The implementation of alternative harvest systems which are able to accelerate the kinetics of growth of plants, is extremely important to decrease the time of crop. In this sense, Electro-Hydroponic culture, i.e., the application of an electric field in the nutrient solution of the hydroponic culture emerges as an alternative and interesting harvest system. The objective of the present study was to investigate the effect of the electric field applying different intensities of direct current (DC) at the galvanostatic regime (50, 37.5, 25 and 12.5 mA) on the growth of lettuce (Lactuca sativa) plants in hydroponic culture. Fifty lettuce plants were used in a nutrient solution, from which 4 groups composed of ten lettuces each one, were subjected at 12.5, 25, 37.5 and 50 mA, respectively. A fifth group of ten lettuces was used as a reference test, i.e., without application of DC. The experiments were carried out during 16 days. The results reveal that the kinetics of growth of the lettuce is dependent on the applied current; actually it is observed an increase in the foliate area of the plants cultivated in the presence of DC than that obtained in the reference test. Furthermore, the plants subjected at 12.5 mA, revealed an increase in the foliate area of 65.3% and 73.2% in comparison with the reference test.
The population’s world growth, the decrease of the cultivation lands, as well as the decrease of the water for watering, promote a serious problem in terms of production of foods and famine in some countries of the world. Nowadays, two cultivation forms exist: the traditional cultivation, at open sky and the cultivation in greenhouses. The first is for the sowing of all vegetable products, in greenhouses is related to the cultivation of vegetables like the tomato, lettuce, strawberries, etc.; this type of cultivations are performed without soil (soil-free), the so- called “hydroponic cultivations”. The hydroponic cultivations are of bigger productivity and quality than the cultivations done at open sky, due to the fact, that hydroponic cultivation permits a better control in the illnesses derived from the environmental conditions, decreases the harvest-production times and promotes a competitive market condition [
The cultivation without soil (soil-free) is the most employed technique is the technique more used to produce vegetables in greenhouse; it requires a continuous supply of nutrients, which is given by means of a nutrient solution (NS) that contains the essential elements for the good development of the cultivations [
Lemström (2008) used an electrostatic generator and applied a voltage gradient of approximately 10 KV・m −1. It was found that the treated plants were greener, more robust and often they showed an important increment in the yield [
The lettuce is par excellence considered the leaf vegetable, given its culinary high quality as fresh salad. It is cultivated in the entire world under different cultivation systems, to sky open and low greenhouse, in soil and in hydroponic [
On the basis of the previous statements, the objective of this investigation was to stimulate the growth of the lettuce, using an electrolytic conventional system with two electrodes, at different galvanostatic regimes. The hypothesis was that when applying the electric field in the nutrient solution it is promoted the migration of the cations and anions to the electrodes and at the same time to the root of the plant with different levels of intensity of electric current (DC).
This investigation was carried out in the experimental field of the Faculty of Agricultural Sciences (FCA) of the Autonomous University of Morelos (UAEM), located at 18˚58'53" of north latitude and 99˚13'58.4" of longitude west, to an altitude of 1804 m. The climate is semiwarmsubwet with rains in summer and it presents temperatures between 9˚C and 32˚C [
