Effects of magnetized fresh water on seed germination and seeding growth of cotton

Magnetized water treatment technology is usually used to improve poor quality water, and there is still a lack of study on fresh water. To understand the biological effects of different strength magnetized fresh water (MFW), seed germination and potted experiments on cotton were carried out to study the effects of MFW with different magnetic intensity (0, 100, 300, 500 mT). Results showed that the surface tension coefficient of MFW reduced by 7.3–10.5%, whilst dissolved oxygen concentrations increased by 8.8–12.7%. Germination strength indexes of cotton cultivated with MFW significantly increased, showing potential and vigor indexes of 16.8–22.4% and 47.4–78.0%, respectively. The emergence rate of cotton irrigated with MFW was faster and higher, with recorded values of 7.7–13.1%. The net photosynthetic rate (Pn) and instantaneous water use efficiency (iWUE) of cotton increased significantly, whereas the stomatal limit value (Ls) decreased. In all, results suggest the total biomasses of MFW irrigated cotton have significantly increased. Therefore, it is suggested that MFW may more effectively promote the utilization of water and light in cotton under magnetic field intensities of 300–500 mT. The results can provide guidance for the efficient utilization of magnetized fresh water in arid and semi-arid areas.


INTRODUCTION
As a new type of green and pollution-free water treatment technology (Esmaeilnezhad et al. ), magnetization is simple, efficient, and low input (Luo et al. ). It has been widely used in wastewater treatment ( Ji et al. ), water purification (Yao et al. ), scale reduction (Sohaili et al. ), construction (Ghorbani et al. ), materials (Pour et al. ), textiles (Lipus et al. ), and aquaculture (Hassan et al. ). The basic principle of magnetized water is that after the liquid water passes through a certain intensity magnetic field at a given flow rate, a series of changes have taken place in the physical and chemical properties of water under the influence of Lorentz force (Chibowski & Szcześ ), which appears to create the possibility of improving the production capacity of fresh water (Ambashta & Sillanpää ). The development of magnetized water research has achieved good results in agricultural irrigation (Selim & Selim ; Sultan et al. ), and study on irrigation experiments with magnetized brackish water showed reduced harm of brackish water, promotion of crop growth, and increased crop yields (Hachicha et  seedlings. Studies on the utilization of light energy of crops by magnetic water showed that the net photosynthetic rate, stomatal conductance, intercellular CO 2 concentration and water use efficiency of Populus × euramericana 'Neva' in magnetized brackish water irrigation were all increased, while transpiration rate and stomatal limit values decreased compared with that of unmagnetized water (Liu et al. ). Alfaidi et al. () found that the contents of chlorophyll a, b, carotenoids, total pigment, soluble protein, and total protein in guinea grass (panicum maximum) leaves significantly increased after irrigating with magnetized water. Research indicates that the growth promoting effect of magnetized water appears to be related to the magnetic field strength and irrigation water quality. Massah et al. () indicated that the intensity of the magnetic field and the type of treated water had a significant effect on the germination and growth characteristics of wheat seeds. The germination rate of seeds treated with 400 mT of distilled water was the highest (53.3%), the fresh weight of seedlings treated with 600 mT of distilled water was the highest, and the root length of wheat seeds treated with 400 mT of groundwater was the largest (155.3 mm).
In summary, remarkable achievements have been made in irrigated wheat, corn, broad bean, and eggplant with magnetized water; nevertheless, research on irrigating cotton with magnetized water is scarce. At the same time, most of the studies on magnetized water irrigation focus on the application of brackish water, while there are few studies on magnetization of fresh water. Therefore, it is of interest to explore the effects of MFW with different magnetic fields on the growth of cotton, especially on the fragile and sensitive seedling stage of cotton growth. Thus, this paper target the analysis of cotton seed germination, seedling emergence, seedling growth, photosynthetic characteristics parameters, and biomass distribution pattern, along with studying physical and chemical properties of MFW, and the effects of MFW with different magnetization intensities (0, 100, 300, 500 mT). Cotton seedling growth and photosynthetic characteristics were discussed, and suitable magnetization intensities for cotton seed germination and seedling growth determined. The results can provide theoretical basis and technical support for the efficient utilization of fresh water resources in arid and semi-arid areas.

Overview of test area
The experimental area is in the Kunqi River alluvial plain

Magnetizers and magnetized water devices
Three external sintered Rufe-B CHQ permanent magnet magnetizers (Shanghai Juncai Magnetic Materials Co., LTD., China) were used with magnetic field strengths of 100, 300, and 500 mT. The effective magnetic field area was 8 cm × 10 cm and magnetic field intensities was calibrated with a 5180-Gaussian Meter (F.W. BELL Co., USA). The magnetized water device is composed of a water box, peristaltic pump, magnetizer, water pipeline, and valves ( Figure 1). Water pipelines are of PVC with a 2.5 cm diameter (cross-sectional area of 4.91 cm 2 ), and 10 cm of effective magnetic distance (i.e. effective pipiline length through which the magentic field was applied). As shown in Figure 1, 100 L of fresh water placed in the water box and pipelines opened, one at a time, through manually controlled valves. A peristaltic pump (0.74-12 L h À1 ) was used to circulate the water. A section of the circulating pipeline was placed between the two poles of the magnetizer, and the magnetic induction line was cut perpendicular to the magnetic field. The flow rate was adjusted to 0.5 m s À1 by the peristaltic pump, and the flow was cyclically magnetized by the magnetic field. The magnetization time was 30 min, and the retention time of the magnetized water was 8 days (Coey & Cass ).

