Correlation Between Soil Water Retention Capability and Soil Salt Content

The soil moisture retention capability of Chao soil and coastal saline Chao soil in Shandong and Zhejiang provinces were measured by pressure membrane method. The main factors influencing soil moisture retention capability were studied by the methods of correlation and path analyses. The results indicated that < 0.02mm physical clay and soil salt content were the main factors influencing soil moisture retention capability. At soil suction of 30-50 kpa, the soil salt content would be the dominant factor.

Study on Soil Infiltration Capability and Its Impact Factors of Different Land-use Types in Purple Soil Region

Soil infiltration capability is the hot spot topic of soil erosion studies and soil physical and chemical properties have great influence on it. A new infiltration method point- source infiltration method was used to precisely evaluate the infiltration capability in different purple soil land- use types. And correlation analysis on soil physical and chemical properties and soil infiltration capability of different land- use types was performed. Results showed that:( i) there is a large difference among soil physical and chemical properties in different land- use types,soil water content,non- capillary porosity,capillary porosity,content of > 0. 25 mm aggregates and organic matter content in the top soil are greater than those in the subsoil;( ii) soil infiltration capability showed differences among different land- use types. Land use showed great effects,in general,the order of decrease on initial infiltration rate and average infiltration rate was: woodland slope > slope farmland >grassland,the order of decrease on steady infiltration rate was: slope farmland > woodland > grassland and the time reaching stable state was:slope farmland > woodland > grassland;( iii) correlation analysis showed that there was a significantly positive correlation between initial infiltration rate and wet sieve MWD value and structural damage rate,and it had a significantly negative correlation with capillary porosity;( iv)steady infiltration rate and non- capillary porosity showed the significantly positive correlation,and it had a significantly negative correlation with the soil bulk density;( v) the average infiltration rate and non- capillary porosity and structural damage rate showed a positive correlation and the correlation coefficient was large and there was a negative correlation between average infiltration rate and soil bulk density and capillary porosity,and the absolute value of correlation coefficient was relatively large. The results of this study can provide the theoretical basis for soil infiltration study in purple soil area.

Characteristics, Fertility Status and Fertility Capability Classification of Steep Slope Soils of the Dschang Cliff (Cameroon Western Highlands)

Mountainous ecosystem soils are subject to colonization nowadays for agricultural purposes due to an increasing population in towns making the detailed characterization of such soils indispensable. This work aims to characterize the steep slopes soils of the Dschang hills and to evaluate their fertility level for agricultural valorization. Thus, four soil profiles were dug at various topographic positions (summit (SP), shoulder (MP), backslope (BP) and footslope (PP)) following a toposequence. Samples of disturbed and undisturbed soils were taken and analyzed in the laboratory according to standard methods. The Fertility Capability Classification (FCC) and simple limitation methods were used to identify major agricultural constraints. The main results show that profiles thickness is moderate, between 0 and 120 cm, with a high sand content (at least 50%) over the entire toposequence, especially at the surface. The study site has four types of soils, namely Eutric Cambisols (ochric) in SP and Leptic Eutric Cambisols (Humic) in MP, Eutric Cambisols (Humic) in BP and Stagnic Oxygleyic Dystric Gleysols (Humic) in pp. The soils are very acidic at PP, moderately acidic at BP and SP and slightly acidic at MP. Organic matter is higher at the surface than at depth at the topographic segments of MP, BP and PP and low to SP. The C/N ratio is high (>17) in all profiles except P4 (<10). In addition, the cation exchange capacity (CEC), the sum of exchangeable bases, total nitrogen and available phosphorus is low in all profiles. The Ca/ Mg/K balance in all the profiles shows a cation imbalance and a relatively high concentration of exchangeable potassium compared to the ideal situation (76% Ca, 18% Mg and 6% K). The major constraints to crop production are: aluminum toxicity (a) and nutrients leaching (e), textural discontinuity (LS), flooding (g), low nutrient reserve (k), sand (S), clay (C) and slope (t). Hence the fertility capacity classes of these soils are CCaegk (PP), SSek (BP), SSte (MP) and LSaek (SP). To improve the yield, it will require off-season crop cultivation, fertilization and liming, and earthworks.

