Determination of soil salinity based on WET measurements using the concept of salinity index

We evaluated the Malicki and Walczak model (MW) and its appropriately modification (MMW) in the prediction of the electrical conductivity of the soil solution (σ_p), utilizing the WET dielectric sensor. In the MMW approach, the prediction of σ_p requires determination of the WET‐based salinity index (X_s) and clay and sand contents of the soil. MMW appears to be more effective than MW in all cases except for the cases of finer soils when σ_p > 3 dS m^?1.     

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。     

Mapping soil salinity in 3‐dimensions using an EM38 and EM4Soil inversion modelling at the reconnaissance scale in central Morocco

Large areas of Morocco require irrigation and although good quality water is available in dams, farmers augment river water with poorer quality ground water, resulting in salt build‐up without a sufficient leaching fraction. Implementation of management plans requires baseline reconnaissance maps of salinity. We developed a method to map the distribution of salinity profiles by establishing a linear regression (LR) between calculated true electrical conductivity (σ, mS/m) and electrical conductivity of the saturated soil‐paste extract (ECe, dS/m). Estimates of σ were obtained by inverting the apparent electrical conductivity (ECa, mS/m) collected from a 500‐m grid survey using an EM38. Spherical variograms were developed to interpolate ECa data onto a 100 m grid using residual maximum likelihood. Inversion was carried out on kriged ECa data using a quasi‐3d model (EM4Soil software), selecting the cumulative function (CF) forward modelling and S2 inversion algorithm with a damping factor of 3.0. Using a ‘leave‐one‐out cross‐validation' (LOOCV), of one in 12 of the calibration sites, the use of the q‐3d model yielded a high accuracy (RMSE = 0.42 dS/m), small bias (ME = ?0.02 dS/m) and Lin's concordance (0.91). Slightly worse results were obtained using individual LR established at each depth increment overall (i.e. RMSE = 0.45 dS/m; ME = 0.00 dS/m; Lin's = 0.89) with the raw EM38 ECa. Inversion required a single LR (ECe = 0.679 + 0.041 × σ), enabling efficiencies in estimating ECe at any depth across the irrigation district. Final maps of ECe, along with information on water used for irrigation (ECw) and the characterization of properties of the two main soil types, enabled better understanding of causes of secondary soil salinity. The approach can be applied to problematic saline areas with saline water tables.     

Utilizing a DUALEM‐421 and inversion modelling to map baseline soil salinity along toposequences in the Hunter Valley Wine district

In the oldest commercial wine district of Australia, the Hunter Valley, there is the threat of soil salinization because marine sediments underlie the area. To understand the risk requires information about the spatial distribution of soil properties. Electromagnetic (EM) induction instruments have been used to identify and map the spatial variation of average soil salinity to a certain depth. However, soils vary with depth dependent on soil forming factors. We collected data from a single‐frequency and multiple‐coil DUALEM‐421 along a toposequence. We inverted this data using EM4Soil software and evaluated the resultant 2‐dimensional model of true electrical conductivity (σ – mS/m) with depth against electrical conductivity of saturated soil pastes (EC_p – dS/m). Using a fitted linear regression (LR) model calibration approach and by varying the forward model (cumulative function‐CF and full solution‐FS), inversion algorithm (S1 and S2), damping factor (λ) and number of arrays, we determined a suitable electromagnetic conductivity image (EMCI), which was optimal (R² = 0.82) when using the full solution, S2, λ = 3.6 and all six coil arrays. We conducted an uncertainty analysis of the LR model used to estimate the electrical conductivity of the saturated soil‐paste extract (EC_e – dS/m). Our interpretation based on estimates of EC_e suggests the approach can identify differences in salinity, how these vary with parent material and how topography influences salt distribution. The results provide information leading to insights into how soil forming factors and agricultural practices influence salinity down a toposequence and how this can guide soil management practices.     

