Foliar and Soil Application of Potassium Nitrate Affects the Tolerance of Salinity and Canopy Growth of Perennial Ryegrass (Lolium perenne var Boulevard)

Two experiments were conducted to determine the effect of KNO3 application on perennial ryegrass salinity tolerance. Two NaCl levels (0 and 60 mM) factorially combined with four KNO3 (KN) levels (0, 5, 10 and 15 mM) as the treatments. The KN was applied either to the soil or foliarly sprayed. The results showed that in both experiments the increased salinity significantly reduced the vegetative characteristics of ryegrass. In the salinity treatment, supplying KN at 10 mM concentraion increased the fresh and dry weight as well leaf area, however, the growth of the plants was lower at the 0 and 15 mM concentration of KN. The concentration of N, NO3, P and K was reduced in the salinity treatments, but the concentration of Na and Cl was increased. Salinity (NaCl60) significantly reduced the K/Na ratio, while it was increased when the KN was increased in the solution. The concentration of Cl was significantly reduced when KN increased in the solution so that its concentration in NaCl60 and 0 mM KN was 75% in soil and 66.6% in foliar sprays treatment, respectively, higher than that in NaCl60 and 15 mM treatment. Combination of both salinity and KN concentration remarkably increased the proline content. The concentration of chlorophyll was reduced in NaCl60 treatment however; additional supplying of KN increased the chlorophyll concentration. In NaCl60 treatment, the highest survival plants were observed at 10 mM KN as either foliar or soil application. It seems that the reduced Cl concentration, increased proline and K/Na ratio were the main reason for the improved tolerance for salinity of the perennial ryegrass in the 10 mM KN concentration.