorption rates. P desorption could be described as a second-order reaction, except when rock phosphate was applied. In an acid soil, P desorption followed exclusively zeroorder reaction kinetics and no differences between P forms were observed. The results of conventional methods did not agree with the EUF data. It was concluded that the EUF method supplies more comprehensive information on the P status of a soil.     

Relationship between EUF-K contents,K uptake and sugar yield of sugar beet in deep loess soils

Summary In field experiments with varying K fertilization (1981 and 1982) changes in EUF-K contents were studied in deep loess soils of Southern Lower Saxony under sugar beet. A significant positive linear relationship was found between EUF-K contents at 20°C and 200 V (15 mA) of the topsoils and quantities of K absorbed by sugar beet in both years. The corresponding regression lines for 1981 and 1982 are almost parallel, the only difference being the yield level which was higher in 1982.The relationship between EUF-K contents at 20°C of topsoils and sugar yields showed the same parallelism for the two years. Not much increase in sugar yield was found at EUF-K contents over 12 mg/100 g soil at EUF-K 80°C/EUF-K 20°C ratios between 0.5 and 0.7. To attain a sugar yield of 10 t/ha an EUF-K 20°C value of at least 12 mg/100 g soil is required for these deep soils at the beginning of the K uptake period. This finding confirms experiences gained over an 8-year period at the Tulln Sugar Factory (Austria) with fertilizer recommendations based on EUF.     

Characterisation of the magnesium status of soils by means of the EUF-Mg fractions

Summary On the basis of pot experiments carried out on soils with different Mg contents using ryegrass, it could be established that Mg uptake by ryegrass is closely related to Mg in the EUF extracts. The Mg contents in the EUF extracts are therefore suitable indices of actually and potentially available Mg in soils.The ratio between Mg in the EUF extracts and Mg deposited on the electrode + filter varies. The absolute amount of Mg in the EUF extracts increases with increasing Mg content of the soils. The higher, however, the total desorbable Mg the lower are the Mg contents in the EUF extracts in comparison with the Mg contents deposited on electrode + filter. Besides total desorbable Mg the EUF-Mg fractions are influenced as well by the organic and inorganic CEC and by soil pH. The amount of EUF filtrate flowing through filter and electrode also has an influence on the amount of Mg in the EUF filtrate.Consequently for a proper evaluation of available soil Mg total EUF-Mg (Mg in the EUF filtrate + Mg deposited on electrode + filter) should be used.     

Responses of microbial components of the rhizosphere to plant management strategies in a semiarid rangeland

Summary Easily soluble heavy-metal fractions from different soils, a garbage-sewage sludge compost and peat were extracted by EUF. Blanks were determined by extracting distilled water. As the rubber seal of the extraction chamber contained Zn, the obtained Zn values were not reliable. The relative standard deviations of extracted micronutrients were 29.1% for Fe and 20.5% for Mn, Fe, Mn, Zn, Cu, Pb, Cd and Cr were not only found in the filters but also in the extracts.The extraction of CrIII and CrVI solutions showed that CrVI mainly migrated into the anode extract. CrIII was found mainly in the cathode filter and cathode extract, a smaller part however was obviously oxidized to CrVI and migrated into the anode extract. Consequently, CrIII and CrVI in soils could not be distinguished unequivocally by EUF.The amounts of Zn, Cu, Pb and Cd extracted by EUF from various substrates were small compared with the quantities extracted by 2N HCl. The heavy metal contents of the leaves were mostly in the order of those of the EUF extract.Several vineyard soils as well as peat were mixed with increasing quantities of Grünsalz (green salt), a fertilizer consisting mainly of iron sulphate. High amounts of Grünsalz (100–200 g/200 g soil) were necessary to raise soluble Fe in calcareous soils. In peat, however, small Grünsalz additions (1 g/50 g peat) were sufficient. Soluble Mn and Cu increased too when Grünsalz was added to soil or peat. These results give valuable information on how grapevine chlorosis can be reduced by the use of Grünsalz or mixtures of peat and Grünsalz.     

