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United States Department of Agriculture

Agricultural Research Service

Assessment of Salinity and Irrigation/Drainage Practices
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1 - Abstract
2 - Introduction
3 - Mobile Four-Electrode Sensing System
4 - Mobile Electromagnetic Sensing System
5 - Mapping Theory and Software
6 - Conclusions
7 - References
The achievement of efficient irrigation and effective salinity control requires periodic information of soil salinity levels and distributions within the crop rootzones and fields of irrigated lands, in order to
  • Inventory conditions of soil salinity
  • Assess the adequacy of leaching and drainage
  • Guide management practices
In addition, practical procedures are needed for delineating the sources of salt-loading and for mapping the distribution and extent of drainage problem areas.
The achievement of such an assessment technology begins with a practical methodology for measuring soil salinity in the field, which is complicated by its spatially variable and dynamic nature caused by the effects and interactions of
  • Varying edaphic factors
    • Soil permeability
    • Water table depth
    • Salinity of perched groundwater
    • Topography
    • Soil parent material
    • Geohyrology
  • Management induced processes
    • Irrigation
    • Drainage
    • Tillage
    • Cropping practices
  • Climate-related factors
    • Rainfall, amount and distribution
    • Temperature
    • Relative humidity
    • Wind
When the need for repeated measurements and extensive sampling requirements are met, the expenditure of time and effort to characterize and map a project's salinity condition with conventional soil sampling and laboratory-analysis procedures becomes prohibitive.
A more rapid, field-measurement technology is needed that:
  • Accounts for the spatial location of the measurement sites involved with the required large intensive and extensive data sets
  • Provides a systematic methodology for evaluating management effects
  • Is capable of proving changes or differences in an area's salinity condition over time
Such a technology has been recently developed. It is an integrated system comprised of:
  • Rapid, mobile instrumental techniques for measuring bulk soil electrical conductivity (ECa) in the field as a function of spatial position on the landscape
  • Procedures and software for inferring salinity from ECa
  • Computer-assisted mapping techniques capable of associating and analyzing spatial databases
  • Appropriate spatial statistics to infer salinity distributions in root zones and changes over space and time
Two kinds of mobilized, instrumental systems have been developed for purposes of field salinity measurement:
  • One based solely on the use of four-electrode units to measure ECa
  • The other using an electromagnetic induction sensor, either alone or together with four electrodes
The remainder of this document briefly describes these two systems and gives some examples of their utility.
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Last Modified: 4/7/2006
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