Potassium replenishment capacity of illitic soils at their minimal exchangeable K in relation to clay mineralogy

Potassium replenishment capacity of eight soil series with varying illite content of their clay fraction were studied at their minimal exchangeable K through green house experiments. Higher minimal K levels were found in soils with high initial K status. Maximum K uptake values were associated with high minimal K. The % illite also had a significant relationship with minimum K levels. Average daily rates of K replenishment of soils varied between 0.25 and 0.67 mg kg^?1 soil after reaching minimum K. The K replenishment rates were found highly correlated with minimal exchangeable K (0.96^**). Amount of clay failed to attain the level of significance with K replenishment rate. Soils with higher illite content in their clay showed high K replenishment rates.     

Sorption of isotopically exchangeable and non-exchangeable phosphate by some soils of Colombia and Brazil, and comparisons with soils of southern Nigeria

Fourteen soils from Colombia and Brazil provided a wide range of sorption characteristics. Curves of sorbed phosphate that was exchangeable to ³²P were described by Freundlich's equation, and of non-exchangeable phosphate by Temkin's equation. Exchangeable phosphate was associated with aluminium in poorly-crystalline oxides and in organic complexes. Non-exchangeable phosphate was related to aluminium in organic complexes, and especially to the ratio of AI/C in them. In Nigerian soils similar mechanisms controlled sorption of phosphate but oxides and organic complexes of iron were important. The concentration of phosphate in solution when affinities of soil for exchangeable and non-exchangeable phosphate are equal, and the importance of organic matter, are discussed in relation to soil management and to responses of crops to fertilizer phosphate. The results indicate that sorption curves should not be split into sections.     

Contributions of incorporated residue and living roots to aggregate-associated and microbial carbon in two soils with different clay mineralogy

We conducted a study to investigate the role of aggregates in the stabilization of residue‐ and root‐derived C in an illitic Mollisol and a kaolinitic Oxisol under the following treatments: (i) incorporated residue, (ii) growing plants, and (iii) both incorporated residue and growing plants. Residue‐C dynamics were followed in soils incubated with ¹³C‐labelled wheat residue with and without unlabelled growing wheat plants. Root‐C was traced by growing wheat plants with and without unlabelled wheat residue in a ¹³CO₂‐labelling chamber. After 46 and 76 incubation days, residue‐ and root‐C were measured in four aggregate size classes and in microbial‐C. Both soils had greater residue‐derived than root‐derived total aggregate‐associated C at day 76, which we attributed to the larger residue‐C than root‐C inputs at the start of the experiment. On an aggregate basis, the ratio of residue‐derived over root‐derived C decreased in most size fractions over time, indicating a greater potential for longer‐term root‐C than residue‐C stabilization by aggregates in both soils. At both sampling days, all aggregates > 53 µm had greater residue‐C concentrations in the illitic soil than in the kaolinitic soil and this difference increased with increasing aggregate size. This suggested a greater affinity of illite clay than kaolinite clay to bind with fresh residue‐derived compounds into larger aggregates and hence a greater importance of aggregates in stabilizing residue‐C in illitic compared with kaolinitic soils. The stabilization of root‐C by aggregates was less affected by clay mineralogy and thus less dependent on the affinity of clay minerals to bind with root‐derived compounds.     

The influence of continuous rice cultivation and different waterlogging periods on the morphology, clay mineralogy, Eh, pH and K in paddy soils

The effect of different rice plantation periods on the properties of selected soils on an alluvial plain was studied. Soils were sampled in fields cultivated for 6, 16, 26, and over forty years. In each rice cultivated and nonrice cultivated field, three soil profiles and six nearby auger holes were studied. This study indicated that continuous rice cultivation changed the soil moisture regime from xeric to aquic, the soil color from brown to grayish, and the surface horizons from mollic to ochric epipedon. With increasing duration of cultivation, the abundance of redoximorphic features increased and the soil structure changed from granular or blocky to massive. Therefore, the soil order changed from Mollisols to Inceptisols. No illuviation and eluviation of clay minerals occurred as a consequence of the rice cultivation. X-ray diffraction analysis showed that the clay minerals in the nonrice cultivated field were illite, vermiculite, montmorillonite, kaolinite, and chlorite, and, in the rice field, they were illite, montmorillonite, kaolinite, and chlorite, respectively. However, with increasing the period of cultivation, the amount of illite and vermiculite decreased while the amount of montmorillonite increased. The pH values of the saturated soil surface during the middle stage of rice growth shifted toward neutrality. The Eh of the surface horizons of the paddy soils under the field conditions were +40, −12, −84, and −122 mV, respectively, while the Eh in the nonpaddy soils were close to +90 mV. The amounts of organic matter and available Fe, Mn, Zn, and Cu increased, while the available K decreased in the paddy soils. Published in Russian in Pochvovedenie, 2008, No. 1, pp. 95–101. The text was submitted by the author in English.     

