田间土壤含水量的原位测定——TDR仪的应用

本文介绍了ＴＤＰ仪的原理和使用方法，并根据实际使用情况对该仪器的田间适用性进行了评价，研究表明，该仪器适用于田间原位测定，且精度较为满意，ＴＤＲ仪具有快速、精确和使用方便等优点，应用前景广阔。     

TDR研制与应用方面的若干进展

通过分析近年来国内外关于TDR的文献，总结了TDR研制与应用方面的若干新进展，概括了在使用TDR时应注意的几个问题。结果表明，线圈型TDR探针可很好地解决TDR探针在物理长度上的限制；多功能TDR探针可用来同时测定含水量与基质势、含水量与土壤热学性质、含水量与盐度和温度。当温度在5～45℃之间变化时随着温度的升高，TDR在沙壤土中测定的土壤含水量降低，而在粘壤土和有机质含量高的土壤测定的土壤含水量值升高。TDR探针应以合适的角度插入土壤，同时尽量避免摇摆、两探针不平行插入等误操作。     

基于EMI的小泊湖退化湿地土壤盐分的空间分布

采用电磁感应(EMI)、地统计学半变异函数和Kriging空间插值方法研究小泊湖退化湿地土壤盐分的空间分布。结果表明:土壤表观电导率(ECa)和0—40cm土壤盐分含量呈线性显著正相关,说明在小泊湖湿地土壤表观电导率的变化可以用以反映土壤盐分含量的变化;半变异函数分析表明,土壤盐分具有强空间相关性[C/(C0+C)0.5],其空间分布主要是由结构性因素引起的;高斯模型(R2=0.98)插值土壤盐分表明,土壤盐分空间分布与退化湿地的空间分布表现出明显的一致性,放牧活动强烈的退化区域土壤盐分相对较高,说明小泊湖湿地退化后土壤盐分含量高于未退化湿地,土壤盐分含量在一定程度上能反映湿地退化的程度,可为湿地退化防治监测提供依据。     

基于遥感与电磁感应仪数据的土壤盐分空间变异性

针对目前黄淮海平原存在的土壤盐渍化问题,以河南省封丘县为研究区,利用遥感影像与磁感应电导率仪 （EM38）在田间定位、定点测量,对研究区土壤盐分的空间变异性进行研究。利用Kriging、指数回归和回归-Kriging 3种不同的方法对土壤盐分空间变异性进行分析。结果表明：土壤电导率在一定的区域范围内具有空间结构特征,符合指数模型分布,具有极强的空间自相关性。通过3种不同的方法对土壤盐分的空间变异性进行分析,结果表明Kriging法、指数回归法及回归-Kriging法在描述土壤盐分空间分布的总体趋势上相似,但指数回归法与回归-Kriging法对于盐分的分布表达更具体,更细致。综合运用多种数据源的方法,即遥感影像数据与EM38测量数据相结合,经典统计学与地统计学方法相结合的方法,能够提高土壤盐分空间预测的精度,结果表明研究区土壤盐分由北向南、自西向东有逐渐升高的趋势,具有明显的趋势效应。     

基于电磁感应仪的河口地区底聚型盐分剖面特征的解译

针对长江河口地区存在的盐渍化问题,以该地区分布较广泛的底聚型盐分剖面类型为研究对象,通过电磁感应仪EM38测量与田间采样,建立了磁感式表观电导率和土壤电导率之间的多元回归模型。在分析土壤盐分剖面分布特征的基础上提出了Logistic模型,并运用该模型对盐分剖面进行了参数拟合和验证。结果表明：磁感式表观电导率水平读数和垂直读数呈极显著线性相关,回归模型和Logistic模型均具有很好的预测效果。通过模型精度检验,二者的预测精度差异不显著,但Logistic模型所需参数少,表明该文提出的Logistic模型不仅能降低待估参数数量,同时还具有较高的预测精度。该研究结果为利用电磁感应仪快速、精确地进行土壤盐分预测及土壤次生盐渍化的防控提供了一定的理论参考。     

基于电磁感应仪的黄河三角洲地区土壤盐分时空变异特征

针对黄河下游三角洲土壤盐渍化的空间复杂性与发生反复性,运用磁感式大地电导率仪EM38及其移动测定系统,结合GIS与地统计学方法,对该地区典型地块两个关键季节土壤盐分的时空变异特征进行了分析.结果表明,土壤表观电导率与盐分呈极显著相关性;各时段土壤盐分都表现出多层次空间结构的复合尺度效应,且短程变异构成了土壤盐分空间异质性的最主要部分;土地利用方式差异使得秋季时段土壤盐分呈弱各向异性,地形因素导致春季时段土壤盐分各向异性比在全步长域波动,但在整个研究尺度上仍为各向同性.空间分析表明,结构性因素主导了土壤盐分空间分布格局,随机性因素是加快该分布格局形成的重要因素;春季时段研究区总体表现出积盐趋势,且盐分变动幅度主要集中在10.0g/kg范围内.电磁感应仪与GIS的结合运用为不同尺度土壤调查与质量评价提供了新的途径,并为农业水土资源的决策管理提供指导.     

