Modified ECa – ECe protocols for mapping soil salinity under micro-irrigation

Abstract

Climate change will increase the frequency and intensity of drought in water-scarce agricultural areas that rely on irrigation. The increased strain on finite water resources for irrigated agriculture will cause a shift from sprinkler and flood irrigation to micro-irrigation. Micro-irrigation results in complex 3-dimensional salinity patterns. Current field-scale apparent soil electrical conductivity (ECa) directed soil sampling protocols and guidelines are inadequate for mapping the complex local-scale 3-dimensional nature of salinity resulting from water applications by micro-irrigation systems (i.e., drip, buried drip, micro sprinklers, bubblers, etc.). A field study was conducted to develop additional ECa-directed soil sampling guidelines to map local- and field-scale variability in salinity under drip-irrigation systems within a commercial nut production orchard (i.e., pistachio orchard) using hard (i.e., salinity or ECe, electrical conductivity of the saturation extract) and soft data (i.e., geospatial ECa measurements), which required an accurate ECa – ECe calibration. The revised ECa-directed soil sampling guidelines for drip irrigation on a mature pistachio orchard indicate that a single soil core should be taken 0.9–1.2 m perpendicular to the drip line within the tree root system, rather than at the drip line, to improve the ECa – ECe calibration. Calibration of ECa to ECe, improved from R2 = 0.25 to R2 = 0.73 for site Flores D01, and from R2 = 0.17 to R2 = 0.72 for site Flores D05. The improved guidelines broaden the scope of application of ECa-directed soil sampling to map field-scale salinity on orchards under drip irrigation. The information presented is of value and benefit to producers, agriculture consultants, irrigation practitioners, cooperative extension specialists, Natural Resources Conservation Service field staff, and soil and water researchers.