Analysis of Disinfection in Greenhouse Soils with Medium-Temperature Steam Produced by Solar Energy

: The soils of agricultural crops begin to suffer from arvenses and pathogens that are harmful to new crops after going through several production cycles. The chemical control of these pathogens is carried out through fumigants, which are applied at doses necessary to reduce the infectious potential at levels acceptable for crops. However, this may affect the biological, physical and chemical environment of the soil and, at the same time, the crops due to the toxic residues of these fumigants. In this work, the analysis of the pasteurization process of greenhouse soils sown with saladette tomato ( Solamun lycopersicum ) and cucumber ( Cucumis sativus L.) was carried out, using water vapor for the pasteurization process at a temperature of 120 ◦ C, obtained from a parabolic cylindrical solar concentrator (PCC), eliminating the use of boilers that conventionally require this method and use a lot of electrical energy, which increases the cost of the procedure and also causes the pollution of the environment. An experimental design was built for which tests were carried out at different steam emission times for each tomato and cucumber test soil. For each emission, it was necessary to reach 80 psi of pressure, with a steam exit time of a maximum of 160 s. Once this disinfection technique was applied, the presence of microorganisms such as Cladosporium sp, bacteria, pathogens and fungi was determined by various culture media. By means of this, the pathogens eliminated were veriﬁed, which were promoted by the process with respect to the test soil.


Introduction
Renewable energies are considered as those that are inexhaustible, considering the period of humanity's existence [1].The use of these renewable energies in production processes has taken on greater importance in recent decades, as the production of socalled non-renewable energy such as coal, oil and natural gas is finite.Regarding oil, it is calculated as no more than 100 years, so there is a shortage or lack of this resource; however, this study is not new.The first serious study carried out was in 1866, where Aguste Mouchout [2][3][4][5][6][7] used parabolic cylindrical concentrators to heat water and produce steam.Currently, various alternatives are sought for the production of energy and especially the production that is used in various processes and applications, such as agriculture.In agricultural processes, it has been sought to use cutting-edge technology to streamline crop systems such as automated tractors and surveillance drones in the monitoring of crops without the presence of humans.In the case of crop products, one of the great challenges is to eliminate the various pests, fungi, arvenses and bacteria that attack crops, without the use of toxic chemicals such as methyl bromide, which has been used for decades for soil disinfection, but in the long run, its toxicity affects soil and crop nutrients without raising the cost of soil and crop cleaning processes, which is why it is relevant to Appl.Sci.2023, 13, 11055 2 of 16 promote the use of soil disinfectants with an ecological approach, such as the solarization process [8].This process allows for the destabilization of bacteria due to the increase in temperature; however, various disadvantages have been described such as the challenging removal of the plastic coverture after many hours of sun exposure.Although the method is efficient and manages to control pests and diseases transmitted by the soil (nematodes and weeds, etc.) there is no adequate control of the temperature, and therefore, this fluctuation causes some bacteria to resist disinfection.In this work, we propose a new method for disinfecting agricultural soils using medium-temperature steam produced by an automated PCC where the temperature, pressure and exposure time are controlled.These systems were developed to produce working steam using solar energy and produce electrical energy through turbines.Structural engineering changes were made to the PCC so that it was capable of injecting saturated water vapor into greenhouse soils in a controlled and directed manner.Thus, discharges of saturated steam (≤120 • C) were carried out regarding the soil in the tomato and cucumber greenhouse to carry out disinfection.To control the pathogens and bacteria that could be eliminated, control soil that had not been disinfected by any method was used.Moreover, we demonstrate that the steam production method works even in times of low direct radiation, thus making this method efficient at any time of the year [9,10].

