Measurement of soil salinity using electromagnetic induction in a paddy with a densic pan and shallow water table

Rice (Oryza sativa L.) has become a monoculture in the saline lands of the Ebro Valley, Spain. The studied farm has produced rice since the 1970s; one exception was 1999, which enabled us to map the soil salinity. The farm had lateral salinity variations mirrored by the development of rye grass (Lolium multiflorum Lam.) planted in 1999. Our objective is to prove the value of a non-deterministic method using electromagnetic induction (EMI) to map the salinity of the rootable layer in the unfavorable circumstances of a paddy having shallow saline and quasi-artesian water table underneath a continuous densic layer. From our EMI readings and soil sampling, we draw a map of the electrical conductivity of saturated paste extracts (ECe) of the upper soil layer (0-40 cm), with ECe ranging from 1.6 to 20.8 dS m(-1) and a mean of 7.9 dS m(-1). A main achievement was the establishment of an easy procedure not requiring either: (i) knowledge regarding the salinity of the water table or the relationships between EMI readings and the deep soil composition; or (ii) a normal distribution of the EMI readings or of the ECe; or (iii) assumptions about the physical dimensions of the EMI readings. Our procedure will allow ECe to be mapped on other similar salt-affected paddies, helping to decide if a paddy can be planted with alternate crops for production, weed control, or soil structure improvement.