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。     

矿区农田土壤重金属分布特征与污染风险研究

对渭北旱原矿区130个农田土壤样品的Cd、Cr、Cu、Pb、Zn含量进行了测定,结果显示,Cd、Cu、Pb平均含量均高于陕西省土壤背景值,而Cr和Zn含量低于背景值。利用地统计方法得到的土壤重金属含量分布图显示,土壤各重金属含量由西向东呈下降趋势,水泥厂周边土壤重金属含量最高。相关性分析和主成分分析结果表明,5种重金属之间呈极显著正相关,说明其存在较高的同源性或复合关系。第1主成分主要由Cd构成,且主要反映了人为活动的影响,而第2主成分中的Cr所占负荷最高,体现了成土母质的作用,Cu、Pb和Zn含量受人为活动和成土母质共同影响。分别利用污染负荷指数(PLI)法和潜在生态危害指数(PER)法对研究区域土壤污染风险进行了评价,评价结果为煤矿区呈无污染或轻微到中度污染,水泥厂区土壤呈中度污染水平,单一元素污染程度由高到低依次为Cd、Pb、Cu、Cr、Zn。     

Delineating water management zones in a paddy rice field using a Floating Soil Sensing System

Paddy rice fields are kept inundated during most of the growing period. This requirement is challenging to achieve because of the lack of suitable technologies to detect rapidly percolation prone zones within these fields. The objective of this study was to evaluate a methodology to identify water leakage areas to support precision soil–water management at a within-field level. Therefore, a Floating Sensing System (FloSSy) was designed to record the soil apparent electrical conductivity (EC_a) of a paddy field both under dry and inundated conditions using the electromagnetic induction sensor EM38. Comparison of EC_a data sets obtained under inundated and dry conditions showed that the EC_a measurements under inundated condition (EC_a-i) were more strongly related to soil properties due to the absence of variability in soil moisture and the increased stability of the floating sensing platform. Therefore, we proceeded with the EC_a-i measurements and grouped them into two classes using a fuzzy k-means classification method. These classes showed significant differences in water infiltration: lower EC_a values represented a higher infiltration rate and vice versa. This effect was attributed to differences in soil texture, more specifically the sand content, and its effect on water retention. It was concluded that an EC_a-i survey with FloSSy allowed the detection of soil heterogeneity linked to downward water fluxes which has a potential to support precision soil–water management in inundated fields.     

Effect of soil salinity on growth of irrigated plantation Eucalyptus in south-eastern Australia

Management of salinity may include establishing trees in saline areas to enhance discharge and may enable productive use of saline land. Field studies of the performance of trees in saline conditions are generally confined to the initial years after planting, and little quantitative data are available on the relationship between the growth rates of eucalypt species to soil salinity in field conditions at later ages (e.g. 10 years). In this study, the growth of irrigated Eucalyptus globulus, E. grandis and E. camaldulensis is examined in relation to soil salinity measured using an electromagnetic induction device (EM38).The EM38 was found to be an effective tool in determining survival and growth responses of three Eucalyptus species to levels of soil salinity. Differences in measured tree survival, stand volume and leaf area index were correlated with soil salinity. Of the three species, E. globulus performed best in terms of survival and volume growth to age 10 years under slight to moderate salinity conditions, while E. camaldulensis performed best under moderate to severe soil salinity. The ranking of these species for salinity tolerance is consistent with pot trials and younger field trials.This study highlighted the high spatial variability associated with soil salinity, and studies relating the growth of trees in the field should best be analysed on an areal or stand basis, thereby accounting for variability of salt stored in the soil, and reducing the influence of inter-tree competition on growth-salinity relationships. These results have implications for site selection and management of eucalypts in saline areas.     

Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts

Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (EC_e) maps were obtained through electromagnetic induction surveys (EC_a readings) and district-specific EC_a-EC_e calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The EC_a-EC_e calibration equations were highly significant (P < 0.001) in all districts. EC_a was not significantly correlated (P > 0.1) with WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC_a mainly depended upon EC_e, so that the maps developed could be used effectively to assess soil salinity and its spatial variability. The surface-weighted average EC_e values were low to moderate, and ranked the districts in the order: Tunisia (3.4 dS m⁻¹) > Morocco (2.2 dS m⁻¹) > Spain (1.4 dS m⁻¹) > Turkey (0.45 dS m⁻¹). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m⁻¹), high in Spain (4.6 dS m⁻¹), moderate in Morocco (estimated at 2.6 dS m⁻¹), and low in Turkey (1.4 dS m⁻¹). Salt loads in drainage waters, calculated from their salinity (EC_dw) and volume (Q), were highest in Tunisia (very high Q and very high EC_dw), intermediate in Turkey (extremely high Q and low EC_dw) and lowest in Spain (very low Q and high EC_dw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts.     

A method for spatial prediction of daily soil water status for precise irrigation scheduling

Available water holding capacity (AWC) and field capacity (FC) maps have been produced using regression models of high resolution apparent electrical conductivity (EC_a) data against AWC (adj. R² = 0.76) and FC (adj. R² = 0.77). A daily time step has been added to field capacity maps to spatially predict soil water status on any day using data obtained from a wireless soil moisture sensing network which transmitted hourly logged data from embedded time domain transmission (TDT) sensors in EC_a-defined management zones. In addition, regular time domain reflectometry (TDR) monitoring of 50 positions in the study area was used to assess spatial variability within each zone and overall temporal stability of soil moisture patterns. Spatial variability of soil moisture within each zone at any one time was significant (coefficient of variation [% CV] of volumetric soil moisture content (θ) = 3-16%), while temporal stability of this pattern was moderate to strong (bivariate correlation, R = 0.52-0.95), suggesting an intrinsic soil and topographic control. Therefore, predictive ability of this method for spatial characterisation of soil water status, at this site, was limited by the ability of the sensor network to account for the spatial variability of the soil moisture pattern within each zone. Significant variability of soil moisture within each EC_a-defined zone is thought to be due to the variable nature of the young alluvial soils at this site, as well as micro-topographic effects on water movement, such as low-lying ponding areas. In summary, this paper develops a method for predicting daily soil water status in EC_a-defined zones; digital information available for uploading to a software-controlled automated variable rate irrigation system with the aim of improved water use efficiency. Accuracy of prediction is determined by the extent to which spatial variability is predicted within as well as between EC_a-defined zones.     

Comparison and sensitivity of measurement techniques for spatial distribution of soil salinity

In Khorezm, a district of Uzbekistan situated in the Aral Sea Basin, soil salinization is an important driver of soil degradation in irrigated agriculture. The main objective of this study was to identify techniques that enable rapid estimation of soil salinity. Therefore, bulk electrical conductivity of the soil (EC_a-meas) was measured with three different devices (2P, 4P, and CM-138) and electrical conductivity of the soil paste (EC_p-meas) was measured with the so-called 2XP device. These measurements were compared with independent estimates of EC_a-calc and EC_p-calc based on laboratory measurements of the saturated extract, EC_e, of soil samples from the same sites. Soil salinity could be assessed satisfactorily with all four devices. EC_p-meas could be well reproduced by the 2XP device (R ² = 0.76), whereas EC_a-meas estimates using 2P, 4P, and CM-138 in the field were less accurate (R ² < 0.50). The sensitivity of all devices to the main ions Cl⁻ and Ca^{2 +} suggests that the measuring principles are similar for all instruments. The devices can therefore be used interchangeably. Field assessment of soil salinity was considerably enhanced by the use of CM-138, because large areas can be quickly assessed, which may be desirable in spite of the lower accuracy.     

