Title : soil sterilization
Visit Count : 2913 Time(s)
Upload Date : 8/13/2016 - 4 Year(s) ago
Category : agricultural technical notes
Saturday, August 13, 2016
Visit Count : 2913 Time(s)
Upload Date : 8/13/2016 - 4 Year(s) ago
Category : agricultural technical notes
1. Cover the ground: mulch is the most important factor in preventing weed growth. Nearly any barrier that blocks light works as a mulch. Bark and other decorative mulches work, but dried leaves, cardboard and newspapers are also effective. organic mulches improve soil structure, and add nutrients, particularly when used near the end of the growing season. They also keep the soil cool and reduce water loss to evaporation. Landscape fabrics are thin barriers covered with tiny holes. They are typically made of plastic, but may also be sheets of burlap or other natural fibers, or recycled plastics. They are effective at blocking weed growth while allowing water and air into the soil. They should be used in conjunction with thick, effective mulch. Solid plastic sheets are another alternative for covering the ground and blocking growth of weeds.
2. Solarization: This technique can be modified for cooler times of the year and cooler climates which we will be talking about, but before that, let's go over the basic idea of solarization. One of the best nonchemical ways to get rid weeds, and some diseases and pests, is to solarize your soil. While normally this technique is used in areas with lots of sun and high temperatures, it can be modified for cooler areas and for cooler times of the year. The results may not be as long lasting or effective, but it can sure help if you are having a battle against weeds. Solarization is a simple nonchemical technique that captures the radiant heat and energy from the sun and causes physical, chemical, and biological changes in the soil. These changes lead to control, or suppression, of soilborne plant pathogens such as fungi, bacteria, nematodes, and pests along with weed seeds and seedlings. Solarization consists of covering the soil with a clear plastic tarp for 4 to 6 weeks during a hot period of the year when the soil will receive maximum direct sunlight. When properly done, the top 6 inches (15 cm) soil will heat up to as high as 125° F (52 ° C).
3. Steam treatment: is the ideal sanitation method for contaminated soils or grounds with a relatively high level of soil fatigue. This process was developed originally in the Netherlands and involves leading pressurized steam into either a coffin type box with outlet holes or perforated hosepipe under a heavy grade PVC sheet secured at the edges by long sandbags or other means. With a boiler output of 454kg (1,000lb) steam per hour it is possible to sheet steam an area of approximately 75 — 93m2 (800 — 1,000sq ft) in one operation.One of the obvious advantages of sheet steaming over the grid method is the tremendous saving in labour, whereas its main disadvantage lies in the difficulty of achieving adequate penetration of the steam, which may take several hours to reach sufficient depth.
4. Methyl bromide: is an odorless, colorless gas used to control a wide variety of pests in agriculture and shipping, including fungi, weeds, insects, nematodes (or roundworms), and rodents. Agricultural growers inject methyl bromide about two feet into the ground to sterilize the soil before crops are planted. Although the soil is covered with plastic tarps immediately after a treatment, 50 to 95 percent of the methyl bromide eventually enters the atmosphere. More information on soil fumigants can be found here. Methyl bromide is also used to treat commodities such as grapes, asparagus, logs, and other imported goods to prevent introducing pests to the United States. Treatments often fulfill official quarantine requirements for international shipments.
5. Metam sodium: Preplant soil fumigation with metam sodium is used worldwide to control soilborne diseases. The development of accelerated degradation of pesticides in soil, including metam sodium, results in reduced pesticide efficacy.
lettuce seed bioassays: have proven to be an easy and inexpensive means of testing the toxicity of some types of contaminants of concern in water and sediments, including heavy metals and some pesticides and other organic toxicants. For high school classes, lettuce seeds provide distinct advantages over most other test organisms: they are inexpensive, easy to culture, and require no upkeep between experiments. Although any variety of lettuce might work, Lactuca sativa L. var. Buttercrunch is the standard species recommended for bioassays by the U.S. Environmental Protection Agency, the Food and Drug Administration, and the Organization for Economic Cooperation and Development. Within any one species, individuals respond differently when exposed to any particular chemical. Between species, there are even greater differences in chemical sensitivities. You can test this idea by comparing your lettuce seed results with bioassays using another organism such as water fleas (Daphnia sp.).
1. Soak lettuce seeds for 20 minutes in a 10% bleach solution (add 1 part household bleach to 9 part deionized or distilled water). Then rinse five times. This kills fungal spores that can interfere with seed germination. Note: Tap water can be used if you do not have access to deionized or distilled water, but it will introduce more variability into your experiment because of the varied minerals and other compounds it contains; 2. For water samples, place a 7.5-cm paper filter in each 9-cm petri dish. Add 2 ml of water sample to each dish; 3. For sediment or soil samples, place 3 grams of sample in the bottom of each petri dish and cover with filter paper. If the sample does not contain enough moisture to saturate the filter paper, add up to 2 ml deionized water as needed; 4. Prepare a control by setting up dishes using 2 ml deionized or distilled water as your test solution; 5. To each dish, add 5 lettuce seeds, spaced evenly on the filter paper so that they do not touch each other or the sides of the dish; 6. Place the dishes in a plastic bag, and seal it to retain moisture. Incubate in the dark at constant temperature (preferably 24.5 degrees C) for 5 days (120 hours); 7. At the end of this time, count how many seeds in each dish have germinated, and measure the root length of each to the nearest mm. Look carefully at the plants to make sure you are measuring just the root, not the shoot as well.
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