Use of adsorption and buffer capacity in soil testing for phosphorus

Abstract

The methods used to predict phosphorus (P) fertilizer requirements use extractable P levels. The inclusion of soil P buffer capacity with extractable P levels to improve fertilizer P prediction accuracy should be further investigated for Mediterranean soils. The objectives of this study, were to characterize the P adsorption properties of selected soils and to compare different soil P buffering capacity indices to determine their contribution to predict P fertilizer requirement. Twenty‐one soils were collected and P adsorption isotherms determined. On 11 soils wheat was grown in the greenhouse and P requirement determined. The Langmuir adsorption isotherm described the P adsorption of all soils. The prediction of crop P requirement was improved by the inclusion of a soil P buffer capacity index in the prediction equation. The index proposed by Salmon is easy to determine under routine soil analyses and does not require special analytical equipment. However, clay content can be used to predict the Salmon buffer index for similar soils.     

A potential method to incorporate quantity/intensity into routine soil test interpretations

Abstract

Exchangeable potassium (K), extracted with 1M ammonium acetate, widely used as the measure for plant available K does not estimate the K supplying capacity of the soil. This research was undertaken to quantity the K supplying capacities of some Missouri soils and evaluate a modified K Quantity‐Intensity (Q/I) approach for adaptation into routine soil analysis. The K supplying capacities as analyzed by the modified Q/I and plant removal were measured on the 0–20 cm and 20–40 cm depths of Broseley loamy fine sand (loamy, mixed, thermic Arenic Hapludalf), Mexico silt loam, (fine, montmorillonitic, mesic Udollic Ochraqualf), Waldron clay loam [fine, montmorillonitic (calcareous) mesic Arenic Fluvaquemt] and the 0–20 cm of Sharkey clay (very fine, montmorillonitic, nonacid, thermic Vertic Haplaquet). The dominant clays in the clay fractions were identified by X‐ray diffraction to be composed of montmorillonite and illite. The high linear coefficient of correlation (R₂ = 0.92**) between the potassium buffer capacity index (KBC Index) and cation exchange capacity [CEC, sum of exchangeable Ca, Mg, K, Na, and Neutralizable Acidity (NA)] suggests that KBC Index of soils with similar clay mineral compositions, but different clay quantities, could be estimated from the measured CEC. Plant K uptake was highly linearly correlated with K quantity (Kq, R₂ =0.98**) as measured by the modified Kq/i method. It appears to be possible, using the KBC Index derived from the CEC, to calculate a Kq/i value with a single measurement of the K in equilibrium with 0.01 M CaCl₂. With the modified Kq/i method, and using this approach, a total plant available K model is presented. This modified Kq/i approach offers the opportunity for soil testing laboratories to complete a calculation for total plant available K with only one additional measurement of the equilibrium K in 0.01 M CaCl2. This would facilitate the fine tuning of soil test interpretation by basing K fertilizer recommendations on the quantity of plant‐available K in the soil.     

上海土壤磷的吸附特性及缓冲性能的研究

本文以上海土壤为对象,研究选定了土壤磷等温吸附试验条件为:水土比10,平衡时间6天,控温25℃,磷加入量为100,200,400,600μgP/g土,溶液基质为0.01M CaCl₂。磷缓冲能力试验条件为:平衡时间2天,磷加入量为20,40,100,200μgP/g土。根据Freundlich, Tempkin和Langmuir方程计算的土壤吸附指标与土壤类型及土壤性质有密切关系,是土壤磷素肥力的重要指标。反映土壤缓冲能力的“磷肥指标”与土壤有机质、粘粒、活性铝及pH值相关较好。上海几种主要土壤中以青紫泥的最大吸附量(X_m),0.2ppm P吸附量和“磷肥指标”为最高,其次为青黄土,沟干泥和黄泥头,最小为夹沙泥。应用磷吸附指标与“磷肥指标”来预测土壤需磷量,初步试验是可行的,但实际应用还需进一步试验研究。     

Effect of extractant and selected soil properties on predicting the optimum phosphorus fertilizer rate for growing soybeans under field conditions