Prediction of the soil-depth salinity-trend in a vineyard after sustained irrigation with saline water

Remote sensing combined with an ability to look deeper than the soil surface is currently high in demand. This study was conducted through scaling down the amount of soil data from a saline irrigation water experiment to see if one can still capture the essential soil salinity depth trends within the data, to a level that can enhance the ability of remote methods. A saline irrigation experiment with 6 water qualities was conducted for 8 years on 1.2 ha of vineyard land near Robertson in the Western Cape Province of South Africa. Soil water was sampled at regular intervals at 5 depths between 0.15 and 1.2 m with suction cup lysimeters at a fixed time following each irrigation. Electrical conductivity of the soil water (EC_sw) was determined after sampling. Data collected over the full 8-year period were investigated for depth trends in EC_sw, seeking trend lines with lowest polynomial order that were still significantly predict the salinity profile. At all treatment levels a first order polynomial equation, fitted to the salinity profiles, significantly predicted the salinity trends. The EC_sw value at only two depths could therefore be used to calculate total salt accumulation and soil water quality below the root zone. The implication is that considerable value can be obtained from minimal measurements both in estimating salt accumulation in the soil profile and predicting water quality in return flow from saline irrigation.     

Monitoring scale-specific and temporal variation in electromagnetic conductivity images

In semiarid and arid landscapes, irrigation sustains agricultural activity but because of increasing demands on water resources there is a need to make gains in efficiency. As such spatial variation of soil properties such as clay and salinity needs to be understood because they strongly influence soil moisture availability. One way is to use electromagnetic induction because apparent soil electrical conductivity (EC_a) is related to volumetric soil moisture (θ), clay and salinity (EC_e). However, depth-specific variation has not been explored. Our aim is to generate electromagnetic conductivity images (EMCIs) by inverting DUALEM-421 EC_a and show how true electrical conductivity (σ) can be correlated with θ, clay, EC_e and bulk density (ρ) on different days post-irrigation (i.e., 1, 4 and 12 days). Two-dimensional multi-resolution analysis (MRA) is used to show how spatio-temporal variation in σ is scale-specific and how soil properties influence σ at different scales. We study this beneath a pivot irrigated alfalfa crop. We found that σ on days 1 and 4 was correlated with θ (Pearson’s r = 0.79 and 0.61) and clay (0.86 and 0.80) and the dominant scale of variation occurred at 9.3–18.7 m (50.21 % of total variation), >74.7 m (23.18 %) and 4.7–9.3 m (16.29 %). Between 9.3–18.7 and 4.7–9.3 m the variation may be a function of the cutter width (8 m), while >74.7 m may be change in clay and EC_e and gantry spacing (~48 m). The sprinkler spacing (1.2 and 1.6 m) explains short-scale variation at 1.2–2.3 m.     

Artificial neural network and time series models for predicting soil salt and water content

Volumetric water content of a silt loam soil (fluvo-aquic soil) in North China Plain was measured in situ by L-520 neutron probe (made in China) at three depths in the crop rootzone during a lysimeter experiment from 2001 to 2006. The electrical conductivity of the soil water (EC_sw) was measured by salinity sensors buried in the soil during the same period at 10, 20, 45 and 70 cm depth below soil surface. These data were used to test two mathematical procedures to predict water content and soil water salinity at depths of interest: all the available data were divided into training and testing datasets, then back propagation neural networks (BPNNs) were optimized by sensitivity analysis to minimizing the performance error, and then were finally used to predict soil water and EC_sw. In order to meet with the prerequisite of autoregressive integrated moving average (ARIMA) model, firstly, original soil water content and EC_sw time series were likewise transformed to obtain stationary series. Subsequently, the transformed time series were used to conduct analysis in frequency domain to obtain the parameters of the ARIMA models for the purposes of using the ARIMA model to predict soil water content and EC_sw. Based on the statistical parameters used to assess model performance, the BPNN model performed better in predicting the average water content than the ARIMA model: coefficient of determination (R²) = 0.8987, sum of squares error (SSE) = 0.000009, and mean absolute error (MAE) = 0.000967 for BPNN as compared to R² = 0.8867, SSE = 0.000043, MAE = 0.002211 for ARIMA. The BPNN model also performed better than the ARIMA model in predicting average EC_sw of soil profile. However, the ARIMA model performed better than the BPNN models in predicting soil water content at the depth of 20 cm and EC_sw at the depth of 10 cm below soil surface. Overall, the model developed by BPNN network showed its advantage of less parameter input, nonlinearity, simple model structure and good prediction of soil EC_sw and water content, and it gave an alternative method in forecasting soil water and salt dynamics to those based on deterministic models based on Richards’ equation and Darcy's law provided climatic, cropping patterns, salinity of the irrigation water and irrigation management are very similar from one year to the next.     