滨海棉田土壤盐分时空分布特征研究

在黄河三角洲滨海一农田试验田共采集3期（春、夏、秋三季）EM38表观电导率数据,运用经典统计学和地统计学方法,分析试验区盐分时空分布特征。结果如下：垂直方向电导率相关系数均大于0.8,具有强相关性,水平方向相关系数在-0.2到0.2之间,相关性很弱。土壤盐分分布呈底聚型。变异系数比较显示,同期数据中,表层变异强度最强,底层变异强度最弱。半方差分析中各层块金值与基台值之比大多在25%~75%,盐分空间上偏向于中等空间相关性。棉花长势赋值后生成空间插值图,对比同期电导率插值图,将盐渍化程度划分成4个等级。分析按等级重分类后的栅格插值图中各盐渍土等级所占比例值,表层中非盐化土所占面积比已由初期的5.54%增加到11.93%,轻度盐化土所占面积比增加了42个百分点。     

土壤表面CO_2通量的原位测定方法

研究介绍了一种土壤表面CO2通量原位测定的方法及装置。利用二氧化碳对红外线气体具有特殊吸收、土壤空气与大气间对流和扩散的原理,设计了一条测定土壤表面CO2通量的技术路线进行原位测定。本测定装置由两部分组成:仪器和气体收集容器。用胶管连接仪器和气体收集容器,形成一个闭路系统,即可完成瞬间或某一时间段土壤表面二氧化碳浓度值测量工作,通过公式计算得到通量值。本方法和装置可用于陆地生态系统土壤二氧化碳的释放或吸收的原位测定;用于自然状况下多地点、多样地(点)土壤表面二氧化碳通量测定,具有便携、花费小、简单易操作、直接、快速等优点。     

TDR研制与应用方面的若干进展

通过分析近年来国内外关于TDR的文献,总结了TDR研制与应用方面的若干新进展,概括了在使用TDR时应注意的几个问题。结果表明,线圈型TDR探针可很好地解决TDR探针在物理长度上的限制;多功能TDR探针可用来同时测定含水量与基质势、含水量与土壤热学性质、含水量与盐度和温度。江温度在5－45℃之间变化时随着温度的升高,TDR在沙漠土中测定的土壤含水量降低,而在粘壤土和有机质含量高的土壤测定的土壤含水量值升高。TDR探针应以合适的角度插入土壤,同时尽量避免摇摆、两探针不平行插入等误操作。     

Field level digital mapping of soil mineralogy using proximal and remote‐sensed data

Primary (e.g., quartz) and secondary (clay) minerals are key factors determining the physical and chemical characteristics of soil. Understanding spatial distribution of minerals at the field scale would, therefore, be of potential benefit for soil management. However, current analysis requires time‐consuming laboratory procedures and computational quantification analysis (e.g., SIROQUANT). Furthermore, mineral composition (e.g., quartz, kaolinite, illite and expandable clay minerals) must sum to 100. We aimed to add value to laboratory data by developing multiple linear regression (MLR) relationships between mineralogy and ancillary data such as digital numbers (DNs) (i.e., Red [R], Green [G] and Blue [B]) acquired from remotely sensed air‐photographs and soil apparent electrical conductivity (EC_a – mS/m) measured from proximal sensing electromagnetic (EM) instruments (i.e., EM38 and EM31). To account for composition, we compare results from the MLR approach with those from additive log‐ratio (ALR) transformation of mineralogy prior to MLR modelling. This approach together with various ancillary data and trend surface parameters (i.e., scaled Easting and Northing) has greater precision and less bias of prediction than the MLR approach using untransformed data. Our approach also enables predictions to sum to 100. We conclude that the most useful ancillary data to predict the abundance of quartz, kaolinite and illite are B DNs and EM31, while expandable clays are best predicted with R DNs, EM38 and scaled Northing. The use of ancillary data to map mineralogical components combined with ALR‐MLR is an effective approach, with resulting maps providing insights into soil and water management issues consistent with farmer experience.     