Abstract

Precise P fertilizer recommendations depend on the concentration of P removed by a given soil test extractant and the effect of other soil properties. Soybeans were grown several years on five Oxisols with a number of established soil P levels. A model was developed to maximize net return as a function of the P extracted by three methods and the optimum P fertilizer rate at each site. To account for site effects, other soil properties were then evaluated in individual combinations with extractable P by multiple regression. Mehlich‐3, Bray‐1, and resin extractable P accounted for 67, 57, and 62% of the variation in optimum P fertilizer rate, respectively. When clay content or surface area was included, the percentages increased to 84, 84, and 95%.In general, other soil properties reflecting P sorption, such as P adsorption maximum, P buffering coefficient, and measurements of clay type, were less effective than percentage clay or surface area. Two additional studies were conducted for one season to validate this approach. The results were excellent on one soil, but underestimated the optimum P rate on another. There was a difference in clay type between the two sites, indicating that perhaps the approach developed should be restricted to kaolinitic soils which predominate in the region     

Phosphate sorption by red mediterranean soils from Greece

Abstract

In nineteen surface horizons of red Mediterranean soils from various locations of Greece, phosphorus (P) sorption experiments were conducted and the sorption characteristics were studied in relation to soil properties. Phosphate sorption data were fitted both to the Langmuir and Freundlich equations. From these equations, the following P sorption parameters were determined from the Freundlich equation, X = ACⁿ, the parameters A (the phosphate sorbed at C = 1 mg P/L), n (the P sorption intensity), the P sorption index (PS = X/log C) and maximum P sorption (Xmfr). From the Langmuir equation, C/X = 1/KXm + C/Xm, the parameters K (showing the bonding energy), maximum P sorption (Xmla), the quantity of P adsorbed at a standard concentration of 0.2 mg P/L (P0.2), and P maximum buffering capacity (PMBC). The Freundlich parameter A was strongly correlated to the clay and sesquioxides ("free”; iron and aluminum oxides and amorphous iron oxides) content. Seventy‐four percent of the variance of this parameter was explained by clay and “free”; iron (Fe) content. The Freundlich parameter n was significantly correlated with pH and amorphous iron oxides content, while 52% of its variance was explained by amorphous Fe and dithionite extrac‐table aluminum (Al). The P sorption maxima calculated from the Freundlich equation were in general lower than those calculated by the Langmuir equation. Both these parameters were strongly correlated with clay and more slightly with sesquioxides content. About 50% of their variance was explained by clay content of the soils. The P sorption index was strongly correlated with the clay content and less strongly with dithionite‐extractable Fe and Al. The P‐buffering capacity calculated from the data of Langmuir equation was also strongly correlated with these two parameters. In addition, clay content and dithionite‐extractable Fe and Al were well correlated to the amounts of P required to obtain an equilibrium concentration of 0.2 mg P/L while 61% of the variation of this parameter was explained by the clay and the dithionite‐extractable Fe content. From these findings, it seems that for the red Mediterranean soils from Greece, P sorption is affected by clay content and iron and aluminum oxide contents.     

Phosphorus Buffering Capacity Indices as Related to Soil Properties and Plant Uptake

ABSTRACT

Evaluation of the plant-available phosphorus (P) in calcareous soils is commonly performed by removing a portion of solid phase P using chemical extractants. Critical soil test values, however, may be affected by variation in sorption and buffering behavior of different soils. The objective of this study was to evaluate the importance of buffering capacity indices to predict P uptake by wheat (Triticum aestivum). Eleven surface soil samples were assayed for a number of P intensity (CaCl₂-P) and quantity (Olsen-P, Colwell-P, and Resin-P) factors. Some phosphorus buffering indices were obtained from P sorption equations. A single-point index of buffering was also determined experimentally. In a greenhouse experiment, wheat was grown for 35 and 70 days on the same soils and P uptake was determined. Nonlinear and linear equations described the P sorption data (P < 0.001). Buffering indices derived from these equations were highly correlated with single-point index of capacity. Clay content was the most important soil property affecting the buffering capacity factor. The phosphorus intensity index (CaCl₂-P) was weakly related to P uptake (P < 0.05). Among the quantity factors only Resin-P was significantly correlated with P uptake. Buffering indices showed significant but inverse relationships with P uptake only at 70 days harvest (r = ?0.69 to ?0.71; P < 0.05). Combination of intensity or quantity factors with buffering capacity indices, such as intensity/capacity or quantity/capacity indicators, improved considerably the ability to account for variations in P uptake by wheat.     

pH buffering capacity of acid soils from tropical and subtropical regions of China as influenced by incorporation of crop straw biochars

Purpose

The key factors influencing pH buffering capacity of acid soils from tropical and subtropical regions, and effects of soil evolution and incorporation of biochars on pH buffering capacity were investigated to develop suitable methods to increase pH buffering capacity of acid soils.