Water holding effect of subalpine dark coniferous forest soil in Gongga Mountain, China

Because of the distinction of soil property and humus content, soil water content is not ideal to indicate whether it is suitable to the growth of plant. Mainly based on the PF-a numerical value denoting the water regime of soil and connected with the growth of plant, the study combined the moisture percentage of soil with PF to research in quantity the interrelation between the moisture percentage and PF in different succession phases of subalpine dark coniferous forest in Gongga Mountain. The results showed that: (1) In the same PF value, the moisture percentage in humus horizon increased gradually with the devel-opment of the succession of the dark coniferous forest; The moisture percentage of over-mature forest was the highest and>mature forest>half-mature forest>young growth forest; (2) With the increase of soil depth, the soil bulk density increased and the moisture percentage decreased, but the difference in the percentage of moisture was not notable in different succession phases. (3) In different succession series, the vegetation affected the soil water characteristics by increasing the soil organic matter, improving the soil construction, receding the soil bulk density and enhancing the soil porosity; (4) The humus horizon of the dark coniferous forest soil has the highest water holding capability in this region.

INFLUENCES OF SLOPE GRADIENT ON SOIL EROSION

The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying with the slope gradient were investigated by using the kinematic wave theory. Furthermore, the critical slope gradient of erosion was driven. The analysis shows that the critical slope gradient of soil erosion is dependent on grain size, soil bulk density, surface roughness, runoff length, net rain excess, and the friction coefficient of soil, etc. The critical slope gradient has been estimated theoretically with its range between 41.5 degrees similar to 50 degrees.

Global Freshwater Storage Capability across Time Scales in the GRACE Satellite Era

Freshwater is recharged mainly by rainfall and stored inland for a period of time,which is directly affected by its storage capability.The storage capability of river basins has different spatiotemporal features that are important for the predictability of freshwater resources.However,the estimation of freshwater storage capability(FSC)remains a challenge due to the lack of observations and quantification indices.Here,we use a metric that characterizes hydrological“inertia”after rainfalls to analyze FSC over the 194 largest global major river basins based on satellite observations from the Gravity Recovery and Climate Experiment(GRACE)and simulations from the Community Land Model version 5(CLM5).During 2003–16,the global land was observed to retain 28%of precipitation after one month based on GRACE observations,and the simulation depicts that the retained proportions decrease from 42%after one day to 26%after one month,with smaller FSC partly attributed to wetter conditions and higher vegetation densities.The root zone contributes about 40%to the global land FSC on daily to monthly time scales.As the time scale increases,the contribution from the surface soil decreases from 26%to 14%,while the contribution from the deep soil increases from 4%to 10%.Snow contributes over 20%of land FSC,especially over high latitudes.With six decades of CLM5 long-term simulations,it is revealed that the change of FSC in most basins is related to internal climate variability.The FSC of river basins which displays the proportion of precipitation retained on land is worthy of further attention regarding the predictability of water resources.

Estimation of the effectiveness of multi-criteria decision analysis and machine learning approaches for agricultural land capability in Gangarampur Subdivision, Eastern India

Land suitability analysis(LSA)is an evaluation method that measures the degree to which land is suitable for certain land use.The primary aims of this study are to identify potentially viable agricultural land in the Gangarampur subdivision(West Bengal)using Multiple Criteria Decision Making(MCDM)and machine learning procedures and to evaluate the efficacy of the employed methodologies.The Analytic Hierarchy Process(AHP)model was used to assign relative weights to the fifteen various criteria in this suitability analysis,and then the Fuzzy Complex Proportional Assessment(FCOPRAS)model was applied using the AHP’s normalised pairwise comparison matrix,whereas the Waikato Environment for Knowledge Analysis(Weka)Software was used to apply machine learning algorithms to the field data.The Random Forest(RF)model,on the other hand,is a better fit for the locational study of soil potential.According to the RF findings,areas of 14.67 per cent(15368.46 ha)are excellent(ZONE Ⅴ)for growing crops,approximately 22.30 per cent(23367.9 ha)are highly suitable(ZONE Ⅳ),and 23.63 per cent(24762.12 ha)are moderately suitable(ZONE Ⅲ)for cultivation,respectively.The numbers for FCOPRAS are roughly 15.39%(16130.52 ha),22.54%(23620.65 ha),and 19.79%(20733.26 ha).The Receiver Operating Characteristic(ROC)curve and accuracy measurements of the results indicate the high accuracy of the applied models,with Random Forest and FCOPRAS being the most popular and effective techniques.This study will make an important contribution to evaluations of soil fertility and site suitability.This will help local government officials,academics,and farmers scientifically use the land.

