Calcium and magnesium do not alleviate the toxic effect of sodium on the emergence and initial growth of castor, cotton, and safflower

Abstract

Castor (Ricinus communis), cotton (Gossypium hirsutum), and safflower (Carthamus tinctorius) are industrial crops frequently considered to be raised under high salinity of the soil or irrigation water. Sodium is the most common ion causing salinity, but other ions can also be found in toxic level. This experiment had the objective to evaluate if the presence of calcium and magnesium in the irrigation water alleviates the toxic effect of sodium in the emergence and initial growth of these three oilseed crops. Seeds were sown in trays for evaluation of emergence and in pots for evaluation of plant growth. The treatments consisted of simulations of the Na+:Ca2+:Mg2+ molar ratio found in the irrigation water of the Trans-Pecos region of the States of New Mexico and Texas, USA. The saline solutions were equivalent to 0, 50, 100, 150, 200, and 250% of the salt composition found in the reference water. Some solutions contained the three salts, while others contained only Na+, and the electrical conductivity varied from 0.7 to 13.7dSm−1 among treatments. For the analysis of plant growth, the treatments were imposed after seedling emergence, and the plants were harvested after 30 days.In castor and safflower, the salinity effect was associated with the electrical conductivity rather than with the salt composition. The cotton genotype had been previously selected to be tolerant to Na+, but it was sensitive to Ca2+ and Mg2+. Safflower plants did not survive 30 days under exposure to salinity higher than 9.6dSm−1 with any salt composition. In conclusion, Ca+2 and Mg+2 did not alleviate the toxic effect of Na+, and the mechanisms of salt tolerance in cotton were ion-specific.