Applicability of the Four‐Probe Technique under Extremely Variable Water Contents and Salinity Distribution

A drip‐irrigated cotton field was used to test the applicability of the four‐probe technique for measuring the salinity of the soil solution. The formation factor ( F ), which relates measured bulk soil electrical conductivity (EC a ) to calculated salinity (EC w ), is highly dependent on soil water content. Good results were obtained even though soil water content is extremely variable in drip‐irrigated soil. Only 15% of the calculated salinity values deviated from a range chosen as a reasonable criterion (± 20% of water‐content‐corrected soil extracts), and this deviation was attributed to an unrepresentative water content value of the sampled soil. The calculation procedures produced similar values when slightly different parameters were used in calculating EC w from EC a .