Disinfection of Agricultural Soils
The soils and substrates used in greenhouse production, both in horticulture and in the production of ornamental or forestry plants, can host a large number and variety of organisms that find favorable living conditions in them.To this biotic phase of the soil belong fungi, bacteria, nematodes and arthropods, among others.Some of them have parasitic activity in crops and can cause significant losses in terms of the quantity and quality of agricultural productions.
These pathogens can act on plants at various stages of their development: semifinished seeds, emergency plants, roots, necks and aerial parts in contact with infected soil.In some cases, the presence of these pathogens can lead to the complete disqualification of the soil for certain crops, forcing the farmer to use more or less drastic means of soil disinfection.This problem is of vital importance in modern agriculture, where intensive monoculture is often tended to, especially under greenhouse conditions (relative humidity, temperature, etc.), which are very favorable for the development of some pathogens.In a greenhouse, soil pathogens enter mainly by irrigation water and also by remains adhering to the machinery used to prepare the substrate or by the footwear of the personnel working inside the greenhouse, although sometimes they can enter with the dust dragged by the incoming air through doors and windows [11][12][13][14][15][16][17][18][19].
Due to the favorable conditions existing in the plantations, the pathogen populations of agricultural substrates tend to increase when they are not renewed or disinfected.The search for solutions to the infection of previously cultivated soils and substrates has led to the development of various disinfection methods.From an economic point of view, this translates into a decrease in the risk of quantitative and qualitative losses in crops and a greater quality and productivity in crops due to their high effectiveness and economy.The most used methods in the last 50 years have been chemical fumigants, mainly methyl bromide.Other widely used chemicals are a mixture of methyl bromide and chloropicrin, methane-sodium, dazonet and 1,3-dichloropropene.The widespread use of chemical methods has caused a series of environmental problems in the health and sustainability of agricultural soil.The search for alternatives to chemical treatments for the elimination of harmful microorganisms and arvenses in the soil is a major challenge for agricultural research, since they sometimes leave contaminating residues in the soil that are dangerous to health and can be of high persistence [20][21][22][23][24][25].
At present, there is a great diversity of physical methods used for the disinfection of soil in open fields and agricultural substrates.The equipment used for each varies according to the nature of each method.The use of physical methods for this purpose appears to be a good alternative since it is intended to eliminate all chemical waste from the application.They are classified as thermal, mechanical and electrical.
Physical methods of thermal control are those that generate an increase in the temperature of organisms by applying heat to them, an increase that leads to their elimination.These methods were initially developed by Koch and Pasteur in 1859 in their search for bacteriological control techniques, and later on, they began to be studied more intensively in the 1930s, when it was discovered that the proteins of organisms coagulated and inactivated the enzymes with heat.However, the development of heat treatments occurred in the 1950s, when various works were carried out to determine the lethal thermal points of pathogens, nematodes, insects and viruses, a temperature at which these organisms are destroyed if it is maintained long enough [26][27][28][29].
The most studied thermal methods in the open field have been solarization, direct flame, infrared radiation, microwaves and the use of steam [30].Each of these methods has drawbacks that have prevented their widespread use.Sometimes, it has been the lack of efficiency; for others, it has been low profitability or work capacity.This is not the case in the treatment of substrates in greenhouses, where conditions are more controlled.Currently, the most used thermal method in the disinfection of substrates in greenhouses is the application of steam.This method consists of stacking the material to be disinfected and covering it with a plastic awning.Lances coupled with high-power boilers are used to introduce the steam through the material; it is necessary to wait several hours for the disinfection to be completed.Subsequently, the material can be introduced into the trays for planting horticultural plants in greenhouses, which, once developed, will be transplanted to the open field.The same process is also carried out using large autoclaves, where steam is introduced through fixed pipes at a high pressure.
An alternative method to static disinfection with steam is the use of microwaves in the treatment of seed trays a few centimeters thick (up to 8-10 cm), circulating continuously through a specific module.This method has given good results in research; however, the work capacity and energy cost are still high compared to those of the treatment with water steam [31][32][33].
Given these drawbacks, it is advisable to look for alternatives that may improve efficiency with the same principle of disinfection (application of heat) and incorporate disinfection into an automated seeding train.Thus, it is essential to establish models for the design of soil disinfection systems or continuous agricultural substrates.One of the possible means of transmission for this purpose is the application of heat by convection.In addition to the aforementioned drawbacks of heat treatment with static water vapor, most traditional greenhouses in Mexico, with little technology for crop management and climate control, disinfect the soil or agricultural substrates with chemicals such as sodium hypochlorite or methyl bromide.The greenhouses that have cutting-edge technology in the planting system, in which disinfection is carried out with steam or hot water, do so in static.

