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1.
Ammonia volatilization following surface application of urea to tilled and no-till soils: A laboratory comparison 总被引：1，自引：0，他引：1
Philippe Rochette Denis A. Angers Martin H. Chantigny J. Douglas MacDonald Nicole Bissonnette Normand Bertrand 《Soil & Tillage Research》2009,103(2):310
Broadcasting of urea to agricultural soils can result in considerable losses by NH3 volatilization. However, it is unclear if the impact of this practice on NH3 emissions is further enhanced when performed on no-till (NT) soils. The objective of this study was to compare NH3 volatilization following broadcasting of urea to NT and moldboard plowed (MP) soils. Intact soil cores were taken shortly after harvest from NT and MP plots of three long-term tillage experiments in Québec (Canada) and stored for 4.5 months prior to incubation. Urea (14 g N m−2) was applied at the soil surface and NH3 volatilization was measured for 30 d using an open incubation system. Mean cumulative NH3 losses were greater (P < 0.001) in NT (3.00 g N m−2) than in MP (0.52 g N m−2). Several factors may have contributed to the higher emissions from the NT soils. Urease activity in the top 1 cm of soils was on average 4.2 times higher in NT than in MP soils. As a result, hydrolysis of urea occurred very rapidly in NT soils as indicated by enhanced NH3 emissions 4 h after application of urea. The presence of crop residues at the surface of NT soils also decreased contact of the urea granules with the soil, possibly reducing adsorption of NH4+ on soil particles. Lower volatilization on the MP soils may also have partly resulted from a fraction of urea granules falling into shallow cracks. Field trials are needed to confirm our finding that NT soils bear greater potential for NH3 volatilization following surface application of urea than MP soils. 相似文献
2.
A cell consisting of a chloride-selective electrode and a nitrate-selective electrode was directly put in the soil suspension to determine the concentration ratio NO3?/Cl? for studying the adsorption of these two ions by three soil samples from variable charge soils. It was found that such factors as the iron oxide content of the soil, the pH of the suspension, the concentration of the respective anion, the kind of accompanying cations, and the dielectric constant of solvent etc. can all affect the amounts and the ratio of the two anions adsorbed. The adsorption was chiefly caused by coulombic force, but another mechanism, presumably a covalent force between the anion and the metal atom on the surface of soil particles, may also be involved, at least for chloride ions. 相似文献
3.
恒电荷土壤胶体对Cu2+ 、Pb2+ 的静电吸附与专性吸附特征 总被引：23，自引：2，他引：23
供试土壤胶体对Cu2 、Pb2 的吸附强度用pH50 值表示 ,其大小次序为 :土 >黄绵土、黑垆土 >黄褐土。离子强度实验和表面络合反应机制证明恒电荷土壤胶体对Cu2 、Pb2 的吸附含有专性吸附 ,n值可作为判断专性吸附与静电吸附比例的特征值 ,低pH值时 ,以水解 -络合吸附为主 ;高pH值时 ,以水解 -络合与沉淀吸附为主。静电吸附和专性吸附的比例与pH有关 ,各土壤胶体专性吸附百分数大小为 :黄褐土 >土 >黑垆土 >黄绵土。不同土壤胶体在同一介质中对Cu2 、Pb2 的固有络合常数logKintM 值及固有络合ΔG m 负值大小次序与吸附强度大小一致。在定pH定浓条件下 ,考虑离子之间的相互作用时 ,土壤胶体对重金属离子的吸附过程可用BDM等温式描述。供试土壤胶体对Cu2 、Pb2 专性吸附ΔG m 的大小与固有络合ΔG m 接近且大小次序也一致。 相似文献
4.
Urea, labelled with15N, was applied, at rates equivalent to 0–400 kg N ha?1, to mixed L + F horizon soil materials from a jack pine (Pinus banksiana Lamb.) forest. The L + F materials were held at 13°C and 33 kPa moisture in three experiments lasting from 6 to 128 days. In the first experiment the immobilization of fertilizer N was determined, in the second the stimulation of microbial activity was measured, and in the third urea reactions in a forest floor without microorganisms were examined. Urea stimulated microbial activity and microbial mineralization of soil N. Total amounts of N immobilized and recovered as organic N, after 128 days, increased with rate of application from 50 to 400 kg urea-N ha?1. The pH and C contents of water extracts of soil increased with increasing rates of urea application. Organic matter in a forest floor treated with urea was shown to solubilize after microbial activity was inhibited by gamma radiation, and this suggests that chemical C release was brought on by the urea. Results from this study were consistent with the hypothesis that microbial activity in urea-treated soil is stimulated by increased availability of C in soil. 相似文献
5.
