Potassium and Sodium Interrelations in Growth and Alkali Cation Content of Safflower

Application of Na often improves the growth of many crop plants resistant to Na. Part of this is due to “sparing” action of Na on K. Often Na improves the growth of some species regardless of K level. It has been suggested that safflower (Carthamus tinctorius L.) also responds to Na even in the presence of ample K. However, the information regarding the interactions of Na and K in this plant is scanty. This paper reports the effects of Na at different levels of K on the growth and accumulation of alkali cations in different parts of the plant. The plants were grown for 24 days in nutrient solutions under controlled environments. The nutrient solutions contained six levels (0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 meq/liter) of K and 2 levels (0 or 4 meq/liter) of Na. Other nutrients were supplied at their optimum concentrations. Both growth and alkali cation content of the plants were affected by K and Na treatments. Sodium increased the plant growth by about 40 to 50% at all K treatments. Visual K deficiency symptoms were delayed and were less severe when Na was added to the treatment solutions as compared to the treatment where no Na was supplied. Potassium concentrations in all above ground plant parts were directly related to K treatments. Potassium concentrations were lower in older blades than in younger blades when plants were K deficient, regardless of Na treatment. With more supplied, K concentrations were higher in the older leaves than in the younger. Addition of Na to the treatment solutions depressed the K concentration in all plant parts studied when K was deficient. However, in younger blades this effect was noticed even at higher K supply. Sodium concentrations in the above ground plant parts were strongly reduced by excess K in the solutions. Potassium and Na concentrations in the stem were higher as compared to other above ground plant parts. Calcium and Mg concentrations in the stem and older blades decreased with increase in K regardless of Na treatments. The older blades had higher concentrations of Ca and Mg than the other above ground plant parts. Addition of Na to the treatment solutions did not affect the accumulation of Ca in any plant part, whereas the Mg concentrations in all above ground plant parts were significantly increased by Na treatment. Information gained from these studies indicates that application of Na to safflower can give better growth and Na can also substitute for K especially when K supply is low.