土地利用方式对黄土丘陵土壤CaCO_3含量及分布的影响

本文以具有典型黄土丘陵特征的砖窑沟流域为例,对该流域梁峁地主要土壤类型上不同土地利用方式下0～200cm层土壤剖面CaCO3含量进行了分析。结果表明:土壤CaCO3含量耕地>林地>荒草地;耕地土壤CaCO3有明显的累积层,累积深度约在20～100cm之间;林地累积层深度约在20～60cm之间;而荒草地无明显累积层。这种现象与一般干旱半干旱地区不同。     

北京市延庆县不同土地利用方式下的土壤可蚀性研究

以北京市延庆县上辛庄小流域为研究区域,选择区内农地、杏林、侧柏林、乔灌混交林这4种土地利用方式,通过对土壤水稳性团聚体特征、有机质含量变化以及土壤可蚀性K值进行计算和分析,研究了该区不同土地利用方式下的土壤可蚀性差异特征。结果表明,不同地类土壤团聚体破坏率表现为:农地>杏林>侧柏林>乔灌混交林,林地土壤团聚体结构破坏率显著低于农地(p < 0.05)。农地土壤有机质含量随土层深度的增加呈现一定的上升趋势,林地的土壤有机质含量随土层深度的增加而减小。不同土地利用方式的土壤可蚀性K值存在差异,表现为:乔灌混交林<侧柏林<杏林<农地。表层0-20cm土层土壤可蚀性K值小于20-40cm土层,表明其土壤抗侵蚀能力高于深层土壤,反映出保护表层土壤的重要性。对土壤可蚀性影响因子的分析结果表明,土壤黏粒含量、有机质含量和水稳性团聚体与土壤可蚀性K值的相关关系最为密切(p < 0.05)。     

不同土地利用方式下土壤抗冲性动态变化特征及其影响因素

采用原状土冲刷槽法,以桉树人工林、茶园、撂荒地、枇杷园、杉木人工林土壤为研究对象.研究了土壤抗冲性动态变化特征及其影响因素.结果表明:土壤初始径流含沙量均较大,但随着冲刷时间的延长径流含沙量逐渐降低,并在3～6 min后逐渐趋于稳定;土壤抗冲性能随冲刷时间的延长呈波状变化,但总体上仍符合随冲刷时间延长,抗冲性增强的规律;土壤抗冲性能随冲刷时间的变化可用幂函数方程很好的拟合,其相关指数介于0.717～0.989;土壤抗冲性主要受容重、坡度、植物根系等因素的影响.其中<1 mm须根是增强土壤抗冲性能的关键因子.<1 mm须根根长、根表面积、根体积与土壤抗冲性强化值△ANS呈显著或极显著正相关,其相关系数介于0.926～0.980.     

伊金霍洛旗不同土地利用方式下的土壤养分特征

为分析内蒙古鄂尔多斯市伊金霍洛旗在4类土地利用方式(灌木林地、采矿用地、天然牧草地和农地)下,土壤养分质量分数的差异性,运用野外采样和室内化验、分析相结合的方法,测定4种土地类型在0～30 cm土层的土壤有机质和全量氮磷钾质量分数及pH值.结果表明:1)4类土地在0～ 30 cm土层的土壤有机质和全氮质量分数存在显著差异,土壤全磷量和全钾量差异不显著(P＜0.05),土壤有机质质量分数依次为农地＞天然牧草地＞灌木林地＞采矿用地,土壤全量氮磷钾最大值分别为天然牧草地、天然牧草地和灌木林地,最小值分别为采矿用地、灌木林地和天然牧草地;2)在垂直剖面上,采矿用地和天然牧草地的有机质质量分数随着土层深度的增加逐渐减小,农地和灌木林地的有机质质量分数最大值出现在20～30 cm深度的土层,4类土地的土壤全氮量和全磷量均有随土层深度的增加而下降的趋势,全钾量随土层深度的变化不明显.4类土地的土壤全氮和全钾质量分数整体而言较为理想,全磷和有机质质量分数欠缺.农地全磷质量分数基本能满足主要作物的生长需求,有机质和全氮质量分数不能满足主要作物的生长需求.本研究可为内蒙古中部工矿开采区土地合理利用以及退化的生态环境恢复等提供科学依据.     

