Comparison of Geonics EM38 and Dualem 1S electromagnetic induction sensors for the measurement of salinity and other soil properties

The electromagnetic induction (EMI) Geonics EM38 (G‐EM38) and Dualem 1S (D‐1S) sensors are used frequently for assessment of soil salinity and other soil characteristics in irrigated agriculture. We compared these two sensors to determine whether they could be used interchangeably for the measurement of apparent soil electrical conductivity (ECa) in horizontal (ECa‐h) and vertical (ECa‐v) coil receiver modes. Readings were taken at 201 locations identified in three irrigation districts in both modes, and statistical comparisons were made on the raw data and from maps of a 2‐ha irrigated field made using 1680 horizontal mode readings. Both sensors gave the same ECa‐v readings (mean G‐EM38 and D‐1S difference = 0), whereas the ECa‐h readings were slightly greater with the Geonics EM38 than with the Dualem D‐1S (mean difference = 0.075 and 0.05 dS/m for the 201 and 1680 observations, respectively). The degree of coincidence between both sensors for soil profile ECa classification was acceptable: 82% for normal profiles (i.e. ECa‐h/ECa‐v < 0.9) and 90% for inverted profiles (i.e. ECa‐h/ECa‐v > 1.1). In practical terms, Geonics EM38 and Dualem 1S sensors could be used interchangeably with similar or very close results.     

长江三角洲地区滩涂土壤盐分空间分布特征研究

盐碱地盐分空间分布精准识别及形成机理解析对盐碱地科学利用具有重要意义。针对传统点状采样监测方法工作量大、代表性差和检测费用高等问题,本研究采用电磁感应仪精准调查技术对上海崇明某滩涂农场进行土壤盐分空间分布评估,全面快速获得盐分空间分布信息,解析土壤盐分形成机理,进而分类分区分级指导农业生产和科学精准改良。结果表明：土壤表观电导率(EC_a)和土壤盐分含量呈显著线性正相关关系(R²>0.9,P<0.05),土壤表观电导率的变化可以用来表征土壤盐分含量的变化;通过克里金插值研究区内土壤盐分的空间变异分布状况发现,研究区土壤盐分空间分布不均匀,有近80%区域存在轻中度盐碱化问题;通过定点取样土壤盐碱剖面评价,发现研究区土壤盐分具有较强的表聚性和变异强度,且变异系数随土壤深度增加不断减小;将表观电导率解译出的土壤盐分和土壤pH、有机质含量及主要组成离子含量进行相关性分析,剖析出该区域盐渍化类型以硫酸盐型为主,海水浸渍侧渗和地下水返盐影响是该区域盐渍化形成的主要原因。本研究实现了对土壤盐碱化快速、大范围、科学且动态的监测,对于全面提升盐碱地农...     

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。     

Identifying potential management zones in a layered soil using several sources of ancillary information

Variation in soil texture has a profound effect on soil management, especially in texturally complex soils such as the polder soils of Belgium. The conventional point sampling approach requires high sampling intensity to take into account such spatial variation. In this study we investigated the use of two ancillary variables for the detailed mapping of soil texture and subsequent delineation of potential management zones for site‐specific management. In an 11.5 ha arable field in the polder area, the apparent electrical conductivity (EC_a) was measured with an EM38DD electromagnetic induction instrument. The geometric mean values of the EC_a measured in both vertical and horizontal orientations strongly correlated with the more heterogeneous subsoil clay content (r = 0.83), but the correlation was weaker with the homogenous topsoil clay content (r = 0.40). The gravimetric water content at wilting point (θg_{(?1.5 MPa)}) correlated very well (r = 0.96) with the topsoil clay content. Thus maps of topsoil and subsoil clay contents were obtained from 63 clay analyses supplemented with 117θg_{(?1.5 MPa)} and 4048EC_a measurements, respectively, using standardized ordinary cokriging. Three potential management zones were identified based on the spatial variation of both top and subsoil clay contents. The influence of subsoil textural variation on crop behaviour was illustrated by an aerial image, confirming the reliability of the results from the small number of primary samples.     

基于磁感式土壤表观电导率空间变异性的插值方法比较

针对目前黄河三角洲地区存在的土壤盐渍障碍问题,以该地区典型地块为研究对象,运用磁感大地电导率仪(EM38),结合GIS与地统计学研究了不同样点密度下土壤表观电导率的空间变异特征,确定了最佳的空间插值模式,并采用偏差指数对各分布图层的空间相似性进行了评价。结果表明：不同样点密度下的土壤表观电导率均呈中等变异强度,并服从对数正态分布;各样点密度下的土壤表观电导率均表现为强空间相关性,其空间变异主要表现在小于10 m的田间尺度上,且对于预测精度,泛克立格>普通克立格>反距离权重>局部多项式。偏差指数法分析表明,各插值方法分布图的空间相似性均随样点密度的降低而下降;对于相同的样点密度减小比例下的空间信息保留度,泛克立格>普通克立格>反距离权重>局部多项式,采用泛克立格法可以在保证预测精度的基础上合理降低样点密度。该研究为黄河三角洲地区盐渍土地磁感式田间数据采集的合理密度确定以及优化空间插值模式选取提供了理论依据与技术参考。     