Contribution of non-exchangeable potassium on its quantity-intensity relationships under K-depleted soils

ABSTRACT

Quantity-Intensity (Q/I) parameters were used for elucidating the role of buffering properties of soils through K depletion. Winter wheat was sown in a greenhouse pot experiment until K-depletion and soils were analyzed with NH₄OAc and NaBPh₄ (1 min incubation period). Q/I isotherms (partitioned in exchangeable and non-exchangeable form) were constructed for the soils before and at the end of the K-exhaustion experiment. Results showed that NaBPh₄-K correlated better than NH₄OAc-K with intensity parameter (AR_e^K) or labile K (-ΔΚ₀) in K-depleted soils (r = 0.41 and 0.70), indicating the importance of non-exchangeable K in K dynamics. The latter was confirmed from the comparison of buffering characteristics between initial and K-depleted soils which showed that among the soils studied there was a group whose increase in buffering capacity (PBC^K_t) was due to non-exchangeable K fixation. Furthermore, NaBPh₄-K was well predicted by the sum of exchangeable K and the quantity of K that has to be applied to achieve K balance as derived from Q/I isotherms (EK₀ + CK₀). Finally, relationships were found between Q/I parameters of the initial soils (-ΔΚ_0i, ΕΚ_0i, ΕΚ_ri, CK_0i) and the K-depleted ones (ΕΚ_rd, ΕΚ_0d, CK_0d, CK_rd) which allowed corresponding prediction of the initial parameters (r² = 0.78–0.87).     

Plant availability of isotopically exchangeable and isotopically nonexchangeable phosphate in soils

Isotopically exchangeable P (IEP) is usually considered to be completely plant‐available and the major source of P for plant uptake. The aim of the present study is to test whether plants can, besides IEP, also use non‐IEP and if part of the IEP has an equilibrium concentration in soil solution which is below the minimum concentration, C_Lmin, and can therefore not be taken up by plants. A pot experiment was carried out with maize for two years on two soils, an acid sandy and a neutral loamy soil, either without P fertilizer or fertilized with ten P sources of different solubility. Throughout both years of the study, pots were kept moist either without plants or planted twice with maize (Zea mays L., cv. Athletico). At the end of the experiment, plant P uptake, P concentration in the soil solution (C_L), and P accessible to isotopic exchange within 5 d (E_5d) were measured. Plant growth decreased the E_5d which was about equal to P uptake by maize for most treatments in the acid soil. But for some treatments, i.e., five in the acid and eight in the neutral soil, P uptake was up to 50% larger than the decrease of E_5d, indicating that plants had, besides IEP, also used P from non‐IEP sources. At adequate P supply, both soils had an E_5d of about 100 mg P (kg soil)^–1, but about 30 to 40 mg kg^–1 of this IEP had an equilibrium P concentration in the soil solution below C_Lmin of 0.1 μmol L^–1 at which P would actually not be plant‐available. This study shows that plants take up P mainly from IEP, but not the whole IEP is plant‐available. Furthermore, plants may also use P from non‐IEP sources.     

Determination of CEC and exchangeable Ca and Mg in non-saline calcareous soils

A method is proposed for determination of CEC and exchangeable cations in non-saline calcareous soils. The saturating solution used, 0.5 d Lithium formate in 80% methanol at pH 8.2, does not dissolve CaCO₃.The method is simple and less laborious than any other known method.     

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.     

Critical pH and exchangeable Al of four acidic soils derived from different parent materials for maize crops

Purpose

The purpose of this study is to determine the critical soil pH, exchangeable aluminum (Al), and Al saturation of the soils derived from different parent materials for maize.

Materials and methods

An Alfisol derived from loess deposit and three Ultisols derived from Quaternary red earth, granite, and Tertiary red sandstone were used for pot experiment in greenhouse. Ca(OH)₂ and Al₂(SO₄)₃ were used to adjust soil pH to target values. The critical soil pH was obtained by two intersected linear lines of maize height, chlorophyll content, and yield of shoot and root dry matter changing with soil pH.

Results and discussion

In low soil pH, Al toxicity significantly decreased plant height, chlorophyll content, and shoot and root dry matter yields of maize crops. The critical values of soil pH, exchangeable Al, and Al saturation varied with soil types. Critical soil pH was 4.46, 4.73, 4.77, and 5.07 for the Alfisol derived from loess deposit and the Ultisol derived from Quaternary red earth, granite, and Tertiary red sandstone, respectively. Critical soil exchangeable Al was 2.74, 1.99, 1.93, and 1.04 cmol_ckg^?1 for the corresponding soils, respectively. Critical Al saturation was 5.63, 12.51, 14.84, and 15.16% for the corresponding soils.