Field-scale assessment of deep drainage risk

Improving irrigation efficiency is of primary importance in arid and semi-arid regions of the world as a consequence of increasing incidences of soil and water salinisation. In the cotton-growing regions of Australia salinisation is generally a result of inefficient irrigation practices, which lead to excessive deep drainage (DD). There is therefore the need to apply a relatively inexpensive approach to assessing where inefficiencies occur and make prediction of suitability of existing and new water storage sites. However, physical methods of measuring DD, such as flux meters and lysimeters, are time-consuming and site-specific. In this paper we apply a rapid method for determining the spatial distribution of soil in an irrigated cotton field in the lower Gwydir valley. First, EC_a data (using EM38 and EM31) were used to determine a soil-sampling scheme for determining soil information such as clay content and exchangeable cations to a depth of 1.2 m. The soil data and water quality information were input into the SaLF (salt and leaching fraction) model to estimate DD rate (mm/year). In developing the relationship between EC_a and estimated DD, three exponential models (two-, three- and four-parameter) were compared and evaluated using the Aikakie information criteria (AIC). The three-parameter exponential model was found to be best and was used for further analysis. Using the geostatistical approach of multiple indicator kriging (MIK), maps of conditional probability of DD exceeding a critical cut-off value (i.e. 50, 75, 100 mm) were produced for various rates of irrigation (I=300, 600, 1,200 and 1,500 mm/year). The areas of highest risk were consistent with where water-use efficiency was problematic and thus leading to the creation of perched water tables. The advantage of this approach is that it is quick and is applicable to situations where efficient use of water is required. The results can be used for irrigation planning, particularly in the location of large irrigation infrastructure such as water reservoirs.     

基于EM38-MK2的滨海土壤电导率精确解译模型

以黄河三角洲为研究对象,通过土壤样品分层采集进行室内分析获得土壤电导率(1∶5)及采用EM38-MK2在采样点测量水平和垂直模式下土壤表观电导率,应用回归及多元逐步回归模拟分析的方法,研究土壤表观电导率与不同深度土层土壤电导率的相关性,并进行精度验证,以获得基于新型电磁感应仪的不同剖面深度处土壤电导率精确解译模型,实现区域尺度土壤盐分在不同剖面深度处空间分布格局快速评定.研究结果表明:多模式下测定的土壤表观电导率与不同土层土壤电导率呈现不同程度的显著性相关;联合多模式下土壤表观电导率解译土壤电导率的精度高于单一模式;表层土壤电导率协同土壤表观电导率可以提高亚表层及底层土壤电导率的预测精度.本研究可以为快速调查土壤盐渍化及盐渍土改良与利用提供思路,以节约成本和提高效率.     

长江河口地区典型地段土壤盐分特征研究

运用电磁感应仪EM38,结合GIS技术和地统计方法对长江河口地区典型地段土壤含盐量的空间变异性进行研究。结果表明,3个研究区土壤盐分含量的变幅有较大差异,其中以寅阳镇为最大,其次为大兴镇,北新镇土壤盐分变化幅度最小;各研究区土壤盐分含量均符合正态分布且均属于中等变异强度;各研究区的土壤盐分含量均表现为强的空间相关性,寅阳镇和北新镇土壤盐分含量半方差函数均符合球状模型,大兴镇土壤盐分含量半方差函数为指数模型。Kriging插值结果表明,各研究区土壤盐分的空间分布均呈现出条带状和斑块状格局;从空间尺度上来看,研究区土壤盐分南部高于北部;3个研究区土壤盐分含量具有明显的差别,寅阳镇土壤盐分含量明显高于其他2个镇,北新镇土壤盐分含量最低。     

