Effect of Humic Acid on Growth Characteristics, Phosphorous and Potassium Uptake and Photosynthesis Pigments of Pistachio Seedlings under Drought Stress

Water deficit is the main growth-limiting factor for pistachio (Pistacia vera L.) production in semiarid and arid soils of Iran. The objective of this study was to evaluate the effect of humic acid application on root and shoot growth characteristics, phosphorus (P) and potassium (K) uptake and photosynthetic pigments of P. vera L. seedlings under drought stress condition. This study was carried out in greenhouse condition as a factorial experiment based on a randomized complete block design with two factors including drought stress (in three levels: 80% (control), 60% and 40% of field capacity moisture content) and humic acid (in three levels including control, 1 g HA kg-1 soil and 2 g HA kg-1 soil) in three replications. Results indicated that leaf area, dry weights of leaf and stem, shoot and root dry weights, chlorophyll contents and shoot and root P content decreased by increasing of soil drought levels, while the reverse result was found in carotenoids and shoot and root K concentrations. application of humic acid leads to significant increase (P≤0.05) in shoot length (17 %), leaf area (39 %) root dry weight (31 %), leaf dry weight (16 %), Stem dry weight (28 %), total plant dry weight (19 %), total chlorophyll (37 %), carotenoids (19 %), root P concentration (10 %), shoot P concentration (23 %) and K content in root (11 %) and shoot (22 %) in all moisture levels. It can be concluded that application of humic acid (especially at level of 2 g HA kg-1 soil) results in improve of the plant growth properties and tolerance to drought stress due to increase of photosynthesis pigments and enhance of shoot and root P and K contents.