PAM的土壤保水性能研究

有机高分子聚合物能对土壤水分特征产生重要影响,为阐明聚丙烯酰胺(PAM)对黄土高原主要土壤类型(黄绵土、黑垆土和塿土)的保水作用,采用土柱法研究了PAM用量分别为54.5,112.9,169.4和225.8 mg/kg对3种土壤的持水性能、土壤饱和导水率和土壤蒸发量的影响,并以不添加PAM为对照。结果表明,PAM提高了黄绵土和黑垆土的持水量,而对土娄土效果不明显。在土壤导水率方面,PAM对黄绵土的改善效果最明显,除添加225.8mg/kg PAM的处理外,土壤饱和导水率随PAM用量的增加而增大;黑垆土的饱和导水率与对照相比也有一定提高,但添加225.8 mg/kg PAM的处理除外;土娄土的饱和导水率在施入PAM后降低。在一定土壤含水量条件下,保水剂抗蒸发作用明显,随PAM用量的增加,各土壤的蒸发量均减少,其中土娄土、黑垆土和黄绵土添加225.8 mg/kg PAM的处理与对照相比,蒸发量分别减少24.5%,55.8%和33.7%。说明在一定用量范围内,PAM可以提高黄土高原主要类型土壤的持水和导水性能,并且可以减少土壤水分的蒸发。

耕作对土壤入渗性能的影响

耕作影响降雨入渗、径流、土壤侵蚀过程。研究采用新型的坡地降雨条件下土壤入渗能力的径流-入渗-产流测量方法和仪器,野外观测宁夏南部山区坡耕地与撂荒地土壤入渗性能,揭示耕作对土壤入渗性能影响的规律。在坡度为20°、土壤表层含水量11.3%的坡地进行测量。采用的降雨强度为:20,40,56mm·h-1。结果表明,新型测量方法和仪器可以很好地测量坡面土壤入渗性能的全过程,并且具有省水、省工、操作方便的特点,且测量精度高。对比测量结果表明,坡耕地的初期土壤入渗性能在小雨强条件下略高于撂荒地的入渗性能,而在大雨强条件下则一直低于撂荒地的入渗性能。随雨强的增大坡耕地的入渗性能急剧减小,而撂荒地的入渗性能基本不受雨强变化的影响。坡耕地土壤的入渗性能(土壤结构)对降雨强度极为敏感,而撂荒地具有稳定的土壤结构和入渗性能。在3种雨强下,坡耕地的产流时间均比撂荒地提前。与撂荒地相比,各种雨强条件下坡耕地的稳定入渗率都较撂荒地明显降低。

坡度对坡面土壤侵蚀的影响分析

在运动波理论基础上 ,就影响土壤侵蚀的主要因素 ,包括降雨超渗净雨量 ,坡面流水深、流速和切应力 ,以及土壤抗冲蚀能力等随坡度的变化关系进行了理论分析· 并进一步对坡面土壤侵蚀的坡度界限做了较细致分析 ,表明坡度界限是一个变量 ,随颗粒粒径、容重、坡面糙率、径流长度、降雨入渗差值 (净雨量 ) ,以及土壤摩擦系数等因素的不同而改变 ,给出了界限坡度的变化规律 ,并得出一般情况下土壤侵蚀的坡度界限值应在 4 1 5°～

渝北水源区水源涵养林构建模式对土壤渗透性的影响

土壤渗透性是评价土壤水源涵养作用重要指标之一,其受制于许多外在和内在因素的影响,与植被类型、土壤结构、土壤种类和降雨强度等关系密切。为探讨不同构建模式水源涵养林对土壤渗透性能的影响,以裸地为对照,以土壤初渗速率,稳渗速率,平均渗透速率和渗透总量表征土壤渗透性,对重庆北部水源区8种不同构建模式的水源涵养林地的土壤渗透性及其与理化性质的关系进行研究。结果表明:不同模式水源林地和同一模式林地不同层次土壤渗透性能存在较大差异,各林地土壤渗透性随土壤深度的增加而降低,母质层土壤渗透性受林分类型和林分结构等外界条件的干扰较小,差异不显著;8种林地土壤渗透性均好于裸地,各林地土壤渗透性能大小依次为:广东山胡椒×杉木混交林>马尾松×柳杉混交林(火烧迹地)>四川大头茶×四川山矾混交林>毛竹×四川山矾×马尾松混交林>马尾松×广东山胡椒混交林>马尾松×四川大头茶混交林>广东山胡椒×四川杨桐混交林>毛竹纯林>裸地,根据土壤渗透能力可将8种模式林分类型分为4类:第1类,广东山胡椒×杉木混交林和马尾松×柳杉混交林,土壤渗透性最好;第2类,四川大头茶×四川山矾混交林,土壤渗透能力较好;第3类,毛竹×四川山矾×马尾松混交林、马尾松×广东山胡椒混交林、广东山胡椒×四川杨桐混交林、马尾松×四川大头茶混交林,土壤渗透性好;第4类,毛竹林和裸露地,土壤渗透性最差。以广东山胡椒和杉木混交的林分模式的土壤渗透性最好,毛竹纯林地最差,毛竹纯林对提高土壤渗透性作用较差,营林时适当增加毛竹林中其他树种的混交比例可增强林地土壤渗透性能。通用经验方程对各林分土壤入渗过程的拟合效果最好,比较适用于描述本研究区域水源涵养林地土壤入渗特征的模型,Kostiakov方程拟合效果次之,Horton方程最差;结合相关分析,筛选出9个极显著或显著影响土壤渗透性能的土壤理化性质因子,通过主成分分析法,得到土壤渗透性能综合参数α及与其极显著相关因子的综合参数β,并构建土壤渗透性各指标及其综合参数α与β的线性回归模型,为重庆北部的水源涵养林建设和防治水土流失提供理论依据。

