The Effect of Irrigation with Magnetized Water on the Symbiosis Between Soybean and Rhizobium

Since rainfall occurs often in the fall and winter, water is an important limiting factor to subsequent growing crops especially those in hot seasons like soybean. Therefore, there is a growing focus on increasing water use efficiency in crops in recent years. Recently, an irrigation technique so-called magnetized water has been introduced to increase water use efficiency. The researchers have reported that the physical and chemical properties of water including electrical conductivity, volatility, pH, solubility, surface tension, and viscosity can be affected by its passage through the magnetic field. Subsequently, these changes lead to alterations in soil electrical conductivity, soil nutrient mobility, soil water holding capacity, water passage through the soil profile and soil pH. Increased water use efficiency in soybean (11%) and many leguminous crops have been demonstrated through their irrigation with magnetized water. However, those studies have provided no information about the status of bacterial nodulation on legume root in such an irrigation method. Therefore, the main purpose of this study was to investigate the effect of irrigation with magnetized water on five soybean varieties on their symbiosis with specific bacteria (Bradyrhizobium japonicum). The experiment was conducted in the open air at the Bu Ali Sina University of Hamedan in 2018. A completely randomized design with two factors (soybean cultivar and irrigation water type) and eight replications was applied. The soybean cultivar had five levels (Amir, Zan, Saba, Kosar, and Hobbit) and irrigation water type had two levels (untreated and magnetically treated water). An equal volume of water (1 liter) was added to each pot every two days. Before adding water to pots for the irrigation with magnetized water, we passed it through a magnetic tube with a 35 cm long, 1-inch radius and a 0.68 T magnetic field intensity. On August 26, the plants of the half of replications were harvested to measure shoot dry weight, root dry weight, number of nodules, nodule dry weight, shoot nitrogen content and root nitrogen content. On September 10, the plants of the other half of replications were harvested to measure individual seed yield and its components (number of pods per plant, number of seeds per pod and 100-seed weight). By dividing the seed yield obtained from each pot to the total volume of water added to each pot during the growing season, water use efficiency can be calculated. The soybean seedlings irrigated with magnetized water were green 1 to 2 days earlier than those irrigated with untreated water. The number of seeds per pod was not affected by soybean cultivar, irrigation water type, and their interaction. In other traits, the simple effects of soybean cultivar and irrigation water type and their interaction were significant at the 5% level of probability. The cultivars of Amir and Saba irrigated with magnetized water led to a higher shoot dry weight to root ratio, indicating the allocation of more resources to the shoot than to the root. The number of nodules formed on the root of all soybean cultivars (Amir (33.7%), Zan (55.3%), Saba (40.1%), Kosar (62.7%) and Hobbit (51.6%)) increased when they were irrigated with magnetized water. However, only in Zan (0.70%) and Kosar (45.1%), irrigation with magnetized water significantly increased the dry weight of nodules. The individual seed yield in all soybean cultivars (Amir (34.8%), Zan (35.1%), Saba (43.4%), Kosar (26.8%) and Hobbit (21.3%)) was significantly increased by irrigation with magnetized water, indicating an improved water use efficiency in soybean irrigated with magnetized water. Based on previous research, the most suitable soil pH range for bacterial growth and activity was found to be between 6.5 and 7.0. On the other hand, other researchers have shown that irrigation with magnetized water reduces the soil pH by approximately 0.5 units. Hence, in our experiment, irrigation with magnetized water probably caused the initial soil pH which was 7.6 to be closer to the optimal range for bacterial activity. Also, according to previous study, bacterial activity is also dependent on soil dry conditions. On the other hand, other researchers have shown that irrigation with magnetized water increases soil water storage capacity due to reduced water vaporization. Therefore, in our experiment, irrigation with magnetized water probably provided good moisture conditions for bacterial activity. The results showed that the irrigation of soybean with magnetized water improved its symbiosis with its specific rhizobium. Improved symbiosis increased plant seed yield and water use efficiency. Therefore, improved symbiosis by irrigating soybean with magnetized water can reduce the reliance on nitrogen fertilizer application in this plant. It can also improve the status of soil fertility for other crops in crop rotation.