Effect of Rooting and Canopy of Pistachio Trees with Different Ages on Some Soil Properties in Robat Plain

The effects of trees through their root system and shading on soil characteristics lead to their effect on fertility, protection, and improvement of soil quality. In order to investigate the effect of trees age and canopy on some soil characteristics, soil samples were taken from the depths of 0-30, 30-60, and 60-90 cm from two middle canopy and edge canopy areas of 9-, 17-, and 25-years-old pistachio orchards and three control positions (without tree) in Robat Plain, ​Shahr-e Babak City. Soil characteristics were measured by standard methods. After the factorial test with two factors of land use and depth, the analysis of significant parameters was done in a split-split plot design and in the form of a completely random design including age (main factor), distance (first sub-factor), and soil depth (second sub-factor) in three replicates. The results showed that pistachio trees had no effect on the percentage of clay content, apparent specific gravity, mean weight diameter of soil grain, and equivalent calcium carbonate. The effect of orchard age was significant only on soil basal respiration and available potassium, and the highest amount of soil basal respiration and available potassium belonged to the 9-year-old trees. By increasing the distance from the tree, the average percentage of organic carbon, total nitrogen, available phosphorus and microbial respiration decreased and the growth average showed a significant increase. With increasing soil depth, average organic carbon, total nitrogen, available phosphorus and microbial respiration decreased significantly. Also, the interaction effect of age, distance from the tree, and soil depth on growth and microbial respiration was significant. In general, the changes in soil properties in the studied pistachio orchards were affected more by soil depth and canopy, so that soils in the surface layer and the middle canopy were in a more favorable condition. Considering the higher absorption of pistachio tree roots from the edge canopy, in order to prevent the reduction of soil fertility, in addition to applying fertilizer based on the results of soil test, attention should be paid to fertility managing and use of organic matter in these orchards.