Mechanisms of fixation and release of ammonium in paddy soils after flooding II. Effect of transformation of nitrogen forms on ammonium fixation

An incubation experiment under aseptic and septic conditions using ¹⁵N-labelled NH₄⁺-N and NO₃^–-N, was carried out to study the effect of N transformations after flooding on NH₄⁺ fixation in a paddy soil from China. After flooding ammonification was favoured, providing NH₄⁺ for fixation by clay minerals. NH₄⁺ fixation was more pronounced under low redox potential (E_h) conditions. Close correlations existed between exchangeable NH₄⁺, E_h, and non-exchangeable NH₄⁺. Therefore, two major conditions for NH₄⁺ fixation induced by flooding in paddy soil were found, namely flooding promoted net production of NH₄⁺ due to the deamination of organic N and, in addition, decreased the E_h of the soil. A lower E_h was caused by reduction and dissolution of Fe oxide coating on the clay minerals' surfaces, eliminating the obstacles for NH₄⁺ diffusing into or out of the interlayers of clay minerals. A higher concentration of exchangeable NH₄⁺ from deamination of organic N would drive NH₄⁺ diffusing from the soil solution into the interlayers of clay minerals. ¹⁵N-labelled NO₃^– incorporated into the flooded soil was not reduced to NH₃. The addition of NO₃^– retarded the decrease in the soil E_h and, therefore, NH₄⁺ fixation.     

Effect of residence time on the kinetics of nonexchangeable ammonium release from illite and vermiculite

The fraction of nonexchangeable ammonium (NH₄⁺) can play an important role in N cycling of soils as a sink (fixation) or a source (release) of NH₄⁺. Recently fixed nonexchangeable NH₄⁺ especially seems to be a significant source for N release. The aim of our study was to determine the effect of residence time on the kinetics of nonexchangeable NH₄⁺ release from illite and vermiculite. Calcium-saturated illite and vermiculite, containing NH₄⁺ that was “fixed” for one and 60 d, were extracted with a H-resin for 0.25 to 384 h. Both clay minerals “fixed” significantly more NH₄⁺ in 60 d than in 1 d, but vermiculite “fixed” more NH₄⁺ than illite. The kinetics of nonexchangeable NH₄⁺ release from illite and vermiculite were well described by the Elovich equation and by a heterogeneous diffusion model. In vermiculite the percentage of nonexchangeable NH₄⁺ release decreased from 84% to 78% when the time of fixation increased from 1 to 60 d. In illite time of residence has not influenced the complete release of newly fixed NH₄⁺.     

Mechanisms of fixation and release of ammonium in paddy soils after flooding III. Effect of the oxidation state of octahedral Fe on ammonium fixation

An experiment with two typical paddy soils from China and two clay minerals was conducted to study the effect of reduction of octahedral Fe^III on fixation of NH₄⁺ ions. Reduction of octahedral Fe^III was achieved by treating soils and clay minerals with dithionite‐citrate‐bicarbonate (DCB) followed by dialyzing the samples under oxygen free conditions. Reduction of Fe^III increased the negative charge of interlayers and resulted in a significantly higher ammonium fixation. Close positive correlations were found between the Fe²⁺ concentration or the ratio of Fe²⁺/Fe³⁺ and non‐exchangeable NH₄⁺‐N. Therefore, it is concluded that the reduction of octahedral Fe induced by flooding is one of the important prerequisites for the pronounced ammonium fixation in flooded soils. However, the relation between ΔFe²⁺ and Δfix‐N was not stoichiometric.     

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.     

钾对铵离子在蛭石矿物表面吸附与层间固定的影响

在K+、NH4+不同施用顺序的情况下研究了蛭石对NH4+的晶层固定 ,证实了K+的存在对NH4+的矿物晶层固定不具有影响。在Ca2+-NH4+二元系统和Ca2+-NH4+-K+三元系统中 ,对NH4+在蛭石表面的吸附进行了研究 ,结果同样显示 ,K+对NH4+在蛭石表面的吸附位点不具有竞争作用。     

Clay mineralogical and ammonium fixation characteristics of some tropical upland rice soils

Abstract

In view of the agronomic and economic significance of NH₄ fixation in soils, an attempt has been made to relate this to the most reactive mineral constituents of soils ‐ the clay minerals, under the temperature‐moisture regimes normal to tropical upland rice soils. Laboratory fixation study was done with NH₄, concentrations similar to those common in soils upon N fertilization, and under alternate wetting and drying at ambient temperatures rather than at 100°C as in many published studies.

