Department of Agriculture, Payame Noor University, Tehran, Iran
Damghan Pistachio Research Station, Damghan, Iran
Humic acid is a biochemical constituent of humus and increases root biomass and shoot growth by improving absorption of nutrients. In order to study the effects of humic acid on root and shoot growth and leaf nutrient contents of pistachio seedlings, an experiment was conducted of completely randomized design with five treatments in three replications. In the first step seeds of Pistacia vera cv. Badami-Riz-Zarand were planted in plastic pots containing vermiculite in March 2013. The humic acid treatments were of five levels (0, 20, 40, 60 & 80 g) and were applied to the seedlings at the four-leaf stage. Results showed that humic acid had significant effect on the plant length, internode distance, root length and width (root expansion) and root fresh and dry weight. The greatest effect was seen for 60 g of humic acid and the least in control treatment (0 g humic acid). In measuring leaf nutrient content in different humic acid treatments, the greatest amounts of Zn, Cu and Mn were in the 40-g humic acid treated plants. Overall, considering growth characteristics and leaf nutrient content, the best results for pistachio seedlings were obtained with about 60 g humic acid. Presumably, through an increase in root expansion, humic acid causes better absorption of nutrients and increased shoot growth. Therefore, humic acid can be used to increase shoot growth and expansion of root system in pistachio seedlings.