The effect of saline water and type of irrigation on soil moisture and physico-chemical properties

With rapid population growth and increasing demand for food, water shortage is one of the challenges of development in countries, because more than 98% of the water on the earth is salt water. In addition, the use of some fresh water sources is also limited. Such a situation will worsen with time. This limitation is more in dry and desert areas that have little rainfall and their distribution is not suitable. The country of Iran, which is located on a dry belt and its rainfall is less than a third of the global amount, is one of those areas that is facing a lot of water stress. Due to the lack of rainfall in the country and, on the other hand, the lack of scientific use of the country's natural and agricultural areas, the ground has been laid for the destruction of natural ecosystems. Accordingly, due to the limited supply of fresh water for agricultural purposes in the world, especially in dry areas, saline water is widely used to irrigate crops to provide the water needed by plants. Due to the use of saline water with a high concentration of salt, especially sodium salt in the soil, it causes a decrease in production efficiency and destruction of the physical and chemical properties of the soil. Since most of the water resources are consumed in the agricultural sector, an appropriate irrigation pattern should be used to prevent soil degradation and erosion in addition to increasing crop yields. Clay pot irrigation is one of the methods that has a better performance than other irrigation methods such as surface and drip type. This type of irrigation is suitable in dry areas that have high evaporation and transpiration and are associated with water crisis.

In order to carry out this research, first, 36 holes with a depth of 60 cm and a diameter of 50 cm were dug, and in 18 holes, a clay pot was placed with a height of 40 cm and a diameter of 5 cm, and 18 holes were selected as control and without clay pot. Three soil samples were taken from a depth of 50 cm at the beginning and at the end of the research period. Soil changes were made by irrigation with saline water and the characteristics of pH, EC, Na, SAR, organic matter, P, K, Ca, Mg and soil texture were measured. Considering that three types of water with different salinity (1200, 2200 and 3200 umho/cm) were used, three sources of water each with a volume of 200 liters were placed beside the location of implementation. By using the variety of saline water that existed in this area, bringing the EC of water to the level required for the research was done in the laboratory and stored in the relevant water sources. Cultivation of two plants, Rosa damascena and Hibiscus sabdariffa, was tested. Soil moisture (by weight) was measured monthly at a depth of 60 cm.

Examining the pH of the soil samples shows that there is not much difference in the value of this characteristic of the soil of the research area, such that the range of this characteristic varied between 8-8.4. Changes in the EC of the investigated area at the beginning of the project fluctuated between 4.4 and 5.2 mg/liter. After the implementation of the saline water plan, it has been affected, such that the range of this feature has been varying between 16.5-9.7 mg/liter. Measuring the amount of Na at the time of starting the work showed that the range of changes fluctuated between 43.3-43.85 mg/liter. Total Ca and K were measured as 19.7-24.2 mg/liter, while the amount of this feature changed between 26.5-18.4 mg/liter after the completion of the project. The amount of SAR of soil samples at the beginning of the implementation of the project was between 13-3-17, but after the implementation of the project, this range changed between 12-7-18-4. The range of total cations of the soil samples collected at the beginning of the research varied between 43.5-43.5 mg/liter. But after the end of the project, this range changed to 103.5-72.8 mg/liter. Examining the texture of the soil samples at the start of the project showed that the range of clay changes varied between 14-15%, but after the completion of the research, it changed between 10-14%. The amount of silt in the soil samples at the time of starting the project was 43-47%, while this value changed to 44-48% in the samples after the end of the plan. Examining the amount of sand in the soil samples at the beginning of the research showed that the range of changes was between 42-39%, which did not change at the end of the project.

In this research, the effect of two irrigation methods with saline water on soil moisture and physical and chemical properties was investigated. The results showed that compared to the average of all characteristics, clay pot irrigation performance was better. The work process in this irrigation method is such that the clay pot plays the role of a filter and suitable water is provided for the plant. In this type of irrigation, the transfer of water is limited to the area of ​​the plant's roots, which causes an increase in soil moisture in this area, and improves the plant's performance. In other words, the distribution of moisture in the soil during percolation clay irrigation is such that the water enters the root area of ​​the plant uniformly, which, in addition to meeting the water requirement, also reduces the temperature of the soil. But in drip irrigation, moisture is placed on the soil surface, after which the moisture spreads horizontally on the soil surface and the water does not penetrate deep into the soil. This situation causes evaporation and transpiration to increase and plant roots face water stress. Also, soil solutes cause the soil to become salty through evaporation. In addition, water salinity also increases the intensity of soil salinity, which leads to soil degradation and erosion. Therefore, for the continuation of exploitation in dry and desert areas, it is necessary to use the appropriate method of irrigation in order to sustainably exploit the land without harming its ecosystem components, including the soil. Therefore, according to the existing methods of irrigation, the clay pot type is more important than other types of methods. It can thus be concluded that due to the lack of fresh water resources in Sistan and the limited flow of water from Afghanistan and the existence of subsurface saline water sources, it is necessary to use them, that the use of clay irrigation method has a positive effect on the vegetation and the improvement of the environmental situation and the continuation of exploitation.