Results of the investigation show that soil clays with dominant vermiculite and montmorillonite fix the greatest proportion of applied NH₄ (94 and 91%), followed by beidellite (72%) and x‐ray amorphous (45–64%) clays. Fixation is negligible (10%) in the clay with mineral suite consisting of hydrous mica, halloysite, and chlorite. Crystallinity of minerals seems to influence NH₄ fixation appreciably.     

Ammonium fixation by soil and pure clay minerals

Abstract

Fixation of the ammonium ion (NH₄ ⁺) by clay minerals is an alternate way of building the nitrogen (N) pool in soil to optimize N crop recovery and minimize losses. Clay minerals (illite, montmorillonite, and vermiculite) and an illitic Portnoeuf soil were used to compare NH₄ ⁺ fixation abilities. Total N determination and X‐ray diffraction analysis were performed on each of the minerals and the Portnoeuf soil controls, and NH₄ ⁺ saturated batches were subsequently desorbed by potassium chloride (KCl) after 4096 hours. Total N was determined for each employing either Kjeldahl digestion only, or pretreating with hydrofluoric‐hydrochloric acid (HF‐HCl) before the Kjeldahl digestion. The total N for the soil was 38% more after pretreatment with HF‐HCl. The total N determined after pretreatment with HF‐HCl for the NH₄ ⁺ saturated and subsequently KCl desorbed minerals was found to be highest in vermiculite. The cation exchange acapacity (CEC) of each of the minerals was determined, and highest CEC was found in montmorillonite [83.07 cmol(+)/kg]. X‐ray diffraction analysis revealed collapse of the vermiculitic clay lattice from an initial d‐spacing of 13.1 angstrom to 10.4 angstrom after desorprion by KCl. This suggested the existence of sequestered NH₄ ⁺ between the 2: 1 vermiculitic clay interlayer lattice.     

Fixation and defixation of ammonium in soils: a review

Fixed NH₄⁺ (NH₄⁺ _f) and fixation and defixation of NH₄⁺ in soils have been the subject of a number of investigations with conflicting results. The results vary because of differences in methodology, soil type, mineralogical composition, and agro-climatic conditions. Most investigators have determined NH₄⁺ _f using strong oxidizing agents (KOBr or KOH) to remove organic N and the remaining NH₄⁺ _f does not necessarily reflect the fraction that is truly available to plants. The content of native NH₄⁺ _f in different soils is related to parent material, texture, clay content, clay mineral composition, potassium status of the soil and K saturation of the interlayers of 2:1 clay minerals, and moisture conditions. Evaluation of the literature shows that the NH₄⁺ _f-N content amounts to 10–90 mg kg⁻¹ in coarse-textured soils (e.g., diluvial sand, red sandstone, granite), 60–270 mg kg⁻¹ in medium-textured soils (loess, marsh, alluvial sediment, basalt) and 90–460 mg kg⁻¹ in fine-textured soils (limestone, clay stone). Variable results on plant availability of NH₄⁺ _f are mainly due to the fact that some investigators distinguished between native and recently fixed NH₄⁺ while others did not. Recently fixed NH₄⁺ is available to plants to a greater degree than the native NH₄⁺ _f, and soil microflora play an important role in the defixation process. The temporal changes in the content of recently fixed NH₄⁺ suggest that it is actively involved in N dynamics during a crop growth season. The amounts of NH₄⁺ defixed during a growing season varied greatly within the groups of silty (20–200 kg NH₄⁺-N ha⁻¹ 30 cm⁻¹) as well as clayey (40–188 kg NH₄⁺-N ha⁻¹ 30 cm⁻¹) soils. The pool of recently fixed NH₄⁺ may therefore be considered in fertilizer management programs for increasing N use efficiency and reducing N losses from soils.     

