Cabbage (Brassica oleracea var. capitata) originates from the south and western coast of Europe. Annual world production is about 55 million tons of fresh heads from 2.6 million ha (FAOSTAT, 2001).
For high production the crop requires a cool, humid climate. The length of the total growing period varies between 90 (spring-sown) and 200 (autumn-sown) days, depending on climate, variety and planting date, but for good production the growing period is about 120 to 140 days. Most varieties can withstand a short period of frost of -6°C, some down to -l0°C. Long periods (30 to 60 days) of -5°C are harmful. The plants with leaves smaller than 3 cm will survive long periods of low temperature but when the leaves are 5 to 7 cm, the plant will initiate a seed stalk and this leads to a poor quality yield. Optimum growth occurs at a mean daily temperature of about 17°C with daily mean maximum of 24°C and minimum of 10°C. Mean relative humidity should be in the range of 60 to 90 percent.
Generally, the heavier loam soils are more suited to cabbage production. Under high rainfall conditions, sandy or sandy loam soils are preferable because of improved drainage. The fertilizer requirements are high: 100 to 150 kg/ha N, 50 to 65 kg/ha P and 100 to 130 kg/ha K.
Cabbage is moderately sensitive to soil salinity. Yield decrease due to soil salinity at different levels of ECe is: 0% at ECe 1.8, 10% at 2.8, 25% at 4.4, 50% at 7.0 and 100% at ECe 12.0 mmhos/cm.
Row spacing is dependent on the size of heads required for markets or between 0.3 and 0.5 m for heads of 1 to 1.5 kg each and 0.5 and 0.9 m for heads up to 3 kg each. An optimum production can be reached with a plant density in the range of 30000 to 40000 plants/ha. Planting can be by direct seeding with a seed rate of 3 kg/ha, or by transplanting from open field beds and from cold frames which are used to protect the crop from cold during germination and early plant development.
Cabbage is characterized by slow development during the first half of the growing period, which may be 50 days for early maturing and up to 100 for autumn-sown, late maturing varieties (establishment and vegetative periods; 0 and 1). During the following periods (yield formation and ripening periods, 3 and 4) the plant doubles its weight approximately every 9 days over a total period of 50 days. In the beginning of the yield formation period (3), head formation starts, followed by a sudden decrease in the rate of leaf-unfolding. Eventually, leaf unfolding ceases completely, whilst leaf initiation continues. This results in the formation of a restrictive skin by the oldest folded leaves within which younger leaves continue to grow until the firm, mature head is produced during the ripening period of 10 to 20 days (4). Depending on variety, the head can be pointed or round, green or red, smooth or crinkled. Crop rotation of at least 3 years is recommended to combat soil-borne diseases.
The graph below depicts the crop stages of cabbage, and the table summarises the main crop coefficients used for water management.