Salinity and Irrigation Method Affect Mineral Ion Relations of Soybean

Abstract

Soybean [Glycine max(L.) Merrill] is moderately salt tolerant, but the method of irrigation used for crop production under saline conditions may influence the uptake and distribution of potentially toxic salts. This field study was conducted to determine the effects of application of saline waters by different methods, namely, drip and above‐canopy sprinkler irrigation, on the ion relations of soybean cultivar “Manokin”. Salinity was imposed by adding NaCl and CaCl₂ (1:1 by weight) to nonsaline irrigation waters. Saline treatments with electrical conductivity (EC _i ) of 4 dS m⁻¹ were compared with nonsaline controls (EC _i  = 0.5 dS m⁻¹). Ion concentrations in leaves, stems, roots, and when present, pods were determined at four stages of growth: vegetative, flowering, podding, and grain filling. Both Na⁺ and Cl⁻ were excluded from the Manokin leaves and stems when plants were drip‐irrigated and the uptake of these ions occurred solely via the root pathway. However, when saline water was applied by sprinkling, the ions entered leaves by both foliar absorption and root uptake and their concentrations in the leaves were about 9‐fold higher than in those under saline drip irrigation. Regardless of treatment, leaf‐K was highest during the vegetative stage, then decreased with plant age as K⁺ was mobilized to meet nutrient demands of the developing reproductive structures.

Keywords:

• Chloride
• Drip irrigation
• Foliar absorption
• Ion exclusion
• Sodium
• Sprinkler irrigation

Acknowledgments

The authors are indebted to Donald A. Layfield for mineral ion analyses and to Phyllis Nash for statistical analysis. Terence Donovan, John Draper, and James Poss provided skilled technical assistance.