The Effect of Humic Acid on Alleviating Drought Stress Effects in Tomato (Lycopersicum esculentum Mill.)

To study the effect of humic acid on alleviating the deleterious effect of drought stress in tomato (Lycopersicum esculentum Mill.), a factorial experiment based on randomized complete block design with three replicates and nine treatments was conducted. The treatments were 100, 50 and 25 % of field capacity (FC) irrigation with three humic acid levels (0, 500 and 1000 mg.L-1). Drought stress caused decrease in chlorophyll content, fresh weight of shoot and root, dry weight of root and number of fruit per plant. Humic acid improved tissue relative water content, chlorophyll content and fresh and dry weight of shoot. Also, treatment with 50 percent FC and 1000 mg.L-1 humic acid improved chlorophyll and relative water content and fresh weight of shoots and roots. Similarly, treatment with 25 percent of FC and 500 mg.L-1 humic acid increased chlorophyll content, relative water content and fresh and dry weight of roots. The chlorophyll content, tissue relative water content and fresh weight of shoot and root increased 20, 40 and 38 percent, respectively in 25 % FC and 500 mg.L-1 humic acid. However, fruit numbers per plant, fresh and dry weight of fruit were not affected by the treatments significantly. In conclusion, 1000 mg.L-1 humic acid in moderate drought stress (50 % FC) with 500 mg.L-1 humic acid in high drought stress were effective to alleviate the adverse effect of drought stress.