Vegetative growth characters
The impact of irrigation with magnetized and non-magnetized water, on the vegetative growth characters of tomato in 2018 and 2019 seasons are presented in Fig 5. The obtained results indicate that irrigation with magnetic water significantly increased all vegetative growth characters; plant height, number of branches, number of leaves and foliage fresh weight; in both seasons compared with the irrigation with non-magnetic water (control treatment). The increased percentage in the different vegetative growth characteristics were recorded at rates ranging from 6.9% for plant height at first season to 20.6% for number of branches at second season. These results are in agreement with those obtained by
Yusuf and Ogunlela (2015 and
2017a) and
Dawa et al., (2017) on tomato plants. In addition, similar results recorded by
Dawa et al., (2013), Sadeghipour and Aghaei, (2013) and
Shahin and Mashhour (2016) on pea, cowpea and cucumber, respectively. In this respect, the stimulatory impact of magnetic water may be explained by the effects of magnetic water on plant metabolism, such as photosynthesis, hormonal and enzyme activities and movements to endogenous solute, especially of carbohydrates, plant growth regulators and enzymes. Additionally,
Eşitken and Turan (2004) reported that magnetic water has an effect on plant nutrient element uptake from growth media for strawberry plants.
Effect of using different concentrations of humic acid (HA) on the vegetative growth characteristics of tomato plants are presented in Fig 6. The results showed, in both seasons, a significant gradual increase in the values of all vegetative growth parameters with each increase in humic acid concentrations compared to the control treatment (0 g L
-1). These findings are in agreement with those obtained by
Aman and Rab (2013) and
Husein and Abou El-Hassan (2015), in tomato plants. This increase in plant growth may be due to the positive effect of humic acid as a plant growth stimulator in increasing cell membrane permeability, respiration, photosynthesis, oxygen and phosphorus uptake and root cell growth. Also, the effectiveness of vitamins transporters in the cell was positively affected by humic acid application
(Canellasa et al., 2015).
The interaction effects of irrigation water types; magnetized and non-magnetized water (MW and Non-MW) and different concentrations of humic acid (HA) significantly affected the vegetative growth characters in both growing seasons as showed in Table 1. The highest values for the four studied characters were recorded when using magnetic water combined with the highest concentrate (3 g L
-1) of humic acid (HA). However, the two treatments combinations MW with 2 g L
-1 HA and Non-MW with 3 g L
-1 HA did not significantly differ from the highest values for all vegetative characters at the two growing seasons, except for number of branches. These results indicated that using the magnetic water with humic acid led to the possibility of reducing the amount of humic acid by one-third without affecting the aforementioned growth characteristics, except for a number of branches. However, the lowest values were gained when using the treatment combination (Non-MW with 0 g L
-1 HA). The obtained results are in harmony with
Dawa et al., (2013), which confirmed that the interaction of irrigation with magnetized water with adding of humic acid on the pea plant led to the highest values of vegetative growth and yield. In this regard, the enhancement of growth due to magnetic treatments at the different concentrations of humic acid may be attributed to the physiochemical changes of natural water by weakling the hydrogen bonds between water molecules, which reduces surface tension, increases minerals dissolvability and provides adequate nutrients for plant growth, development of roots and shoots
(Selim et al., 2009).
Ripe fruit yield and its components
The results of the effects of water irrigation types, humic acid concentrations and their interactions on the fruit yield and its components of tomato are shown in (Fig 7 and 8) and (Table 2), respectively. Concerning the influences of MW, the results reflected that irrigation with MW significantly increased the mean values of the characters; number of clusters per plant, number of fruits per plant, early yield and total fruit yield compared with irrigation using Non-MW in both growing seasons. The percentage of increase in early yield at irrigation with MW was 21 and 23% for the first and second season respectively, over irrigation with Non-MW. However, the percentage of increase in total yield at irrigation with MW was 20 and 22% for the first and second season respectively, over Non-MW. These results generally, are in agreement with those obtained by
Dawa et al., (2017) on tomato plants. They reported that the irrigation with magnetic water had significant impacts on tomato yield and its components characters. The stimulating effect of irrigation with magnetized water may be due to improving and increasing free-living micro-organisms population and activity in soil, which in turn enhance root development, increase water and mineral uptake and produce plant hormones that might be responsible for better growth of tomato plants. Also, magnetic treatments enhance the activation of phytohormone and bio-enzyme systems, which then affects various metabolic pathway activities as well as increasing the frequency of water absorption.
