Greenhouse Production Systems
Soil Culture
In soil culture, also known as in-ground culture, crops are raised on level ground as well as in mounded beds (See Figure 14.1). Soil culture is more often used in growing vegetables (e.g., tomatoes, lettuce, cucumbers, and peppers) rather than ornamental crops such as herbs, roses, freesia, and foliage plants as well as popular with smaller commercial and organic growers. The soil should be well drained, fertile, have a medium to light texture and be high in organic matter. The soil in a greenhouse should be worked as deeply as possible to break any existing hardpans or those that may have developed because of repeated traffic over the area. Fumigation or pastuerization of the soil is a must before each crop or at least once a year. This will help to destroy disease, nematodes and weeds. If soil is steamed, hold it at 180 degrees F (82°C) for 4 hours. Production techniques used in soil culture are similar to intensive crop production methods used in the field. Although soil is readily available at most places where a greenhouse is located most commercial growers, no longer rely on soil culture in the greenhouse as they did a few decades ago. Some of the reasons include insect and disease pressures and costly fumigation.
Greenhouse Soils Amended with Compost or Manure
Field soil in a greenhouse is usually amended with a large volume of organic matter such as well-made compost before growing greenhouse vegetables. Apply the compost or manure before the soil is fumigated so weed and disease pests in the compost and manure are destroyed. If uncomposted manure is used it should be applied at least 4 months prior to harvest to avoid contamination from human pathogens such as E. coli. Greenhouse soils amended with compost or manure may or may not require additional fertilization or liming for good plant and root growth.
National Organic Program Standards for Compost
The National Organic Standards Final Rule (USDA National Organic Program (NOP) states that any plant and animal material can be composted for organic production, provided that it does not contain any synthetic substances is prohibited by the National List or any incidental residues that would lead to contamination. However, recognizing that background levels of pesticides are present in the environment (referred to as unavoidable residual environmental contamination "UREC" in the regulations) and may be present in organic production systems, NOP regulation does not mandate zero tolerance for synthetic pesticide residues in inputs, such as compost.
NOP Standards on Composts Used for Crop Production
Composted plant and animal manures (Section205.203(c)(2)) are those that are produced by a process that: (i) established an initial C:N ratio of between 25:1 and 40:1; and (ii) maintained a temperature of 131 to 170 degrees F for 3 days using an in-vessel or static aerated pile system; or (iii) a temperature of between 131 and 170 degrees F (77°C) for 15 days using a windrow composting system, during which period, the materials must be turned a minimum of five times. Records documenting compost production methods must be maintained for on-farm produced compost as well as for compost obtained from an outside source.
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