Solar Energy Concentrating Systems
The search for technology for producing energy through renewable resources has been developing for several decades.The use of wind energy, biomass, geothermal energy and, above all, solar energy has made great advances and improvements.After obtaining energy through renewable energies, the application of these methods in other areas of knowledge was begun, seeking to use them in other processes and systems in order to replace the energy produced by hydrocarbons that come from non-renewable resources and that significantly pollute the environment.There are three methods of generating energy from solar radiation: thermal, photovoltaic and thermoelectric.The systems can also be classified according to the temperature they work at-for example, low, medium and high [34].
In low-temperature thermal systems, a solar collector transforms the incident solar energy into another form of useful energy, and the thermal transfer is carried out from an energy source (the sun) to a fluid, without the concentration of solar energy.The incident flux can be of the order of 1 kWm −1 ; radiation is used in a wavelength range of λ = 0.3 µm and 3.0 µm, with temperatures between 40 • C and 120 • C.These collectors use both direct and diffuse solar radiation and do not require solar tracking systems.Its applications are focused on water heating systems, building heating and air conditioning.
In the case of medium-temperature systems, reflective concentrators (for example, parabolic cylindrical concentrators, PCC) are built using large optical surfaces, such as mirrors or prisms.The overall reflectivity of the system is of the order of 90%.In these systems, only the direct component of the radiation is exploited.Optical systems are used to increase the intensity of the solar radiation that is directed on a receiving surface that absorbs it.It is necessary to follow the sun and for the flows to not be stationary.These systems are composed of two fundamental parts, the concentrator and the receiver, and can reach temperatures from 100 to 400 • C and produce working steam that can be used in turbines for the generation of electrical power and other processes [35].
For high-temperature systems, high-temperature solar thermal power plants are used for the transformation of solar energy into electricity through a thermodynamic cycle; these reflect the direct solar radiation that affects them in a receiver located high above the ground, in which the mirrors are located so that all the energy is transported at the same time by radiation [36][37][38][39].
For all of the above, since medium-temperature systems such as PCC can be used to produce working steam, we propose using this steam to disinfect greenhouse soils.The output of the system will no longer be to produce electrical energy but to carry out a constant exposure of vapor to greenhouse soil with temperatures above 100 degrees.On one hand, the latter allows for the elimination of weeds and bacteria, and on the other, it also stands as an alternative to the solarization method that uses pollution and involves difficulties in removing the plastic.Finally, by using a PCC, one can control the temperature, pressure and steam output flow through the system instrumentation, which is not possible with the conventional ecological method.This allows for the standardization of the disinfection process and crops' growth.On the other hand, it is evident that the steam production of a PCC has its greatest efficiency in the months of high direct radiation, that is, from March to June of each year.Nevertheless, in this work, we also seek to demonstrate that the disinfection process using this technological proposal is efficient even in the months of low direct radiation.This is why the tests were carried out in the months of low and medium radiation in the city of Xalapa, which is located in the northern area, at the coordinates 19 • 32 north latitude and 96 • 55 west longitude at an altitude of 1460 m above sea level (http://xalapa.gob.mx/(accessed on 3 September 2023) from November 2021 to March 2022.

Biological Analysis
The method used for the analysis of the samples disinfected with PCC is the method for identifying microorganisms through the observation of their growth in artificial food substances prepared in a laboratory.The food material in which the microorganisms grow is the culture medium, and the growth of the microorganisms is the culture [40].A culture medium must contain the necessary nutrients and growth factors and must be free of all contaminating microorganisms [41,42].To the culture, dyes are added, which act as indicators of acid formation or as growth inhibitors of some bacteria.At this stage, we took the samples obtained after the steam injection to analyze the effects they had on the microorganisms that were in the control soils (soil without any treatment) for the two types of crops worked on and with the different steam injection times.Thus, the objective of this analysis was to isolate bacteria, fungi and actinomycetes in selective culture media and identify different culture media specific for microorganisms [43,44].
For the microbiological analysis, the soil sample that was analyzed in each test with the parabolic cylindrical concentrators (PCC) had a weight of 10 g, and the soil sample was placed in a 250 mL Erlenmeyer flask; then, 1 mL of the mixture was taken with an automatic micropipette and transferred to a test tube containing 9 mL of sterile distilled water until reaching 10 −10 .After that, 1 mL of the 10 −1 dilution was taken and placed in the center of a Petri dish containing the culture medium for PDA fungi (potato dextrose agar) and bacteria (bacteriological agar).This was performed for solutions 10 −3 , 10 −6 and 10 −10 , under the laminar flow hood.Later, a striatum was performed on each of the mL placed in their respective Petri dishes.This was carried out for culture media for fungi and bacteria.They were placed in a bacteriological stove at 28 • C for three weeks.After this time, periodic reviews were carried out, and the colonies of microorganisms formed in each medium were quantified, as well as colony-forming units (CFU•g −1 of soil).Finally, samples were taken from each colony grown in each culture medium to determine at the genus level the species of fungi and bacteria present in the soils disinfected with the PCC.

