Soil sterilization
"Sterilization" is the removal or killing of all life forms from a substrate or medium. The term "Sterilization" is absolute in itself, meaning, a medium may either be "sterilized" or "unsterilized". In other words, "sterilization" can never be semi, partial or half.
Soil sterilization
Soil is a very common substrate for the plants since the evolution of the first land plant during the palaeozoic era. A soil can harbor plenty of soil microbes, which eventually constitute below ground biodiversity. The soil microbes (including bacteria, fungi, nematodes) may be beneficial, natural or harmful.
Harmful microbes cause substantial loss in the yield and economy. The soft targets of harmful microbes are always seedlings and young growing plantlets. It becomes paramount important to make the nursery substrate free from harmful microbes. This can be achieved through the sterilization of nursery soil. Different soils have different compositions, textures, densities, nutrients and living organisms. Soils are very hard to penetrate by the sterilizing agents. Sterilization also kills the beneficial microbes too. There are other techniques (e.g., tyndallization) which kill only the harmful microbes, but not the useful ones. These techniques can be adapted to make soils and nursery beds healthy and free from harmful microbes. Soil sterilization is a very challenging job.
Sterilization is the misnomer of all these techniques and adapted in general used for making soils free of harmful microbes.
Below are the techniques used for making soil free of harmful microbes.
Harmful microbes cause substantial loss in the yield and economy. The soft targets of harmful microbes are always seedlings and young growing plantlets. It becomes paramount important to make the nursery substrate free from harmful microbes. This can be achieved through the sterilization of nursery soil. Different soils have different compositions, textures, densities, nutrients and living organisms. Soils are very hard to penetrate by the sterilizing agents. Sterilization also kills the beneficial microbes too. There are other techniques (e.g., tyndallization) which kill only the harmful microbes, but not the useful ones. These techniques can be adapted to make soils and nursery beds healthy and free from harmful microbes. Soil sterilization is a very challenging job.
Sterilization is the misnomer of all these techniques and adapted in general used for making soils free of harmful microbes.
Below are the techniques used for making soil free of harmful microbes.
Autoclaving
An autoclave is ideally a large-scale pressure cooker that runs on the principle of "steam-underpressure". Very first autoclave was developed by Charles Chamberland, a pupil of Louis Pasteur. It is a laboratory instrument and is useful for the sterilization of small quantities of soil for the nursery beds and experimentation. Autoclave is a closed chamber for wet-heating. In autoclave various temperatures can be achieved at different pressures.
Table showing relationship between the pressure and temperature of steam
When maintained for 30 minutes, the steam in the autoclave penetrates the soil and kills various organisms at different temperatures.
Table showing organisms killed at temperature sustained for 30 minutes
Autoclaving is an easy and fast method of soil sterilization. Autoclaving does not change the organic content and pH of the soil. However, it has adverse effects on soil texture.
Table showing relationship between the pressure and temperature of steam
| Pressure (psi) | Temperature (°C) |
| 0 | 100 |
| 10 | 115 |
| 15 | 121 |
| 20 | 136 |
| 25 | 130 |
When maintained for 30 minutes, the steam in the autoclave penetrates the soil and kills various organisms at different temperatures.
Table showing organisms killed at temperature sustained for 30 minutes
| Temperature (°C) | Organisms killed |
| 48.8 | Water molds |
| 62.7 | Most pathogenic bacteria, worms, centipede |
| 71.1 | All pathogenic bacteria |
| 82.2 | Seeds of weeds |
| 100 | Heat resistant weed seed and viruses |
| 121 | Heat-resistant endospores of bacteria |
Autoclaving is an easy and fast method of soil sterilization. Autoclaving does not change the organic content and pH of the soil. However, it has adverse effects on soil texture.
Content first created on 15-11-2020
last updated on 22-01-2024
last updated on 22-01-2024
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