Materials and methods

A total of 24 acid soils collected from southern China were used. The pH buffering capacity was determined using acid–base titration. The values of pH buffering capacity were obtained from the slope of titration curves of acid or alkali additions plotted against pH in the pH range 4.0–7.0. Two biochars were prepared from straws of peanut and canola using a low temperature pyrolysis method. After incubation of three acid soils, pH buffering capacity was then determined.

Results and discussion

pH buffering capacity had a range of 9.1–32.1 mmol kg^–1 pH^–1 for 18 acid soils from tropical and subtropical regions of China. The pH buffering capacity was highly correlated (R ²?=?0.707) with soil cation exchange capacity (CEC) measured with ammonium acetate method at pH 7.0 and decreased with soil evolution due to the decreased CEC. Incorporation of biochars at rates equivalent to 72 and 120 t ha^?1 increased soil pH buffering capacity due to the CEC contained in the biochars. Incorporation of peanut straw char which itself contained more CEC and alkalinity induced more increase in soil CEC, and thus greater increase in pH buffering capacity compared with canola straw char. At 5% of peanut straw char added, soil CEC increased by 80.2%, 51.3%, and 82.8% for Ultisol from Liuzhou, Oxisol from Chengmai and Ultisol from Kunlun, respectively, and by 19.8%, 19.6%, and 32.8% with 5% of canola straw char added, respectively; and correspondingly for these soils, the pH buffering capacity increased by 73.6%, 92.0%, and 123.2% with peanut straw char added; and by 31.3%, 25.6%, and 52.3% with canola straw char added, respectively. Protonation/deprotonation of oxygen-containing functional groups of biochars was the main mechanism for the increase of pH buffering capacity of acid soils with the incorporation of biochars.

Conclusions

CEC was a key factor determining pH buffering capacity of acid soils from tropical and subtropical regions of China. Decreased CEC and content of 2:1-type clay minerals during evolution of tropical soils led to decreased pH buffering capacity. Incorporation of biochars generated from crop straws did not only ameliorate soil acidity, but also increased soil pH buffering capacity.

     

水溶性有机碳在各种粘土底土中的吸附：土壤性质的影响

Clay-rich subsoils are added to sandy soils to improve crop yield and increase organic carbon (C) sequestration; however, little is known about the influence of clay subsoil properties on organic C sorption and desorption. Batch sorption experiments were conducted with nine clay subsoils with a range of properties. The clay subsoils were shaken for 16 h at 4 ^oC with water-extractable organic C (WEOC, 1 224 g C L^-1) from mature wheat residue at a soil to extract ratio of 1:10. After removal of the supernatant, the residual pellet was shaken with deionised water to determine organic C desorption. The WEOC sorption was positively correlated with smectite and illite contents, cation exchange capacity (CEC) and total organic C, but negatively correlated with kaolinite content. Desorption of WEOC expressed as a percentage of WEOC sorbed was negatively correlated with smectite and illite contents, CEC, total and exchangeable calcium (Ca) concentrations and clay content, but positively correlated with kaolinite content. The relative importance of these properties varied among soil types. The soils with a high WEOC sorption capacity had medium CEC and their dominant clay minerals were smectite and illite. In contrast, kaolinite was the dominant clay mineral in the soils with a low WEOC sorption capacity and low-to-medium CEC. However, most soils had properties which could increase WEOC sorption as well as those that could decrease WEOC sorption. The relative importance of properties increasing or decreasing WEOC sorption varied with soils. The soils with high desorption had a low total Ca concentration, low-to-medium CEC and low clay content, whereas the soils with low desorption were characterised by medium-to-high CEC and smectite and illite were the dominant clay minerals. We conclude that WEOC sorption and desorption depend not on a single property but rather a combination of several properties of the subsoils in this study.     

