20.4 VEGETABLE MARKET TYPES Fresh Vegetable Market Production Major fresh market vegetable producing states are California, Florida, Arizona, Texas, and Oregon. It is common for production of a crop to be conducted in progression as the season changes. Florida produces “new” (not stored) potatoes in March, followed by Georgia in April, and North and South Carolinas in May. Virginia supplies the fresh market potatoes on the eastern United States in June and July, while Maine produces most of the “new” potatoes in summer to early fall. However, with competition from other production areas, this traditional production pattern has been significantly disrupted. Processing Vegetable Production Vegetables for processing are commonly produced in regions where summer temperatures are moderate. The cool temperature allows vegetables to mature more slowly, thereby giving producers some flexibility in the development of harvesting times. Warm-season vegetables are produced in the Great Lakes regions, focusing on crops like sweet corn, peas, cabbage, beets, and carrots. The lake effect moderates the climate in the region for high-quality produce. Major producing states are Minnesota, Wisconsin, Ohio, and New York. Irrigated vegetable production also occurs in the western states of California, Oregon, and Washington. 20.5 SOILS OF MAJOR PRODUCTION REGIONS As previously stated, vegetables are produced commercially in the field or the greenhouse. Field production generally occurs on soils that are well drained, loamy, and high in organic matter. Vegetables have high water content, some containing about 90 percent by weight of water. Regular supply of water is critical to the production of high-quality vegetables. It is important that the soil drain well while maintaining the capacity to retain adequate amounts of water all the time, hence the preference for loam and high organic matter for optimal soil textural properties. However, light sandy soils may be used, if adequate irrigation and fertilization are provided. High organic matter provides high CEC for nutrient retention for high soil fertility. Some soils in production areas in places like New York, Michigan, and Florida have high organic content. Few crops require special production media that has excessive moisture. In fact, crops like Chinese water spinach and watercress are aquatic vegetables. 20.6 GREENHOUSE VEGETABLE PRODUCTION Greenhouse vegetable production is by the method of in-ground culture or hydroponics. Hydroponics is the technology of growing plants by delivering the plant growth nutrients through a liquid medium (see Chapter 13). Sometimes, the plant roots are suspended directly and only in water fortified with fertilizers. However, most producers commonly grow plants in artificial media for physical support, and deliver nutrients by the drip fertigation (i.e., the fertilizer is delivered through the irrigation) system. Because vegetables are eaten fresh, it is critical that they not be contaminated with soil in production. Greenhouse production of vegetables using the 20.6 Greenhouse Vegetable Production 627
hydroponics culture is a very attractive and most desirable method of production of fresh produce. 628 Chapter 20 Growing Vegetables Outdoors 20.7 THE IMPORTANCE OF MULCHES IN VEGETABLE PRODUCTION Mulching is an old practice in crop production used to accomplish several goals, chief among which are to control weeds, to retain soil moisture, reduce soil compaction, add organic matter to the soil (in the case of organic mulches), and keep produce clean from soil contamination. Materials used for mulching may be natural (organic) or artificial, each with its advantages and disadvantages. Organic Mulches Originally, mulches were of plant origin, the most common being straw. Organic mulches are an inexpensive way of achieving the benefits of mulching in addition to the potential to enrich the soil upon decomposition. However, to be effective, organic mulches should decompose slowly. Further, they were also prone to contamination by weed seeds. Plastic Mulches Plastic mulches are widely used in modern commercial vegetable production. Their use in horticultural production began in the 1960s. Plastic mulches modify the microclimate of plants, by modifying the absorbidity and reflectivity of solar radiation. They also reduce the soil water loss via evaporation from the soil. The plastic material is available in several colors, of which three are most widely used. These are black, clear, and white-on-black. In modern production, plastic mulch is often used in a production system called plasticulture. In this system, growers use drip irrigation as the means of watering and fertigation. The system is also used for weed control and some pest control in the soil by way of fumigation. Advantages of plastic mulches include the following: they provide weed control, reduce soil moisture loss and increase water use efficiency, reduce soil compaction, provide a means of soil pest control by solarization or fumigation, and modify soil temperature keeping soil warm in cool weather. Some crops mature early because of modified soil conditions. Further, the produce is clean because of lack of contact with soil. Disadvantages of plastic mulching include the following: producers require special equipment for laying the mulch. The used mulch has to be disposed off because it is not biodegradable. Also, the microirrigation system needed is initially expensive to install. Installation of the Plastic Mulch The first step is to prepare the soil to incorporate organic matter properly and with the proper tilth. Clods, coarse organic matter, and other hard objects like rock interfere with the laying of the plastic. All soil amendments and soil nutrient evaluation should be performed prior to laying down the plastic. Plastic is laid on firm, flat, raised beds for easier installation and improved drainage. Raised beds allow the edges of the plastic to be more securely tucked under the soil and resist dislodging during strong winds. Also, it is important for water not to collect on top of the bed. Plastic laying machines are available. Many of these are multipurpose and are capable of forming the bed, laying the mulch, as well as laying the microirrigation system. It is advantageous to install plastic mulch in the fall season when the nematode population is high, the weather is conducive (not wet), and creates and opportunity for early spring planting.