Rapid salinization alters nitrogen cycling and reveals the potential of perennial grasses for nutrient retention in coastal agricultural fields

Saltwater intrusion (SWI) is rapidly transforming coastal agricultural landscapes through rising soil salinity, altered nutrient cycling, and declining crop productivity. On Maryland’s Lower Eastern Shore (USA), we examined how salinization affects nitrogen (N) in soils, porewater, and plants under land management strategies representing common farmer responses to SWI: perennial grass establishment, restoration, and abandonment. Across three saltwater-intruded farms and over three years, soil electrical conductivity (EC 1:5 ) increased two- to fourfold, soil sodium (Na) four- to sixfold, and porewater electrical conductivity (EC) twofold, suggesting these fields are rapidly salinizing. Topsoil (0–10 cm) Na and EC 1:5 were strongly correlated (R 2 = 0.88), while relationships between topsoil Na and N were significant but modest (R 2 = 0.33), suggesting that Na explained only part of the variation in soil N pools. Soil inorganic N (nitrate and ammonium) declined, indicating depletion of available N pools under progressing salinization. However, aboveground biomass N increased substantially under Panicum virgatum (perennial grass establishment) and Spartina patens (restoration), accumulating four times more N than abandoned plots. These results demonstrate that perennial grass systems can maintain productivity and accumulate greater aboveground biomass N, even as fields salinize. In contrast, abandoned fields exhibited lower biomass and reduced standing biomass N pools. Establishing salt-tolerant perennials therefore represents an effective strategy for coastal farms transitioning due to sea-level rise and SWI. These findings provide actionable guidance for easement and conservation programs seeking to support adaptive management of salinizing agricultural lands.