Conclusions

Greater soil cation exchange capacity and exchangeable base cations led to lower critical soil pH and higher critical soil exchangeable Al and Al saturation for maize.

     

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.     

Depositional seals in polyacrylamide-amended soils of varying clay mineralogy and texture

Purpose  

Depositional seals, formed when turbid waters infiltrate into soils, lead to a reduction in soil hydraulic conductivity (HC) and enhance runoff and soil erosion. Since clay size particles constitute a dominant proportion of depositional seals, soil texture and clay mineralogy play a significant role in determining the seal’s hydraulic characteristics. Presence of high molecular weight anionic polyacrylamide (PAM) in suspension flocculates fine sediments, and therefore, its application to the soil surface may modify the characteristics of the depositional seal. The impact of PAM on the latter is expected to be influenced by soil properties. The aim of this study was to elucidate the effects of PAM application on clay flocculation and the HC of depositional seals formed in four soils varying in texture (ranging from loamy sand to clay loam), and diverse proportions of clay mineral constituents (kaolinite, smectite, and vermiculite).     

Plant uptake of exchangeable and non-exchangeable potassium. I. Measurement and modelling for onion roots in a Chalky Boulder Clay soil

Uptake of K was measured using a single onion root technique with four soil cylinder diameters, and measuring changes in exchangeable K in the soil. Baldwin's model fitted the measured uptake when only exchangeable K was taken up, but that of Heming & Rowell allowed predictions of uptake of both exchangeable and non-exchangeable K (K_nes) after fitting the necessary parameters. Release of K_nex occurred in both 3 mm and 6 mm cells (root densities of 14cm cm"⁻³ and 3.5 cm cm⁻³) in 10 days. Predictions were made for longer times and differing soil water contents: after four weeks at a water content midway between field capacity and wilting point the contribution of K_nex to total uptake was significant (up to 60%) for plants with high root densities.     

The effect of pig slurry on exchangeable potassium in calcareous soils

Pig slurry in quantities of 200, 400, 500, 600, 800, and 1000 m³ ha^-1 year^-1 was added to two calcareous soils, which differed in concentration and type of clay minerals. The soils were cultivated with two successive crops of pepper and tomatoes grown in containers. A control was given no slurry. The soils were analysed after harvesting for exchangeable K⁺. Differences in exchangeable K⁺ were studied in relation to the concentration and type of clay minerals. The soil with the higher clay content and of the illite type retained K in the exchangeable form to a much greater extent than the soil with the low clay content. In the soil with the lower clay content, of the interstratified illitic — montmorillonite type, very little K was incorporated into the exchange complex. The exchange capacity being low, the amount of K added had little effect on the level of exchangeable K⁺.     

Availability of polycyclic aromatic hydrocarbons in aging soils

Purpose  

The soil contamination by hydrophobic organic contaminants (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), poses great threats to human health and ecological security and attracts worldwide concerns. The total HOC concentrations overestimate its available fraction to the soil biota. Increased understanding of the availabilities of PAHs in soil environment will have considerable benefits for their risk assessment and be very instructive to food safety and remediation strategies in contaminated sites. However, the availability of PAHs in aging soils and particularly the correlations of the availabilities with their forms in soils have yet to be elucidated. In this work, the availabilities of PAHs in aging soils were evaluated using a sequential mild extraction technique.     

Changes in chemistry and mineralogy of forest soils by acid rain

The goal of the present study was a qualitative and quantitative determination of chemical and mineralogical changes in forest soils due to acid atmospheric depositions. In the NE/SE Vienna Woods soil samples were taken at 4 depths (0 to 5 cm, 5 to 10 cm, 10 to 20 cm, 20 to 30 cm) in the contaminated infiltration zone of stemflow (S) of 8 beech trees (Fagus sylvatica), strongly influenced by acid atmospheric depositions (soil-pH 2.8 to 3.0) and in their non contaminated reference areas (R) between trees, where acid imput is much smaller (soil-pH 5.0 to 6.0). The results show that intensive weathering processes took place in the contaminated soil areas, which show higher clay and silt contents and smaller aggregates, as well as clay illuviation. Moreover, in the top of the contaminated soil areas higher contents of C_t and S_t and of the heavy metals Pb, Zn and Cu could be observed, accompanied by extreme low base saturation (expecially of Ca and Mg) and high Al-saturation (50 to 80% of the CEC). These data were confirmed by analysis of the water saturation extract. Moreover, in the contaminated top soils high amounts of Fe-oxides were found, whereas no “secondary” Al-chlorite (due to its instability at pH-values <4.0) could be traced. The desilification process which took place at the same time could be shown through total element analysis. In the clay-fraction strong weathering led to a loss of layer charge and to the genesis of highly expandable three-layer-silicates which could be determined by X-ray diffraction using n-alkylammonium-chloride technics and other chemical treatments.     

