Information on Cl vs. SO4 salinity effects on alfalfa (Medicago sativa L) dry matter yield (DM) and cation-anion balance is limited. Consequently, we compared Cl and SO4 salinity effects on shoot DM and ionic balance for Archer and Ladak varieties of alfalfa. A modified, flowing Hoagland solution, buffered with CaCO3, was the control: electrical conductivity (EC) = 0.7 dS m-1. Chloride or SO4 salts of K, Ca and Mg were added to the control to get iso-EC solutions (2-11 dS m-1). Shoot cations (Ca, Mg, K, and Na) and their sum (C), anions (Cl, SO4, NO3 and H2PO4) and their sum (A), and DM were measured. Organic anions (C-A) were calculated in mmol(c) kg-1. The calculated hydroponic osmotic potentials (π) were from 1.4 to 1.7 times lower in Cl than in iso-conductive SO4 solutions. As EC increased, DM decreased equally for both varieties in iso-conductive Cl and SO4 solutions. Solution π decreased, shoot H2PO4 declined below its critical level of 65 mmol(c) kg-1, shoot C stayed constant, shoot A increased; and therefore, shoot C-A decreased. The shoot C-A was lower in SO4 solutions. In Cl solutions shoot Cl exceeded the toxic level of 282 mmol(c) kg-1. The DM was correlated positively with π, shoot H2PO4, and C-A, and negatively with shoot Cl and SO4. We conclude that (i) iso-conductive Cl or SO4 salinity depress DM equally, but iso-osmotic SO4 is more depressive; (ii) the yield declines are probably due to any one or a combination of low water potential, toxic shoot Cl and possibly SO4, and deficiencies of shoot P and organic anions; (iii) neutral organic solutes were probably responsible for osmotic adjustment, since total ionic charges (2C) stayed constant; and (iv) P deficiency occurred despite high solution P, due to Cl or SO4 competition in saline environments.
|Number of pages||6|
|Journal||Soil Science Society of America Journal|
|Publication status||Published - Jan 1999|
ASJC Scopus subject areas
- Soil Science