Seed Bed Sterilization – Garth Stang
Introduction – Another way to deplete the soil seed bank is to germinate the weed seeds, and then kill them before the crop comes up. There are many ways to break seed dormancy, like scaring the seeds, and exposing them to light or air. This can be done with heavy harrowing or rotary harrowing. These implements disturb the top inch or less of soil, and will induce germination in seeds at that level. Seeding of the crop is usually done a little while after harrowing. Right before the crop comes up, the weed seedlings that germinated from the harrowing operation are destroyed, usually by flaming or steaming.
Fine tuning – This practice is most commonly used in vegetable production, but can be used in field production too. You want to have the most seeds germinated as possible before killing them and you want to effectively kill them without hurting the crop. In organic systems, this usually has to be by flaming the weed seedlings using a specialised implement.
Considerations – It is very important to not damage the crop seedlings that are just below the surface, so it is important to know what stage the seedlings are at and how long till they emerge. This technique cannot really be used in no-till systems because the straw and trash resting on the surface will burn and cause a large fire.
Costs – The flaming or steaming requires a lot of energy and is quite costly. Exhaust and emissions are produced from the flames.
Personal opinions – This technique is good for depleting the soil seed bank and decreasing the amount of weeds that will be a problem in the crop. It is costly and requires good monitoring of the growth and germination of the crop, but its benefits would pay off.
Soil Sterilization Through Solarization – Brayden Connor
Solarization or solar heating (SH) is a practice in which the soil is mulched with a clear plastic film and then allowed to be heated by the sun. This technique causes the soils temperature and moisture content to rise to a point where it is harmful to delicate organisms such as weed seedlings or seeds. This technique is used as a pre-emergence control for all weeds and plants. Since this technique requires a few weeks of solar radiation to work it is best used as a precursor to a fall seeded crop such as winter wheat.
Solar heating is most effective when the sun is hot and the days are long and so should be most effective in July and August to take advantage of this. Once enough time has been allowed for the soil to heat up and kill the plants and seeds under the plastic film the crop should be planted immediately after the film is removed (Cohen and Rubin 2007).
Care should be taken that rips do not occur in the plastic film to prevent heat from escaping. If tears do occur repairs should be made immediately.
Ecological costs for this strategy are very low as long as the plastic film is disposed of properly. Economic costs will only be the cost of the plastic film and the producer’s time to place the film as well as check for tears and holes through the treatment period.
This mode of control is very practical as it not only destroys weeds but also kills pathogens within the soil which organic producers have limited control options for (Cohen and Rubin 2007). Large areas might be difficult to solarize but is possible if multiple long sheets of plastic are used with spaces in between to allow them to be checked for rips or holes. This option should be considered in areas where soil borne diseases such as sclerotinea are present.
Cohen and Rubin (2007). Thermal Weed Control. In M. K. Upadhyaya, & R. E. Blackshaw (Eds.), Non-Chemical Weed Management (pp. 177-200). Biddles Ltd.