巫山县坡改梯地区不同土地利用方式下土壤质量研究

为了探讨坡改梯地区不同土地利用方式对土壤质量的影响,在巫山县选择了5种不同的土地利用方式,依次为经济作物、粮食作物、豆科植物、经果林和撂荒地等,用因子分析法对其土壤质量进行定量研究。试验结果表明,各土地利用方式土壤质量综合指数从大到小排序为撂荒地（0．609）＞粮食作物（0．519）＞经济作物（0．479）＞经果林（0.248）＞豆科植物（0．063）。其中,撂荒地土壤质量综合指数最高,印证了撂荒地可以在一定程度上恢复地力、培肥土壤;经济作物和粮食作物种类丰富,两者土壤质量综合指数较接近;经果林和豆科植物土壤质量综合指数相对较低,这是因为经果林能产生一种抑制有机质生成的物质,而豆科植物能产生高氮的土壤条件,促使作物从土壤中吸收更多的磷,使土壤质量降低。     

不同土地利用方式对干热河谷地区土壤可蚀性的影响

以四川宁南县金沙江下游的河谷地带为研究区域,选择相同海拔下7种主要的土地利用方式为研究对象,通过室内测试分析,并运用统计和相关分析等方法,研究不同土地利用方式下的土壤可蚀性变异特征。结果表明：在干热河谷区,天然植被水桐树林破坏改为其它土地利用方式后,土壤有机质、全氮、全磷和碱解氮含量显著降低,速效磷和容重没有显著变化,速效钾有一定程度升高,不同利用方式对其影响作用不同,但总体来说改造为合欢林和撂荒草地对土壤理化属性的影响相对较少。相对于天然水桐林,其它土地利用方式土壤可蚀性明显增加,其大小依次为：花椒地〈撂荒地〈草地〈新银合欢地〈桑地〈甘蔗地。相比较而言,无论是天然林地还是人工经济林地,其土壤可蚀性都处于较低的水平;受人为活动影响强烈的农业用地,其土壤可蚀性水平一般较高。说明该地区农业耕作措施可导致土壤对侵蚀营力分离和搬运作用敏感性增强,抗蚀性能较低,更加容易遭受侵蚀,因此在金沙江干热河谷区,从水土保持角度出发,应该尽可能地减少人为活动对土地的干扰,提高土地抵抗侵蚀的能力。     

不同土地利用方式下土壤重金属分布规律及其生物活性变化

为了解不同土地利用方式下土壤环境的质量状况,以崇明岛农田、生活区、工业区、湿地、公路旁和港口码头等6种土地利用方式的土壤为研究对象.研究了土壤重金属Cu,Cr,Pb的分布规律和土壤生物活性的变化.结果表明:与国家土壤环境质量一级标准相比,工业区土壤重金属Cu,Cr,Pb全量均值超标率最高,分别为109.43%,7.08%,147.54%,而湿地超标率最低.不同土地利用方式下土壤酸性磷酸酶和脲酶活性差异较大,但脱氢酶活性变化不明显;微生物中细菌占绝对优势,细菌和放线菌数量变化较小,而真菌数量变化较大;土壤微生物总数从大到小的顺序为:湿地>港口>公路旁>工业区>农田>生活区;而土壤呼吸强度没有显著性变化.     

喀斯特山地不同土地利用方式土壤养分特征研究

不同的土地利用方式影响着土壤的养分特征及土壤质量。对重庆市南川区灌草丛、人工林、果园、旱地、水田、撂荒地6种不同土地利用方式下土壤养分的研究表明:不同土地利用方式间土壤养分存在一定的差异,变化规律也不一致。6种土地利用方式下的土壤有机质、全氮、速效氮、速效磷、速效钾都呈现表聚现象,且有机质、全氮、速效氮都随深度的增加而递减,但全磷和全钾含量并无明显的变化规律。6种土地利用方式各土壤养分指标含量排序各异,退耕后土壤部分养分含量仍较低,初步认为该区土壤养分受人为影响较严重,退耕后土壤恢复能力还较差。     

