Humic Acid Improves Germination, Vegetative Growth, and Yield in Rice (Oryza sativa L.) Under Salinity Stress

Salinity stress is a major constraint for rice growth and productivity. Rice cultivars with considerable salt tolerant capabilities have been developed and improving their performance in the salt-affected lands is crucial. Herein, the effects of humic acid (100 mg/l) as a stress-alleviator and a biostimulant on the germination, vegetative growth, and yield of Giza 179 rice cultivar under increased salinity (0.55, 3.40, 6.77, 8.00 mS/cm) were investigated. The humic acidinduced effects were also validated in salt-affected field. Salinity retarded Giza 179 germinationrelated traits which were associated with a significant decline in Gibberellic acid (GA(3)) content and a-amylase activity. Also, salinity reduced the Giza 179 vegetative growth which was correlated with accumulation of shoot Na+, proline, and total soluble proteins (TSP), induction of membrane injury, and reduction of photosynthetic pigments. Humic acid significantly decreased most of the salinity-induced injury; however, it increased the salinity-induced synthesis of proline and TSP. The deteriorative effects of salinity during germination and vegetative stages were translated into significant reduction in grain yield and quality whereas the ameliorative effects of humic acid against salinity were reflected in better overall growth and yield. These results indicate the efficacy of humic acid in maintaining vigorous germination, growth, and yield in salt-affected lands.