Effects of Salinity and Mixed Ammonium and Nitrate Nutrition on the Growth and Nitrogen Utilization of Barley

The absorption and utilization of nitrogen (N) by plants are affected by salinity and the form of N in the root medium. A hydroponic study was conducted under controlled conditions to investigate growth and N uptake by barley (Hordeum vulgare L.) supplied with five different NH4+-N/NO3--N ratios at electrical conductivity of 0 and 8 dS m-1. The five NH4+-N/NO3-N ratios were 0/100, 25/75, 50/50, 75/25 and 100/0, each giving a total N supply of 100 mg N l-1 in the root medium. A mixed N supply of NH4+ and NO3- resulted in greater accumulation of N in plants than either NO3- or NH4+ as the sole N source. Plants produced a significantly higher dry matter yield when grown with mixed N nutrition than with NH4+ or NO3- alone. Total dry matter production and root and shoot N contents decreased with increasing salinity in the root medium. The interaction between salinity and N nutrition was found to be significant for all the variables. A significant positive correlation (r=0.97) was found between nitrogen level in the plant shoot and its dry matter yield.