AGRONOMIC PERFORMANCE OF LETTUCE GROWN IN A GREENHOUSE IN THE FEDERAL DISTRICT UNDER DIFFERENT LEVELS OF MAGNETIC INDUCTION AND THREE IRRIGATION DEPTHS

Objective: The objective of research into the use of magnetically treated water in irrigated agriculture is to reduce the amount of water used while maintaining productivity and product quality. Theoretical Framework: Lettuce stands out among the most consumed and produced vegetables in Brazil. Studies show that magnetically treated water undergoes physical and chemical changes. Method: The experiment was carried out in a greenhouse at Fazenda Água Limpa (FAL), belonging to the University of Brasília (UnB). The different levels of magnetic induction adopted were: T1 – 0.28 Tesla (T); T2 – 0.229T; T3 – 0.029T; T4 – 0 T (control), applied in irrigation, using two depths, 50% and 100% of crop evapotranspiration. Results and Discussion: The different treatments responded significantly to the variables nitrogen, phosphorus, magnesium, sulfur, iron, copper, zinc, crude protein, plant height and diameter. Research Implications: The results indicate that by using the magnetization of water applied in irrigation, it is possible to reduce the amount of water applied without harming nutritional and productive aspects of the crop. Originality/Value: This study contributes to the literature by bringing an innovative and still little studied approach to a technique that can be applied to irrigation. The relevance and value of this research are evidenced by addressing the reduction of water resources applied in agriculture.


INTRODUCTION
Lettuce (Lactuca sativa L.) stands out among the most consumed and produced vegetables in Brazil, since, when consumed fresh, it has nutritional properties as a source of vitamins and minerals (FILGUEIRA, 2003).The cultivation of this vegetable is traditionally carried out in beds using sprinkler and drip irrigation.Due to their sensitivity to climatic factors such as temperature, light and carbon dioxide concentration, plants require monitoring regarding water application (EMBRAPA, 2014).In this scenario, the water supply process is present in the most diverse production sectors, studies have associated the use of magnetized water with properties such as surface tension, pH, viscosity and conductivity (ESMAEILNEZHAD et al., 2017).
Studies show that magnetically treated water undergoes physical and chemical changes, where the clusters of water molecules are reduced, assuming simpler forms, with stronger bonds between them.
The experiment aimed to evaluate the agronomic performance of lettuce, grown in a greenhouse, in the Federal District, under different levels of magnetization applied to irrigation water and under three different irrigation depths.

THEORETICAL FRAMEWORK
These changes allow for greater ease of penetration into plant cell membranes, which suggests acceleration of plant growth (SURENDRAN;SANDEEP;JOSEPH, 2016;TOLEDO;RAMALHO;MAGRIOTIS, 2008).This reduction in the molecular structure of water allows for a larger molecular surface and, consequently, a greater quantity of ions that can come together, enabling greater contact with other molecules.
In general, the aim of research into the use of magnetically treated water in irrigated agriculture is to reduce the amount of water used, maintaining productivity and product quality.Some researchers show that irrigation with magnetically treated water is an ecological alternative and brings numerous benefits to agriculture, such as increased productivity, reduced water consumption, early ripening, better seed germination, reduced diseases, increased quality of plant, increased absorption of nutrients and minerals in seeds and fruits, increased efficiency in the use of fertilizers and reduced operational costs, in addition to allowing the use of lowquality water for irrigation (saline or waste) in saline soil (ABEDINPOUR; ROHANI, 2016; 4 BABALOO et al., 2018;EL-SHAFIK EL-ZAWILY et al., 2019;HOZAYN et al., 2016;KONEFAŁ-JANOCHA et al., 2018;MAHESHWARI;GREWAL, 2009;SILVA;DOBRÁNSZKI, 2014;YUSUF;OGUNLELA, 2017).