Influence of Aluminum Hydroxide on Potassium Release from Two Colombian Soils

Abstract

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non‐exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2∶1 clay minerals and High Terrace with predominantly 1∶1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl‐Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K₂O, respectively. They were used either untreated or prepared by adding AlCl₃ and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10 mM NH₄OAc at pH 7.0 and 10 mM CaCl₂ at pH 5.8 for 120 h at 6 mL h^?1 to examine the release of Kex and Knex. In the untreated soils, NH₄ ⁺ and Ca²⁺ released the same amounts of Kex from Caribia, whereas NH₄ ⁺ released about twice as much Kex as Ca²⁺ from High Terrace. This study proposes that the small ionic size of NH₄ ⁺ (0.54 nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca²⁺ (0.96 nm) cannot have access. As expected for a soil dominated by 2∶1 clay minerals, Ca²⁺ caused Knex to be released from Caribia with no release by NH₄ ⁺. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca²⁺ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl₃ which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH₄ salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.     

盆栽和田间条件下土壤15N标记肥料氮的转化

利用¹⁵N在盆栽条件下研究了铵的矿物固定作用对肥料氮在三种土壤中转化的影响.结果表明,红壤性水稻土不固定肥料铵,但在白土和夹沙土中,56-77%的肥料氮被土壤矿物所固定,这些“新固定”的固定态铵的有效性很高,其中90%以上在30-50天内即被水稻所吸收,或者为微生物所利用转变为生物固定态氮.生物固定态氮对当季作物的有效性远较“新固定”的固定态铵的低.田间微区试验的结果还表明,甚至第二、三季作物吸收的残留肥料氮中,20-86%的氮也系来自固定态铵.作者认为,对具有较强固铵能力的土壤来说,只有了解铵的矿物固定作用,才能正确了解肥料氮的其它转化过程.     

Effects of liming and selected heavy metals on ammonium release in waterlogged agricultural soils

Many farmlands are periodically flooded or ponded by excessive precipitation resulting in changes to soil chemical and biochemical properties. In this study, one set (eight treatments with four replications) of field-moist surface soils (0–15 cm) and their air-dried counterparts obtained from a long-term liming experiment were incubated at 30 °C under waterlogged conditions for 10 days, and the amounts of net NH₄ ⁺-N released (soluble and exchangeable) were determined after extraction with 4 M KCl. Another set of three surface soils were used to evaluate the effect of six heavy metals on the NH₄ ⁺-N release under waterlogged conditions. Results showed that increasing the liming rate from 0 to 17,930 kg ha^?1 effective calcium carbonate equivalent increased the average soil pH from 4.98 to 7.06, averages of the amounts of NH₄ ⁺-N released ranged from 1.6 to 5.2 mg N kg^?1 field-moist soil, and the corresponding amounts released in air-dried soils ranged from 18.9 to 32.9 mg N kg^?1 soil. This increase of the amount NH₄ ⁺-N released in air-dried soil samples is presumably due to a slaking effect. At 5 mmol kg^?1 soil, all six heavy metals inhibited the NH₄ ⁺-N released. The relative effectiveness of the heavy metals in inhibition of the NH₄ ⁺-N released varied among the three soils. Lead(II) was the most effective inhibitor of NH ₄ ⁺-N release in Clarion and Harps soils and Cd(II) in Harps soil. Cobalt(II), Cu(II), and Cd(II) were the least effective inhibitors of NH₄ ⁺-N release in Clarion, Harps, and Okoboji soils, respectively.     

Verhalten von Dünger-NH4 in Böden unterschiedlicher tonmineralischer Zusammensetzung im Inkubationsversuch

Fate of fertilizer ammonium in soils with different composition of clay minerals in an incubation experiment In an incubation experiment with three different soils (gray brown podsolic soil from loess, alluvial gley, and brown earth, derived from basalt) the specific adsorption (fixation) and release of fertilizer NH₄⁺ was investigated. In one treatment 120 mg NH₄–N/kg soil was added, while the other treatment (control) received no nitrogen. Soils samples were taken every ten days and analyzed for nonexchangeable and exchangeable NH₄⁺ and NO₃^?. The experimental results are showing that the specific adsorption of applied NH₄⁺ was related to the type of clay minerals. While the loess soil, rich in illite, and the alluvial soil, rich in expansible clay minerals, bound about 40% of the added NH₄⁺ specifically, the soil derived from basalt with mainly kaolinite bound only about 10 %. From the recently “fixed” fertilizer NH₄⁺ about a half was nitrified during the incubation period of about 9 weeks. In the control there was no significant release of specifically bound NH₄⁺. Obviously this NH₄⁺ is located more deeply in the interlayers of the clay minerals and not available to microorganisms.     