水盐调控措施对苏北海涂油葵生长及土壤盐分分布的影响

为揭示苏北滨海盐碱地水盐调控措施下油葵生长特点及土壤盐分变化规律,通过田间小区试验的方法,研究了不同含盐量的滨海盐土上不同改良措施对油葵生长状况、产量形成及土壤盐分动态的影响。结果表明,轻度盐渍化土壤施用石膏处理的油葵生物量、产量和土壤脱盐率最高,中重度盐渍土施用石膏和覆盖秸秆综合调控措施的油葵生物量、产量和土壤脱盐率最高;生育期内0～20cm土壤盐分是影响油葵产量的首要因素,施用石膏和覆盖秸秆通过影响0～20cm土壤盐分分布,进而影响油葵的生长与产量;采用施用石膏和覆盖秸秆相结合的水盐综合调控措施,兼具雨季增强淋盐和旱季控盐效果,且在中重度盐渍土应用效果优于轻度盐渍土。     

Predicting soil salinity in response to different irrigation practices, soil types and rainfall scenarios

A model was developed to predict rootzone salinity under different irrigation practices on different soil types, with similar rainfall but different monthly distributions. A rootzone daily water and salt balance was performed using eight scenarios: two soil types (coarse textured vs. fine textured), two multi-year series of actual rainfall data and two irrigation practices (surface with fixed number of irrigations and ET-based sprinkler irrigation). All factors influenced the mean electrical conductivity (EC) of the rootzone in the growing season (EC_eS): (i) Surface irrigation led to lower EC_eS than sprinkler irrigation; (ii) Winter-concentrated rainfall caused lower EC_eS than rainfall distributed uniformly throughout the year; and (iii) Coarser-textured soil usually resulted in lower EC_eS than the finer textured. The EC_eS was related to the total precipitation of the hydrologic year and to the annual leaching fraction (LF) but surprisingly not to the seasonal LF. In most cases, the model predicted lower EC_eS than the FAO steady-state approach. Therefore, considering these site-specific features could lead to lower leaching requirements and the safe use of higher salinity water.     

Response of safflower (Carthamus tinctorius L.) to saline soils and irrigation: I. Consumptive water use

Salt-tolerant crops can be grown with saline water from tile drains and shallow wells as a practical strategy to manage salts and sustain agricultural production in the San Joaquin Valley (SJV) of California. Safflower (Carthamus tinctorius L.) was grown in previously salinized plots that varied in average electrical conductivity (EC_e) from 1.8 to 7.2 dS m⁻¹ (0–2.7 m depth) and irrigated with either high quality (EC_i<1 dS m⁻¹) or saline (EC_i=6.7 dS m⁻¹) water. One response of safflower to increasing root zone salinity was decreased water use and root growth. Plants in less saline plots recovered more water on average (515 mm) and at a greater depth than in more salinized plots (435 mm). With greater effective salinity, drainage increased with equivalent water application rates. Seed yield was not correlated with consumptive water use over the range of 400–580 mm. Total biomass and plant height at harvest were proportional to water use over the same range. Safflower tolerated greater levels of salinity than previously reported. Low temperatures and higher than average relative humidity in spring likely moderated the water use of safflower grown under saline conditions.     

Changes in spatial and temporal variability of SAR affected by shallow groundwater management of an irrigated field, California

In the irrigated western U.S. disposal of drainage water has become a significant economic and environmental liability. Development of irrigation water management practices that reduce drainage water volumes is essential. One strategy combines restricted drainage outflow (by plugging the drains) with deficit irrigation to maximize shallow groundwater consumption by crops, thus reducing drainage that needs disposal. This approach is not without potential pitfalls; upward movement of groundwater in response to crop water uptake may increase salt and sodium concentrations in the root zone. The purposes for this study were: to observe changes in the spatial and temporal distributions of SAR (sodium adsorption ratio) and salt in a field managed to minimize drainage discharge; to determine if in situ drainage reduction strategy affects SAR distribution in the soil profile; and to identify soil or management factors that can help explain field wide variability. We measured SAR, soil salinity (EC_1:1) and soil texture over 3 years in a 60-ha irrigated field on the west side of the San Joaquin Valley, California. At the time we started our measurements, the field was beginning to be managed according to a shallow groundwater/drainage reduction strategy. Soil salinity and SAR were found to be highly correlated in the field. The observed spatial and temporal variability in SAR was largely a product of soil textural variations within the field and their associated variations in apparent leaching fraction. During the 3-year study period, the percentage of the field in which the lower profile (90-180 cm) depth averaged SAR was above 10, increased from 20 to 40%. Since salinity was increasing concomitantly with SAR, and because the soil contained gypsum, sodium hazard was not expected to become a limiting factor for long term shallow groundwater management by drain control. It is anticipated that the technology will be viable for future seasons.     