Organotin compounds (OTC) are deposited from the atmosphere into terrestrial ecosystems and can accumulate in soils. We studied the adsorption and desorption of methyltin and butyltin compounds in organic and mineral soils in batch experiments. The adsorption and desorption isotherms for all species and soils were linear over the concentration range of 10–100 ng Sn ml?1. The strength of OTC adsorption correlated well with the carbon content and cation exchange capacity of the soil and was in the order mono‐ > di‐ > tri‐substituted OTCs and butyltin > methyltin compounds. The OTC adsorption coefficients were much larger in organic soils (Kd > 104) than in mineral soils. The adsorption and desorption showed a pronounced hysteresis. Trimethyltin adsorption was partly reversible in all soils (desorption 2–12% of the adsorbed amounts). Dimethyltin, tributyltin and dibutyltin exhibited reversible adsorption only in mineral soils (desorption 4–33% of the adsorbed amounts). Mono‐substituted OTCs adsorbed almost irreversibly in all soils (desorption < 1% of adsorbed amounts). Trimethyltin was more mobile and more bioavailable in soils than other OTCs. It might therefore be leached from soils and accumulate in aquatic ecosystems. The other OTCs are scarcely mobile and are strongly retained in soils. 相似文献
6.
Cd adsorption isotherms were measured on five Israeli soils ranging in specific surface area from 65 to 315m2/g. Retention capacity of Cd ranged from 4.7 × 103 to 10 × 103μg/g soil (8.4 to 17.9 mequiv/100 g soil) and was correlated with the specific surface area. Almost all the adsorbed Cd was exchangeable with 0.5 M CaCl2 and the remaining fraction was extractable in 0.5 M HCl. Plots of Kd, the distribution coefficient of Cd between the solid and solution phases, vs. Γ, the surface density of adsorbed Cd, showed that all soils behave similarly, Kd sharply diminishing with Γ. It was suggested, based on comparison with literature data on Cd adsorption on montmorillonite, that below γ s 0. 5 × 1017 ions/m2, specific adsorption mechanisms prevail whereas above it the adsorption is mainly due to electrostatic interactions and ion exchange. 相似文献
7.
氯甲基吡啶对滴灌棉田土壤微生物群落功能多样性的影响 总被引：3，自引：1，他引：2
已知硝化抑制剂氯甲基吡啶能有效抑制土壤硝化,减少氮的淋洗和硝化-反硝化损失,促进作物对氮素的吸收,但是其对干旱区滴灌条件下土壤微生物群落功能多样性的影响尚不明确。本试验研究了尿素添加氯甲基吡啶(Nitrapyrin)分次随水滴施对干旱区滴灌棉田土壤微生物碳代谢和群落功能多样性的影响。试验采用随机区组设计,设置不施氮肥[CK,0 kg(N)·hm~(-2)]、单施尿素[Urea,225 kg(N)·hm~(-2)]和尿素添加氯甲基吡啶[Urea+nitrapyrin,225 kg(N)·hm~(-2)+2.25 kg(nitrapyrin)·hm~(-2)]3个处理,重复4次,采用Biolog-ECO法进行土壤微生物碳代谢和功能多样性研究。结果表明:与不施氮肥(CK)相比,施用尿素和尿素添加氯甲基吡啶均能显著提高土壤微生物对31种碳源的代谢能力(AWCD)和代谢强度(S)(P0.05),增加土壤微生物多样性和丰富度(Shannon指数、Simpson指数、Mc Intosh指数和Richness指数)以及对各类碳源的利用能力。尿素添加氯甲基吡啶随水滴施后,土壤微生物AWCD值、碳代谢强度、Shannon指数、Simpson指数、Mc Intosh指数以及Richness指数均大于单施尿素处理,且较单施尿素处理分别提高13.83%、9.33%、1.29%、1.34%、11.26%、11.79%(P0.05),均匀度指数则低于单施尿素处理(P0.05)。PCA和聚类分析结果表明,施用尿素和尿素添加氯甲基吡啶对土壤微生物群落功能多样性均产生了显著影响,但尿素添加氯甲基吡啶与单施尿素处理差异不显著;氯甲基吡啶的添加提高了土壤微生物对聚合物、酚酸、羧酸、氨基酸以及胺类的利用,降低了对碳水化合物的利用(P0.05)。上述研究结果得出,在干旱区滴灌棉田,尿素添加氯甲基吡啶分次随水滴施可调控土壤的微生态环境,在一定程度上提高土壤微生物的代谢能力,增加微生物群落功能多样性,缓解因长期施用无机氮肥导致的土壤微生物活性的降低。 相似文献
8.
