INTRODUCTION

Onions are one of the oldest vegetables in continuous cultivation dating back to at least 4,000 BCE. The ancient Egyptians are known to have cultivated this crop along the Nile River. There are no known wild ancestors, however, the center of origin is believed to be Afghanistan and the surrounding region. Onions are among the most widely adapted vegetable crops. They can be grown from the tropics to subarctic regions. This adaptation is primarily due to differing response to day length. Unlike most other species, day length influences bulbing in onions as opposed to flowering. Onions are grouped into three groups based on their response to hours of daylength. The short-day varieties bulb with daylengths of 10-13 hours, intermediate varieties bulb with day lengths of 13-14 hours and are found in the mid-temperate regions of this country. Finally, long-day onions are adapted to the most northern climes of the United States as well as Canada and bulb with daylengths greater than 14 hours.

Bạn đang xem: Onion production

Onions were first brought to this country by early European settlers. These onions were adapted to the temperate climate found throughout the Northeast where the first European settlements occurred. Varieties from warmer regions of the Mediterranean eventually made their way to the Southeastern United States. In particular, varieties from Spain and Italy would become important to the Vidalia onion industry. The first of these varieties came through Bermuda and were thus referred to as Bermuda onions.

Yellow Granex, the standard for Vidalia onions, has its origin from Early Grano. The variety Early Grano 502 resulted in the Texas Early Grano 951C, which became one of the parents for Yellow Granex hybrid. The other parent was YB986, which was selected from Excel, which in turn was derived from White Bermuda. The Granex name is a combination of Grano and Excel, the original parents.

The Vidalia onion industry began in 1931 when a grower by the name of Mose Coleman grew the first short-day onions in Toombs County. These mild onions were immediately popular with customers. At the beginning of the depression, these onions sold for $3.50 a 50 lb. bag, a considerable amount of money at the time. Soon other growers became interested in these mild onions. The industry grew slowly and steadily for several decades.

Its growth was fueled by the fact that the city of Vidalia sat at the intersection of important roads prior to construction of the interstate highway system. In addition, the supermarket chain Piggly Wiggly maintained a distribution center in Vidalia and would buy the onions and distribute them through their stores. Slowly the industry began to gain a national reputation.

In order to help promote the onions further, onion festivals were started in both Vidalia and Glennville in the mid 1970’s. At this time, approximately 600 acres of onions were produced. Growth continued during the next decade. In 1986, the State of Georgia gave Vidalia onions official recognition and defined the geographic area where these onions could be grown. There had been some problems with onions being brought in from other areas and bagged as Vidalia onions. State recognition however did not give the industry the national protection it needed. Finally, in 1989, the industry was able to obtain Federal Market Order 955, which gave the industry national protection. The Vidalia Onion Committee was formed to oversee the Federal market order. Growers are required to register and give check-off funds to support the industry. Growers should check the Georgia Department of Agriculture website or call the Department for information about growing Vidalia onions. Growers are required to be within the defined growing regions, use specific approved varieties, and register with the state of Georgia. The Georgia Department of Agriculture website can be accessed at: http://www.agr. georgia.gov/vidalia-onion.aspx.

The collected money is used for national and international promotional campaigns as well as for research on onion production.

In 1989, the industry began to adopt controlled atmosphere (CA) storage. CA uses a low oxygen, high carbon dioxide refrigerated environment to store onions. This has allowed the industry to expand their marketing opportunities well into the fall months. The adoption of the Federal market order and CA storage has allowed this industry to grow to its current level of approximately 12,000 acres.

TRANSPLANT PRODUCTION AND DIRECT SEEDING

Short-day onions can be grown from both seed and transplants; however, the majority of onions are grown from transplants.

Transplant production begins in late summer with land preparation followed by seed sowing in September. Land for transplant production should not have been in onions or related Alliums for at least three (3) years. Thisis not always possible with fixed center-pivot systems. Sites with a history of onion diseases and severe weed problems should be avoided, however.