Potassium supplying capacity of northeastern Portuguese soils

In Portugal, the response to K application is often inconsistent with the Egner-Riehm values for available K. This is partly related to high K reserves of some soils. Twenty surface soils representative of different parent materials from NE Portugal were studied to determine their K supplying capacity. Continuous cropping with perennial ryegrass permitted the assessment of the relative ability of soils to release non-exchangeable K. Soils were classified in the range of available K from medium to very high. However, their ability to supply K in the short and long term are very different. In some soils K status measured by plant growth does not fall appreciably, whilst others are rapidly exhausted, and 30% of them are very deficient in K. The supplying capacity varied both with the nature of the parent material and the degree of weathering. The soils deficient in K are those derived from basic rocks and those with more weathered clay minerals. This is the case of the soils with the largest content of organic matter where the dominant clay minerals were kaolinite and vermiculite. Soils that have the highest capacity for supplying K are highly micaceous, like those developed from mica schists, phyllites or river alluvium. In fact the amount of K released from non-exchangeable form is well correlated with the amount of illite in the clay fraction. Soil types and K buffer power coupled with available K must be taken into account when planning any application of K.     

Application of the EUF procedure in grape production

Summary The relationships between the nutrient contents in vine leaves and grape yield on the one hand and the nutrient contents in the soil on the other are described on the basis of results from pot and field experiments conducted over several years. The soils were analysed by means of conventional methods as well as by electro-ultrafiltration (EUF). The following results were obtained: The application of high K and P fertilizer amounts in pot experiments increased the availability of Mg, Mn and Fe. A marked rise in the Mg, Mn and Fe contents was observed in the vine leaves. The exchange processes due to fertilizer addition were well indicated by the EUF method, whereas the results obtained by extraction with ammonium lactate (AL) and CaCl₂ were unsatisfactory. Close and highly significant correlations were found between the EUF-P, EUF-K and EUF-Mg contents on the one hand and the P, K and Mg contents in vine leaves on the other. A close correlation also exists (r=0.91^***) between grape yield and EUF-K contents. Grape yield increases with increasing EUF-K values up to 25 mg/100 g/30 min at 20°C in pot experiments (30 cm rooting depth) and only up to 12 mg/100 g/30 min at 20°C in field experiments. The soil in this field experiment had, however, EUF-K values of 12 mg/100 g in the topsoil as well as in the subsoil. When assessing the limit values, it is therefore important to consider the depth of the horizon in which the nutrients are present. After addition of very high amounts of P fertilizer the P contents in vine leaves markedly decrease after one year, as there is a decline in the availability of phosphates. The EUF-P values measured immediately after the application of high doses of P fertilizer can only characterize the P supply status of a soil for a period of one or two years. The P availability after application of different forms of phosphate fertilizers (superphosphate, hyperphosphate) is well indicated by means of EUF, but not by means of the AL method. When assessing the required K and Mg values in the soil (whatever the method) the vine variety has also to be taken into account, whereas the utilization of soil phosphates depends less on the varietal differences.     

Relationships between soil potassium supply characteristics based on soil solution concentration and buffer power and field responses of winter wheat and maize

The relationship between soil K supply, characterised by the soil solution K concentration and the soil K buffer power, and plant K status was investigated for field grown crops. The study was carried out in 15 K fertilisation trials with maize and wheat covering a wide range of agricultural soils and K level. Soil K buffer power was obtained through sorption–desorption curves. For each trial the critical K concentration in the soil solution was deduced from the relationship between the K concentration in the soil solution and the K concentration in shoot tissue water, which was considered as a relevant indicator of the plant K status. At sufficient K levels, the maximal K concentration in the shoot tissue water of maize (145 mM) was lower than that of wheat (175 mM) but the percentages of the critical K concentration in plant tissue water to this maximal K concentration were similar for the two plant species with an average of 75%. The critical K concentration in the soil solution varied between soils. However, a close correlation was found between the critical K concentration in soil solution and the inverse of the soil buffer power at this concentration (r ²=0.981) or the inverse of the square of buffer power (r ²=0.989). On a wide range of soils and field conditions, these two indicators were more able to account for K availability and plant response than exchangeable K content or K saturation ratio of the CEC.     