Availability of nitrogen and phosphorus in forest soils in northeastern Tasmania

Summary Rates of N mineralization and of N uptake were measured in situ in three eucalypt forests and a cool-temperate rainforest, and were correlated with productivity. All of the soils had a high capacity for immobilization, and nitrification was insignificant. Changes in both organic and inorganic P fractions during in situ containment of soils were small. While the concentration of inorganic available P was not related to forest productivity, a measure of labile organic P was closely related both to productivity and to P in the microbial biomass. Estimates of inorganic- and organic-N availability were highly correlated with independent estimates of organic-P availability, and the results are discussed in relation to biological control of nutrient availability in the surface horizons of forest soils.     

Clay mineralogy of some volcanic ash soils in which cristobalite predominates

The clay mineralogical composition of soils on volcanic ashes from Mashū and Kamuinupuri-dake volcanoes, Hokkaido, which are rich in cristobalite, was determined using petrological, X-ray diffraction, differential thermal, and selective dissolution and differential infrared spectroscopic methods.

The cristobalite occurred in abundance in every size of fraction from coarse sand to clay and every soli from approximately 1,700 to 8,400 years old, and was concluded to be of igneous origin. The major clay minerals were allophanelike constituents and allophane with some layer silicates as the minor clay mineral, being similar to those of andesitic ash soils and different from those of volcanic ash soils containing abundant quartz. The quartz of volcanic ashes was presumed to bederived from the groundmass-equivalent portion of the ashes which had been formed from magma at a low temperature.     

Enriched stable isotopes for determining the isotopically exchangeable element content in soils

The proportion of metals in soils in equilibrium with soil solution can be determined using isotopic dilution. For this purpose, an isotope dilution mass spectrometric (IDMS) technique has been applied for the elements Cd, Cr, Cu, Mo, Ni, Pb, Tl and Zn. Conventionally, sorbed amounts of heavy metals in soils are analysed by ethylenediamine tetra-acetic acid (EDTA) extraction. The IDMS technique and EDTA extraction were both applied to 115 soil samples and compared. For Cd, Cu, Ni, Pb and Zn, the results of the IDMS technique correlated well with the results of EDTA extractions ( r _s(Cd) = 0.965, r _s(Cu) = 0.916, r _s(Ni) = 0.878, r _s(Pb) = 0.922, r _s(Zn) = 0.962; all at P < 0.001). For Cd and Zn, no significant differences between the results of both methods could be observed, which suggests that EDTA and IDMS determined the same pool. EDTA extracted more Cu, Ni and Pb than was determined by IDMS (7, 26 and 13%, respectively). The correlation between EDTA extraction and IDMS for Cr was significant but weak ( r _s(Cr) = 0.361). For Tl and Mo, EDTA extraction and IDMS did not correlate, and IDMS yielded larger concentrations than EDTA. This can be explained by the fact that Tl and Mo do not form stable EDTA complexes, which are essential for the EDTA technique. Recovery experiments demonstrated that added Cd, Cu, Mo, Ni, Pb, Tl and Zn could be recovered successfully by IDMS analysis (mean recovery = 103 ± 9%). Adsorption isotherms for soil samples were determined for Tl, thereby demonstrating that IDMS gave a better estimation of the native content of sorbed Tl in soils than EDTA extraction.     

Availability of triazine herbicides in aged soils amended with olive oil mill waste

Amendments are frequently added to agricultural soils to increase organic matter content. In this study, we examined the influence of alperujo, an olive oil mill waste, on the availability of two triazine herbicides, terbuthylazine and atrazine, in two different sandy soils, one from Sevilla, Spain, and the other from Minnesota. The effect of aging on herbicide sorption and bioavailability was also studied. Soils were amended with alperujo at a rate of 3-5% (w:w) in laboratory studies. Apparent sorption coefficients for the triazine herbicides were calculated as the ratio of the concentrations of each herbicide sequentially extracted with water, followed by aqueous methanol, at each sampling time. These data showed greater sorption of terbuthylazine and atrazine in amended soils as compared to nonamended soils, and an increase in the amount of herbicide sorbed with increasing aging time in nonamended soils. The triazine-mineralizing bacterium Pseudomonas sp. strain ADP was used to characterize triazine bioavailability. Less mineralization of the herbicides by Pseudomonas sp. strain ADP was observed in soils amended with alperujo, as compared to the unamended soils, and, despite the increase in sorption with aging in unamended soils, herbicide mineralization also increased in this case. This has been attributed to Pseudomonas sp. strain ADP first using alperujo as a more readily available source of N as compared to the parent triazines. In summary, addition of alperujo to the soils studied was shown to increase triazine herbicides sorption and hence to reduce its availability and potential to leach.