Effect of foliar application of humic acid on growth, yield and fruit quality of tomato (Lycopersicon pimpinellifolium (L.) Mill) under deficit irrigation stress

In order to study the effect of water deficit stress and foliar spray of humic acid (HA) on growth, yield and fruit quality of tomato (Lycopersicon pimpinellifolium (L.) Mill), an experiment was carried out in a split plot based on randomized complete block design with three replications in Research filed of university of Zanjan as during 2016. Treatments consisted arrangement of two irrigation levels (starting irrigation at 100 and 80% ETc) and 4 levels of HA (0, 100, 200 and 300 mg.l-1). The results showed that deficit irrigation significantly decreased growth, yield and leaf relative water content. Foliar application of humic acid improved growth, yield and fruit quality. The highest leaf area, plant length, relative water content, fruit number per plant, fruit weight and yield per plant (59/2 kg) was found with foliar spray of 200 mg.l-1 HA under irrigation 100% ETc. Deficit irrigation significantly increased water use efficiency, total phenol, total soluble solid content, titratable acidity (TA), vitamin C and antioxidants activity. The highest content of lycopene (41.1 mg.g FW-1) and TA (1.55%) was found under irrigation 100 and 80% ETc treatments, respectively with application of 200 mg.l-1 HA. The maximum value of water use efficiency (19.51 kg.m-3) was obtained in 200 mg.l-1 HA under deficit irrigation treatment. Deficit irrigation 80% ETc with reducing 10.1% of fruit yield saved 20% of water as compared to 100% ETc treatment.  According to the results, fpliar application of 200 mg.l-1 HA under normal and deficit irrigation can be proposed to improve yield and fruit quality of tomato.