河北省坝上不同土地利用方式土壤可蚀性研究 —以河北省丰宁县大滩乡三道河为例

计算研究河北省坝上不同土地利用方式土壤可蚀性结果表明 ,弃耕地潜在可蚀性 (其值 6 3.85 5 % ) >人工林地 (5 4 .2 12 % ) >耕地 (5 3.0 2 0 % ) >草地 (5 0 .787% ) ,表明草地为最适合该区发展的土地利用方式。     

岷江流域不同土地利用方式下紫色土壤活性有机碳分布特征及其影响因子

作为土壤质量的重要指标,土壤活性有机碳（SLOC）在土壤许多物理、化学和生物特性中发挥着重要作用。通过对不同土地利用方式土壤进行采样和分析,系统地研究和比较了四川省岷江流域不同土地利用方式（次生林、人工林、灌草丛和坡耕地）SLOC分布特征及其影响因子。结果表明:岷江流域不同土地利用方式土壤机械组成不尽一致,土壤总孔隙度与土壤容重变化趋势相反。不同土地利用方式对土壤养分具有较大影响,土壤有机碳、全氮、全磷和全钾均呈现出一致性规律,大致表现为次生林和灌草丛高于人工林和坡耕地,而不同土地利用方式土壤全磷差异并不显著（p > 0.05）。不同土地利用方式SLOC均呈现出一致性规律,大致表现为次生林和灌草丛高于人工林和坡耕地。不同土地利用方式SLOC垂直方向随土层深度的增加表现出递增趋势,并且降低幅度逐渐减小,坡耕地、灌草丛、次生林和人工林SLOC从表层至底层逐渐递减,呈“T”形分布,“表聚性”较为明显。人工林、灌草丛和坡耕地在10—20 cm SLOC/SOC比例最高,而次生林0—10 cm SLOC/SOC比例最高,不同土地利用方式SLOC/SOC比例均在30—40 cm最低。相关性分析表明,不同土地利用方式SLOC与SOC和全氮均呈极显著正相关性（p < 0.01）,与土壤容重均呈负相关。表明SLOC受土壤养分和机械组成影响较大,其中SOC和全氮是不同土地利用方式SLOC变化的重要影响因素。SLOC与土壤有机碳之间呈极显著正相关关系（R²=0.9961）,说明SLOC能够作为研究不同土地利用方式SOC动态变化的一个敏感性指标而提前反映土壤碳库的动态变化,其含量在很大程度上依赖于所处生境下SOC含量。     

Chemical fractionation of phosphorus in calcareous soils of Hamedan,western Iran under different land use

We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl‐P (labile P), NaOH‐P (Fe‐Al‐bound P), HCl‐P (Ca‐bound P), and residual P (Res‐P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca‐bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (< 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe‐Al‐bound P comprised < 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long‐term fertilization increased P allocation to inorganic fractions, as Ca‐bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe‐Al‐bound P (r = 0.534, p < 0.01), labile P and Ca‐bound P (r = 0.574, p < 0.01), Ca‐bound P and Fe‐Al‐bound P (r = 0.504, p < 0.01), Olsen‐P and CaCl₂‐P (r = 0.821, p < 0.01) was found. Principal‐component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.     

Kinetics of phosphorus release from calcareous soils under different land use in Iran

The rate of phosporus (P) release from soils can significantly influence P fertility of soils. The objectives of this study were to investigate the effects of land‐use types on the kinetics of P release under different management practices and the relationship between kinetic parameters and soil physical and chemical properties from calcareous soils. The kinetics of P release in 0.01 M CaCl₂ was studied in surface samples of 30 calcareous soils planted to garlic, garden, pasture, potato, vegetables, and wheat. Trend in P‐release kinetics was similar between land‐use types. Significantly different quantities of P were released under different land use. The maximum amount (average of five soils) (46.4 mg kg^–1) of P was released in soil under potato and the minimum amount (10.4 mg kg^–1) under pasture. The kinetics of P release from soils can be described as an initial rapid rate followed by a slower rate. Different models were used to describe P release. In general, parabolic diffusion and power equation were found to be appropriate for modeling P release. The P‐release rate for the soils was estimated by parabolic equation for the studied land‐use types. The constant b was lower for pasture and wheat than for garlic and potato. The relationship between the rate of P release with Olsen‐P was linear, while it was curved with respect to the CaCl₂‐P, indicating that release of P was diffusion‐controlled. When the kinetic parameters of models were regressed on soil properties, CaCl₂‐P and CaCO₃ appeared to be the most important soil properties influencing P‐release rates in these soils.     