Some observations on the desorption and distribution behaviour of copper with soil components 总被引：2，自引：0，他引：2
The ability of copper adsorbed by soil components to desorb back into solution was studied by means of experiments using radioactive 64Cu. It was demonstrated that the amounts of copper which can be readily desorbed from soil components are very small. A dialysis equilibration technique was used to examine the distribution of adsorbed copper between individual materials in a multi-component system. Where only adsorption of copper was involved, the distribution of copper between soil materials was found to agree with predictions based on adsorption studies with individual materials. However, where desorption was involved, as in the experiments on the redistribution of copper between components after an initial adsorption, the results were strongly governed by the poor reversibility of copper adsorption. It is clear that desorption or lack of desorption is very important in affecting plant availability of indigenous or added soil copper and in controlling the distribution of copper added to soils. 相似文献
9.
坡缕石包膜对尿素氮行为的影响 总被引：2，自引：1，他引：2
采用静态吸收和土柱淋溶试验方法,分析对比了3种不同用量坡缕石包膜尿素与普通尿素施入土壤后对尿素氮行为的影响,结果表明:在土壤中施用坡缕石包膜尿素较普通尿素减少10.38%～26.24%的氨挥发损失,减少5.88%～27.74%的氮素(NO3--N+NH4+-N)淋溶损失,20%的坡缕石包膜尿素能显著提高土柱土壤NH4+-N含量,3种坡缕石包膜尿素都能极显著提高土柱土壤NO3--N含量.坡缕石包膜后能减少尿素氨的挥发,降低NH4+-N和NO3--N的淋失,提高土壤NH4+-N和NO3--N含量,以20%的坡缕石包膜尿素的综合生态效应最好. 相似文献
10.
砂壤中铜的吸附行为及其影响因素研究 总被引：1，自引：0，他引：1
研究了果园附近砂壤中Cu的吸附行为，并探讨了pH值及土壤有机质对吸附的影响。结果表明，供试土壤对Cu的吸附行为可用Freundlieh方程拟合，电性吸附态Cu较易解吸；而专性吸附态Cu较难解吸。动力学实验表明，最初4h内的吸附量占总吸附量的60％以上，8h后达到平衡；而解吸在最初30min内占了近80％，2h后可达平衡。低pH值时，H^＋和Cu发生竞争吸附，可明显抑制土壤对Cu的吸附；随pH值的升高，抑制作用减弱，其logKd与pH呈线性正相关；在中性和偏碱性范围，pH值对土壤吸附Cu的影响不大。原土去除有机质后对Cu的分配系数降低了10倍。 相似文献
11.
控释肥施用对小麦生长期N2O排放的影响 总被引：16，自引：0，他引：16
通过田间试验,采用静态箱法研究不同施氮水平下控释肥和尿素(N 0、100、200、270 kg hm-2)对麦季N2O排放的影响。结果表明,与对照相比,整个小麦生长季N2O排放量均随尿素和控释肥施用量的增加呈指数增加(32%～164%,p<0.05),但控释肥处理增加程度则较尿素处理缓和;施用控释肥可以有效抑制小麦生长季N2O排放(p<0.05),控释肥对N2O的减排量随着施氮量的增加而增加。小麦产量随尿素施用量的增加呈抛物线增加(24%～43%,p<0.05),随控释肥施用量的增加亦呈抛物线增加(30%～45%,p<0.05);与施用相同水平尿素相比,施用控释肥的小麦产量略有增加,但无显著差异(p>0.05)。单位产量N2O排放量随尿素施用量的增加而呈指数增加(31%～114%,p<0.05),随控释肥施用量的增加而呈抛物线增加(2%～50%,p<0.05);施用控释肥可以有效抑制小麦生长季单位产量N2O排放(p<0.05),控释肥对单位产量N2O的减排量随着施氮量的增加而增加。各处理N2O排放量与土壤水分存在显著正相关(p<0.05),与土壤NH4+-N、NO3--N浓度和土温不呈明显线性关系(p>0.05)。 相似文献
12.