Mechanisms of fixation and release of ammonium in paddy soils after flooding. IV. Significance of oxygen secretion from rice roots on the availability of non-exchangeable ammonium – a model experiment

In a model experiment the effect of O₂ secretion from imitated rice roots on the availability of non-exchangeable NH₄⁺ and N uptake by imitated roots under flooding conditions was investigated. O₂ secretion favoured the mobilization of non-exchangeable NH₄⁺ and increased N uptake by increasing the uptake of NO₃^--N. O₂ secretion resulted in a significant decrease in the concentration of exchangeable NH₄⁺ due to nitrification and in a lower pH of the rhizosphere. The protons are derived from the oxidation of Fe²⁺. In contrast, coating of clay minerals with Fe oxides, which is promoted by O₂ secretion and formation of free Fe oxides in the rhizosphere, may hinder the release of non-exchangeable NH₄⁺.     

Estimating soil ammonium adsorption using pedotransfer functions in an irrigation district of the North China Plain

Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen(NH4⁺_-N) in soil. Desorption and leaching of NH4⁺_-N has led to pollution of natural waters. The adsorption of NH4⁺_-N in soil plays an important role in the fate of the NH4⁺_-N. Understanding the adsorption characteristics of NH4⁺_-N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions(PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture(silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH4⁺_-N adsorption capacity than sandy loam soils.Clay and silt contents significantly affected the adsorption capacity of NH4⁺_-N in the different soils. The adsorption isotherms of NH4⁺_-N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay,silt, and organic carbon contents and Fe²⁺ and Fe³⁺ ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH4⁺_-N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH4⁺_-N adsorption at a regional scale in irrigation districts.     

Ammonium fixation by clay minerals in different layers of two paddy soils after flooding

 The influence of flooding and cellulose addition on the fixation of NH₄ ⁺ in different soil layers of two paddy soils from China (an entisol and an ultisol) was investigated. In both soils the content of total reducing substances (TRS) sharply increased during the first days after flooding and was highest in the anoxic layers. This increase, which was more pronounced in the entisol with the higher total C content, was accompanied by an increase in the concentration of non-exchangeable NH₄ ⁺ in both soils. The increase in mineralization after flooding, resulting in higher concentrations of exchangeable NH₄ ⁺, favoured the fixation of NH₄ ⁺. Although the application of cellulose resulted in higher TRS contents, the fixation of NH₄ ⁺ ions decreased, which may have been the result of microbiological N immobilization. Received: 29 April 1998     

Fixed ammonium and potassium release from two soils

Abstract

Release of native and added K⁺ and NH⁺ ₄ from two soils was monitored during a 166 day incubation/leaching experiment. One soil (Brookston) represented a major soil series In Ontario whereas the other (Harriston) was suspected having a relatively large fixation capacity. Treatments were imposed involving addition of 50 μM g^‐1 soil of K⁺(KCl) or NH⁺ ₄ (NH₄Cl) only or one added after the other on successive days. The addition of either K⁺ or NH⁺ ₄ on day 2 tended to inhibit the release of the other added on day I. Also the addition of either K⁺ or NH⁺ ₄ on day 1 tended to inhibit the sorption or fixation of the other on day 2. The release rate of K⁺ during the 10 to 166 day period was almost constant and not affected by the addition of NH⁺ ₄. Alternatively, the addition of K⁺ on day 2 slowed the release rate of NH⁺ ₄ measured by NO^? ₃ appearance from day 10 to 40 but had no effect thereafter. At the end of the experiment considerably more K⁺ than NH⁺ ₄ was retained suggesting that K⁺ was more firmly fixed. However, the continuing nitrification of NH⁺ ₄ must be contrasted with periodic removal of K⁺ by leaching with 0.01 M CaCl₂ solution since the equilibrium between exchangeable and fixed ions was affected. There were no notable differences between the two soils inspite of a considerable difference in clay content.     

