Effect Leaching Management on the Salinity Changes in the Drip Irrigation System (A Case Study: Semnan)

The main problem of salinity, in addition to reducing agricultural and horticulture products is the gradual decline of their cultivation area. Several factors such as climate and irrigation (precipitation, fraction of leaching), soil type and soil salinity, salinity of irrigation water, uniform distribution of the system and irrigation with saline water affects the soil salinity changes. Therefore, in irrigated agriculture, soil salinity should be reduced and controlled to an optimal level of the economic production. Leaching with proper irrigation management is one of the effective ways to reduce soil salinity. The study was conducted during 2012-2013 in as pistachio garden located in the Safaeieh region of Semnan province. The garden was 100 ha and 2 ha of that was selected for this study with 10 years old pistachio trees equipped to subsurface drip irrigation system. The treatments of this study were three irrigation regimes; control (I1), Irrigation based on irrigation requirement (I2) and I2 plus leaching requirement (I3), three soil depth of 25, 50, and 75 cm from soil surface and time before and after irrigation. The drip line laterals include emitters with 2.26 lph flow rate was buried in 40 cm soil depth. Soil samples to evaluation salt concentration were collected from 25, 50, and 75 soil depth before and after irrigation. To study the impact of different irrigation regimes, soil depth and time (before and after irrigation) and also their bilateral impact a factorial design in randomize block was applied. The results showed that ECe and SAR accumulation decreased after development, growth stage and continued to end growth stage. The results showed that I2 and I3 irrigation regimes were more effective in reducing the amount of sodium from the root zone and the I2 irrigation regime showed better performance in comparison to I3 irrigation regime. Regarding the amount of magnesium in the soil, the I2 irrigation regime was more successful than the I1 and I3 regimens. In I1 irrigation regime, the amount of magnesium at the end growth stage increased compared to the beginning growth stage. Significant decrease in ECe level at the end growth stage compared to the beginning growth stage belonged to the I2 irrigation regime, which suggests that I2 irrigation regime was more successful in ECe leaching during the period of pistachio growth, which attributed to the potential for leaching from the soil surface to the depths below the soil surface. The results showed that excessive water application under saline conditions for any reason, such as leaching not only does not have a beneficial effect on the removal of salts from the root zone, but also may lead to accumulation of salts and damage to the plant. The highest amount of calcium in the soil was recorded 98 days after the first irrigation under the I2 and I3 irrigation regimes which was 52.5 and 58.1 Meq/l, respectively. The lowest amount of this element The I1 and I2 regimens were 40.8 meq/l, respectively, which were recorded in 152 days after the first irrigation. In terms of SAR, the lowest value in the I2 regime was more noticeable than other irrigation regimes. The effects of soil depth of time after the first irrigation showed that there was no significant difference at the depth of 25 cm and 75 cm at the end growth stage compared with the valued recorded in beginning growth stage, but at a depth of 50 cm there was a significant reduction in ECe. The highest ECe value equaled to 14.5 dS/m was recorded at a depth of 75 cm in 98 days after first irrigation. In the I1 irrigation regime at all three depths of 25, 50 and in the I3 irrigation regime at a depth of 75 cm the amount of SAR at the end growth stage were not less than that in beginning growth stage, however, the reduction in SAR was recorded in the I2 irrigation regime at all three depths. Irrigation regime I2 was successful to control the SAR in different soil depth compared to the other two irrigation regimes, which is very important for the next irrigation season to moderate the harmful effects on blossoms. Moreover, it is suggested that in a field, equipped with a subsurface drip irrigation system, leaching water at the end of the season by surface irrigation or heavy subsurface drip irrigation during the rainfall to leach out the accumulated salt to lower soil layers.