Chemical fixation of NH3 to soil organic matter was studied in two Swedish soils with different contents of organic matter: a clay soil with 2.3% C and an organic soil with 36.6% C. 15N‐labelled urea was applied at different rates to both sterilized and non‐sterilized soils. After 10 days, the soils were extracted and washed with K2SO4 and determined for total N and atom% 15N excess. Urea N was recovered as non‐extractable N in sterilized soil corresponding to 9.7% of supplied l5N‐labelled urea in the organic soil and 2.2% in the clay soil. Since no biological immobilization is thought to occur in the sterile soil, this non‐extractable N is suggested to be chemically fixed to soil organic matter. Owing to urea hydrolysis in the clay soil, pH increased from 6.3 to 9.3 and in the organic soil from 5.7 to 6.9 and 8.8, respectively, at the low and high urea supply. 相似文献
13.
《Soil Science and Plant Nutrition》2013,59(6):788-792
Abstract Methane flux was measured monthly from August 2002 to July 2003 at an oil palm plantation on tropical peatland in Sarawak, Malaysia, using a closed chamber technique. Urea was applied twice, once in November 2002 and once in May 2003. The monthly CH4 flux ranged from ?32.78 to 4.17 µg C m?2 h?1. Urea applications increased CH4 emissions in the month of application and emissions remained slightly higher a month later before the effect disappeared in the third month after application (i.e. back to CH4 uptake). This effect was the result of increased soil NH+ 4 content that was not immediately absorbed by the oil palm following urea application, which reduced the oxidation of CH4, resulting in its enhanced emission. By using the Cate–Nelson linear-plateau model, the critical soil NH+ 4 content causing CH4 emissions in the oil palm ecosystem was 42.75 mg kg?1 soil. However, the inhibitory effect of NH+ 4 on the oxidation of CH4 was mitigated by low rainfall and the pyrophosphate solubility index (PSI), where the former might increase oxidation of CH4 and the latter was a reflection of the low soluble substrate for methane production. Thus, the splitting and timing of urea applications are important not only to optimize oil palm yield, but also to reduce soil NH+ 4 content to minimize CH4 emissions and, therefore, its potential negative impact on the environment. 相似文献
14.
Humic acids buffer the effects of urea on soil ammonia oxidizers and potential nitrification 总被引：2，自引：0，他引：2
Humic acids (HAs) play an important role in the global nitrogen cycle by influencing the distribution, bioavailability, and ultimate fate of organic nitrogen. Ammonium oxidation by autotrophic ammonia-oxidizing bacteria (AOB) is a key process in ecosystems and is limited, in part, by the availability of NH4+. We evaluated the impact of HAs on soil AOB in microcosms by applying urea (1.0%, equal to 10 mg urea/g soil) with 0.1% bHA (biodegraded lignite humic acids, equal to 1 mg/g soil), 0.1% cHA (crude lignite humic acids) or no amendment. AOB population size, ammonium and nitrate concentrations were monitored for 12 weeks after urea and HA application. AOB densities (quantified by real-time PCR targeting the amoA) in the Urea treatments increased about ten-fold (the final abundance: 5.02 × 107 copies (g of dry soil)−1) after one week of incubation and decreased to the initial density after 12 weeks incubation; the population size of total bacteria (quantified by real-time PCR with a universal bacterial probe) decreased from 1.12 × 1010 to 2.59 × 109 copies (g of dry soil)−1 at week one and fluctuated back to the initial copy number at week 12. In the Urea + bHA and Urea + cHA treatments, the AOB densities were 4 and 6 times higher, respectively, than the initial density of approximately 5.07 × 106 copies (g of dry soil)−1 at week 1 and did not change much up to week 4; the total bacteria density changed little over time. The AOB and total bacteria density of the controls changed little during the 12 weeks of incubation. The microbial community composition of the Urea treatment, based on T-RFLP using CCA (canonical correspondence analysis) and pCCA (partial CCA) analysis, was clearly different from those of other treatments, and suggested that lignite HAs buffered the change in diversity and quantity of total bacteria caused by the application of urea to the soil. We hypothesize that HAs can inhibit the change in microbial community composition and numbers, as well as AOB population size by reducing the hydrolysis rate from urea to ammonium in soils amended with urea. 相似文献
15.