基于表观电导率和Hydrus模型同化的土壤盐分估算

精细刻画农田土壤盐分运移过程对盐渍化精准治理具有重要意义。该文以磁感式大地电导率仪EM38测定的土壤表观电导率作为数据源,利用表观电导率与剖面土壤盐分之间的反演模型作为观测算子,将集合卡尔曼滤波(ensemble Kalmanfilter,En KF)同化方法应用于土壤水盐运移过程模型(HYDRUS-1D),进行滨海盐渍农田周年土壤盐分动态的模拟,并分析了同化过程的敏感性。结果表明:与单纯使用HYDRUS模型相比,En KF同化方法对模型观测算子的更新,有效提高剖面土壤盐分模拟精度,且En KF同化值的精度优于En KF同化模拟值,在同化过程中的调整量亦最大;敏感性分析结果显示土壤盐分同化过程对状态变量集合数大小不敏感,对观测数据误差和引入观测数据的深度较为敏感,观测数据误差水平越高、引入观测数据的深度越浅其误差越大。研究表明基于水盐运移模型和土壤表观电导率数据的EnKF同化方法能提高土壤盐分的模拟精度,为利用多源数据和机理模型进行较大尺度生态过程模拟预测提供了有效手段。     

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...     

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。     

Soil quality indices for evaluation of long‐term land use and soil management practices in semi‐arid sub‐tropical India

Land use changes and soil management can potentially alter soil quality. A study was conducted to assess the long‐term (>20 years) effects of perennial trees (PT), vegetable crops (VC), rice–wheat (RW) system, sewage‐irrigated fields (SF), maize–wheat (MW) system and uncultivated soils (US) on soil quality. Soil physical quality parameters were significantly affected only in the SF system when compared with the US soil, particularly for bulk density (BD 1·51 Mg m⁻³ in SF vs. 1·34 in US). Among chemical parameters, electrical conductivity was high in SF, and soil nutrients (N, P, K, S, Zn, Fe, Cu and Mn) were well above the critical limits of deficiency in all the systems. Soil parameters were integrated into soil quality indices (SQIs) by unscreened transformation and principal component analysis (PCA). SQI observed under each system were compared with the US to assess the degree of degradation. Mean SQI differences showed that PT (+16·02 per cent), VC (+4·80 per cent), RW (+10·04 per cent), and MW (+11·30 per cent) are aggrading, whereas SF (−2·06 per cent) is degrading with respect to the reference soil (US). Adoption of MW system proved to be better than traditional RW; and in general agricultural crops have a significant advantage than VC, in terms of maintaining soil quality. Sewage irrigation is not a sustainable practice and long‐term use may degrade the soil. Among the SQIs, PCA with nonlinear scoring function (NLSF) based SQI was effective in judging land degradation due to soil quality changes as affected by long‐term land use and soil management practices. Copyright © 2008 John Wiley & Sons, Ltd.     

Potassium is responsible for salinity in soils amended with poultry manure

Abstract

Soil salinity increases when heavy rates of poultry manure are applied to sandy coastal plain soils. Analysis of soils involved in a poultry manure study during 1970, 1971 and 1972 has shown that soil salinity is primarily associated with a high concentration of ? in the soil solution. Although concentrations of other elements increased with the application of poultry manure also, the increases were not sufficient to account for the salinity in these soils.     

Tillage effects on soil aggregation and soil organic carbon profile distribution under Mediterranean semi‐arid conditions

In rainfed semi‐arid agroecosystems, soil organic carbon (SOC) may increase with the adoption of alternative tillage systems (e.g. no‐tillage, NT). This study evaluated the effect of two tillage systems (conventional tillage, CT vs. NT) on total SOC content, SOC concentration, water stable aggregate‐size distribution and aggregate carbon concentration from 0 to 40 cm soil depth. Three tillage experiments were chosen, all located in northeast Spain and using contrasting tillage types but with different lengths of time since their establishment (20, 17, and 1‐yr). In the two fields with mouldboard ploughing as CT, NT sequestered more SOC in the 0–5 cm layer compared with CT. However, despite there being no significant differences, SOC tended to accumulate under CT compared with NT in the 20–30 and 30–40 cm depths in the AG‐17 field with 25–50% higher SOC content in CT compared with NT. Greater amounts of large and small macroaggregates under NT compared with CT were measured at 0–5 cm depth in AG‐17 and at 5–10 cm in both AG‐1 and AG‐17. Differences in macroaggregate C concentration between tillage treatments were only found in the AG‐17 field at the soil surface with 19.5 and 11.6 g C/kg macroaggregates in NT and CT, respectively. After 17 yr of experiment, CT with mouldboard ploughing resulted in a greater total SOC concentration and macroaggregate C concentration below 20 cm depth, but similar macroaggregate content compared with NT. This study emphasizes the need for adopting whole‐soil profile approaches when studying the suitability of NT versus CT for SOC sequestration and CO₂ offsetting.     