电磁感应仪用于土壤盐分空间分布的协同克立格估值研究

以黄河三角洲地区典型地块为研究对象,应用地统计学的半方差函数理论,分析了0～40 cm和40～80 cm土壤盐分的空间变异特征.在对协同区域化变量进行交互半方差分析的基础上,采用协同克立格法,以电磁感应仪EM38测得的土壤表观电导率作为协同变量,对各层次的土壤盐分进行估值.结果表明:受结构性因素和随机性因素共同作用,各层次土壤盐分均表现中等强度的变异和空间相关性;随机性因素是引起土壤盐分空间异质性的关键原因;协同区域化变量间均表现为正相关,且协同区域化变量的空间结构优于单一变量.同普通克立格法相比,协同克立格法估值产生的均方误差减小13.1%～17.8%,平均标准误差减小5.83%～17.6%,预测值和实测值间的决定系数提高37.6%～42.6%.该研究结果为黄河三角洲地区土壤盐渍化的精准定量化、科学管理与合理改良提供了一定的理论基础和实践依据.     

土壤水解酶活性测定方法的研究进展

土壤水解酶直接参与有机物质的矿质化过程,对维持生态系统碳和养分的循环过程起重要作用。但不同研究者和实验室测定过程的差异,常给土壤酶测定方法的选定带来困难。针对这一问题,本文围绕土壤酶活性测定过程中样本贮存方式、酶底物选择以及培养条件等,对近二十多年来的研究成果进行了评述。土壤酶来源广泛,存在形式复杂,直接提取土壤酶还有很大的难度。目前土壤酶活性的测定主要是通过一定量底物在酶催化反应过程中的生成物或剩余物量来实现。基于对硝基酚衍生物为底物的分光比色法,因其成本低廉而被广泛使用。针对国际上未能建立统一的测定方法而导致研究数据之间难以进行比较的现状,作者认为现阶段土壤水解酶测定过程中应注意以下几点:1)尽量采用新鲜土样或短时间低温冷藏的土样;2)酶底物种类的选择应与国际接轨,采用饱和底物浓度使其反应速度接近最大值;3)缓冲液的pH值可与土壤pH值相近;4)4 h内培养的土壤酶,可忽略微生物抑制剂的使用。建议我国在近期内:1)应丰富土壤水解酶种类的研究;2)注重灵敏度高、需样量小以及培养时间短的荧光分析技术的应用;3)在强化典型土壤酶动力学特征研究基础上,尽快规范土壤酶活性的测定方法。     

基于电磁感应的典型干旱区土壤盐分空间异质性

为研究干旱区土壤盐分空间异质性,指导农业生产实践,运用大地电导率仪（EM38、EM31）对研究区域进行移动式磁感调查,获取表观电导率（ECa）。同时,通过27个校准点的采样和ECa测量,建立土壤盐分的电磁感应解译模型。干旱区土壤盐分质量分数与EM38、EM31水平模式读数（H38、H31）显示出良好的相关性（R=0.935）,可以利用ECa结合GIS和地统计学知识研究土壤盐分的空间分布。采用两种方法进行研究：一种是先利用解译模型获取磁感调查点的土壤盐分质量分数,然后进行地统计分析研究其空间分布;另一种是先利用地统计分析研究H38和H31的空间分布,然后利用解译模型通过栅格运算计算盐分质量分数,精度检验显示前者预测值与实测值之间的相关性更好（R2, 0.888＞0.873）;标准差较低（std. 0.414＜0.426）,具有更高的预测精度。研究结果表明,基于电磁感应研究干旱区土壤盐分空间异质性是切实可行的,这对于土壤盐渍化的快速诊断,指导农业生产和促进精准农业的发展具有重要的意义。     

Determination of discrete element model parameters required for soil tillage

The dynamic interaction that occurs in the soil tillage process includes a high rate of plastic deformation and soil failure, characterized by flow of the soil particles. The discrete element method (DEM) seems to be a promising approach for constructing a high-fidelity model to describe soil–implement interaction. Proper prediction of this interaction using DEM depends upon the model parameters. However, there is no robust method for determining the parameters for discrete element models. In this study, the determination of parameters was based on in situ field tests, which consisted of sinkage tests performed with different penetration tools. Based on each test, a plot of force versus displacement, or a so-called “real curve,” was drawn. Discrete element models were built in correspondence with the field tests. “Simulation curve” plots were obtained from the results of the simulation of force versus displacement. In order to minimize the area difference between the real and simulation curves, an inverse solution technique using the Nelder–Mead algorithm of optimization was employed. The optimization results of this particular problem are sensitive to the initial estimate of the parameters. In order to achieve a unique solution, the initial estimate must be close enough to the proper value of the parameters. An energy method and elastic–plastic rule were developed to determine the initial estimation for the optimization process. The described methodology was verified experimentally and numerically; good correlation was achieved between the soil mechanical behavior obtained by experiments and the discrete element simulations.     