Dong-Mei Zhou Huai-Man Chen Shen-Qiang Wang Chun-Rong Zheng 《Water, air, and soil pollution》2003,145(1-4):109-121
This article studied the interaction of cadmium (Cd) and lowmolecular weight organics in Indicotic black (IB) soil.Cadmium adsorption isotherm in this soil was satisfactorilysimulated using Freundlich equation as Q = 905.6C0.49 with high correlation (r2 = 0.984), and its adsorption quantity increased with increasing pH. The presence of citricacid and EDTA significantly reduced Cd adsorption in soil,which was due to the formation of soluble Cd-organic complex. Concentration of cadmium ions in equilibrium solution was determined and percentages of [CdH2Cit+]/[Cd-complexTotal],[CdHCit]/[Cd-complexTotal] and [CdCit-]/[Cd-complexTotal] vs. pH were successfully calculated. Desorption percentage ofCd, adsorbed in the presence of citric acid and EDTA decreased, compared with that adsorbed in NaNO3 media. It suggeststhat free sites for Cd adsorption in soil increased in thepresence of organic acid. When o-phenylenediamine, pyrocatechol and aminoethonic acid appeared in Cd equilibrium media, Cd adsorption quantity increased by increasing cation exchange ofpositively charged cadmium complex with soil at low pH. Compared with that performed in the absence of these organics, the exchangeable Cd, desorbed by 0.1 mol L-1 NaNO3, reduced obviously, which suggests that Cd-complex was moredifficult to be desorbed than Cd2+. Moreover, % Cd desorbedwas linearly correlated with the reverse of the total Cd adsorptionunder unsaturated adsorption. 相似文献
16.
Song Li Yue Li Xueru Huang Feinan Hu Xinmin Liu Hang Li 《Journal of Soils and Sediments》2018,18(3):863-873
Purpose
The extensive application of phosphate fertilizers could produce a series of environmental problems by adsorbing on the surface of soil particle and migrating into water during soil erosion. Therefore, this study is to explore the effects of phosphate on soil aggregate stability and soil erosion and to analyze the mechanisms of phosphate enhancing soil erosion from the scope of soil charge density, electric field, and particle interaction.Materials and methods
A variable charged soil (0–20 cm) was pre-treated firstly by KCl, K2HPO4, and KH2PO4, respectively. Under the conditions of KCl, K2HPO4, and KH2PO4 solutions with concentrations of 0.0001, 0.001, 0.01, 0.1, and 1 mol L?1, (1) the amounts of soil particle transport and erosion intensities were measured using rainfall simulation with electrolyte solutions instead of rainwater; (2) the aggregate stabilities were measured by weighing the particles and micro-aggregates of <2, 5, and 10 μm after soil aggregate breakdown in electrolyte solutions; and (3) the zeta potentials of soil particles were measured in electrolyte solutions.Results and discussion
The application of K2HPO4 and KH2PO4 in soil strongly enhanced soil aggregate breakdown and soil erosion, while in KCl application, soil aggregates were stable and erosion did not occur. Moreover, the intensities of soil aggregate breakdown and soil erosion for K2HPO4 application were much stronger than that for KH2PO4 application. Phosphate, especially K2HPO4, strongly increased surface negative charge density of soil particles and thus increased the electrostatic repulsive pressure between adjacent soil particles in aggregates, and as a result, the soil erosion intensity increased. However, the surface charge density was not increased by the increased pH, specific adsorption, and dispersion force adsorption but possibly attributed to a non-classic induction force adsorption arising from the anionic non-classic polarization in the strong electric field around soil particle surface.Conclusions
The application of phosphate decreased aggregate stability and stimulated soil erosion through increasing charge density of particle surface by a new non-classic induction adsorption of phosphate.17.