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。     

Soil organic carbon temperature sensitivity of different soil types and land use systems in the Brazilian semi‐arid region

Quantifying the sensitivity of soil organic matter decomposition (SOM) to global warming is critical for predict future impacts of climate change on soil organic carbon stocks (SOC) and soil respiration, especially in semi‐arid regions such as north‐eastern Brazil, where SOC stocks are naturally small. In this study, the responses of the labile and recalcitrant carbon components and soil respiration dynamics were evaluated in three different soil types and land use systems (native vegetation, cropland and pasture) of the Brazilian semi‐arid region, when submitted to temperature increase. After 169 days of incubation, the results showed that an increase of 5°C generated an average increase in CO₂ emission of 12.0%, but which could reach 28.1%. Overall, the labile carbon (LC) in areas of native vegetation showed greater sensitivity to temperature than in cropland areas. It was also observed that recalcitrant carbon (RC) was more sensitive to warming than LC. Our results indicate that Brazil's semi‐arid region presents a substantial vulnerability to global warming, and that the sensitivity of RC and of LC in areas of native vegetation to warming can enhance SOC losses, contributing to positive feedback on climate change, and compromising the productive systems of the region. However, further studies evaluating other types of soil and texture and management systems should be carried out to consolidate the results obtained and to improve the understanding about SOM decomposition in the Brazilian semi‐arid region.     

Analysis of soil fertility and its anomalies using an objective model

In this work, the use of an objective method, the formulation of the Rasch measurement model, which synthesizes data with different units into a uniform analytical framework, is considered to get representative measures of soil fertility potential in an experimental field. Thus, two types of information about the soil were obtained from soil samples taken at 70 locations: first, the textural components were determined, and, secondly, deep (ECa‐90) and shallow (ECa‐30) soil apparent electrical conductivity, approximately 0–90 and 0–30 cm depths, respectively, were measured. A latent variable, denominated soil fertility potential, was defined. It is supposed, and later it is verified, that all soil properties previously indicated have a marked influence on the latent variable. The adequate assignment of categorical values across properties measures and the good fit of the data are checked as a previous phase to properly compute the Rasch measures. After applying the Rasch methodology, it was obtained that both electrical conductivities are the most influential properties on soil fertility potential, getting moreover a ranking of all soil samples according to their fertility potential and the unexpected behaviors, called misfits, of some soil samples, which constitute a very useful information to better match soil and crop requirements as they vary in the field, being a rational basis for a site‐specific crop management.     

滴灌对干旱区绿洲防护林土壤盐分的淋洗作用

为了探清滴灌对防护林地土壤水盐分布、不同滴灌年限林地根系分布、不同滴头距离处理下土壤盐分淋洗特征的影响,采用了野外监测方法,在喀拉米吉镇绿洲进行了对比试验。结果表明,目前的灌溉制度基本没有阻碍林木根系生长,但根系分布在滴灌作用下有上移的趋势。建议：塔里木河下游绿洲沙枣防护林在前几年种植中,可选择较窄的滴头距离淋洗土壤盐分;虽然滴灌在第1、2、3年对盐分的影响深度基本没有阻碍根系的生长,且随着林龄的增长,滴灌年限越大,淋洗深度越大,但是滴灌对根系周围的洗盐作用是局部范围内的,建议每年进行1次大水漫灌。     

Spatial distributions of soil chemical and physical properties prior to planting soybean in soil under ridge‐, no‐ and conventional‐tillage in a maize–soybean rotation

