Effects of Salinity and NO3:NH4 Ratio on Yield and Quality in Canola (Brassica napus L.)

Abstract

The effect of salinity and NO₃ : NH₄ ratio (0:100, 75: 25, 50:50, and 25:75) in the nutrient solution on growth, yield quality and N metabolism in hydroponically grow canola (Brassica napus L.) was evaluation. Both fresh and dry weights of leaves were significantly lower when a high concentration of either NO₃ (100%) or NH₄ (75%) was the sole N source in the nutrient solution. In nonsaline condition, increasing of both NH₄ and NO₃ ratio in the nutrient solution reduced photosynthetic (pn) rate, however in salinity condition the reduction of pn became more pronounced at a higher ratio of NH₄ in the nutrient solution. The yield in terms of the fresh and dry weight of seed per plant was significantly increased at the 75:25 (NO₃ : NH₄) treatments. Total fat in nonsaline condition was increased with increasing NH₄ ratio in the nutrient solution, however in saline condition it was reduced, at high NH₄ ratio in the nutrient solution. The increase of tissue N concentration was nearly proportional to the NH₄ concentration in the nutrient solution. The activity of nitrate reductase (NR) was increased by increasing NH₄ from 0 to 50% and then reduced at a higher ratio of NH₄ in the solution. Salinity increased NH₄ concentration so that the saline condition had nearly twice high NH₄ concentration in the leaves. The increase of NH₄ concentration induced by salinity could be partially the reduction of NH₄ assimilate because of the shortage of carbohydrate.