利用圆盘入渗仪测定不同土地利用类型土壤吸渗率

探讨利用圆盘入渗仪测定不同利用类型土壤吸渗率的适用性,该文选用盘径分别为10和20 cm的圆盘入渗仪对3种利用土壤(菜地、草地和茶园)在0、-3、-6、-9 cm 4个压力水头下的吸渗过程进行测定。研究以Vandervaere法为参考方法,对Philip法、Haverkamp三维吸渗法、Haverkamp三维吸渗改进法的适用性进行比较分析。结果表明:吸渗率的不同计算公式所适应的吸渗过程时间尺度不同,且Haverkamp三维吸渗法所得吸渗率值与参考方法最接近。盘径对吸渗率测定差异的影响不显著。除0 cm压力水头外,不同利用类型土壤吸渗率差异显著,且不同压力水头下测得3种土壤吸渗率大小排序不同。当压力水头为-9和-6 cm时,菜地吸渗率(0.0104和0.0119 cm/s0.5)显著高于茶园(0.0017和0.0025 cm/s0.5)(P0.05);当压力水头为-3 cm时,茶园吸渗率(0.0370 cm/s0.5)显著高于菜地和草地(0.0147和0.0132 cm/s0.5)(P0.05)。该研究可为南方丘陵区土壤水力参数的测定提供理论依据。     

Density separation of soil organic matter across three land uses in calcareous soils of Iran

ABSTRACT

The aim of this study was to examine the usefulness of physical and chemical fractionation in quantifying soil organic matter (SOM) in different stabilized fraction pools. Soil samples from three land use types in Lorestan province, Southwest Iran were examined to account for the amount of organic carbon and nitrogen in different SOM fractions. Size/density separation and chemical oxidation methods were applied to separate the SOM fractions including particulate organic matter (POM), Si + C (silt and clay), DOC (dissolved organic C), rSOM (oxidation-resistant organic carbon and nitrogen) and S + SA (sand and stable aggregates). The values obtained for TOC, TN, and HWC were highest in forest lands followed by the range and agricultural lands. Among the SOM fractions, S + SA showed the highest values (5.75, 5.77 and 20.6 g kg^?1 for agriculture, range and forest lands respectively) followed by POM, Si + C, rSOM, and DOC. The concentrations of C and N in the labile fractions obtained the higher values than in the stabilized fractions. Forest lands had the highest amounts of organic C and N among all fractions whereas agricultural lands showed highest values for inorganic C content of soils in different fractions.     

Potassium release from sand,silt and clay fractions in calcareous soils of southern Iran

The release of non-exchangeable potassium from 24 calcareous soils of divergent mineralogy, from southern Iran, was examined. Sand, silt and clay particles were fractionated after dispersion with an ultrasonic probe. Samples were extracted with 0.01 M CaCl₂ for 30 successive 2-h periods. The clay fraction released the largest amount of K in each soil. Cumulative K released ranged from 175 to 723, 35 to 128, and 71 to 146 mg kg^?1 contributing 20–90, 4–39 and 2–54% for clay, silt and sand fractions, respectively. The lower proportion of K released from sand and silt fractions can be explained by the presence of a high content of CaCO₃ and quartz in these fractions. The release kinetics for the non-exchangeable K data showed that parabolic diffusion and power function were the best fitting kinetic models. This indicated that slow diffusion of K from the mica interlayer positions is the main rate-controlling process. Cumulative K released and constant b values of parabolic diffusion model correlated significantly with the mica content of the clay fraction.     

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.     