咸淡水交替灌溉下土壤盐分再分布规律的室内实验研究

咸水灌溉是解决目前淡水资源短缺的重要途径。为寻求合理的咸水农田灌溉方法,进行了不同矿化度和不同灌水模式的室内土柱咸淡水交替灌溉模拟试验,分析了咸淡水交替灌溉条件下土壤溶液电导率(EC)值和钠吸附比(SAR)的变化规律。结果表明：两种灌水模式下,灌水结束时土壤溶液EC值在22.5 cm处达到最高,且4 g/L>2 g/L,且与试验初期相比,土壤溶液EC值明显提高,土柱整体积盐明显。灌水模式对土壤溶液EC值的影响大于矿化度;两种灌水模式不同矿化度处理的SAR值变化规律基本一致。     

Improved diffusion methods for determination of inorganic nitrogen in soil extracts and water

Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications, and simplify the processing of samples for N-isotope analysis. In these methods, the soil extract is treated with MgO, or MgO plus Devarda‘s alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert NH₄ ⁺-N, NO₃ ^–-N, and/or NO₂ ^–-N to NH₃-N. The NH₃ thereby liberated is collected in H₃BO₃-indicator solution in a Petri dish suspended from the Mason-jar lid and determined quantitatively by acidimetric titration. With the modifications described, analyses can be performed on 10- to 100-ml samples of water, 0.5MK₂SO₄, 1MKCl, 2MKCl, or 4MKCl, at temperatures between 20 and 30°C. Recovery from 10 or 20ml was quantitative in 18–80h with up to 4mgN; recovery from 50 or 100ml was quantitative in 3–13 days with up to 2mgN. Removal of H₃BO₃ for N-isotope analysis by the Rittenberg process was effected using methanol. Mason-jar diffusion methods are much simpler and more convenient than conventional steam distillations. Comparative studies showed that quantitative determinations are more accurate and precise by diffusion than by distillation. Received: 15 May 1996     

Sequential extraction methods for soil organic nitrogen

(pp. 833–841)

In order to learn the status of available soil nitrogen (N), two sequential extraction methods (A and B) were tested. Proposed methods are as follows.

(A) Extraction with water, KCl, acetic acid, 1/15 M phosphate buffer, sulfuric acid, and NaOH.

(B) Extraction with water, KCl, 0.01 M sulfuric acid, 0.1 M sulfuric, 0.2 M sulfuric acid and 0.4 M sulfuric acid.

1) NO₃-N was only detected in a solution extracted with water. Major N in an extract with KCl was in ammonium form. Extracts with phosphate buffer and sulfuric acid contained organic-N only. When these two fractions were examined by size exclusion chromatography (HPLC-SEC), only one major peak in each extract appeared.

2) Minerals, such as Al and Fe in each extract were determined using ICP (Varian Co., Ltd.). With the increase in concentration of sulfuric acid, the high Fe concentration in each extract increased. On the other hand, much higher Al was found in extracts with lower concentrations of sulfuric acid compared to Fe.

3) Though some crop species such as spinach and carrot show the potential to take up organic-N in a soil applied with organic matter, this sequential soil-nitrogen extraction method may be useful to evaluate availability of soil nitrogen fertility with more accuracy compared to conventional methods in the case of these superior crop species.     

福建黄泥田肥力质量特征与最小数据集

黄泥田为福建省主要中低产田类型之一,约占水稻土面积的30%。为解析关键限制因子及开展黄泥田肥力质量评价,进而实施针对性的改良措施,采用配对采样方法,采集福建省20对典型黄泥田与邻近同一微地貌单元内高产灰泥田表层土壤,分析了两种土壤类型28项属性因子指标差异及其原因,并采用主成分分析等方法构建福建省黄泥田肥力质量评价因子最小数据集,通过加权指数法分别计算最小数据集土壤肥力质量指数与差异显著因子构成的重要数据集土壤肥力质量指数。结果表明,与灰泥田相比,黄泥田的有机质含量低19.1%,全氮、全磷、全钾含量分别低14.8%、29.9%和25.4%,碱解氮、有效磷和速效钾含量分别低17.8%、56.7%和39.3%,CEC、交换性钙、交换性镁含量分别低12.9%、50.6%和30.8%,有效铁、有效硼和有效锌含量分别低25.6%、33.3%和44.1%。黄泥田的物理性黏粒、0.001 mm黏粒和容重分别较灰泥田高20.8%、25.6%和12.3%,而孔隙度低19.3%。黄泥田过氧化氢酶活性较灰泥田高20.4%,脲酶活性较灰泥田低40.4%。用主成分分析方法从上述19项有显著差异的因子构成的重要数据集中归纳出累计贡献率达76.22%并能反映黄泥田综合肥力特征的6个主成分,建立了由CEC、全钾、有效磷、有效硼和孔隙度5项因子组成的黄泥田肥力评价最小数据集,相应的黄泥田最小数据集土壤肥力质量指数仅相当于灰泥田的69.5%,通过与重要数据集的土壤肥力质量指数相关分析比较,最小数据集可代替重要数据集对福建省黄泥田土壤肥力质量进行正确评价。