Evaluating routine agronomic soil tests for coastal soil salinity detection in the mid-Atlantic

Abstract

Coastal salinity is a growing concern for managing agricultural soils in the eastern United States, including the Delmarva Peninsula. The saturated paste (SP) extraction, which is the standard method for measuring soil salinity in arid climates, is not widely available in the eastern United States and its effectiveness in humid coastal soils is unknown. We evaluated the Mehlich-3 (M3) routine agronomic soil test as an alternative to SP and ammonium acetate (AA) extractions on samples from 13 Delmarva agricultural fields with known salinity issues. Soils were analyzed for electrical conductivity (EC) by SP extract (EC_e) or deionized water (1:2 and 1:5 soil-to-water ratios; EC_1:2 and EC_1:5). Extractable cations (Na, Ca, Mg, and K by SP, M3, and AA) were used to calculate exchangeable sodium percentage (ESP), sodium cation ratio (SCR), and sodium adsorption ratio (SAR). We noted significant positive relationships between SP-extractable Na and both M3-extractable and AA-extractable Na (r² = 0.81 and 0.77, respectively). Soil SCR values calculated from M3 and AA exhibited significant linear relationships (r² = 0.82–0.88) with ESP_SAR and SAR. Strong positive linear relationships were also noted between M3-extractable Na and EC_e (r² = 0.81). Reclassification of salinity using predicted EC_e from M3-Na and SCR_M3 were similar to standard classification methods. We suggest M3 as a cost-effective and accessible option for salinity assessment in coastal soils of the Eastern United States. Further field studies linking soil salinity to crop health and yields are needed to validate soil salinity interpretations prior to widespread adoption of M3-based salinity assessments.