土壤固化剂研究现状与展望

阐述了土壤固化剂国内外研究的现状、种类、特点和应用,分析了土壤固化剂的固化机理和固化性能,指出了土壤固化剂研究和应用领域中存在的若干问题及研究方向,最后对其应用前景做了展望。

重庆缙云山酸雨区森林土壤酸缓冲机制及影响因素

为探讨酸雨区森林土壤的酸缓冲机制,采集重庆缙云山4种典型林分(针阔叶混交林、常绿阔叶林、毛竹林和灌木林)不同土层土壤样品,研究森林土壤酸缓冲特性及其影响因素。结果表明:①同一土壤在不同的pH阶段其酸缓冲能力相差很大,这是由于土壤不同缓冲机制所造成的。当pH>3.0时,土壤中起主要缓冲作用的是土壤有机质、CEC、交换性Al 3+等;当pH<3.0时,土壤的主要缓冲机制为土壤矿物质的风化,土壤pH成为影响缓冲作用的主要因素。②在pH>3.0时,不同土壤酸缓冲能力相差较大,4种林分土壤平均缓冲能力大小为灌木林(25.58mmol/kg)>常绿阔叶林(23.81mmol/kg)>针阔叶混交林(19.43mmol/kg)>毛竹林(17.12mmol/kg),且同一林分表层土壤酸缓冲能力大于下层土壤。③当pH<3.0时,所有土壤的缓冲能力都急剧增强,pH越低,土壤酸缓冲能力越强,在同一pH阶段不同土壤酸缓冲能力相近。④按照对酸害容量划分,4种林分土壤全部属于易受害、稍易受害土壤,酸沉降极易对植物造成伤害,强烈建议对缙云山森林土壤进行改良,提高其土壤pH值和酸缓冲能力,同时,加大对环境的监控,减小酸雨发生频率。

天然沸石对土壤保肥性能的影响研究

通过模拟土柱淋洗试验 ,探讨了沸石对华南地区退化坡地土壤养分保持能力的影响 ,分析了土柱淋洗后土壤养分的变化 .结果表明 ,在华南地区 4种退化坡地土壤上 ,土柱淋洗液中N和K的含量随着沸石用量水平的增加而下降 ,不同水平沸石处理的淋洗液中P含量都极低 (痕量 ) .模拟土柱淋洗后土壤中的有效N、有效P和有效K含量随着沸石用量的增加而提高 ,表明不同水平沸石处理对提高土壤的保肥能力均具有不同程度的促进作用 .随着沸石用量的增加 ,土壤中的无机磷也有不同程度的增加 ,增加最显著的无机磷形态是铝磷 ,其次是铁磷 ,而钙磷和闭蓄态磷则没有明显差异 .沸石的施用不会增加土壤淋洗液中硝态氮含量 .

四川盆地丘陵区秸秆还田少免耕对土壤水分特征的影响

四川盆地丘陵区季节性干旱严重,为了阐明秸秆还田少免耕对土壤持水保水性能的影响和抗旱节水效果,采用压力膜法,测定了4年定位试验田的土壤水分及其能态变化特征。结果表明：秸秆还田少免耕土壤水吸力与土壤含水量之间具有明显的幂函数关系,可用幂函数方程θ=a Sb进行拟合;秸秆还田免耕增加了10-20 cm土层通气空隙的当量孔径,降低了无效空隙的当量孔径,改善了心土层土壤结构;秸秆还田提高稻田耕层土壤持水性能,增加土壤水分库容量;秸秆还田后通过增加土壤有机质提高了土壤毛管空隙含量,提高土壤有效水含量;秸秆还田提高土壤耐旱性能和供水能力,不同耕作方式的耐旱性秸秆还田免耕优于秸秆还田间耕。