Experimental design and process
The magnetized water device mentioned above was used to magnetize fresh water, whilst unmagnetized fresh water was used as a control. A total of four water clusters were formed, including unmagnetized fresh water (FM0), 100 mT magnetized fresh water (FM1), 300 mT magnetized fresh water (FM3) and 500 mT magnetized fresh water (FM5). A series of experiments including cotton seed germination, potted experiments in a cotton field, and physicochemical properties test were carried out for each cluster. The objective was to analyze the influence and mechanics of MFW under diversified magnetic field intensities on cotton seed germination and seedling growth.

Experiment 1-seed germination test
Seed germination tests were performed as described in a previous study with three repetitions (Fu et al. ). Fifty cotton seeds of the same size and full grain were selected and arranged evenly in a petri dish with tweezers. The petri dish was then marked and covered with a layer (1.7 mm) of fine filter paper (qualitative filter with 3 μm of mesh size). 20 mL of cluster water was added to the corresponding culture dish and the seeds were covered with a layer (the same as the filter paper layer described previously). After having absorbed enough water (24 h), the excess water was drained, and the seeds were placed in the culture dish in the incubator at 28 ± 1 C, with a light intensity of 800 Lx. The numbers of germinations were recorded every day, and the corresponding cluster water (5 mL) was added every day to maintain the moisture content of the filter paper. The radicle length of cotton seeds was measured on the eighth day. The germination condition was evaluated by calculating germination potential (GP), germination rate (GR), germination index (GI), and vigor index (VI) as follows (Mosse et al. ): where, N 4 and N 8 are the numbers of seeds germinated in 4 and 8 days, respectively; N T is the total number of seeds; G t is the number of seeds germinated at day t (D t ); L is the average radicle length of seed on the eighth day.

Experimental 2-potted experiments in a cotton field
To simulate a cotton field growth environment, all potted plants were buried, randomly divided, and repeated three times for each cluster. Saline alkali soil from 0-20 cm depth (Table 1)  (N 12%, P 18%, K 15%) 6.4 g, organic fertilizer (organic matter >35%) 24 g. After, the fertilizer and soil were evenly mixed, 7.065 L of cluster water was irrigated to the corresponding plastic basin. Each pot was seeded with 20 cotton seeds, with a sowing depth of 2-3 cm. As in the field, the soil surface was covered with plastic film mulch after sowing.
Fourteen days after sowing, the rate of emergence was measured and only 4 cotton plants were kept in each pot, with the remaining seedlings being removed. The length of cotton seedlings was then measured, the dust on the surface removed, and fresh weight of the seedling measured after washing and drying. For that purpose, seedlings were placed in an oven at 105 C for 1 h and dried at 75 C.
The dry weight of the seedling was measured after cooling Thirty days after final singling, the net photosynthetic rate (P n ), stomatal conductance (G s ), intercellular CO 2 concentration (C i ), and transpiration rate (T r ) of the main functional leaves (from the top to the bottom of the fourth leaf) of cotton seedlings were measured using LC Pro SD full-automatic portable photosynthetic instrument (UK ADC) equipped with an LED artificial light source. Then, the stomatal limit L s ¼ 1 À C i /C a (C a is atmospheric CO 2 concentration) and instantaneous water use efficiency WUE ¼ P n /T r were calculated (Liu et al. ). When determining the photosynthesis parameters of cotton seedlings, according to the meteorological environment conditions during 10:00-12:00 am in a cotton field, the light intensity was set as 1,100 μ mol m À2 s À1 , the concentration of CO 2 was 36 μ mol mol À1 , and the temperature was 30 C. The SPAD value of chlorophyll in cotton seedling leaves was measured using the SPAD-502 Plus Chlorophyll Meter (Konica Minolta, China). Forty days after final singling, the cotton seedlings were removed slowly. The cotton branches were then cut with fruit scissors, the dust was removed from the surface, the cotton branches were washed and dried, and the dry weight of each part was weighed.