典型干旱区土壤盐分空间异质性的步长大小优化选择

采用不同步长研究典型干旱区土壤盐分空间变异的半方差函数参数,并对比精度进行优化选择,进而研究其空间异质性。对研究区域进行移动式磁感调查,获取大地表观电导率信息,经校正解译成土壤盐分信息,拟合不同步长下最优半方差函数,对比误差参数优选最优步长。研究结果表明,地统计插值拟合半方差函数以15m为最佳步长,具有高拟合精度;对土壤盐分空间异质性预测精度较高。     

Soil salinity in Aceh after the December 2004 Indian Ocean tsunami

The 2004 Indian Ocean tsunami inundated about 37,500 ha of coastal farmland in Aceh, and crops planted after the tsunami were severely affected by soil salinity. This paper describes the changes of soil salinity over time on tsunami affected farms and the implications for resuming crop production after natural disasters.Soil salinity and salt leaching processes were assessed across the tsunami affected region by measuring soil apparent electrical conductivity (ECa) using an electromagnetic induction soil conductivity instrument (EM38) combined with limited soil analysis. The ECa was measured 5 times between August 2005 and December 2007 in both the vertical (EMv) and horizontal (EMh) dipole orientations at 23 sites across Aceh. The level of salinity and direction of salt movement were assessed by comparing changes in mean profile ECa and relative changes in EMv and EMh.Eight months after the tsunami the average soil salinity in the 0-1.2 m soil depth varied from ECe 22.6 to 1.6 dS m⁻¹ across sites in the affected region and three years after the tsunami it varied from 13.0 to 1.4 dS m⁻¹. Soil salinity tended to be higher in rice paddy areas that trapped saline tsunami sediments and held seawater for longer periods. Leaching of salts occurred slowly by both vertical displacement and horizontal movement in surface waters. Hence, soil salinity persisted at a level which could reduce crop production for several years after the 2004 tsunami. High soil salinity persisted three years after the tsunami even though there had been more than 3000-7000 mm of accumulated rainfall to leach salts. The slow leaching is likely to have been due to the loss of functional drainage systems and general low relief of the affected areas.Monitoring of soil salinity with EM38 assisted local agricultural extension agencies to identify sites that were too saline for crops and determine when they were suitable for cropping again. The methodology used in this study could be used after similar disasters where coastal agriculture areas become inundated by seawater from storm surges or future tsunamis.     

Drainage and desalinization of heavy clay soil in Portugal

The Leziria Grande area consists mainly of poorly drained, saline clay soils of marine origin. Three experimental fields were laid out to find whether subsurface drainage can be effective in lowering the groundwater table and improving desalinization.Subsurface drainage results in a lower groundwater table than does surface drainage. With increasing spacing, the groundwater remains at a higher level for longer periods, which is expressed here by the sum of exceedances of the groundwater table above 30 cm during winter.Soil salinity, expressed as EC_1:2, and sodicity, expressed as E.S.P., decreased during the first 3 years, in which precipitation varied between 600 and 750 mm and the average drain outflow was about 250 mm. The leaching efficiency decreased with time, indicating that the removal of salt is a slow process in fine-textured soil.Application of gypsum lowered the E.S.P. The infiltration rate and the drain outflow increased. Although the total amount of salts in the drainwater was 40% higher than for the untreated plots, no lower EC_1:2 values were found. This is ascribed to spatial variability in soil salinity.