The effect of changes in salinity and irrigation method on the growth of Rose and Hibiscus sabdariffa crops in the Sistan plain

Today, water security is one of the important limitations of development, especially in dry and desert areas. Because these areas not only have low rainfall, but also this low rainfall is not properly distributed. Despite the increase in irrigation efficiency in some agricultural methods, the limitation of freshwater resources in some areas makes it necessary to use salt water in agriculture. However, the use of these water sources has negative effects on the soil and the environment. So the salinity of soil and irrigation water reduces crop yield and puts soil resources at serious risk. It is possible to increase the crop yield and control soil erosion by using the appropriate irrigation method. The problem of salinity in plants is due to the accumulation of excessive amounts of sodium chloride, which is widely spread in coastal areas, soils of dry areas, and fertile lands. Studies have shown that the use of saline water, especially in conditions of equal fertilization between treatments, often reduces the absorption of important nutrients such as nitrogen due to the existence of a significant relationship between the absorption of water and nutrients. Research in the north of Golestan province showed that salinity causes a significant decrease in plant biomass. The effect of salinity stress on the accumulation of sodium, potassium, and chlorine in the plant was significant and the highest amount of ions was accumulated in the leaves. The plant's root system is selective in absorbing and transferring sodium to its aerial parts.

To do this research, first, by selecting 36 experimental units, holes with a diameter of 50 cm and a depth of 60 cm were dug in the center of each one, and then the treatments were prepared. This research is in the form of treatments consisting of irrigation factor (clay and drip irrigation method), salinity level (salinity up to 1200, salinity up to 2200, and salinity up to 3200 µmhos cm-2), and plant (Rose and Hibiscus sabdariffa) in three repetitions and it was done factorial randomized complete blocks design. Three water sources each with a capacity of 200 liters were placed at a height of less than two meters from the ground. Rose plant was prepared in the form of potted seedlings and Hibiscus sabdariffa seeds were planted in the greenhouse and after about two weeks in March, it was transferred to the field. The growth height of the plants, as well as the crown, the diameter of the plant stem, and the number of their branches in the growing season were measured. Also, three soil samples were collected and their characteristics of salinity, acidity, and texture were measured. In order to analyze the data, the statistical method of analysis of variance (ANOVA) and the least significant difference (LSD) test were used to compare the average of the studied indicators using MSTAT-C software and SPSS software.

The results of variance analysis of some growth traits of the studied species showed that seedling height and stem diameter were affected by different levels of salinity and the values ​​of this plant characteristic showed a statistically significant difference. The reason for the decrease in plant growth in a plant that is irrigated with more salinity is that the presence of salt in the soil exceeds the tolerance threshold of the plant, and as a result, the accumulation of excess salt in the root zone is a limiting factor for plant growth. According to the results of the effect of irrigation methods, as well as the interaction effect of salinity and irrigation method on the aforementioned indicators, there was no statistically significant difference. The interaction effect of plant and water salinity levels on the values ​​of these variables was significant. The comparison of the average data showed that the height of the studied species was significantly increased by using the clay irrigation method. The maximum diameter of the stem was also measured in the clay irrigation method, which was associated with an increase of 1.7\% compared to the drip irrigation method. Also, the results show that the highest values ​​of the studied variables are related to the rose flower plant, which is 1.7 and 3 times more than the sour tea plant, respectively. Clay irrigation causes water to be transferred to the root area of ​​the plant, which improves the performance and growth of the plant by providing the required moisture around the root. In other words, the way to distribution soil moisture in clay irrigation takes place in the form of percolation and uniformly around the root of the plant, which causes the moisture to be placed directly around the root area and thus affects the growth of the plant. In addition, the canopy data and the number of branches showed that there is no significant difference between them.

This research tested the effect of different levels of water salinity and clay and drip irrigation on the establishment of plants in the Sistan plain, considering the existence of a water shortage crisis in the region, in order to use saline water on two plants, rose and Hibiscus sabdariffa. The results showed that clay irrigation performance was better than drip irrigation at all salinity levels. Because in the drip irrigation method, with the occurrence of drought stress, it reduces plant growth compared to the clay irrigation method. In addition, in the drip irrigation method, water is placed on the soil surface and deep penetration is limited, and as a result, the increase in humidity in the subsurface layers is less. In the clay irrigation method, due to deep penetration and uniform distribution of moisture in the soil profile, the amount of moisture stored in the soil increases.