Influence of potassium chloride on desorption of cadmium sorbed on hydroxyaluminosilicate-montmorillonite complex

Cadmium adsorption and desorption on a synthetic hydroxyaluminosilicate-montmorillonite (HAS-Mt) complex were investigated in comparison with a montmorillonite (Mt) and hydroxyaluminum-montmorillonite (HyA-Mt) complex.

Kinetics studies of Cd adsorption on Mt, HyA-Mt and HAS-Mt complexes were conducted at pH 5.0, using a 10^-7 M Cd(NO₃)₂ solution in a solid to solution ratio of 100 mg to 100 mL. After 240 min reaction, 94, 88, 32% of the added Cd were removed from the solutions of the Mt, HyA-Mt, and HAS-Mt systems, respectively. Considering the magnitude of the cation exchange capacity of the clay and complexes, affinity of Cd ions was highest for the HAS-Mt complex.

Desorption experiment was conducted using 1 M KC1, 1 M KNO₃, and water. The desorption rate of Cd sorbed on the Mt was the highest, 90 and 59%, using KC1 and KNO₃, respectively, while, that on the HyA-Mt and HAS-Mt was around 30% and much lower than in the case of Mt, using both chemical reagents. Water could not desorb the adsorbed Cd at all. The difference in the desorption rate between KC1 and KNO₃ was due to the complex ion formation of Cd with the anionic species.

The adsorption of Cd by Mt varied with the nature of intercalated materials, namely, HyA and HAS. The extent of the desorption of Cd decreased due to intercalation of HAS and HyA. In the soil environment, Mt is commonly intercalated with HyA and/or HAS. Our data indicated that the formation of HyA- and HyA-Mt complexes should lead to Cd accumulation in soil environments. In addition, the application of potash (KC1) fertilizer would enhance the desorption of the Cd accumulated in soils.     

Speciation of hydroxyaluminosilicate and hydroxyaluminum ions as affected by the presence of montmorillonite: Extraction experiment with potassium chloride and speciation by 27Al-NMR

The changes of Al species in the presence of montmorillonite (Mt) with aging were investigated using 27Al-nuclear magnetic resonance and inductively coupled plasma atomic emission spectroscopy after extraction with 1 mol L^-1 KCl. Composition of the Al species in a hydroxyaluminosilicate (HAS) solution with a Si/Al molar ratio of 0.63 without Mt was not appreciably affected by 42 d of aging. In the absence of Mt, the concentration of Al13 ([Al0₄Al¹²(OH)₂₄- H₂O)₁₂]₇₊) in the HAS solution with a Si/Al molar ratio of 0.09 and hydroxy-aluminum (HyA) solution decreased during 42 d of aging, suggesting that degradation (or polymerization) of Al13 took place upon aging. In the presence of Mt, Al₁₃ was adsorbed onto Mt from the HyA and HAS(0.09) solutions. The adsorbed Al₁₃ was partly recovered by 1 mol L_-1 KCl from HyA- and HAS(0.09)Mt complexes after 42 d of aging, suggesting that at least a part of the adsorbed Al₁₃ was exchangeable and the rest was considerably stabilized by adsorption onto Mt. The desorption ratios of Al from the HyA- and HAS(O.09)Mt complexes accounted for 25 to 30% and 6 to 8% of total Al adsorbed, respectively. The species of Al desorbed from these complexes consisted mainly of Al₁₃ and Al_NON. The Al_NON was attributed to electrically asymmetric Al including HAS and/or polymer HyA ions.     