《Communications in Soil Science and Plant Analysis》2012,43(4):447-459
Abstract Eleven selected soils from Denmark and Tanzania were treated with ammonium acetate (controls), EDTA, and dithionite‐EDTA (DE) to fractionate iron and (manganese) oxides. The amounts of cobalt adsorbed were determined from a 3 μM equilibrium cobalt solution, corresponding to the cobalt level in natural soil solutions using sodium nitrate (0.2 M) to suppress non‐specific adsorption, by the extracted soils as well as by two synthetic iron oxides. No significant correlations were found between cobalt adsorption and the contents of organic matter and extractable manganese, presumably due to their low contents in the soils investigated. Close correlations were, however, found between the amounts of cobalt adsorbed, especially fractions thereof, and the contents of iron oxides. The amounts of cobalt adsorbed by the DE‐ex‐tracted soils, void of iron (and manganese) oxides, were attributed to the clay silicates. The remaining cobalt adsorption, i.e. the difference between cobalt adsorbed by acetate‐extracted and DE‐extracted samples, was attributed to the iron oxides. This portion of adsorbed cobalt was well described by considering soil iron oxides composed of only two fractions, an EDTA‐extractable fraction of high reactivity and a less reactive fraction corresponding to the difference between DE‐extractable iron and EDTA‐extractable iron. The amounts of cobalt adsorbed by the soil iron oxides were well predicted from the contents and specific surface of the two iron oxide fractions in soil together with the amount of cobalt adsorbed by the synthetic iron oxides. 相似文献
18.
The kinetics and heats of phosphate adsorption were measured on the <2 μm Na-saturated fractions of three allophanc-rich soils from Japan. Between 50 and 2250 μmol P g?1 as sodium phosphate were added to the soil fractions at pH 5 and pH 7, and at initial concentrations of 5 and 25 × 10?4m to avoid aluminium phosphate precipitation. An initial ‘instantaneous’ adsorption associated with exposed sites and, simultaneously, two inverse exponential rates of adsorption on internal and freshly forming external sites were observed. These rates are attributed to changes in the microstructure of allophane and to the desorption of organic matter held on allophanic surfaces. This interpretation is strongly supported by corresponding changes in the heats of adsorption with time. Calorimetry clearly indicates that when very large amounts of phosphate are added, new and very reactive surfaces are progressively exposed. More phosphate was adsorbed when the soil was acid and when the soil contained less organic matter. 相似文献
19.
苏南水稻土对铜离子专性吸附的初步研究 总被引：3，自引：1，他引：3
六十年代以来,土壤对多价离子特别是重金属离子的专性吸附,已日益成为土壤化学领域中一个受人注意的问题。土壤胶体中铁、锰、铝、硅等氧化物及其水合物和土壤有机质是专性吸附的主要载体[12,16,17,19,20,21],它们对许多重金属元素的专性吸附所引起的富集过程,起着控制这些金属元素在土壤溶液和海水中浓度的作用[9,15,18];一些微盒营养元素在土壤中的移动及其对植物的有效性,也深受土壤中氧化物胶体的专性吸附的影响[11,14,21]。因此,铁、锰等水合氧化物对重金属离子的专性吸附的研究,不仅是土壤化学领域,而且也是土壤环境保护和地球化学等领域中的重要研究课题。 相似文献
20.
Phosphate adsorption of some Bavarian soils . Phosphate adsorption isotherms were established in buffered (pH 4.6, 5.5, 7.0) and some in unbuffered (0.01 M CaCl2) systems for 9 soil profiles, 6 of which represent loess soils in various stages of development. In the P-equilibrium concentration range of 0–10?4 mole/l two to three ranges can be identified, each of which obeys the Langmuir equation. In the lowest concentration range (0–0.2·10?4 mole/l) adsorption is linearly related to equilibrium concentration. For the different Langmuir ranges the adsorption maxima (b) increase and the adsorption coefficients (k) decrease with increasing equilibrium concentration. The maxima depend on buffer-pH in the order 5.5<4.6<7.0. A single point method similar to the one recently proposed by Bache and Williams (1971) was succesfully applied to obtain b from a single measurement using a significant correlation between b from complete isotherms and the ratio of P adsorbed to that in solution after the addition of a fixed amount of P (0.8–1,6 mg P/g of soil). The b-values in the equilibrium concentration range of 1–20·10?4 mole/l depend mainly on soil pH (negative) and clay (positive) (multiple correlation coefficient r = 0.858). The common reason for this appears to be the amount of exchangeable Al which is also significantly correlated with b. During soil development the depth function of b changes due to decalcification, drop of pH and migration of clay and iron oxides. 相似文献