Factors affecting potassium fixation in calcareous soils of southern Iran

Potassium fixation capacity and mineralogical analysis of 24 representative soils, collected from southern Iran, were studied. Potassium fixation analysis was performed by adding six rates of K from 0 to 1000 mg kg^?1 soil in a plastic beaker and shaking for 24 h. Mineralogical analysis showed that the clay fractions were dominated by smectite, chlorite, mica, palygorskite, vermiculite and quartz. In general, the studied soils fixed 8.5–55% of the added K. The potassium fixation capacity of the studied soils was significantly correlated with smectite content (r ² = 0.87), clay content (r ² = 0.60), cation-exchange capacity (r ² = 0.79) and NH₄OAc-K. Wetting and drying treatment and incubation time had significant effects on K fixation. The average percentage increase in K fixation following the wetting and drying treatment was 24 and 30% for surface and subsurface soils, respectively. The average percentage increase in K fixation with increasing residence time was 79 and 56% for surface and subsurface soils, respectively. Because K fixation is a diffusion process, time and increased concentration of soluble K (because of soil drying) are factors affecting the rate of K diffusion from a soil solution to the interlayer positions of the expansible 2:1 clay minerals.     

灌溉施用氮肥后氮素在土壤中的转化及淋失状况: 土柱模拟研究

A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH₄⁺-N + NO₃^--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH₄⁺-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH₄⁺-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH₄⁺-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH₄⁺-N fixation or volatilization in the soil during the fertigation process.     

Release of nonexchangeable NH4-N after planting of ryegrass in relation to soil content and as affected by nitrate supply

The uptake of N by ryegrass grown in pot culture on a range of soils differing widely in content of nonexchangeable NH₄-N (topsoils: 117 to 354 mg kg^?1 soil; subsoils: 117 to 270 mg kg^?1 soil) was measured to indicate whether the amounts of NH₄-N released from clay minerals were correlated with soil NH₄-N. After two cuts soil analysis revealed that the amounts of mobilized nonexchangeable NH₄-N were between 3.5 and 25.2 mg kg^?1 from topsoils and between 0 and 8.2 mg kg^?1 from subsoils. There was no correlation between soil nonexchangeable NH₄-N content and release. The NH₄-N extracted with 1 N HCl and the actual N uptake of the plants correlated highly significant. Assuming that the whole of the NH₄-N released was taken up by ryegrass, NH₄-N accounted for 11.2 to 75.0% of total N uptake from topsoils and 0 to 37.3% from subsoils. The release of nonexchangeable NH₄-N was increased by the application of nitrate.     

湖南几种耕地土壤固定添加铵的动力学研究

通过野外调查取样、室内培养试验和分析测定，研究了湖南省几种成土母质发育的旱地土壤和稻田土壤固定添加铵的动力学特性。结果表明，供试土壤对添加铵的固定速度很快，尤其在反应的前8～12h内速度更快，12h后速度逐渐变慢，24h以后，土壤对外源铵的固定已基本达到平衡。数学拟合表明，一级动力学方程和Elovich方程两种动力学模型能较好地拟合供试土壤固定添加铵的动力学特性，经统计均达极显著水平，抛物扩散方程也有较好的拟合效果，零级方程较差。由一级动力学方程求得的不同土壤固铵动力学参数：理论最大固铵量（A）、反应速率常数（b）以及反应半时值明显不同。耕型石灰性紫色土、耕型酸性紫色土、耕型棕色石灰土和耕型石灰岩红壤的理论最大固铵量和反应半时值分别为212．3mg kg^-1、179．0mg kg^-1、142．9mg kg^-1.13．7mg kg^-1和29．75h、25．96h、27．18h、23．49h；紫泥田、河沙泥、灰泥田和红黄泥的理论最大固铵量和反应半时值分别为86．2mg kg^-1、68．7mg kg^-1,31．8mg kg^-1、19．1mg kg^-1和14．50h、15．10h、15．51h、18．43h。耕型石灰性紫色土、耕型酸性紫色土、耕型棕色石灰土和耕型石灰岩红壤的反应速率常数分别为0．0233 h^-1、0．0267h^-1、0．0255h^-1、0．0295h^-1；紫泥田、河沙泥、灰泥田和红黄泥的反应速率常数分别为0．0478h^-1、0．0459h^-1、0．0447h^-1、0．0376h^-1.除耕型石灰岩红壤以外，旱地土壤的理论最大固铵量和反应半时值均明显大于水田土壤，而反应速率常数明显小于水田土壤。