# Analysis of Disinfection in Greenhouse Soils with Medium-Temperature Steam Produced by Solar Energy
## 1 Introduction
### 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: semi-finished 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 [PERSON] and [PERSON] 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].