约旦河谷土壤含盐量变化对其灌溉农业可持续发展的潜在危害研究

The integrated effect of irrigation and agricultural practices on soil salinity in the Jordan Valley （JV）, where over 60% of Jordan’s agricultural produce is grown, was investigated in this study during 2009-2010. Due to the differences in agricultural operations, cropping patterns, irrigation management, and weather conditions, 206 top- and sub-soil samples were taken every 1 to 3 km from representative farms along a north-south （N-S） transect with 1 to 2 km lateral extents. Soil electrical conductivity of saturated extract (EC_se), Ca, Mg, K, Na, Cl, and Na adsorption ratio （SAR） were determined in saturated paste extracts. Results indicated that about 63% of soils in the JV are indeed saline, out of which almost 46% are moderately to strongly saline. Along the N-S transect of the JV, EC_se increased from 4.5 to 14.1 dS m^-1 in top-soil samples. Similar increase was observed for the sub-soil samples. The major chemical components of soil salinity; i.e., Ca, Mg, and Cl, also showed a similar increase along the N-S transect of the valley. Moreover, compared to previous field sampling, results showed that changes in soil salinity in the JV were dramatic. In addition, it was found that Cl imposed an existing and potential threat to sensitive crops in 60% of the soils in the JV, where Cl concentrations were greater than 710 mg L^-1. Under the prevalent arid Mediterranean conditions, improving the management of irrigation water, crops, and nutrient inputs and increasing water and fertilizer use efficiencies should be indispensable to conserve and sustain the already fragile agricultural soils in the JV.     

渭干河灌区土壤水盐空间变异性研究

根据直线和网格布点法布置的150个取样点的测定资料,应用经典统计分析方法．探讨了垦荒地土壤电导率和重量含水率的空间变异性,并给出了不同置信水平及精度要求下两者的合理取样数目。应用自相关和半方差分析方法进一步讨论了土壤电导率及土壤重量含水率的空间变异结构和半方差函数模型。结果表明,垦荒地土壤电导率和重量含水率的空间变异都是有结构的,土壤电导率的最大相关域为9m,土壤重量含水率的最大相关域为6．4m。两者的半方差函数可用有基台的线型模型拟合。     

微咸水灌溉下土壤水盐动态及对作物产量的影响

华北平原农业灌溉用水非常紧缺,水资源日益缺乏与粮食需求日益增多之间的矛盾尖锐。充分利用微咸水资源是缓解这一矛盾的重要途径之一。该文以中国农业大学曲周试验站1997－2005年冬小麦和夏玉米微咸水灌溉田间长期定位试验为基础,研究了充分淡水、充分淡咸水、关键期淡水、关键期淡咸水和不灌溉等5个处理下土壤饱和电导率和含盐量的动态变化,探讨了微咸水灌溉对冬小麦和夏玉米产量的影响。结果表明：土壤水盐动态呈受灌溉和降雨影响的短期波动和受季节更替影响的长期波动;在正常降雨年份,使用微咸水进行灌溉是可行的,不会导致土壤的次生盐渍化;微咸水灌溉虽然导致冬小麦和夏玉米产量降低10%～15%,但节约淡水资源60%～75%。如果降雨量达到多年平均水平以及微咸水灌溉制度制订合理,微咸水用于冬小麦/玉米田间灌溉前景广阔。     

暗管排水对大棚土壤次生盐渍化改良及番茄产量的影响

为探讨防治设施土壤次生盐渍化的措施,于发生次生盐渍化的大棚土壤内埋设埋深40cm,间距6m及埋深70cm,间距8m的塑料暗管,研究土壤电导率(EC)、饱和导水率、体积质量等基本理化性质的变化,分析暗管排水对次生盐渍化土壤改良及番茄产量的影响。结果表明:埋设暗管可以明显降低次生盐渍化土壤的EC值,尤其是暗管上方的EC值显著低于对照;同时,土壤饱和导水率增加,体积质量降低而总孔隙度升高;番茄平均单果质量增加,产量显著提高,各项指标均表现为埋深70cm,间距8m暗管的处理优于埋深40cm,间距6m的处理。埋深70cm,间距8m暗管的处理在大棚土壤次生盐渍化改良中的效果优于埋深40cm,间距6m的处理。     

控释肥硫膜对酸性棕壤淋溶特性的影响

为预测硫包膜控释肥施用后大量硫膜残留对土壤生态系统造成的危害,设置硫膜材料添加量不同的室内淋溶试验,以研究控释肥硫膜材料对土壤淋溶特性的影响。研究结果表明;成分和量等同于硫膜的粉状硫磺可显著改变酸性棕壤淋溶液的pH和EC值及K^＋、Na^＋、Ca^2＋、Mg^2＋、SO42-的浓度,5次淋溶累计淋失的K^＋、Na^＋、Ca^2＋、Mg^2＋、SO4^2-随粉状硫磺加入量的增加而增加。而硫包膜尿素处理除对土壤SO4^2-、K^＋淋溶影响不明显外,对其他指标的影响较明显。试验同时发现,由于硫膜和粉状硫磺的物理形态不同,短期内对土壤淋溶特性的影响也有较大差异,但粉状硫磺的表现可以反映硫膜积累并转化后对土壤的影响。     

不同淋洗模式下干旱区盐渍土改良效果分析

通过开展室外土柱模拟淋洗试验,选择间歇淋洗与连续淋洗两种淋洗模式,分析不同灌水总量和不同灌水频次相互组合条件下盐渍土的改良效果。结果表明:(1)灌水量相同情况下,间歇淋洗滤出液的电导率高于连续淋洗,间歇淋洗的淋洗效果好于连续淋洗;(2)灌水量不同条件下,滤出液体积随灌水量的增加而增多,灌水量越大盐分淋洗效果越好;(3)淋洗结束后,土壤pH值较淋洗前均有下降,与土壤盐分有相同的变化趋势;灌水量越大,脱碱效果越好。在本试验条件下,盐分淋洗效果以15L分3次给水的间歇淋洗方式最优,淋洗效率为11.58g/L,土壤pH值均由8.42下降到8.07。可供制定维持农田水盐平衡的节水灌溉制度以及盐碱地改良参考。