Determination of physicochemical properties of magnetized water
In order to clarify the mechanism, the physicochemical properties of magnetized water, including surface tension, dissolved oxygen content, electrical conductivity (EC), and

Data processing and analysis
Data were recorded in Excel 2016 and analyzed using SPSS  Table 2). The increased range of GP was greater than that of GR, while the amplitude of VI was greater than that of GI, indicating that fresh water magnetization could significantly improve seed strength and enhance the germination potential of cotton. This is consistent with the results of studies on the application of magnetized water to promote the germination of wheat seeds (Massah et al. ). As reported, smaller water cluster structure and higher dissolved oxygen after magnetization of fresh water were found, which provide good water and gas environments for seed germination and are conducive to improved seed germination (Surendran et al. ). Comparing cotton seeds cultivated with fresh water against those under different magnetized intensities, the results suggested that GI's cotton seeds cultivated by FM3 improved the most, whereas GP, GR, and GI of cotton seeds treated with FM1 were slightly larger than FM5. At the same time VI was slightly smaller than FM5, but none of them was significant (P > 0.05).

Effect of MFW on the emergence rate of cotton
High seedling emergence rate and seedling uniformity are the guarantees for high and stable yield (Mo et al. ).
The emergence of cotton seeds started 3 days after sowing ( Figure 2). With the increase of emergence time, the emergence rate of cotton gradually increased and tended to stabilize. As shown in Figure 2, the emergence rate of cotton under MFW irrigation was faster and higher when compared to freshwater irrigated seeds. The emergence rate and full seedling formation of cotton irrigated with FM0 was 77.3% and 8 d, respectively, while the emergence In general, the most remarkable seeding emergence was by FM3, followed by FM5 and FM1.
The seedling strength was analyzed by seedling length, young root length, seedling fresh weight, seedling dry weight, and seedling water content. The cotton seeds were removed 14 days after sowing and seedling activity indexes were measured and analyzed (Table 3) respectively, compared to FM0 (Figure 3(b)). In addition, 40 d after final singling, the number of cotton leaves irrigated with FM1, FM3, and FM5 increased by 20.0%, 46.7%, and 26.7% (Figure 3(c)), respectively, while the single leaf area increased by 20.1%, 47.0%, and 33.8% ( Figure 3(d)), respectively, compared to FM0. Generally speaking, FM3 had the greatest promoting effect on cotton growth, followed by FM5 and FM1.

Effect of magnetized fresh water irrigation on photosynthetic parameters of cotton
The P n of cotton irrigated with FM3 and FM5 increased by 33.9% and 32.8%, respectively, nevertheless there was no significant difference between FM1 and FM0 (Figure 4(a)).
The T r of cotton irrigated with FM1 was slightly smaller than FM0, and the T r of cotton irrigated with FM3 and FM5 was slightly increased, but not significant (Figure 4(b)).
The G s of cotton irrigated with FM3 and FM5 increased by 69.6% and 40.2%, respectively; however, there was no significant difference between FM1 and FM0 (Figure 4(c)).
The C i of cotton irrigated with FM3 and FM5 increased by 51.3% and 37.9%, respectively, yet there was no significant difference between FM1 and FM0 (Figure 4(d)). Compared with FM0, the iWUE of cotton irrigated with FM3 and

Effects of magnetized fresh water irrigation on cotton biomass and its distribution
The cotton biomass showed a significant difference between magnetized and unmagnetized fresh water, but not a significant difference among different magnetization intensities ( | Characteristic photosynthetic parameters of cotton irrigated with magnetized and unmagnetized fresh water. FM0 represents unmagnetized fresh water, while FM1, FM3 and FM5 represent fresh water treated with magnetic field intensity of 100, 300, and 500 mT, respectively. Pn, Gs, Ci, Tr, iWUE and Ls represent the net photosynthetic rate, stomatal conductance, intercellular CO 2 concentration, transpiration rate, instantaneous water use efficiency and stomatal limit, respectively. Different letters within a column indicate significant differences among all treatments at P < 0.05.

CONCLUSIONS
The surface tension coefficient of magnetized fresh water (MFW) decreased by 7.3-10.5%, the dissolved oxygen content increased by 8.8-12.7%, and the water molecular activity was significantly improved. The emergence rate of cotton irrigated with MFW was 7.7-13.1%, and the seedling vigor indexes were significantly increased (P < 0.05). MFW could improve the emergence and seedling vigor of cotton by increasing GP and VI of seeds. The P n and iWUE of cotton irrigated with MFW were increased by 32.8-33.9% and 22.3-24.4%, respectively, and MFW promoted Figure 5 | Changes of physicochemical properties magnetized fresh water. FM0 represents unmagnetized fresh water, while FM1, FM3 and FM5 represent fresh water treated with magnetic field intensity of 100, 300, and 500 mT, respectively. STC, DO, and EC represent the surface tension coefficient, dissolved oxygen content, and electrical conductivity, respectively. Different letters within a column indicate significant differences among all treatments at P < 0.05. morphological development and biomass by improved cotton photosynthesis and water use efficiency. The water molecular activity of MFW with 300-500 mT magnetic field intensity was best, which was beneficial to the growth of cotton seedlings. The results can provide guidance for the efficient utilization of MFW in arid and semi-arid areas. However, this study only focused on the magnetization of fresh water quality and its effect on the growth of early cotton seedlings, while the effects of magnetized water with different water quality on the physiological growth characteristics, yield, and quality of cotton at the later growth stage need to be further studied.