Mobilization of non-exchangeable K by ryegrass in five Moroccan soils with and without mica

Intensive cropping of Italian ryegrass (Lolium multiforum L.) in pots was used to assess the contribution of non-exchangeable K to plant uptake. The soils used were: two soils high in mica (illite) developed on recent alluvium plus two smectitic (beidellitic) soils and a soil of mixed mineralogy rich in mica. Four K treatments were used (0, 28.6, 143, and 286 mg kg^-1 soil) with 8 successive monthly cuttings. A response of plant K uptake to added K was observed in all soils. Both 1.0 M NH₄0Ac and 0.2 M CaCl₂ extractable K were depleted to a minimum level specific for each soil. The minima were lower in the old upland soils compared to the young alluvial soils. Uptake of K by Italian ryegrass induced K release from the non-exchangeable K to replenish the plant available pool of K ions. The release of mica interlayer K in the alluvial and in the high K smectitic soil supplied sufficient K to plants even under intensive cropping. The rate of mobilization of interlayer K was low in the smectitic soil with lower K. The lowest release rate was in the old high mica soil. Iron coatings may have inhibited mobilization of interlayer K. The rates of mobilization cannot be predicted from mineralogical and K-extraction data only. The rates of K uptake and the rates of K release by ryegrass under intensive cropping are potential values which can be used for modelling K availability to plants in the soils studied.     

土壤中积累态磷的化学耗竭

积累态P是指肥料P未被植物利用而积累于土壤中的那一部分P素,本文用一次平衡法、流动技术法和阴离子树脂膜等不同方法来研究土壤中积累态P的化学耗竭。研究表明,解吸出的P量随时间的增加而增加,P解吸过程符合二级动力学方程,各处理中P的释放过程快慢程度是PK＞NPK＞NK,红壤的释放量和释放速度均比潮土的要大且快。解吸P量与土壤速效P和植物吸收P均有显著相关。土壤中积累态P最大表观利用率为总P量的45％左右。     

Studies of slowly available potassium in soils of New Zealand

Summary The concentration of K in the soil solution at zero change of non-exchangeable K (Co) was determined at 20°C and 50°C for six topsoils of widely different clay mineralogy. This was done with and without prior removal of the K that was exchangeable to dilute salt solutions in a two to three hour leach. Except for one case Co was greater for leached than for not leached samples, particularly at the higher temperature. This is attributed to rapid edge-weathering during leaching caused by interlayer penetration at the clay edges by calcium, sodium or hydronium ions. It is assumed that K newly exposed in this manner is not immediately exchangeable but that it exerts an influence on the equilibrium concentration of K in solution.Among soils Co was not related to the K available to ryegrass nor to the non-exchangeable K fraction of the uptake by ryegrass. However, much reduced values of Co were obtained after depletion by ryegrass in the new two soils examined.     

A comparative study of the soil zinc fractions determined by chemical methods and electro-ultrafiltration (EUF) and their relations to zinc nutrition in rice

Rice (IR 42) was grown on two soils differing in zinc status for 30 days with and without Zn under submerged conditions in pots. The fate of soil zinc was characterized by extraction of the soil successively with copper acetate and sodium hypochlorite and by EUF extraction. Most of the applied zinc was extracted by copper acetate and represented as complexed fraction. There exists a close and significnat relation between Cu(OAc)₂-extractable zinc and Zn extracted by EUF for 5 minutes at 50 volts (r=0.98). The EUF-extractable zinc and Cu(OAc)₂-extractable zinc were significantly correlated with the zinc content in the plant (r=0.82). The data from this investigation suggest the possibility of Zn fractionation with the EUF technique and the fractions obtained agree closely to those determined by chemical methods. The results obtained indicate that Zn in soil is held by weak organic bonding and that the extractions by Cu(OAc)₂ and/or EUF-5 minutes serve as a useful basis for extimating zinc availability in rice soils.