Transformation kinetics of inorganic P forms in relation to calcareous soil properties of western Iran

This study was conducted to investigate the effect of time on chemical forms of P in 10 calcareous soils of western Iran. Phosphorus was added to soils at the rate of 200 mg kg^?1 as KH₂PO₄. The samples were incubated for 1, 7, 15, 30, 60, 90 and 120 days at 25°C and constant moisture. After incubation, P was fractionated by the sequential extraction procedure: soluble and exchangeable P (NaHCO₃-P) Al + Fe-P (NaOH-P), Ca-P (HCl-P) and residual P (Res-P). The distribution of added P into different fractions consisted of two phases involving initial rapid retention followed by a slow continuous retention. In general, the majority of the P applied entered mostly in the HCl-P and Res-P fractions. After 120 days incubation, the HCl-P fraction remained the most dominant in all soils. A combination of silt and sand content of the soils together explained between 88.5 and 83.3% of the variance inNaHCO₃-P and HCl-P transformation rates, respectively, 76.6 and 72.8% of which is explained by silt alone. CaCl₂-P and electrical conductivity (EC) together accounted for 66.3% of the variation in the rate constant of NaOH-P. The release rate of Res-P was not significantly related to soil properties.     

Occurrence and hydrological effects of water repellency in different soil and land use types in Mexican volcanic highlands

Little is known on the hydrological behavior of the volcanic ash soils, which are characterized by extremely high porosities and hydraulic conductivities. In this study the occurrence and hydrological effects of water repellency were investigated at a plot scale for different types of land use and volcanic soils in Mexican volcanic highlands from Michoacan, Mexico: [1] fir, pine and oak mixed forest soils developed from lavas, [2] soils developed from volcanic ashes and pyroclastic sediments under sparse fir, pine and oak forest and shrubland, [3] pine and oak forested soils developed from lavas and pyroclastic sediments, and [4] bare soils on recent ash sediments in plain surfaces. Soil water repellency was assessed using the water drop penetration time test and rainfall simulations were performed on circular plots (50 cm in diameter) during 30 min and at an intensity of 90 mm h^− 1 in order to study the hydrological response of each area. The return period for storms with a similar intensity in the area is 10 years. The shape and depth of the wetting front after simulated rainfall was also analyzed. Soil water repellency showed a high variability among the different studied zones. Organic matter content, soil texture and acidity were the most important factors for developing hydrophobicity. A wide range of soil water repellency classes (hydrophilic to severely water-repellent soils) has been found in soils under dense fir, pine and oak mixed forests or shrubland, while inexistent or slight water repellency has been observed in soils under sparse forest or at bare ash-covered areas. At a plot scale, marked differences in the hydrological behavior of the studied land use and soil zones were observed after the rainfall simulations. Soil water repellency contributes to fast ponding and runoff generation during the first stages of rainstorms. Runoff was enhanced in water-repellent forested soils (average runoff coefficients between 15.7 and 19.9%), in contrast to hydrophilic or slightly water-repellent soils, where runoff rates were lower (between 1.0 and 11.7%). Shallow and irregular wetting fronts were observed at water-repellent zones, reducing the soil water storage capacity. The implications of soil water repellency in soil hydrology and erosion risk in the area shed light on the soil hydrology of the studied ecosystems, and can contribute to develop better management policies.     

Adsorption isotherms of some heavy metals under conditions of their competitive adsorption onto highly calcareous soils of southern Iran

Recently, application of sewage sludge or effluents resulted in raising the concentrations of some heavy metals in some agricultural soils of Iran. Experiments were conducted to evaluate the competitive adsorption of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) on six calcareous soils. Adsorption characteristics were evaluated by equilibration of 1 g of each soil sample with 20 ml of 0, 10, 20, 30, 40, 50, 100, or 200 mg L^?1 of their nitrate solutions and 0.01 M NaNO₃ as background electrolyte. Furthermore, solid/liquid distribution coefficients (K_d) of studied metals, as an index of soil capacity to resist a change of the soil solution concentration, were calculated. Results indicated that amounts of adsorbed Pb, Cu, Zn, and Cd increased with increase in their concentrations in the contact solutions, but this trend was more pronounced for Pb and Cu than the others. For all studied soils and metals, Langmuir equation described the adsorption behavior fairly well. Furthermore, Langmuir and Freundlich equation parameters were positively correlated to cation exchange capacity (CEC) and smectite contents; whereas, they were negatively correlated to sand content. Considering K_d values, the selectivity sequence of the metal adsorption was Pb > Cu > Zn > Cd. Therefore, the risk of leaching and also plant uptake of Zn and Cd will be higher as compared to those of the other elements.