Coastal stressors reduce crop yields and alter soil nutrient dynamics in low-elevation farmlands

Saltwater intrusion (SWI) driven by sea level rise (SLR) is transforming coastal agricultural fields along the Eastern Seaboard of the United States. In these regions, salinization is an increasing challenge for farmers, yet practical experience and effective management strategies for saline soils remain limited. To assess crop performance and nutrient dynamics under SWI, we conducted a four-year crop rotation, including sorghum (Sorghum bicolor), barley (Hordeum vulgare), and chloride-excluding (CE) soybean (Glycine max) across three SWI-affected farms and one no-salt site on the Lower Eastern Shore of Maryland, USA. We showed that sorghum exhibited the highest resilience to SWI of the evaluated crops, maintaining relative yields above 0.50, with better germination and survival under stress conditions, including drought, soil saturation, and herbivory. For all crops, yields increased with distance from the tidal waters, but barley frequently failed under saturated winter soils and soybean had more instances of zero yields in the plots. We found a strong inverse relationship between elevation above mean sea level (eMASL) and elevation relative to mean higher high water (eMHHW) and soil electrical conductivity (EC). Whereby soil EC increased exponentially below 0.75 m eMASL and 0.63 m eMHHW indicating key thresholds for crop success in low-lying coastal agricultural areas. Available soil phosphorus (P), ammonium (NH₄⁺), and nitrate (NO₃⁻) pools decreased over time in SWI-affected plots, whereas this decline was not observed at the no-salt site. Losses of P were up to 50% of the initial concentration. Our findings underscore the vulnerability of low-elevation coastal farmland to yield and nutrient loss and highlight the need for long-term adaptation strategies, including salt-tolerant crops and alternative land-use planning, to maintain agricultural viability in these transitional landscapes.