Effects of Biochar and Biosolid on Adsorption of Nitrogen,Phosphorus, and Potassium in Two Soils

Increasing the retention of nutrients by agricultural soils is of great interest to minimize losses of nutrients by leaching and/or surface runoff. Soil amendments play a role in nutrient retention by increasing the surface area and/or other chemical processes. Biochar (BC) is high carbon-containing by-product of pyrolysis of carbon-rich feedstocks to produce bioenergy. Biosolid is a by-product of wastewater treatment plant. Use of these by-products as amendments to agricultural soils is beneficial to improve soil properties, soil quality, and nutrient retention and enhance carbon sequestration. In this study, the adsorption of NH₄-N, P, and K by a sandy soil (Quincy fine sand (QFS)) and a silty clay loam soil (Warden silty loam (WSL)) with BC (0, 22.4, and 44.8 mg ha^?1) and biosolid (0 and 22.4 mg ha^?1) amendments were investigated. Adsorption of NH₄-N by the QFS soil increased with BC application at lower NH₄-N concentrations in equilibrium solution. For the WSL soil, NH₄-N adsorption peaked at 22.4 mg ha^?1 BC rate. Biosolid application increased NH₄-N adsorption by the WSL soil while decreased that in the QFS soil. Adsorption of P was greater by the WSL soil as compared to that by the QFS soil. Biosolid amendment significantly increased P adsorption capacity in both soils, while BC amendment had no significant effects. BC and biosolid amendments decreased K adsorption capacity by the WSL soil but had no effects on that by the QFS soil. Ca release with increasing addition of K was greater by the WSL soil as compared to that by the QFS soil. In both the soils, Ca release was not influenced by BC amendment while it increased with addition of biosolid. The fit of adsorption data for NH₄-N, P, and K across all treatments and in two soils was better with the Freundlich model than that with the Langmuir model. The nutrients retained by BC or biosolid amended soils are easily released, therefore are readily available for the root uptake in cropped soils.     

Effect of organic matter on the parameters of the selective sorption of cobalt and zinc by soils and their clay fractions

The sorption and ion-exchange behavior of Co(II) and Zn in the soil-equilibrium solution system was studied for different types and varieties of native soils and their clay fractions before and after mild oxidation with H₂O₂ to remove the organic carbon. The parameters of the ion-exchange adsorption and the selectivity coefficients of the (Co(II), Zn)/Ca ion exchange were determined using different models for describing the relationship between the dissolved and sorbed forms of the metals. These were the empirical Langmuir and Freundlich adsorption isotherms and the model of the ion-exchange adsorption based on the acting mass law. It was found that the soil organic matter played an important role in the selectivity of the ion-exchange adsorption of Co(II) and Zn by the soils and their clay fractions. This was confirmed by an abrupt decrease (to almost 1) of the selectivity coefficients of the Co²⁺/Ca²⁺ and Zn²⁺/Ca²⁺ exchange after the treatment of the clay fraction with hydrogen peroxide.     

Calcium-Ammonium Selectivity of Two Benchmark Soils from Botswana as Assessed by Competing Semi-empirical Ion Exchange Equations

The effectiveness of lime-ammonium-nitrate (LAN) as a nitrogen (N) fertilizer in weathered soils depends on the respective selectivity for ammonium (NH₄) and calcium (Ca) by the soils. The study assessed Ca²⁺/NH₄⁺ exchange selectivity of two benchmark soils from Botswana and examined the soil fertility management implications. Surface horizons (0–20 cm) of Pellustert and Haplustalf were equilibrated with 50 ml stock solution containing variable concentrations of Ca²⁺ and NH₄⁺. The Ca²⁺/NH₄⁺ exchange data were fitted into the Vanselow (K_V), Gaines and Thomas (K_GT), Davies (K_D), and the regular solution (K_RS) equations. The selectivity coefficients for the Ca²⁺/NH₄⁺ exchange reactions varied widely with the soil exchanger composition except for the relatively stable K_RS. The selectivity coefficients indicated strong preference for NH₄⁺ to Ca²⁺. The thermodynamic exchange constant, K_ex, was 5.75 ± 1.24 in the Pellustert, indicating preferential adsorption of NH₄⁺, but not in the Haplustalf with K_ex = 0.92 ± 0.27. The free energy for Ca²⁺/NH₄⁺ exchange (ΔG°_ex) was negative (?4.26 ± 0.59 kJ mol^?1) in the Pellustert but slightly positive in the Haplustalf (0.34 ± 0.87 kJ mol^?1). In conclusion, the soil-NH₄ complex was more stable than soil-Ca complex in the Pellustert, indicating LAN as a N fertilizer would have greater potential effectiveness in the Pellustert than in the Haplustalf.     