保水剂对土壤持水性能影响的模拟研究

通过室内模拟试验,利用正交回归设计研究了丙烯酸盐类保水剂对土壤持水性能的影响,并推导出土壤有效水含量与土壤质地、保水剂粒径及其使用剂量关系的数学模型。结果表明:土壤质地、保水剂用量对土壤有效水含量的影响达到极显著水平,而保水剂粒径对土壤有效水含量的影响不显著。保水剂颗粒与土壤质地、与保水剂用量成负效应,保水剂用量与土壤质地成正效应。这一数学模型可以用于指导该类保水剂在生产的使用。

包气带粘性土层的防污性能试验研究及其对地下水脆弱性评价的影响

大量文献资料分析表明,平原地区地下水脆弱性主控因素为地下水位埋深、包气带土层及其特征,而包气带粘性土层的截污性能及其厚度则又是脆弱性主要的影响因子。试验研究结果显示,粘性土的截污容量大小可以通过模拟淋滤实验测试得出,有效阻隔足额厚度也可计算得出。根据不同粘性土层的截污容量、有效阻隔厚度等,可以评判土层的污染防护能力,并可据此评价平原区地下水的脆弱性。

水蚀作用下土壤抗蚀能力的表征

研究区为黄土高原南部淳化县泥河沟流域 ,在未经翻耕的自然或人工 (耕地 )坡面上 ,选择 5 6个 1m2样地 ,(土壤为黄土 ,体积含水率 7.1%～ 2 0 .1%,干容重 1.0 1g/cm3～ 1.2 9g/cm3) ,采用南京土工仪器厂出产的WI- 3型便携式直剪仪 ,对表层 0～ 5cm土层进行现场取样剪切 ,3次重复剪切的结果表明 ,表层土壤抗剪强度与土壤含水率及容重均密切相关。抗剪强度起初随含水率增加而缓缓增大 ,在含水率 12 %～ 14%时达最大 ,然后较迅速减弱。容重的影响表现为 :随容重增大 ,土壤抗剪强度呈直线趋势较快增大。通过室内降雨侵蚀实验 (坡面面积为0 .3m× 1.0m ,雨强分别为 1.39、1.49、1.88和 2 .6 6mm/min) ,经对收集的溅蚀物及冲刷物称重分析发现 ,无论击溅侵蚀还是径流击溅共同作用 ,在土壤干容重不变 ( 1.2 g/cm3)情况下 ,试验土壤含水率达 16 %时 ,其抗蚀能力最强。考虑到容重的影响 ,把抗剪强度作为抗蚀力指标还是较为合理的。对于表层为松散状态的坡面 ,将分别采自农耕地、荒地、草地、灌木地表层的原状土块 ( 2 5cm× 6cm× 2 .5cm)用水饱和后 ,置于长 10 0cm、宽 6 .2cm、高 6 .0cm的冲刷槽中 ,在坡度 15° ,流量 5L/min条件下进行等时冲刷。用冲刷前后同一土样重量之差除以流量 ,即可求出冲刷模数值。

香根草根系固土拉力的原位测定

应用锚杆拉力计和项目组自行设计改进的剪切箱,原位测定了不同深度(10 cm,20 cm)分蘖期香根草根系固土、单根拉力。结果表明,在给香根草施加载荷初期,根系都会发生弹性形变,荷载与位移都按比例增加,呈现一定的线性关系。当载荷超过根系抗拉极限后,随着拉力的继续增加,根系发生塑性形变,载荷与位移关系逐渐偏离直线,反映出非线性弹性特征,测定的土体样方与土体分离。但与裸土样方相比,在施加同样载荷的情况下,有根样方位移明显要小于无根样方,说明香根草具有一定的固土能力,并且根系入土越深,植物固土能力越强。

红壤溶磷菌的筛选及溶磷能力的比较

对不同利用方式下红壤的溶磷菌进行筛选，得到7株优势菌株，观察并测定了各初选菌株的菌落特征、生长速度及溶磷能力。结果表明，7株溶磷菌株的HD／CD值（溶磷圈直径HD与菌落直径CD的比值）范围在1．47～3．45之间，有效溶磷量在11．27～136．27mg·L^-1之间，均具有较强溶磷作用。其中，CY06菌株在固体培养条件下的HD／CD值和液体培养条件下的有效溶磷量均显著高于其他菌株，且该菌株对磷酸铝的有效溶磷量显著高于其他难溶磷酸盐，有望成为开发红壤高效微生物磷肥的优良微生物资源。