Once a site has been selected, a soil test should be taken to determine the optimum level of fertility and soil pH. The University of Georgia has specific recommendations for plant bed onions. Therefore, when submitting a soil sample to the University of Georgia’s Soil Test Laboratory, make sure to indicate that they are for transplant or plant bed onion production. The site should be deep turned to bury any residue from the previous crop. Several different seeders are available for transplanting. These should be set to sow 60-70 seed per linear foot. As an example, using a Plant-It Jr. four-hopper transplanter, set the plates to No. 24. This should give the needed seeding rate for plant beds. Vacuum seeders are also a good choice and can accurately deliver seed in the amounts and to the depth required. Other seeders can be used as long as they are capable of sowing 60-70 seed per linear foot and can consistently plant the seed at the proper depth (1/4-1/2 inches).

The plant bed soil should have a pH range of 6.0-6.5 for optimum growth. Soils in Georgia are generally acidic, therefore, if your soil pH is low, applications of lime are recommended. Dolomitic lime is preferred over calcitic lime because it supplies both calcium and magnesium while adjusting the pH. Changing soil pH is a relatively slow process, therefore if low pH is suspected early soil testing and lime application is advantageous to insure the soil pH is corrected in sufficient time for planting. Soil pH can take several months to change with lime applications.

Nitrogen recommendations on Coastal Plain soils range from 100 to 130 pounds of nitrogen per acre. On Piedmont, Mountain, and Limestone Valley soils apply 90 to 120 pounds per acre. Table 1 indicates the phosphorus and potassium recommendations based on soil residual phosphorus and potassium levels.

In addition, boron should be applied at one (1) pound per acre. If zinc results are low, five (5) pounds per acre of zinc should be applied. Sulfur is critical for proper onion production. This is particularly true on the Coastal Plain soils of South Georgia that are very low in sulfur. Sulfur at a rate of 20-40 pounds per acre will be required to produce quality onion transplants on these sandy loam soils.

It is critically important that seedbeds be irrigated regularly to develop a good plant stand. A tenth of an inch of water applied several times a day may be needed to insure consistent soil moisture. See section on irrigation.

Plants are ready for harvest in about eight to ten weeks. Good quality transplants will be about the diameter of a pencil when ready. Transplants are pulled and bundled in groups of 50-80 plants and tied with a rubber band.

Approximately one half of the tops are cut from the transplants, usually with a machete. Harvested transplants are transported to the field in polyethylene net or burlap bags. Onion transplants can experience a ‘heat’ in these bags, which greatly reduces transplant survival. Care should be taken with transplants so they are not stored for excessively long periods of time in these bags, nor should they be left in the sun for too long. Planning is critical, harvest only enough plants that can be reasonably transplanted that day. Overnight storage in these bags should be avoided whenever possible, but if necessary they should be removed from the field to a cool dry location.

Alternatively, onions can be directly sown in the soil for production. This eliminates all of the fertilizer and other management requirements of transplant production. Timing and seedbed preparation are critical for successfully growing onions from direct seeding.

For direct seeding, onion seed should be sown on October 15th plus or minus one week. This is later than sowing for transplant production, but is required to avoid undue seed-stem formation (flowering) in the spring. Thesoil should be prepared so that it is free of clods and plant residue. The soil surface should be smooth with the proper amount of soil moisture. Soil that is too wet will clog the sowing equipment. Soil that is too dry may result in the seeder riding up on the soil and not sowing the seed at the proper depth. Seed should be sown with a precision seeder such as a vacuum planter set to sow seed at 4-6 inches in-row at a depth of 1⁄4 - 1⁄2 inches deep. The plant stand will be similar to transplanted onions with four rows on a slightly raised bed with 12-14 inches between the rows. Direct sowing can save a tremendous amount on costs and labor; however, care must be exercised to correctly sow the seed since you will only have one chance to get it right.

Table 1. Recommendations for phosphorus and potassium based on soil test analysis for plant bed onion production.

Xem thêm: Bố Cao 1M68 Con Gái Quyền Linh Cao Bao Nhiêu ? Hé Lộ Sự Thật Quyền Linh Cao Bao Nhiêu

*

VARIETY SELECTION AND CHARACTERISTICS

As mentioned earlier, the type of onion grown in South Georgia is a short-day onion that bulbs during the short days of winter (>11 hours daylength). Although limited research has been done in this area, it may be possible to grow intermediate-day onions in North Georgia; however, they would not be as mild as the south Georgia Vidalia onions.