Phosphorus sorption and availability indices as affected by properties of calcareous soils

Abstract

The Olsen solution is usually considered the best extractant for estimating P availability in calcareous soils, but predictability of the response to P fertilizers is often low under field conditions. In this study, soil characteristics influencing P sorption and extractability were evaluated. Forty‐one soils varying in CaCO₃, pH, and clay content were selected from pastures to minimize the effect of recent P additions. A P sorption index (PSI) determined from a single addition of 150 mg P/100 g soil was related to soil Ca and CaCO₃, but the correlation coefficients were rather low (r = 0.46 and 0.38, respectively). A P availability index (PAI), determined from the increase in extractable soil P after adding 50 mg P/kg to a suspension and allowing it to dry, was correlated quite well with cation exchange capacity and clay content (r = ‐0.61 for each) in soils with pH < 8.8. The PAI also had a positive relationship with the density of the processed soil sample (r = 0.60). The relationship between PAI and soil Ca (r = ‐0.51) was also better than that between PSI and soil Ca. Inclusion of initial soil P and organic carbon along with CEC increased the predictability of PAI from 37% to 59%. In soils with pH > 8.8, soil pH was the dominant factor controlling the PAI (r = 0.92).     

Potassium Buffering Capacity of Sandy Soils from Thua Thien Hue Province,Central Vietnam,as Related to Soil Properties

Most agricultural production in central Vietnam relies on sandy soils distributed along the sea coast. Because of their low exchangeable potassium (K) and low cation exchange capacity (CEC), careful adjustment of K fertilization on these soils is needed to minimize K leaching. Quantity/intensity curves were established on 24 sandy soils from Thua Thien Hue Province from which K buffering capacity (PBC) was calculated and compared with basic soil properties. Potassium buffering capacity was found to correlate best with soil texture and only a little with humus content, although these two characteristics are responsible for CEC. A simple equation based on sand content, which is easier to determine than clay content, is proposed to calculate optimum exchangeable K level as a function of target K level in soil solution.     

Copper Adsorption by Soils and its Relations with Plant Growth

Copper adsorption studies were conducted with 13 neutral to calcareous-alkaline soils. The data followed a Langmuir isotherm with two linear parts at low (part 1) and high (part 2) concentration of Cu in equilibrium solution. The ?pCu + 2pOH’? values show that part 1 and 2 stem largely from adsorption and precipitation reactions of Cu, respectively. The bonding energy and differential buffering capacity were significantly higher for part 1 while adsorption maximum and supply parameter were significantly higher for part 2 of the isotherms. Carbonate content, soil pH, organic matter, CEC and clay content were in that oder the predominant factors in elevating adsorption maximum, bonding energy coefficient and differential buffering capacity as well as decreasing supply parameter of soils. However, soil organic matter was the major determinant of strength of Cu adsorption. Copper potentials, adsorption maximum and differential buffering capacity were significantly correlated with dry matter production and Cu uptake in maize. The parameters of intensity factor predicted better the variation in yield and Cu uptake than the conventional soil test methods.     

Soil properties affecting volatilization of ammonia from soils treated with urea

Abstract

The effects of various soil properties on ammonia (NH₃) volatilization from soils treated with urea were studied by measuring the NH₃ evolved when 20 soils selected to obtain a wide range in properties were incubated at ‐0.034 mPa soil moisture potential and 30°C for 10 days after treatment with urea. The nitrogen (N) volatilized as NH₃ from these soils represented from 0 to 65% of the urea‐N applied and averaged 14%. Simple correlation analyses showed that loss of NH₃ was negatively correlated (P<0.1%) with cation‐exchange capacity, silt content, and clay content and was positively correlated (P <0.1%) with sand content. Loss of NH₃ was also negatively correlated with total nitrogen content (P<1.0%), organic carbon content (P<1.0%), hydrogen ion buffering capacity (P<5.0%), and exchangeable acidity (P<5.0%), and was positively correlated with calcium carbonate equivalent (P <1.0%) and with soil pH after incubation with urea (P<1.0%), but was not significantly correlated with initial soil pH or soil urease activity. Multiple linear regression analyses indicated that the amount of urea N volatilized as NH₃ from the 20 soils studied increased with increase in sand content and decreased with increase in cation‐exchange capacity. They also indicated that soil texture and cation‐exchange capacity are better indicators of potential loss of urea N as NH₃ from soils fertilized with urea than are hydrogen ion buffering capacity or initial soil pH.     