METHODOLOGY
The experiment was carried out inside a greenhouse at Fazenda Água Limpa (FAL), belonging to the University of Brasília (UnB) and located at the geographic coordinates of latitude 15°56'50" S and longitude 47° 56'02" W. The altitude of the site is 1,080 m above sea level.The region's climate is type Aw, according to the Köppen-Geiger climate classification (PEEL et al., 2007), tropical with a dry season, with an average temperature of 23.2°C and average rainfall of 1,660 mm year-1, concentrated between the months of october to april.
The magnetization of water occurs when its flow passes through a magnetic field, which is formed by magnets.The magnetic field varies in intensity, depending on the size and shape of the magnets; however, once the magnets are installed, the magnetization intensity remains unchanged.
To carry out water magnetization, three different magnetizers were used, installed at the beginning of each main line, of the respective treatments, namely: Jiangsu YLD Water Processing Equipment Co., Ltd.(T1), Structured Water agriculture magnetizer (T2) and Industrial Magnetizer Technologies Inc. (T3).
The design used was completely randomized (CR), with a factorial scheme with eight treatments and five replications each.The different levels of magnetic induction adopted were: T1 -0.28 Tesla (T); T2 -0.229 T; T3 -0.029T; T4 -0 T (control).
Each replication consisted of 12 black polyethylene pots with a capacity of 12.5 liters, four per line, with the central line being used as a useful area for the experiment, containing a red latosol collected at a depth of 20 cm as substrate.The spacing between pots was 20 cm, and the experiment was conducted with one plant per pot.Each plot had the following dimensions: 0.95 m wide and 1.90 m long, with a total area of 1.805 m², and a total of 240 pots.
To correct soil acidity and fertility, an analysis of the collected soil was carried out, with the parameters corrected to the levels recommended for the crop, according to the planting region.
The lettuce seedlings, cultivar Vanda, were purchased from a horticultural store, in plastic trays with two hundred cells.
The culture was transplanted after correcting the soil with basic fertilizer, using one seedling per pot.Irrigation was carried out with the respective treatments at a frequency of four times a day, according to water needs, taking into account evapotranspiration.The first irrigation at eight o'clock and subsequent irrigations spaced three hours apart.Irrigation schedules were conducted during farm staff working hours to ensure supervision of application across all irrigations.Irrigation was carried out using drippers, one dripper per pot, with a flow rate of 6 liters per hour, each.
To verify the different responses of lettuce to different irrigation depths, one hundred percent of the evapotranspiration and fifty percent of the evapotranspiration were considered.
To verify the effect of the different irrigation levels, the following variables were analyzed: • Number of leaves: after harvesting, all the leaves of each plant from all treatments were separated using a knife and the number of leaves per plant was counted; • Fresh mass of the aerial part: after harvesting, the aerial part was separated from the roots and, with the aid of a digital scale graduated in 0.001 g, the total aerial part was weighed; • Mass: the plants, after harvesting, were weighed on a digital scale, graduated in 0.001g; • Diameter: with the help of a measuring tape, the plant diameter was measured; • Productivity: Using the weight value of the plants, a calculation was made to estimate the production in an area of one hectare; • Macro and micronutrient content: to quantify macro and micronutrient content, leaf samples were sent to the Soloquímica Laboratory.
The data were subjected to analysis of variance, and the means were compared using the Tukey test, at a 5% probability level.The analyzes were carried out using the computer program System for Analysis of Variance (SISVAR) (FERREIRA, 2000).

RESULTS AND DISCUSSION
The interaction between the different levels of magnetic induction had a significant effect on the variable nitrogen.The interaction that obtained the highest average was the control, without magnetization, with the irrigation depth of 50% of the crop's evapotranspiration, presenting an average of 25.79 g Kg-1 (Table 1).
As said by Resende et al. (2005), lettuce is a crop made up basically of leaves and responds greatly to nitrogen fertilization; Nitrogen deficiency slows down plant growth and induces absence or poorhead formation, older leaves become yellowish and fall off easily.

Table 1
Average values of nitrogen depending on different magnetization levels.Phosphorus levels were significantly affected by the interaction between different levels of magnetic induction and irrigation depths, with the highest average observed for the control with an irrigation depth of 50% (Table 2).

Table 2
Average values of phosphorus depending on different magnetization levels.0.0075 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Among the functions of potassium (K) is enzymatic activation, regulation of the opening and closing of stomata and osmotic control of tissues; In this context, adequate management of soil fertility It is a powerful tool for achieving potential productivity of cultivars (OLIVEIRA JUNIOR; CASTRO; OLIVEIRA, 2018).Potassium levels were not significantly affected by the interaction between the different levels of magnetic induction and the irrigation depths.The highest average observed was for the treatment with 0.280 T and the 100% irrigation depth (Table 3).This result demonstrates that it is possible to reduce the applied irrigation depth with no significant reduction in potassium concentration in leaves.

Table 3
Average values of depending on different magnetization levels.The interaction between the magnetization applied to the irrigation water and the different irrigation depth did not significantly affected the calcium variable, with the 100% crop evapotranspiration depth, with 0.280 T magnetization, presenting the highest average, with a value of 8.69 g Kg-1 (Table 4).