For the germination of the lettuce (Lactuca sativa) seeds, a plastic rigid tray was used with 28 cm of wide 54.5 cm of long, 4 cm of height and 200 square cavities with perforation in the base for drainage. The substrate to germinate the seed was the Mixture Sunshine® mix 3, with the addition of moss of Canadian origin. The mixture was composed of Canadian moss, vermiculite, carbonates to adjust the pH (5.9 - 6.2), a moistening patented agent and a formulation bases of fertilizers. All the above-mentioned allows the retention of the water and a good aeration, the mixture is innocuous and free of overgrowth seeds, which does not require any fumigation or disinfection before its use; the moistening patented agent of Sun Gro Horticulture is not leached, neither it suffers chemical decomposition [
On the other hand, several nutritious solutions (NS) were prepared containing 30%, 60% and 80% of a standard Steiner formulation. These solutions were employed in different stages of the growth of the plants [
For the growth of the plants, five tubes of polyvinyl chloride (PVC) with 150 cm of longitude and 10.16 cm of diameter were implemented as the Electro-hydroponic cell. The cell had five perforations of 4.45 cm in the superior section, distributed each 25 cm. Reductions of PVC and valves with 1.27 diameter cm were settled in each end of the tubes for purging the system. Polyethylene sheets were also used with 1.27 cm of thickness as a support for the lettuce seedling in the system of hydroponic production. Flat graphite electrodes of 1.5 cm of wide, 10 cm of longitude with geometric area of 15 cm2 and electroactive area of 12 cm2, approximately, were placed in the Electro-hydroponic cell as anode and cathode, correspondingly (
Four power sources were used in the Electro-hydroponic system; three built at the Center of Investigation in
COMPOUND | STEINER 100% Mg∙L−1 | STEINER 80% Mg∙L−1 | STEINER 60% Mg∙L−1 | STEINER 30% Mg∙L−1 |
---|---|---|---|---|
Ca(NO3)2 | 1080 | 864 | 648 | 324 |
KNO3 | 515 | 412 | 309 | 155 |
K2SO4 | 110 | 88 | 66 | 33 |
MgSO4 | 501 | 401 | 301 | 150 |
KH2PO4 | 103 | 82 | 62 | 31 |
COMPOUND | g (L−1) | g (vol・NS)−1 |
---|---|---|
H3BO3 | 0.00288 | 172.8 |
MnCl2∙4H2O | 0.00181 | 108.6 |
ZnSO4∙7H2O | 0.00022 | 13.2 |
CuSO4∙5H2O | 0.00018 | 10.8 |
H2MoO4 | 0.00002 | 1.2 |
Fe-EDTA | 0.03787 |
Engineering and Applied Sciences (CIICAp), by means of an average convertor (CONVER-TLAX) of 120 V CA to CD/12V, 5 A, as well as another convertor (LODESTAR) of 12 V 3.5 A and 12 - 24 V, 3.5 A. Voltmeter professional, Steren, model MUL-600.
The fifty lettuce plants with a similar size were selected and transplanted in the tubes R-1, R-2, R-3 R-4 and R-5 (Electro-hydroponic cell) containing 12 liters of NS at 80% with pH of 5.5, the tubes were identified as R-1 which was used as a reference test i.e., at 0 mA, then experiments were also carried out in galvanostatic regime applying different current intensities: R-2, R-3, R-4 and R-5 at 50 mA, 37.5 mA, 25 mA and 12.5 mA, respectively. The nutrient solution was changed with a weekly frequency.
After 39 days of growth, the lettuce plants were harvested to measure the foliate area using an equipment LI-COR, Biosciences, model LI-3100C AREA METER. It is worth mentioning that the 39 days correspond to the total time of the experiment i.e., 23 days are associated with the germination and transplant steps, which were carried out in a plastic rigid tray, while 16 days were employed to promote the growth of the plants in the Electro-hydroponic system.
Data of the diameter and foliate area were taken for each plant during the hydroponic process, in an attempt to follow the kinetics of growth of the lettuce subjected at different applied current intensities.
Two values of the foliate diameter were measured for each plant using a ruler. These values were employed to obtain an average diameter. It is important to mention that the diameter measurements were carried out in five plants at 7, 10, 12 and 16 days, as shown in Tables 3-6, respectively. The best results were obtained with the lowest current intensity (12.5 mA), as shown in