Kuzin et al., (1986) suggested that magnetic fields modulate the rate of recombination of free radicals during normal plant metabolism, however the basic mechanisms responsible for the magnetic stimulation of plant growth remain a mystery and the effects of magnetic exposure on plant growth still require more explanation. Other authors suggest that magnetic fields might affect the activity of ion channels or ion transport within cells (
Garcia-Sancho and Javier, 1994).
Varying concentrations of humic acid (HA), significantly affected the fruit yield and its components in tomato plants. Whereas, the mean values for the number of clusters per plant, number of fruits per plant and total fruit yield traits significantly increased with each increase in humic acid (HA) concentrations in the two seasons studied, as shown in the Fig 8. However, for early yield trait the treatments 1, 2 and 3 g L
-1 of HA did not significantly different from each other, in the second season. These results reflect a general agreement with those obtained by
Kumar et al., (2017) and
Jayasinghe and Weerawansha (2018) on tomato plants. While these results did not agree with
De Lima et al., (2011), who did not find a significant effect of adding of tomato plants with humic acid on the characteristics of the crop and its quality, except for the T.S.S. parameter. Through the previous results, the positive effect of adding humic acid may be due to the role of humic acid in improving some of the soil characteristics such as improve water holding capacity, pH buffering and thermal insulation
(McDonnell et al., 2001). Humic acid assimilates contains minor and major elements which activates or inhibits enzyme and causes changes in membrane permeability resulting in protein synthesis and activating biomass production, which in turn stimulates plant growth
(El-Ghamry et al., 2009).
Regarding the effects of the interaction between two types of irrigation water (MW and Non-MW) and the four different concentrations of humic acid (HA), the obtained results listed in Table 2 showed that, tomato plants irrigated with MW combined with 3 g L
-1 HA, gave the highest value for all fruit yield and its component traits, without significant differences from the interaction treatment between plants irrigated with MW and 2 g L
-1 HA for number of clusters and fruits per plant at the second season and for early fruit yield at the two growing seasons. Also, the results indicated that the treatment combination MW and 2 g L
-1 HA did not significantly differed from the treatment Non-MW and 3 g L
-1 HA for all yield traits. These results reflect the possibility of reducing the humic acid (HA) concentrate when irrigating with magnetized water to about 33% without affecting the tomato yield and its components. These results reflected similar trends to those reported by
Dawa et al., (2013), who studied physiological response and productivity of pea plants to irrigation with magnetized water under different concentrations of humic acid (HA). These results could probably be generally explained on the basis that the passing the water through a magnetic field increases the number of water molecules in the volume unit and increases the ability of water molecules to absorb nutrients. Magnetic water treatment has found to have a pronounced effect on plants productivity (
Teixeira and Dobranszki 2014).
Chemical composition of rip fruit
Significant variations in chemical compositions properties of tomato fruit were obviously due to types of irrigation water. Irrigation with MW gave significantly higher values for lycopene content, vitamin C, total soluble solid and dry matter content as compared with Non-MW in 2018 and 2019 seasons (Fig 9). On the other hand, various concentrations of humic acid (HA) treatments reflected the significant positive effect on chemical composition traits. The highest concentrate of humic acid 3 g L
-1) produced significantly higher value for all above-mentioned characters. A gradual significant increase in the values was also observed with each increase in the humic acid (HA) concentrate, as shown in Fig 10. The enhanced effects of addition of HA on tomato plants were also obtained by
Kazemi (2013). These results reflected similar trends to those reported by
Husein and Abou El-Hassan, (2015) and
Kumar et al., (2017), on tomato. Generally, these authors found that tomato plants responded to different magnetic water and adding of humic acid, were recognized as a vital step in stepping up the fruit yield quality.
The differences between the mean values of the lycopene content, vitamin C, total soluble solid and dry matter percentage, appeared to be significantly influenced by the interaction effects between the types of water (MW and Non-MW) with the different concentrations of humic acid (HA), in the two seasons (Table 3). The results, generally, illustrated that the addition of humic acid as 3 g L
-1 HA, combined with MW, resulted in the highest mean values in all the above-mentioned treats. Also, the results indicated that the treatment combination MW and 2 g L-1 HA did not significantly differed from the treatment, Non-MW and 3 g L
-1 HA for all traits. These results reflected the general trends of the finding of
Kazemi, (2013) and
Kumar et al., (2017) on a tomato plant. The results are in harmony with
Al-Tarjuman et al., (2020) on the productivity of tomato plant. Moreover, the effects of magnetic field on plant metabolism, such as photosynthesis, hormonal and enzyme activities and movements to endogenous solute, especially of carbohydrates and hormones transported from regions of synthesis to the fruits and growth zone
(Ali et al., 2014).