Table 4
Average values of depending on different magnetization levels.The same was observed for magnesium, with the interaction not presenting a statistical effect (Table 5).

Table 5
Average values of depending on different magnetization levels.12.85 P < 0.05 (treatment) 0.5420 P < 0.05 (repetition) 0.0000 P < 0.05 (interaction) 0.1479 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
According to Stipp & Casarin (2010), even though sulfur may be partially supplied by the atmosphere and organic matter, artificial sources of this nutrient cannot be avoided, requiring a very careful recommendation to be successful.in the use of this element.
For sulfur, the different irrigation depths and magnetization levels significantly affected the average values, with the highest average being presented for the control with 50% irrigation (Table 6).

Table 6
Average values of depending on different magnetization levels.When there is a deficiency of this secondary macronutrient, protein synthesis is inhibited because sulfur is a participant in two essential amino acids (cystine and methionine), as a result of which plants have a lower chlorophyll content and less developed roots (RAIJ, 2011).Results with sulfur fertilization are not only obtained in vegetables, most crops have shown a satisfactory response (SOARES et al., 2017).
As mentioned by Ramos et al. (2018), the mineral iron is an essential micronutrient for vegetables, whose function is to stimulate plant development and facilitate the occurrence of metabolic reactions that activate enzymes participating in the process photosynthetic.In this way, iron is essential for the proper functioning of the process respiratory, nitrogen fixation and transfer of electrons (ALEXANDRE et al., 2012).A deficiency of this metal can be noticed initially in the youngest leaves that assume yellowish color and, as a consequence, the inhibition of chlorophyll synthesis, which can become whitish (LAURETT et al., 2017).
The interaction between the different irrigation depths and magnetization levels statistically affected the average values for iron, with the highest average being presented for the treatment with 50% irrigation and 0.029 T, obtaining averages higher than the 100% depth cultivated in the same period (Table 7).

Table 7
Average values of depending on different magnetization levels.0.0460 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
It was observed that manganese levels varied between treatments, but not statistically, at the 5% level.Despite this, for the magnetization of 0.280 T, the 100% irrigation depth presented superior results.These results demonstrate that, for manganese, it is possible to reduce the water applied without loss of nutrient levels (Table 8).

Table 8
Average values of depending on different magnetization levels.

10
Copper is considered an essential micronutrient for plants, it acts in the constitution of many enzymes and proteins, maintaining fundamental performance in processes such as photosynthesis, respiration, detoxification of superoxide radicals and lignification (SOUZA et al., 2018).Its deficiency can drastically induce a reduction in enzymatic activities, while excess can cause toxicity (CUNHA FILHO, 2013).
It was observed that copper levels varied between treatments, with the maximum obtained being in treatments with 50% irrigation depth and without magnetization (Table 9).

Table 9
Average values of depending on different magnetization levels.The interaction between treatments presented statistically significant results, with the highest average being observed for the treatment with 0.280 T and irrigation depth of 100% of ETc, while the lowest average was observed for the first depth of 100% without magnetization (Table 10).

Table 10
Average values of depending on different magnetization levels.According to Yuri et al. (2006), zinc in leaves is associated with low molecular weight complexes, free ions and insoluble forms in the cell wall, and can become inactive inside the cell through complexation with phosphorus.Its essentiality for the function and/or structure of several dehydrogenases, proteinases and peptidases found in plants was reported by Welch & Norvell (1993), being classified as a partially mobile element in plants (PEASLEE; ISARANGKURA; LEGGETT, 1981).
The average boron values did not present a significant result (Table 11).Once again, this result demonstrates that it is possible to maintain statistically equal averages by reducing the water applied in irrigation.

Table 11
Average values of depending on different magnetization levels.0.2665 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
The different magnetization levels and the different amounts of water applied, according to the depth differentiation, affect the protein content averages.The treatment with the highest average was reducing irrigation to 50% without magnetization (Table 12).