The foliate area is one of the most important variables in the evaluation of the growth of the plants; the appropriate determination of the same one is fundamental for the correct interpretation of the production processes in a vegetable species. It was measured the area to foliate for each plant at 16 days of growth in the tubes, these measurements were compared with that obtained with the witness (R-1) i.e., with the experiment performed in the absence of electric direct current. In the first set of experiments (labeled as experiment 1), it was evaluated the effect of the current intensity on the foliate area and % of increment. It is possible to observe in
Tube | mA | FOLIATE DIAMETER (cm) | |||||
---|---|---|---|---|---|---|---|
Plant 1 | Plant 2 | Plant 3 | Plant 4 | Plant 5 | Average | ||
R-1 | - | 11.25 | 7.65 | 7.00 | 9.75 | 8.90 | |
R-2 | 50.00 | 9.55 | 10.00 | 10.65 | 9.50 | 9.90 | |
R-3 | 37.50 | 11.25 | 10.00 | 9.50 | 9.00 | 9.90 | |
R-4 | 25.00 | 7.50 | 8.00 | 12.00 | 11.00 | 9.60 | |
R-5 | 12.50 | 8.25 | 10.00 | 13.00 | 10.50 | 10.40 |
Tube | mA | FOLIATE DIAMETER (cm) | |||||
---|---|---|---|---|---|---|---|
Plant 1 | Plant 2 | Plant 3 | Plant 4 | Plant 5 | Average | ||
R-1 | - | 14.55 | 11.00 | 11.50 | 12.00 | 13.30 | |
R-2 | 50.00 | 11.50 | 12.75 | 14.75 | 10.50 | 12.40 | |
R-3 | 37.50 | 13.75 | 12.50 | 11.00 | 12.00 | 12.30 | |
R-4 | 25.00 | 14.00 | 14.00 | 13.50 | 12.50 | 13.50 | |
R-5 | 12.50 | 12.25 | 13.50 | 15.50 | 12.00 | 13.30 |
Tube | mA | FOLIATE DIAMETER (cm) | |||||
---|---|---|---|---|---|---|---|
Plant 1 | Plant 2 | Plant 3 | Plant 4 | Plant 5 | Average | ||
R-1 | - | 15.50 | 11.00 | 11.50 | 13.50 | 12.90 | |
R-2 | 50.00 | 11.50 | 13.50 | 14.75 | 11.00 | 12.70 | |
R-3 | 37.50 | 15.50 | 13.50 | 13.00 | 12.00 | 13.50 | |
R-4 | 25.00 | 14.50 | 15.00 | 13.50 | 12.50 | 13.90 | |
R-5 | 12.50 | 12.50 | 14.00 | 16.00 | 13.90 | 14.10 |
Tube | mA | FOLIATE DIAMETER (cm) | |||||
---|---|---|---|---|---|---|---|
Plant 1 | Plant 2 | Plant 3 | Plant 4 | Plant 5 | Average | ||
R-1 | - | 16.00 | 12.00 | 12.00 | 14.50 | 13.60 | |
R-2 | 50.00 | 12.00 | 15.50 | 15.00 | 11.00 | 13.50 | |
R-3 | 37.50 | 17.50 | 14.50 | 14.50 | 12.50 | 14.80 | |
R-4 | 25.00 | 15.50 | 16.00 | 14.00 | 12.50 | 14.50 | |
R-5 | 12.50 | 13.00 | 15.00 | 17.00 | 15.00 | 15.00 |
Tube | mA | Foliate area (cm2) | % Increment |
---|---|---|---|
R-1 | Control | 904.00 | |
R-2 | 50.00 | 1206.00 | 33.40 |
R-3 | 37.50 | 1279.00 | 41.50 |
R-4 | 25.00 | 1251.00 | 38.40 |
R-5 | 12.50 | 1494.00 | 65.30 |
12.5 mA, which indicates that the current intensity required to favor the kinetics of growth of the plants can be optimized. Actually the best results in the growth of the plants were those shown in R-5, which corresponds to the smallest current intensity, i.e. 12.5 mA.
In
Tube | mA | Foliate area (cm2) | % Increment |
---|---|---|---|
R-1 | Control | 1107.00 | |
R-2 | 50.00 | 1281.00 | 15.70 |
R-3 | 37.50 | 1439.00 | 30.00 |
R-4 | 25.00 | 1489.00 | 34.50 |
R-5 | 12.50 | 1917.00 | 73.20 |
The generation of an electric field by means of the use of the electric direct current employing a two electrodes conventional system as a hydroponic system, showed that the application of different electric current intensities to the system promotes an increase in the kinetics of growth of the lettuce. Furthermore, the best effect on the kinetics of growth of the plant was obtained with the lowest current intensity, since with this condition, the foliate area was the biggest in comparison to the one expressed by the reference plants. On the basis of the presented results, it is possible to conclude that the use of the electric field in the system of hydroponic culture (Electro-hydroponic system) stimulates the growth of the plants, which reveals the potential of this alternative hydroponic system.
Orlando Fuentes-Castañeda is grateful to CONACYT (Mexico) for the postgraduate scholarship received.
Orlando Fuentes-Castañeda,Martha Lilia Domínguez-Patiño,Jorge Domínguez-Patiño,Rosa María Melgoza-Alemán,Oscar Gabriel Villegas-Torres, (2016) Effect of Electric Field on the Kinetics of Growth of Lettuce (Lactuca sativa) in a Hydroponic System. Journal of Agricultural Chemistry and Environment,05,113-120. doi: 10.4236/jacen.2016.53013