Effect of Incorporation of Crop Residues on a Maize–Groundnut Sequence in the Humid Tropics. II. Soil Physical and Chemical Properties

Abstract

A two‐year study (1997–1999) was conducted on a sandy clay loam (Typic Paleudult) at the experimental farm of the Universiti Putra to determine the effects of application of crop residues on changes of some soil properties in a maize (Zea mays L.)–groundnut (Arachis hypogaea) crop rotation system. Five crops of a rotation of sweet corn–groundnut–sweet corn–groundnut–sweet corn were sown with three treatments: recommended inorganic fertilizer [nitrogen (N), phosphorus (P), and potassium (K)] with crop residue (T1), recommended inorganic fertilizer without crop residues (T2) or one‐half of the recommended inorganic fertilizer with crop residues combined with 10 t ha^?1 of chicken manure (T3). Soil organic carbon (OC), soil water content and soil bulk density were not significantly changed. Application of crop residues for two years increased cation exchange capacity (CEC) whereas supplementing crop residues with CM had significantly increased soil pH of the topsoil. Phosphorous in manure treatment had moved down the soil profile, which might cause eutriphication of under ground water, particularly during the rainy season. Based on this work, incorporation of crop residues could be a beneficial practice for improving the fertility of acid soils.     

红壤基质组分对磷吸持指数的影响

在红壤旱地肥料长期定位试验(始于1988年)中,选取了无机肥试验区的NPK、NP、NK、PK,有机无机配施试验区的CK、CK+猪厩肥(BM)及CK+花生秸秆(SR)等7个施肥处理土壤,测定了土壤磷吸持指数(Phosphate sorption index,PSI),分析了PSI与红壤最大吸磷量(Xm)的相关关系,讨论了土壤pH、有机质、黏粒、铁铝氧化物及无机磷酸盐等基质组分对PSI的影响。结果表明:长期施磷或配施有机肥均可显著降低红壤PSI值,随着土壤pH的升高、有机质及铁结合态磷酸盐(Fe-P)含量的增加,红壤PSI显著降低;土壤游离铁铝氧化物及黏粒含量越高,PSI也越大。PSI与Xm呈显著线性相关关系(Xm=0.5PSI+412.8,n=15,r=0.967**,p<0.01),因此,可以用PSI替代Xm来表征土壤固磷能力,亦可由PSI的大小来推断土壤磷的供磷能力。     

RELATION OF SEVERAL PEDOLOGICAL CHARACTERISTICS TO ENGINEERING QUALITIES OF SOIL

An attempt to predict engineering qualities which are needed in soil evaluation and to enhance nonagricultural use of soil survey data was made. Data from a variety of soils were subjected to simple correlation and multiple regression analyses to relate three pedologic characteristics: clay content, cation-exchange capacity (CEC), and organic matter content to two engineering qualitites: plasticity index, and optimum moisture. Simple correlation coefficients showed that clay content and CEC correlated significantly with the engineering determinations. The relationship between organic matter content and these engineering determinations was weaker. Multiple regression analyses showed that the three pedologic characteristics accounted for most of the variation in each of the engineering qualities, and that prediction was feasible.     

长期不同施肥对黄壤磷素吸附–解吸特性的影响

[目的]磷吸附–解吸特性对土壤磷素有效性和环境流失风险有重要影响.研究长期不同施肥对黄壤旱地磷吸附–解吸特性的影响,可为黄壤区合理施用磷肥提供理论依据.[方法]供试黄壤肥力长期定位试验位于贵阳,始于1995年.设有对照(CK)、施氮钾肥(NK)、施氮磷钾肥(NPK)、单施有机肥(M)和有机肥化肥配施(MNPK)5个处理...     

Wheat p requirements on calcareous Morrocan soils: III evaluation by isotherms compared to Olsen extractable P

Abstract

Phosphorus fertilizer recommendations were compared by interpretations from P isotherms, Olsen extractable P and the Mitscherlich‐Bray model based on the Olsen method for 15 soils from the Chaouia (dryland) region of Morocco. The P isotherms were fit to straight line and second degree polynomial equations. The P buffer indexes (PBI) derived from the isotherms were not significantly correlated to P buffer capacities as measured by a single P buffer capacity index, but negatively correlated to Olsen P (r = ‐0.63), relative yield (r = ‐0.76) and P uptake (r = ‐0.66). Phosphorus in solution was a quadratic function of P added in 0.01 M CaCl₂equilibrium solution. The P fertilizer recommendations to maintain soil solution P concentrations at 0.01, 0.12 and 0.20 mg P L^‐1were higher than recommended by direct interpretation of plant response to Olsen extractable P and the quantity based on the Mitscherlich‐Bray model as calculated from Olsen available P values. The P fertilizer recommended to maintain soil solution P of 0.10 mg P L^‐1was significantly correlated with Olsen P (r = 0.71) as was that recommended Mitscherlich‐Bray log transformation model (r = 0.81), and nonlinear least square estimation (r = 0.78). Field research will be needed to evaluate if the P fertilizer recommended to maintain this solution P concentration is adequate for maximum economic wheat grain yield under field conditions     