Detailed information on the profile distributions of agronomically important soil properties in the planting season can be used as criteria to select the best soil tillage practices. Soil cores (0–60 cm) were collected in May, 2012 (before soybean planting), from soil transects on a 30‐yr tillage experiment, including no‐tillage (NT), ridge tillage (RT) and mouldboard plough (MP) on a Brookston clay loam soil (mesic Typic Argiaquoll). Soil cores were taken every 19 cm across three corn rows and these were used to investigate the lateral and vertical profile characteristics of soil organic carbon (SOC), pH, electrical conductivity (EC), soil volumetric water content (SWC), bulk density (BD), and penetration resistance (PR). Compared to NT and MP, the RT system resulted in greater spatial heterogeneity of soil properties across the transect. Average SOC concentrations in the top 10 cm layer were significantly greater in RT than in NT and MP (P = 0.05). NT soil contained between 0.8 and 2.5% (vol/vol) more water in the top 0–30 cm than RT and MP, respectively. MP soil had lower PR and BD in the plough layer compared to NT and RT soils, with both soil properties increasing sharply with depth in MP. The RT had lower PR relative to NT in the upper 35 cm of soil on the crop rows. Overall, RT was a superior conservation tillage option than NT in this clay loam soil; however, MP had the most favourable soil conditions in upper soil layers for early crop development across all treatments.     

Investigating soil physical properties and yield response in a grassland field using a dual‐sensor penetrometer and EM38

Precision‐farming applications are mainly based on site‐specific information of soil properties at the field scale. For this purpose, a number of novel sensor techniques have been developed but not intensively tested under different field conditions. This study presents a combined application of a self‐developed dual‐sensor vertical penetrometer (DVP) for measuring volumetric soil water content (VSWC) and cone index (CI), and an EM38 for soil apparent electrical conductivity (EC_a) in a pasture (1.4 ha). To verify the feasibility of the DVP for interpreting the depth‐specific information in the field, not only the soil physical properties and their geographical coordinates were measured, but also geo‐referenced yield data were collected. We found that the yield pattern was quite similar to the soil water‐content pattern of each layer (layer‐1: 5–15 cm; layer‐2: 15–25 cm, layer‐3: 25–35 cm) and EC_a pattern. Using the map‐based comparisons in conjunction with the statistical analyses, the effect of each measured soil physical property (VSWC, CI, and EC_a) on the yield was investigated. The regression between the yield and VSWC at each layer fitted a quadratic equation (R² = 0.515 at 5–15 cm; R² = 0.623, at 15–25 cm; R² = 0.406 at 25–35 cm). The negative correlation between yield and CI at each layer fitted a linear model with R² ≥ 0.510.     

Evaluation of soil and water conservation measures in a semi‐arid river basin in Tunisia using SWAT

The Merguellil catchment (central Tunisia) is a typical Mediterranean semi‐arid basin, which suffers from regular water shortage aggravated by current droughts. Over recent decades, the continuous construction of small and large dams and soil and water conservation works (i.e. contour ridges) have taken place within this watershed. However, little is known about the effect of these water‐harvesting systems on the water balance components of arid or semi‐arid basins. In this paper, we present the results of a study, which evaluates the impact of the contour ridges on water balance components and erosion at basin scale by using the soil and water assessment tool model (SWAT). Large dams were modelled as reservoirs, small dams as ponds and contour ridges as potholes that fill with water and increase the percolation into the aquifer. The model predicts that contour ridges produce annually a reduction of 32 and 21% in surface run‐off and river discharge, respectively, and an increase in aquifer recharge of 50%. At the same time, retention of a large proportion of entrained sediment (26%) was modelled.     

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.     

IMAGE: a physically-based one dimensional irrigation management model for soil salinity control

Abstract. This paper describes a study of 37 farms in the Batinah region of Oman where fodder crops and date palms are grown using saline irrigation water. Soil water salinities (ε_s) range from 2 to 50 dS m^–1. Soil water salinity depends on irrigation water quality and management factors such as the amount and frequency of irrigation and the area of the irrigation basin relative to the vegetation canopy. An irrigation management model for soil salinity control IMAGE has been developed, based on the salt balance of the profile assuming that the ε_s is in equilibrium with the irrigation water. The input parameters required to run the model include the annual water application, irrigation interval, soil textural class, potential evaporation, the ratio of crop canopy to irrigation basin area and the salinity of irrigation water. Verification of the model using rather uncertain data from a survey of the farms showed that this simple approach predicted ε_s to within 2.5 dS m^–1 in 82% of cases. The model showed that ε_s was highly sensitive to the size of irrigation basin and the amount and scheduling of irrigation, and so provides a tool for optimizing salinity management.