Soil salinity assessment: Methods and …

1 soil salinity assessmentiiiForewordThe technology described in this report for measuring soil salinity has been extensively andsuccessfully field-tested. It is concluded to be sound, reliable, accurate and applicable to a widevariety of useful applications. It is based on proven theory of soil electrical conductivity. Therequired equipment is commercially available. The advocated instrumental methodology ispractical, cost effective and well developed for essentially all general applications.

2 It is cheaper,faster and more informative than traditional Methods of salinity measurement based on soilsampling and laboratory analyses. Software is available to facilitate its use for mapping andmonitoring uses, as is equipment to mobilize and automate the measurements for use in detailedfield-scale assessments. Its usefulness has been demonstrated: 1) for diagnosing soil salinity , 2)for inventorying soil salinity , 3) for monitoring soil salinity , 4) for evaluating the adequacy andappropriateness of irrigation and drainage systems and management practices, 5) for determiningthe areal sources of excessive leaching, drainage and salt-loading in crop lands, 6)

3 Forestablishing the spatial soil information needed to develop prescription farming plans to managefields with spatially-variable salinity conditions, and 7) for scheduling and controlling irrigationsunder saline conditions. It offers the potential to identify the inherent causes of salinization infields, especially when integrated with GIS technology, and to identify mitigation needs,especially when integrated with field-scale deterministic, solute-transport models.

4 The salinityassessment approach advocated in this report offers a more suitable basis for evaluating,managing and controlling soil salinity than do the leaching requirement and salt balanceconcepts/measurements as traditionally applied. National programs need to be implemented tomitigate the substantial problems of secondary salinization that threaten the sustainability ofirrigation in many places in the world. Holistic; meaningful salinity assessment approachesneeded in this regard are illustrated in this report.

5 The presented salinity assessment technologyoffers substantial practical potential to inventory, monitor, manage and control soil and watersalinity, as will be needed to sustain irrigated agriculture and to meet the worlds food needs in thecoming authors wish to acknowledge the valuable advice provided by the staff of the Land and WaterDevelopment Division, who revised and contributed to the general outline of the publication. Thetechnical reviews of the first draft by Messrs Tyagi (Central soil salinity ResearchInstitute, Karnal, India) and van Alphen (International Agricultural Centre, TheNetherlands)

6 Are gratefully of the research findings and recommendations in this publication come from the UnitedStates salinity Laboratory, Riverside, California, and the authors acknowledge the Laboratorystaff for their valuable authors with to express their gratitude to Dr Arumugan Kandiah, Programme Manage of theInternational Programme for Technology and Research in Irrigation and Drainage (IPTRID) ofFAO for his technical and overall support towards the fulfilment of this are also due to Ms Smith Redfern for her valuable assistance in the preparation ofthe final camera-ready text and figures and tables.

7 She also contributed to the improvedpresentation of the salinity assessmentvContentsPage1 INTRODUCTION12 DETERMINATION OF soil salinity FROM AQUEOUS ELECTRICALCONDUCTIVITY5 Principles of aqueous electrical conductivity5 soil water salinity6 soil extract salinity113 DETERMINATION OF soil salinity FROM soil -PASTE AND BULK SOILELECTRICAL CONDUCTIVITY15 Principles of soil and soil -paste electrical conductivities15 Determining soil salinity from saturated soil -paste electrical conductivity29 Determining soil salinity from bulk soil electrical conductivity33 Sensors and equipment for measuring soil electrical conductivity33 Procedures for measuring bulk soil electrical conductivity39 Procedures for interpreting soil salinity48 Comparisons of the different Methods of measuring soil salinity58 Determination of locations of measurement and calibration USES OF salinity assessment TECHNOLOGY63 Diagnosis of soil salinity and saline seeps63 Inventorying soil salinity66 Monitoring soil

8 Salinity69 Developing information for site-specific management70 Evaluating adequacy and appropriateness of irrigation/drainage76 Assessing leaching and salt-loading84 Scheduling and controlling irrigations91 Reclamation of saline soils935 OPERATIONAL AND EQUIPMENT COSTS ASSOCIATED WITH SALINITYINSTRUMENTATION MEASUREMENT TECHNIQUES95 salinity instrumentation: equipment specifications and cost information96 soil salinity survey instruments96 GPS equipment98 Mobilized soil salinity survey systems99 Analytical (laboratory)

9 Conductivity instruments102 soil salinity assessment and mapping software102 Company information103viPageOperational costs associated with the appraisal of soil salinity103 Operational costs associated with conventional sampling105 Operational costs associated with survey instrumentation107 Conventional sampling versus survey instrumentation costs in multi-field (large area) survey applications111 Cost advantages associated with instrument mobilization113 Conclusion117 REFERENCES119 ANNEX 1 Methods for establishing ECe = F(ECa)

10 Calibrations129 ANNEX 2 Circuitry and parts-list for soil EC-meter133 ANNEX 3 Equation for calculating effect of insertion-depth of four-electrodes135 ANNEX 4 Construction of burial-type four-electrode probe137 ANNEX 5 Examples of various special-use four-electrode cells and sensors139 ANNEX 6 Derivation of EMadj equations143 ANNEX 7 Device for positioning EM-38 sensor during hand-held measurements145 ANNEX 8 Schematic and parts-list for soil four-electrode probe147 ANNEX 9 Description of statistical tests for monitoring soil salinity149 soil salinity assessmentviiList of figuresPage1 Diagram of vacuum extractor apparatus for sampling soil water82(A) Imbibition type salinity sensor with spring, housing, and pin in disassembly.