Working Steam Production System
A 2 m-long parabolic cylindrical concentrator (PCC) was used, developed by our work team, and electronic and mechanical adaptations were made to it so that the disinfection process could be carried out on the test agricultural soil.

(a) Initial PCC Connection Tests
The tests with the steam emission produced by the PCC (Figure 1) that were applied for disinfection were carried out in a time interval between 8:37 a.m. until 2:00 p.m. GMT-5 (CDMX) in daylight saving time.Since the time of the location where the PCC was located after 2 p.m, the shade of the greenhouse was projected on it and the process was no longer efficient.On the other hand, for safety reasons, the tests only had a range of a maximum of 80 psi, as the safety valve indicated a maximum pressure of 100 psi; since the method does not need a pressure higher than 100 psi, the pressure considered is adequate.Several tests were carried out with different vaporization times (Tables 1-6) using a pipe with a single vertical tube with four outlet holes, and the system had thermal insulation.The soil used for the tests was cucumber (Cucumis sativus L.) and saladette tomato (Solamun lycopersicum) control soil.Two 5 kg pots were used for each control soil [45,46].

Appl. Sci. 2023, 13, x FOR PEER REVIEW
For the microbiological analysis, the soil sample that was analyzed in each the parabolic cylindrical concentrators (PCC) had a weight of 10 g, and the soi was placed in a 250 mL Erlenmeyer flask; then, 1 mL of the mixture was taken automatic micropipette and transferred to a test tube containing 9 mL of sterile water until reaching 10 −10 .After that, 1 mL of the 10 −1 dilution was taken and plac center of a Petri dish containing the culture medium for PDA fungi (potato dextro and bacteria (bacteriological agar).This was performed for solutions 10 −3 , 10 −6 a under the laminar flow hood.Later, a striatum was performed on each of the m in their respective Petri dishes.This was carried out for culture media for fungi teria.They were placed in a bacteriological stove at 28 °C for three weeks.After t periodic reviews were carried out, and the colonies of microorganisms formed medium were quantified, as well as colony-forming units (CFU•g −1 of soil).Fina ples were taken from each colony grown in each culture medium to determine a nus level the species of fungi and bacteria present in the soils disinfected with th

Working Steam Production System
A 2 m-long parabolic cylindrical concentrator (PCC) was used, developed work team, and electronic and mechanical adaptations were made to it so that th fection process could be carried out on the test agricultural soil.The tests with the steam emission produced by the PCC (Figure 1) that were for disinfection were carried out in a time interval between 8:37 a.m. until 2:00 p.m 5 (CDMX) in daylight saving time.Since the time of the location where the PCC cated after 2 p.m, the shade of the greenhouse was projected on it and the proces longer efficient.On the other hand, for safety reasons, the tests only had a range o imum of 80 psi, as the safety valve indicated a maximum pressure of 100 psi; s method does not need a pressure higher than 100 psi, the pressure considered is a  To begin calibrating the instrument, tests were carried out to determine the heating time of the system, the pressure and the steam outlet time.Data collection was carried out for 5 days to assess the performance of the system under these conditions.These tests were carried out in the period between 12 November to 27 November and 6 December 2021 (Tables 1-6), with a total of 26 tests carried out, from which the following data were collected: the start time, end time, steam outlet time and pressure reached.In addition, through a weather history obtained from the Google Weather page (Version 6.0.12), the maximum and minimum environmental temperature values of each day were also added, and by conducting a calculation between the start time and the end time, other data were obtained in relation to the duration of heating for the system to reach a maximum pressure of 80 psi.It is worth mentioning that the variations in the number of tests each day for this characterization are due to climatic changes; however, for the tests with the soils, we sought to standardize to seven the tests in each session with each of the control soils [47][48][49][50][51][52][53][54][55][56][57][58].
Table 1 shows the data obtained from the first PCC control test, where it is observed that 33 min were required to reach an output steam of 100 psi where the ambient temperature was 22 • C.
In Table 2, we can see that the ambient temperature increased by 2 degrees; therefore, the pressure increases around noon, that is, 11:13 am, reaching a maximum pressure of 110 psi.
The obstruction of clouds in the sky, especially the clouds that manage to cover the sun and therefore the direct radiation, are unpredictable but very noticeable in each test.In test number 4 of Table 4, the pressure dropped from 115 psi to 85 psi due to the climatic changes of that day; as the direct radiation decreased, the pressure of the vapor generated also decreased.However, it stabilized minutes later when the cloud cover moved from the place and allowed for direct solar radiation.
The data found in Tables 1-6 allowed us to understand the behavior of the PCC in relation to the temperature increase times to carry out the phase change of water from liquid to gaseous, as well as the pressure changes, which are related to the steam release times of the system.