A stepwise change of frayed edge site content in biotite in response to the gradual release of potassium from the interlayers

ABSTRACT

Radiocesium (RCs) is selectively adsorbed on weathered micaceous minerals (mica) in soils. Although it is clear that weathered mica has selective adsorption sites for RCs, which have been called ‘frayed edge sites (FES),’ the relationship between the degree of mica weathering and the FES content has not been fully investigated. To evaluate the effect of mica weathering on its FES content, we investigated the changes in the FES content with the release of K⁺ from biotite samples by using sodium tetraphenylborate solution. The FES content was estimated from radiocesium interception potential. The vermiculitic layer charge (Vt charge) was also determined as an indicator of the degree of mica weathering. The amount of K extracted from biotite increased from 154 to 803 mmol kg^?1 as the condition of the K extraction was more intensive (i.e., longer time, lower solid/liquid ratio, and higher temperature). As K⁺ was removed to a greater extent, the FES content increased from 3.96 to 11.5 mmol kg^?1, whereas the Vt charge value increased from 17.1 to 329 mmol kg^?1. At the earlier stage of mica weathering, the formation of FES was proportional to the increasing amount of K⁺ released and to the Vt charges. However, at the later stage of mica weathering, when vermiculite was detected by an X-ray diffraction analysis, FES was not necessarily increased in proportion to the increase in K⁺ released and the amount of Vt charge. These findings indicated that although mica weathering largely increased the FES, the increase was not continuous throughout the weathering stage but evident at the earlier stage of weathering.     

Ammonium increases the net rate of sodium influx and partitioning to the leaf of muskmelon

The influx and partitioning of sodium (Na) is controlled by potassium (K)/Na selectivity/exchange mechanisms. Since ammonium‐nitrogen (NH₄‐N) has been shown to inhibit K absorption and K/Na selectivity/exchange mechanisms control Na influx and partitioning, our objective was to observe if NH₄‐N affects Na influx and partitioning in muskmelon. Muskmelon (Cucumis melo L.) were grown in a pH controlled nutrient solution with 100 mM NaCl in a complete nutrient solution containing either 10 mM nitrate‐nitrogen (NO₃‐N) or NH₄‐N. With NH₄‐N, Na accumulation and partitioning to the leaf blade increased while K absorption was almost completely inhibited. A second study omitted K to simulate the inhibition of K absorption by NH₄‐N and monitored Na accumulation and partitioning as K was depleted in the plant. Sodium accumulation and partitioning to the leaf increased as K decreased in the plant, mirroring the effect of NH₄‐N. Roots appeared healthy in both studies. Our work indicates that at a given level of NaCl stress, NO₃‐N reduces the level of stress experienced by muskmelon plants through reducing the net rate of Na influx and transport to the sensitive leaf blade, not by reducing chloride (Cl) absorption, thereby permitting these plants to “avoid”; this stress.     

THERMODYNAMICS AND THERMOCHEMISTRY OF THE EXCHANGE REACTION BETWEEN NH4+ AND Mn2+ IN A MONTMORILLONITE CLAY

The exchange reaction between NH₄⁺ and Mn³⁺ was studied on a montmorillonite clay at several temperatures and different ionic strengths. Manganese was preferred to ammonium; this preference increased with the temperature and dilution of the dialysate. Comparison with published data concerning exchanges involving NH₄⁺ and the alkaline-earths showed that in the sequence of increasing selectivity: Mg²⁺ < Ca²⁺ < Sr²⁺ < Ba²⁺, Mn²+ lies between Mg²⁺ and Ca²⁺. The enthalpy change was measured calorimetrically and calculated by application of the van't Hoff law to the temperature coefficient of the equilibrium constants. Both values were in good agreement. The excellent recoveries of Mn²⁺ at the end of the exchange reaction and the constancy of the cation exchange capacity over the whole range of surface composition ruled out the possibility of significant adsorption in the MnOH⁺ form. The behaviour of manganese was very similar to that of the alkaline-earth cations.     