Table 12
Average values of depending on different magnetization levels.12.88 P < 0.05 (treatment) 0.0103 P < 0.05 (repetition) 0.0000 P < 0.05 (interaction) 0.3815 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
As reported by (LEMOS, 2020), some authors reported that magnetic treatment of irrigation water provided an increase in viscosity and a decrease in the surface tension of the water, which made so that soil moisture remains longer (AL-OGAIDI et al., 2017;MOSTAFAZADEH-FARD et al., 2011;SURENDRAN;SANDEEP;JOSEPH, 2016).With the reduction in surface tension and the increase in soil moisture, water molecules come into contact with a greater number of molecules, being transmitted through the roots more easily.Lemos (2020), studying the influence of magnetically treated water on the production and irrigation management of lettuce, used two types of water (magnetically treated water -AM and water without magnetic treatment -AC) and four water tensions in the soil to start of irrigations (T1 -15 kPa, T2 -25 kPa, T3 -40 kPa and T4 -70 kPa) verified differentiation in irrigation frequency between treatments, observing a greater number of irrigations with a decrease in water tension in the soil and in the use of common water (without magnetic treatment).According to research carried out by Zlotopolski (2017), it was found that the water tension in the soil when irrigating the lettuce with the control group (without treatment), the soil reached more negative values than the treatment with magnetically treated water.This facts may explain why, even with the reduction in the amount of water applied by irrigation, some variables present statistically superior results.
Although the different levels of magnetization applied to the irrigation water did not present a statistical difference between them, the different irrigation depths presented a significant result, with the depth of 100% presenting a superior result for the magnetizations of 0.029 and 0.229.(Table 13).This result demonstrates that although magnetization does not significantly affect plant height at some magnetization levels, there may be a reduction in the water applied, without loss of height When not applying magnetization or higher levels as 0.280 T.

Table 13
Average values of depending on different magnetization levels.

13
The different levels of magnetization showed statistically significant results for the diameter, with a depth of 50% showing a superior result without magnetization (Table 14).Sronsri et al. (2022), studying the influence of the magnetic generator device on both the quality and quantity of lettuce grown by a circulating hydroponic method, showed the nutrient solution, magnetized by using the magnetic generator, had an impact on plant height, producing better results as compared to the unmagnetized solution.Average plant heights for magnetized and unmagnetized conditions were found to be 3.24 ± 0.80 cm and 2.23 ± 0.74 cm for the first week, while in the second week, plant heights of 5.52 ± 0.88 cm and 3.74 ± 1.09 cm were obtained, respectively.0.2720 P < 0.05 (interaction) 0.1957 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.Lemos (2020), studying the development and production of lettuce irrigated with water subjected to magnetic treatment, found no significant differences (P<0.05) in the modification of the type of water and water tension in the soil to start irrigation in the length results and stem diameter; Furthermore, it was also observed that the use of water subjected to magnetic treatment resulted in a lower value of maximum exposure area of approximately 528 cm2 for magnetically treated water, and 658 cm2 when using ordinary water.
Despite being sold per unit in markets, lettuce is sold in boxes at supply centers in Brazil.
At the main supply center in Brasília (CEASA), the crop is separated into boxes, varying from 3 to 5 kilograms, depending on the marketing season, with the weight of the unit varying between 166.66 and 277.78 grams for classification extra and between 125 and 208.33 grams for the special classification (CEASA, 2023).
Although there was no significant result for the interaction between magnetization and irrigation depths, not all treatments presented averages within the commercial standard.
Treatments with reduced irrigation presented higher averages, falling into one of the crop sales classes (Table 15).

Table 15
Average values of depending on different magnetization levels.For the variable number of leaves, the interaction between treatments showed no statistical difference, as did the fresh mass of the aerial part as expected (Table 16).Lemos (2020), studying the development and production of lettuce irrigated with water subjected to magnetic treatment, did not observe significant differences (P<0.05) for commercial fresh mass, due to the variation in water tension in the soil at the start of irrigation.
However, with water subjected to magnetic treatment, a reduction in commercial fresh mass was observed with an increase in water tension in the soil.

Table 16
Average values of depending on different magnetization levels.0.8811 CV: Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.

CONCLUSIONS
For the variables nitrogen, phosphorus, magnesium, sulfur, iron, copper, zinc, crude protein, plant height and diameter, it was possible to observe that the reduction in irrigation depth with magnetization Applied to irrigation water obtained superior results, demonstrating that the interaction between magnetization and reduction in irrigation is an alternative to reduce the amount of water applied and increase average nutrient values.
Agronomic Performance of Lettuce Grown in A Greenhouse in The Federal District Under Different Levels of Magnetic Induction and Three Irrigation Depths ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.8 | p.1-17 | e08072 | 2024.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.Magnetic Induction and Three Irrigation Depths ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.8 | p.1-17 | e08072 | 2024.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.Magnetic Induction and Three Irrigation Depths ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.8 | p.1-17 | e08072 | 2024.

Table 14
Average values of depending on different magnetization levels.
Coefficient of variation.Averages with identical lowercase letters do not differentiate between each other in the same column.Averages with equal capital letters do not differentiate between them, on the same line.