Test on Cucumber Growing Soil
The test soil was from the greenhouse cucumber cultivation soil [59,60] of the Universidad Veracruzana.This was placed in a conical-shaped container which was perforated at the bottom for water drainage.This test was performed with the tube with four holes at different heights and directions each.The ambient temperature was taken from the Google Weather data (Version 6.0.12)so that the changes over the duration of the test were recorded.Tables 7-10 show the data obtained.In Table 7, it can be seen that the duration of the average heating time of the system is 30 86 , with a standard deviation of 17.24; this is because the maximum time is 69 min since the sky began to cloud, and the minimum time with a clear sky was 19 min at 11:06 a.m.As mentioned previously, the speed with which the temperature increases is greater when more cloudiness is present in the sky, which is why, for test 6, the heating time was 69 min, and a pressure of only 50 psi was achieved.As a consequence, little steam was produced at a low pressure, and with this, the exit time was the lowest at 40 s.In this test, the longest exit time on that day was obtained with 156 consecutive seconds of steam flow.In Figure 2 shows the temperature distribution in the container with soil when the test is carried out and how the steam from the PCC increases the temperature of the test soil.The part shown in red represents the highest temperature at the intake with a value of 51. 69 min, and a pressure of only 50 psi was achieved.As a consequence, little steam was produced at a low pressure, and with this, the exit time was the lowest at 40 s.In this test, the longest exit time on that day was obtained with 156 consecutive seconds of steam flow.
In Figure 2 shows the temperature distribution in the container with soil when the test is carried out and how the steam from the PCC increases the temperature of the test soil.The part shown in red represents the highest temperature at the intake with a value of 51.4 °C.

Test on Cucumber Growing Soil
To carry out the tests on cucumber growing soil, the configuration of test #1 was considered.It was carried out on 25 January to 31 January 2022.Tables 8 and 9 show the results.

Test on Cucumber Growing Soil
To carry out the tests on cucumber growing soil, the configuration of test #1 was considered.It was carried out on 25 January to 31 January 2022.Tables 8 and 9 show the results.In Table 8 shows that the average heating time of the system is 14 min in order to reach 80 psi of pressure.It was also observed that the longest steam output time was 210 s at 11:01 a.m., with a heating time of 13 min.
We can also see that in test 4, we had the longest steam release time, with a maximum of 156 s and a minimum of 40 s.The difference between these values is due to sudden climate changes.On the other hand, in 83.33% of the tests, a pressure of 80 psi could be reached.
Table 9 shows the second test with the cucumber soil; in this, we can see that the ambient temperature was two degrees less than in the first test.However, this ambient temperature was constant during the time of the tests, so the time steam output fluctuated between 112 and 134 s, which is an acceptable variation.On the other hand, the pressure was kept constant at 80 psi. Figure 3 shows the thermal images of the disinfection process, where the surface temperature (a) is 113 degrees Celsius and in (b) it is observed how the heat is distributed towards the edges of the container.Table 9 shows the second test with the cucumber soil; in this, we can see tha ambient temperature was two degrees less than in the first test.However, this amb temperature was constant during the time of the tests, so the time steam output fluctu between 112 and 134 s, which is an acceptable variation.On the other hand, the pres was kept constant at 80 psi.

Test 3, Saladette Tomato Growing Soil-20 Steam Injections
These tests were carried out on 2 and 3 February 2022.The configuration of the remained the same as in the previous tests.In the case of tests with tomato soil, we b with a higher number of steam discharges since the tomato cultivation soil usually sents more contamination, so they were carried out with 12 steam discharges on the day.The results are listed in Tables 10 and 11.As in the tests with cucumber, the tim carry out the tests was from 10 a.m. to 12 p.m., and six tests were carried out.The sy heating time to reach 80 psi and perform the thermal transformation had a maximu 15 s and a minimum of 7 s.The value output times had a maximum of 197 s.