Characterization of clay and fine silt fractions of forest soils by standardized K/Ca sorption isotherms

For better comparison of selectivity characteristics of clay and fine silt fractions sorption isotherms standardized on the cation exchange capacity (CEC) are useful. Due to the effect of the CEC on the sorption isotherms, it is necessary to characterize the exchanging substance with regard to different ion selectivities with standardized potassium/calcium‐(K/Ca) sorption isotherms. This procedure helps to complete the knowledge about the mineralogical composition, which is obtained by X‐ray powder diffractometry. A Haplic Luvisol from boulder marl shows distinct differences in its K selectivity both between different particle size fractions and different horizons. This is partly due to the presence of smectites and vermiculites which are differently distributed within the particle size fractions. The increase of K selectivity with increasing particle diameter in the calcareous C horizon can be attributed to the marginal expansion of mica/illite by Ca²⁺ ions. The K selectivity of individual particle size fractions in different horizons of a Gleyic Cambisol from glacial sand shows major similarities. If pedogenic chlorite is formed, no changes in selectivity characteristics can be observed.     

Ammonium-calcium exchange equilibria in soils and weathered pumices that differ in cationexchange materials

The retention of NH₄+ and Ca²+ on soil and weathered pumice samples containing constant and/or variable charge components was measured in different NH₄CI-CaCl₂ solutions. The NH₄+/Ca²+ selectivity of each sample was evaluated using a quotient of the partition of NH₄+ on the exchange sites and in the solution relative to that of Ca²+. It increased with decreasing pH and increasing NH₄Cl-CaCl₂ concentration for a given equivalent fraction of NH₄+ in the solution. These effects were quantitatively explained in terms of the changes of NH₄+ and Ca²+ concentrations in the solution and in the diffuse double-layer of the ion-exchange material as predicted by the law of mass action and the electric double layer theory. The NH₄+/Ca²+ selectivity of different exchange materials showed a similar variation among their exchange sites and increased in the order humus, allophane and imogolite (Si/Al ratio 0.5) < allophane (Si/Al ratio 1.0), montmorillonite < vermiculite, illite < halloysite. The origin of negative charge, the steric features around the exchange sites and clay-humus interaction are suggested as being important in determining the NH₄+/Ca²+ selectivity.     

Ionic equilibria,selectivity and diffusion of cations in soil as influenced by anion additions

Abstract

An experiment was carried under controlled conditions to investigate the influence of the anions, H₂PO₄ ^‐. and Cl on the ionic equilibria, selectivity and effective diffusion of Rb, K, Na, Ca, Mg in two Indiana soils.

Additon of anions to the soils increased the concentration of cations in soil solution. In both the soils receiving H₂PO₄ ^‐, lower cation concentrations were found in the soil solution than in those receiving Cl^‐ . Additon of H₂PO₄ ^‐and Cl^‐ reduced the ion selectivity coefficient, k, for various homovalent (Rb/K, Rb/Na, K/Na, Ca/Mg) and mono‐divalent ion pairs (Rb/Ca, Rb/Mg, K/Ca, K/Mg). In Zanesville soil treatments receiving H₂PO₄ ^‐ had lower k values for mono‐divalent cations than treatments receiving Cl^‐. However, no such conclusions could be drawn for Raub soil. Soils treated with H₂PO₄ ^‐ had higher k values for homovalent cations than Cl^‐ treated soils. The differences in the selectivity of adsorption in these two soils might be attributable to the differences in the type and nature of exchange materials and cation concentrations on the exchange phase.

