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Most of the soils of the pistachio growing areas of Iran have a high percentage of lime and as a result, the pH is alkaline. Under these conditions, absorption of most of the nutrients required by the plant is faced with problems and the growth and performance of the product is quantitatively and qualitatively affected. One of the ways to adjust the soil pH and better uptake of nutrients from the soil is to reduce the pH of irrigation water using sulfuric acid. Therefore, this study was conducted in collaboration with Sarcheshmeh Copper Complex to investigate the effect of sulfuric acid application in irrigation water on yield, fruit quality, soil chemical properties, available concentration of soil and leaf nutrients and uptake of heavy contaminants in pistachio fruit. For this purpose, the orchard plots with three types of light, medium and heavy soil texture in Rafsanjan city were selected for the project. After selecting the orchards, experimental treatments included four pH values of irrigation water (H1: pH of irrigation water or control; H2: pH = 3; H3: pH = 4; H4: pH = 5) and three times of acid application (T1: March, May and June; T2: March and June; T3: May and June) in the form of a statistical design of split plots based on randomized complete blocks in 3 replications or blocks in each region separately in March 2019 and in 2020 and 2021 was implemented. To determine the amount of acid needed to reach the desired pH, the titration curve of irrigation water in each area was plotted with 1% sulfuric acid. The treatments were applied using a polyethylene tank containing concentrated sulfuric acid at the beginning of the irrigation water inlet of each treatment and adjusting the entry of acid into the water at the time of irrigation of each treatment. The results of measuring the pH of irrigation water during the first year in the plot showed that the values obtained from the titration curve are not sufficient to reach the desired pH and these values should be doubled. Among the soil properties, decrease in pH, salinity, Sodium adsorption ratio (SAR), lime, organic matter, microbial respiration and increase in uptake of phosphorus and trace elements, especially in the second year, occurred under the influence of treatments. The maximum decrease in soil pH in sulfuric acid application treatments compared to the control was 0.3 units and related to light soil. The highest reduction in the percentage of lime in light soil was in the application of irrigation water with pH = 3 and about 5%. Soil salinity decreased in both soil depths depending on the type of soil texture affected by the treatments. The highest decrease was related to the treatment of irrigation water with pH = 3 in medium soil and 4.4 dS m-1. Sodium adsorption ratio in both soil depths, especially in the second year, decreased in all soils due to the application of sulfuric acid in irrigation water and decrease pH, compared to the control. The highest decrease in sodium adsorption ratio occurred at the depth of 40-80 cm in the medium soil and at the rate of 40%. Percentage of organic matter and soil microbial respiration in some treatments of sulfuric acid application in irrigation water decreased so that in light soil and next time in medium soil any decrease in pH of irrigation water can lead to a relative reduction of organic matter and soil microbial respiration, but in heavy soils low pH did not cause such a decrease. In terms of availabile concentration of nutrients in light soil, elements of iron, zinc, manganese and copper increased in both soil depths under the influence of treatments. In the medium soils, zinc, copper and boron elements at both soil depths were affected by the treatments. This effect, which was increasing for zinc and copper elements and decreasing for boron, occurred mostly at pH = 3 and 4. In this soil, the concentration of soil available phosphorus at the depth of 40-80 cm and in both years of the experiment about 1.5 mg kg-1 soil and irrigation with water with pH 3and 4 compared to the control treatment ( Irrigation water with pH = 7.6) increased. In the heavy soils, the available concentration of phosphorus in both 0-40 and 40-80 cm soil depths in the second year under the influence of sulfuric acid application in irrigation water and lowering the pH from 7.6 in the control treatment to 3, from 2 mg kg-1 soil (at the depth of 0-40 cm) increased to 5 mg kg-1 soil (at the depth of 40-80 cm). In this soil at the depth of 0-40 cm, the available concentration of micro-elements zinc and copper in both years and at all three pH (3, 4 and 5) of irrigation water decreased as the result of the application of sulfuric acid compared to the control treatment (irrigation water with pH = 7.6) increased. But at the depth of 40-80 cm, among the micro- elements, only the concentration of zinc under the influence of sulfuric acid application in irrigation water and decreasing the pH from 7.6 in the control treatment to 3, by 0.5 mg in Kg of soil (55% compared to the control treatment) increased. The increase in zinc concentration in the second year was more under the influence of pH = 3 and in the amount of 21 mg kg-1 soil (about three times higher than the control treatment). Despite of the increase in the concentration of available phosphorus in the soil in the orchard with heavy soil, the concentration of leaf phosphorus in this area did not show any change. Considering all the studied features, it can be concluded that in the conditions of this study, reducing the pH of irrigation water to 5 in light soils and in medium and heavy soils to 3 and 4, respectively, is appropriate. According to the characteristics and quality of irrigation water, for this purpose, to reduce the pH of irrigation water to 3, 4 and 5, 198, 200 and 180 liters per hectare, 98% concentrated sulfuric acid was used. Also, due to the lack of significant differences in the most of the important properties studied between two and three applications of sulfuric acid in pistachio orchards and some adverse effects such as relative reduction of organic matter and also relative reduction of soil microbial respiration, twice application of sulfuric acid in irrigation water is recommended. Economic evaluation of the use of sulfuric acid in irrigation water of pistachio orchards based on the values mentioned above and two times uses showed that in the conditions of this study, its application in all three types of soil is completely economical and in medium, heavy and light soil It generated a net profit of 390, 165 and 95 million Rials, respectively.
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