Test 3, Saladette Tomato Growing Soil-20 Steam Injections
These tests were carried out on 2 and 3 February 2022.The configuration of the pipe remained the same as in the previous tests.In the case of tests with tomato soil, we began with a higher number of steam discharges since the tomato cultivation soil usually presents more contamination, so they were carried out with 12 steam discharges on the first day.The results are listed in Tables 10 and 11.As in the tests with cucumber, the time to carry out the tests was from 10 a.m. to 12 p.m., and six tests were carried out.The system heating time to reach 80 psi and perform the thermal transformation had a maximum of 15 s and a minimum of 7 s.The value output times had a maximum of 197 s.It was observed that the greatest vapor release times are those close to midday, since direct radiation from a cloudless sky has its maximum value at that time.Figure 4 shows the thermal distribution of steam through the tomato growing soil.The highest temperature in that image is 75.It was observed that the greatest vapor release times are those close to midd direct radiation from a cloudless sky has its maximum value at that time.

Test 4 with Cherry Tomato Soil-30 Steam Injections
The 30 steam injections on the cherry tomato soil were carried out on 16 Feb 18 February 2022, with the same technical configuration.The data are shown in Ta 14.The variation in the number of tests changes due to the weather on the th cloudy and rainy days began, so the number of tests was lower.

Analysis of the Results of Disinfected Soils
After testing the soils, biological analysis of the samples was carried out, using the methodology mentioned in Section 2.1.Table 15 shows the results of the cucumber soil analyses, starting from the control (or untreated) soil for each dilution.Table 15 shows the microorganisms present in the various treatments in the control soil where cucumber cultivation was established (Cucumis sativus L.), and Table 16 shows the results of the analysis of tomato soils.The presence of microorganisms such as Cladosporium sp. was observed.It is a genus of fungi that includes some of the most common indoor and outdoor molds.The species produce olive to brown or black colonies and have dark pigmented conidia that form in single or branched chains.Many species of the genus Cladosporium are commonly found in living and dead plant material.Some species are plant pathogens, while others parasitize other fungi [46].Cladosporium spores are dispersed by wind and are often extremely abundant in the outside air.Indoors, Cladosporium species can grow on surfaces when there is moisture.Cladosporium fulvum, the cause of tomato leaf mold, has been an important genetic model, in which the genetics of host resistance are understood as Aspergillus niger, a species of fungus harmless to humans and also to most crops [22].The natural chemical compounds of phosphorus are unhealthy.However, in the soil where cucumber cultivation had been established and subjected to six cycles, Xylaria sp. and Penicillum were maintained, and the presence of Cordyceps sp. was reported.Some species of these fungi are parasites, mainly of insects and other arthropods; therefore, they are said to be entomopathogenic fungi.A few are parasites of other fungi.
If a fungus of the genus Cordyceps attacks a host, the mycelium invades and eventually replaces the host's tissues, while the elongated fruiting body (stroma) could be cylindrical, branched or complexly shaped.The stroma has many small, bottle-shaped peritheciums that contain ascus.These in turn contain filiform ascospores that usually open into fragments that are infectious.Some species of the genus Cordyceps are capable of affecting the behavior of their host insect.Cordyceps unilateralis, for example, causes ants to perch on top of a plant before they die, ensuring the maximum distribution of spores from the fruiting body that sprouts from the insect carcass [60,61].
On the other hand, the time of two days and 16 disinfections were not enough to eliminate Cladosporium sp., Penicillum sp. and yeast reported in the control treatment.
It is important to highlight the presence of Bacillus subtilis in the samples with 2 days and 20 cycles of PCC discharge.This is essential from an agricultural point of view since this bacterium is beneficial for plants and is used as a biological control agent and as a promoter of plant growth [62,63].Furthermore, it was observed that as the cycles and disinfection times increase, this beneficial microorganism is eliminated for the cultures.