Addition of H₂PO₄ ^‐ or Cl^‐ enhanced the magnitude of effective diffusion coefficient. (De) of all the cations under considerations. The magnitude of effective diffusion coefficient for cations was lower for H₂PO₄ ^‐ treated soils than Cl^‐ treated soils. Such a reduction in De is related to the reduction in cation concentration in soil solution thereby increasing the buffer capacity for the ions under consideration.     

THERMODYNAMICS OF K–Ca ION EXCHANGE IN SOILS1

Cation exchange characteristics of the K:Ca saturated forms of five soils were measured at 25°C and 50°C. The rates of isotopic exchange of ⁴²K and ⁴⁵Ca were too fast to be measured except that of ⁴²K in the K:Ca Harwell soil at 25°C. The slower isotopic exchange of K in this soil was attributed to the presence of a zeolite, clinoptilolite. The intra-particle diffusion coefficient, D_i, of K in this soil increased with K-saturation to a maximum at about 40 per cent K, probably because of the ‘blocking’ action of the larger hydrated Ca ions at small K-saturations in clinoptilolite. The CEC, measured by isotopic exchange along the K:Ca adsorption isotherm, decreased with increasing temperature probably because some interlayer spaces collapsed. The standard free energy, enthalpy, and entropy changes were negative for the reaction Ca-soil+2K⁺? 2K-soil+Ca⁺⁺. These results seem to show that K is more strongly bound than Ca by the soil and that the Ca-preference shown by the isotherm at small external electrolyte concentration is caused by entropy changes in solution. Calculated activity coefficients of the exchangeable ions changed with K-saturation similarly at both temperatures but values at 50°C were smaller than at 25°C.     

胡敏酸对铵钾在粘土矿物上交互作用的影响

Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+4 and K+have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+4 and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+4 on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.     

Nitrification and denitrification in an acidic soil of tea (Camellia sinensis L.) field estimated by δ15N values of leached nitrogen from the soil columns treated with ammonium nitrate in the presence or absence of a nitrification inhibitor and with slow-release fertilizers

Forty-two-day-old wheat (Triticum aestivum L. var. Asakazekomugi) plants were treated with complete, K-free (—K), Ca-limited (—Ca), and Mg-free (—Mg) nutrient solutions for 10 days using 2 mM NH₄NO₃ as the nitrogen source, which was replaced with 4 mM ¹⁵ NH₄C1 or Na¹⁵NO₃ for the subsequent 2 days to investigate the absorption, translocation, and assimilation of inorganic nitrogen in relation to the mineral supply. In another experiment plants were grown on NO₃ ^?, NH₄ ⁺, NH₄N0₃, and K-free and Ca-limited NH₄N0₃ nutrient solutions for 10 days, and then in the latter three treatments the nitrogen source was replaced with NO₃ ^? and half of the —K plants received K for 6 days to examine the changes in the nitrate reductase activity (NRA).

Wheat plants absorbed NH₄ ^?N and NO₃-N at a similar rate. Influence of K on the absorption of N0₃-N was stronger than that on the absorption of NH₄-N in wheat plants. The supply of K to the —K plants increased the absorption of NO₃-N, while the absorption of NH₄-N still remained at a lower rate in spite of the addition of K. A limited supply of Ca and lack of Mg in nutrient media slightly affected the absorption of NH₄-N. The influence of K was stronger on the translocation of nitrogen from roots to shoots, while Ca and Mg had little effect. When K was supplied again to the —K plants the translocation of NO₃,-N was more accelerated than that of NH₄-N. Incorporation of NH₄-N into protein was higher than that of NO₃-N in all the tissues; root, stem, and leaf. Assimilation of NH₄-N and NO₃-N decreased by the —K and —Mg treatments.

Leaf NRA of wheat plants decreased in the —K and —Ca plants. Higher leaf NRA was found when K was given again to the —K plants than when the plants were continuously grown in K-free media. Replacement of NO₃ ^? with NH₄ ⁺ as the nitrogen source caused a decline of leaf NRA, while the supply of both NH₄ ^?N and NO₃-N slightly affected the leaf NRA.     

