Information is scarce on the interaction of mineral deficiency and salinity. We evaluated two salt-tolerant spinach cultivars under potassium (K) doses (0.07, 0.15, 0.3, and 3.0 mmolc L-1) and saline irrigation (5, 30, 60, 120, and 160 mmolc L-1 NaCl) during germination and growth. There was no interaction between salinity and K. Salinity decreased germination percent (GP), not always significantly, and drastically reduced seedling biomass. 'Raccoon' significantly increased GP at 60 mmolc L-1 while 'Gazelle' maintained GP up to 60 or 120 mmolc L-1. After 50 days under saline irrigation, shoot biomass increased significantly at 30 and 60 mmolc L-1 at the lowest K dose but, in general, neither salinity nor K dose affected shoot biomass, suggesting that salinity supported plant growth at the most K-deficient dose. Salinity did not affect shoot N, P, or K but significantly reduced Ca, Mg, and S, although plants had no symptoms of salt toxicity or mineral deficiency. Although spinach seedlings are more sensitive to salt stress, plants adjusted to salinity with time. Potassium requirement for spinach growth was less than the current crop recommendation, allowing its cultivation with waters of moderate to high salinity without considerable reduction in yield, appearance, or mineral composition.
Keywords: Spinacia oleracea; high-salinity water; potassium deficiency; potassium–salinity interaction; salt-tolerant glycophyte.