Conclusions
In this work, a new methodology was carried out to disinfect soils of greenhouses, using a PCC parabolic cylindrical concentrator that uses solar energy to produce working steam.This has the intention of having an ecological disinfection process without the use of chemicals or working with a qualitative method, that is, without the control of variables for the process to be successful, as in the case of the solarization process.In this proposal, the saturated water vapor generated by the PCC is injected into two types of crop soils, one for cucumber and the other for saladette tomato.For both soils, the temporal control of the increase in the temperature, pressure and vapor release time was carried out.One of the variables that significantly affects the increase in temperature and pressure is the daily climate changes, especially cloudy skies, since this increases the time it takes to reach the useful pressure (which is greater than 80 psi, for the transformation of water to steam).In several tests on both soils, there was a pressure drop, and it was due to this natural phenomenon.However, even with these drops, the vaporization process occurs, although with a short outlet time and a lower pressure.Also, the steam release times remained high when the test was carried out around noon.We consider that this was due to the fact that, having the sun at the zenith, the direct radiation was more efficient when reaching the PCC.
In the pathogen analysis, the microorganisms present in the various treatments were observed in the control soil where cucumber cultivation was established (Cucumis sativus L.).The presence of microorganisms such as Cladosporium sp. was observed; however, in the soil where cucumber cultivation had been established and subjected to eight cycles, Xylaria sp. and Penicillum were maintained, and the presence of Cordyceps sp. was reported.Some species of these fungi are parasites.In the case of tomato cultivation, in the 2-day treatment and 12 disinfections, these were not enough to eliminate Cladosporium sp., Penicillum sp. and yeast reported in the control treatment.This suggests that the process of the vaporization of the soils can promote the production of enzymes and beneficial microorganisms for cultivation; however, this depends on the number of vaporizations and the type of soil.Finally, Bacillus subtilis are eliminated as the PCC discharge times and cycles increase.
For all of the above, it is concluded that the disinfection method using PCC is efficient, the variables of temperature, pressure and steam release time could be controlled in detail through the instruments added to the PCC system, and it is possible to eliminate certain bacteria, as mentioned above.Another relevant result is that, by using this process, we can promote beneficial organisms for the soil and therefore the crop.These new organisms were not found in the control soils at the beginning of the process, but the injection of steam at temperatures above 100 degrees and repetitions of 12 disinfections can encourage its appearance, generating a crop soil that is not only disinfected but also enriched with beneficial microorganisms and enzymes.
Finally, it is important to mention that these tests were carried out in autumn, where the temperatures were not high, fluctuating between 18 to 25 degrees Celsius, yet the results were satisfactory, so with this, we consider that, at higher ambient temperatures (for example, during spring or summer), the pressure and temperature rise times can be improved, and discharges are more continuous and with higher pressures, making the disinfection process faster.

Figure 1 .
Figure 1.PCC used for steam production.

Figure 1 .
Figure 1.PCC used for steam production.

Figure 3 .
Figure 3. (a) Surface temperature of the soil to the outlet pipe at 113 °C; (b) Temperature in the near the edge of the container.

Figure 3 .
Figure 3. (a) Surface temperature of the soil to the outlet pipe at 113 • C; (b) Temperature in the area near the edge of the container.
Figure the thermal distribution of steam through the tomato growing soil.The highest t ture in that image is 75.1 °C.

Figure 4 .
Figure 4. Thermographic view of the cylindrical container.Temperature of 75.1 °C.

Figure 4 .
Figure 4. Thermographic view of the cylindrical container.Temperature of 75.1 • C.

3. 5 .
Test 4 with Cherry Tomato Soil-30 Steam Injections The 30 steam injections on the cherry tomato soil were carried out on 16 February to 18 February 2022, with the same technical configuration.The data are shown in Tables 12-14.The variation in the number of tests changes due to the weather on the third day; cloudy and rainy days began, so the number of tests was lower.

Table 7 .
PCC data with four exit holes.Steam applied to cucumber growing soil.

Table 9 .
Test 2 on cucumber growing soil.

Table 12 .
Test data 4. Cherry tomato soil.Data as of 16 February 2022.

Table 13 .
Test data 3. Cherry tomato soil.Data as of 17 February 2022.

Table 12 .
Test data 4. Cherry tomato soil.Data as of 16 February 2022.

Table 13 .
Test data 3. Cherry tomato soil.Data as of 17 February 2022.

Table 14 .
Test data 3. Cherry tomato soil.Data as of 18 February 2022.

Table 15 .
Cucumber soil analysis results.