Evaluation of P sorption capacity and P extractants for assessing P requirements of maize in Western Nigeria savannah soils.

Abstract

Most of the P extractants developed for soils in temperate countries have not been able to successfully predict P requirements of crops in the tropics. Some workers have, however, suggested the use of sorption capacity at standard equilibrium P concentration to estimate fertilizer P requirements. Phosphorus sorption capacity (psc), determined at 0.2 and 2.0 ug/ml equilibrium P concentrations, were evaluated by greenhouse and field fertilizer experiments on savannah soils of western Nigeria. Correlation coefficients between psc at 0.2 and 2.0 ug/ml P and yield attributes were very low and not statistically significant. The sorption values were also not able to predict P requirement in these soils because psc, and therefore, buffer capacity were low, difficult to measure accurately and did not approximate values required for maximum crop yields.

Field P rates usually exceeded P requirements obtained from psc measurements. However, extractants which were able to indicate P status and availability in the soils correlated significantly with yield. It is suggested, therefore, that soil tests with suitable P extractants in addition to fixation studies which would evaluate P needed to increase soil F to a given level would have to be investigated for meaningful fertilizer recommendations.     

紫色土K+吸附解吸动力学研究

从国家紫色土肥力与肥料效益监测基地定位试验上 ,在第 10年水稻收获后从 0～ 30cm土层采取土壤样品 ,研究土壤K 吸附、解吸动力学过程。结果表明 ,不同施肥处理土壤K 吸附、解吸反应分别在2 4～ 32min和 4 6～ 6 4min达到平衡 ,吸附、解吸平衡量分别为 14 1～ 19 2cmolkg-1和 11 6～ 17 5cmolkg-1。相关分析说明 ,土壤阳离子交换量 (CEC)及粘粒含量是影响吸附平衡时间、吸附平衡量的重要因素 ;CEC、交换钾量是影响解吸平衡时间、解吸平衡量的重要因素。由此可见 ,长期不同施肥对土壤CEC、粘粒及交换钾量产生影响 ,从而影响了紫色土K 吸附、解吸平衡时间及吸附、解吸平衡量。平衡前钾离子的吸附、解吸速度及吸附、解吸率与反应时间lnt间存在良好的线性关系。其中反应速度直线和解吸率直线的斜率、初始反应速度及初始吸附率均与CEC、粘粒含量密切相关。Elovich方程和一级扩散方程分别为描述紫色土K 吸附、解吸反应的最优与最差模型 ,指数方程和抛物线扩散方程拟合性介于Elovich方程和一级扩散方程之间。由此可见 ,紫色土K 吸附、解吸过程不是一个单纯的过程 ,而是一个包括土体膨胀、吸附位活化、表面扩散等诸多因素的复杂过程。     

区域土壤CEC与相关控制因子的空间非平稳关系评估

土壤阳离子交换量(CEC)对土壤的保肥能力具有重要影响。了解土壤CEC的空间分布及相关控制因子的影响有助于区域土壤肥力的精准调控。以往多采用传统的最小二乘(OLS)回归模型探索相关因子对土壤CEC的影响。然而,该类模型是一种总体回归方法,不能反映局部空间区域内相关因子对土壤CEC的影响。采用一种局部空间回归技术——地理加权回归(GWR)探索表层和亚表层土壤中CEC与相关控制因子(土壤黏粒、土壤有机质和土壤pH)之间的空间非平稳关系。结果表明,各控制因子在不同的子区域和深度对土壤CEC的影响均有明显差异;同时,GWR模型有效地揭示了土壤CEC与相关土壤控制因子的空间非平稳关系。所得的空间非平稳关系图可以为更精确地调控区域土壤肥力提供依据。