Effect of salinity and K/Na ratio of irrigation water on growth and solute content of Atriplex amnicola and Sorghum bicolor

Abstract

Total salinity and K/Na ratios in the irrigation water were varied for two different types of plants; sorghum, a moderately salt tolerant crop plant whose growth is inhibited by high NaCl levels, and Atriplex, an extreme halophyte whose growth is stimulated by high NaCl levels. Sorghum growth was significantly reduced at all salinity levels from 50 to 150mM, but Atriplex growth was not reduced until salinity exceeded 100 mM. In both species, growth reductions were increased by increasing the ratio of K to Na from 1/100 to 1/1 in the irrigation water. The amount of K and Na accumulated in the leaves of Atriplex reflected the relative amounts in the irrigation water, but in sorghum most of the increase in the concentration of K + Na was due to the increase in K regardless of the ratio of K/Na in the irrigation water. Nitrate levels in leaves of sorghum were little affected by salinity but were decreased in Atriplex by the combination of high salinity and K/Na ratio. The lower amount of salt accumulation in sorghum was compensated for by greater accumulation of soluble organic compounds, such as proline and soluble carbohydrates, that presumably were osmotically active and could contribute to osmotic adjustment. All of the results supported the general conclusion that, despite differences between glycophytes, such as sorghum, and halophytes, such as Atriplex, in sensitivity to the total soluble salt concentration in irrigation water, in both species growth was reduced more by K/Na ratios of 1/1 and 1/10 than by a ratio of 1/100 at those salinity levels that significantly reduced growth in each species.