Eine Methode zur Bestimmung austauschbarer Kationen in Waldböden

A Method for the Determination of Exchangeable Cations in Forest Soils A simple extraction method with NH₄Cl was developed for determining exchangeable cations in forest soils. The influence of selected parameters (reaction time, concentration of NH₄Cl, filter medium etc.) affecting the amount of extractable cations was tested and a standardisation was done. The cation exchange was completed in less than 4 h. For a quantitative extraction of K, Mg, Ca, and Mn a concentration of 0.05 M NH₄Cl was sufficient. The extractable amount of these cations was always clearly defined. However, extracted Al and Fe increased with the NH₄Cl-concentration. Depending on the soil samples, the exchange is not quantitative even when using a saturated solution. The extractable H⁺ is nearly independent of the NH₄Cl-concentration. Probably considerable amounts are dissociated from organic acids. The optimized method is feasible and can be used for K, Mg, Ca, and Mn as an alternative to percolation methods.     

Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chloride

The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH₄NO₃ and 0.5 M NH₄Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl₂) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one‐to‐one. However, for all heavy metals NH₄Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH₄Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl₂) values and/or contents of OC were taken into account. In comparison to NH₄Cl, NH₄NO₃ proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH₄NO₃ is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation‐exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH₄NO₃ method. However, the applicability of the NH₄NO₃ method to other soils still needs to be investigated.     

Potassium additions on ionic equilibria,selectivity and diffusion of cations in soils

Abstract

In a soil system variation in the concentration of any one ion as induced by external addition might bring changes in the ionic‐equilibria, diffusion rate and strength of adsorption of all the ions involved. In four Indiana soils the changes in ionic equilibria, selectivity coefficient and rate of diffusion coefficient for K, Na, Ca and Mg were investigated at 5 levels of added K. The experiments were carried out under controlled laboratory conditions by incubating soils for 3 weeks at 25C. All soils had a greater fraction of Ca and Mg on the exchange phase than in solution, whereas with K and Na the reverse occurred. Potassium adsorption isotherms for all the soils differed indicating the difference in the nature of soil materials involved. Chalmers soil with high clay content with high exchange capacity had high differential buffer value for K. In all the soils, K was adsorbed preferentially to Na at all the levels of K addition, Calcium was adsorbed preferentially to Mg on the Zanesville and Toronto soils. However, in Chalmers and Raub soils, reverse was observed when the level of K addition was exceeded 1.0 and 0.5 me K/100g soil, respectively. This difference in Mg for Ca is attributed to smaller proportion of Mg saturation on the exchange surface. Divalent cations were preferentially adsorbed over monvalent ions. Increasing levels of K addition increased the diffusion rates of all the ions under consideration. The rate of diffusion for K and Ca were governed by concentrations of these ions on the exchange and solution phase.     

铁和不同形态氮素对玉米植株吸收矿质元素及其在体内分布的影响——Ⅰ.对氮、磷、钾、钙、镁等营养元素的影响

用营养液培养方法研究了铁和两种形态氮素(NO₃^--N和NH₄⁺-N)对玉米植株吸收氮、磷、钾等大量元素和钙、镁等中量元素及其在体内分布的影响。结果表明:与NO₃^--N相比,供应NH₄⁺-N促进了玉米对氮的吸收,在缺铁条件下,降低了对磷、钾、钙及镁的吸收。铁和NH₄⁺-N都显著提高了玉米植株各器官中氮的含量。与NH₄⁺-N处理相比,NO₃^--N处理的新叶中磷含量显著增加,但铁的供应对植物体内磷的含量无显著影响。使用NO₃^--N显著提高了玉米新叶和老叶中钾的含量,根和茎中钾的含量无明显影响。铁的供应降低了新叶和老叶中钾的含量。供铁时,NH₄⁺-N处理的玉米新叶中钙和镁的含量显著低于NO₃^--N处理,而在缺铁时则无显著差异。