Botanical and biological features
The white cabbage (Brassica oleracea var. capitata f. alba L.) is a biennial plant. It forms a head during the first year and produces seeds during the second year. Cabbage has a well developed root system which generally extends 40–50 cm deep into the arable layer.
Cabbage is a cold-resistant plant. The seeds begin to germinate at 2–3˚С. The optimum germination temperature is 18–20˚С. Upon transplanting, well-hardened seedlings withstand short periods of frost with temperatures as low as minus 5–6˚С. The optimum growth temperature is 15–18˚С. In autumn, during head formation, the plant growth and development continues at temperatures as low as 5–10˚С.
Cabbage is moderately sensitive to light conditions. But its moisture requirements are very high: at low levels of soil and air humidity, the plants are stunted, form few leaves and small heads. The optimum soil moisture is 75–80% of field moisture capacity.
Cabbage occupies one of the first places among vegetable crops in absorption of nutrients from soil. Its nutrient requirements are not the same at different stages of development. The largest amounts of nutrients are taken up during head formation. It is vital to ensure an optimum proportion of nutrients in the soil. Nitrogen is the nutrient element cabbage requires throughout the growing season. However, excess of nitrogen and inadequate amounts of phosphorus and potassium in the soil results in the formation of loose heads of low quality. Cabbage prefers loam soils with weakly acidic reaction (рН=6).
The best preceding crops are annual legumes, cucurbits, winter cereals, and onion. For early cabbage varieties, light-soil fields which are more readily warmed up in spring are chosen. Healthy, uniform transplants are a prerequisite for an early harvest. These should be 25–45 days old, depending on the growing technique, and have 3–6 well-developed leaves. The planting pattern is 50 х 35 cm for early cabbage varieties, 70 х 35 cm for mid-season varieties and 70 х 45 cm for late varieties. The seeding rate is 50–90 seeds per 10 m2 of open ground. Cassette or potted seedlings become established more readily since no root system injuries occur during transplanting and, consequently, there are no diseased plants.
To obtain high yields (5–7 kg per 1 m2 or 50–70 ton/ha) with early cabbage varieties, fertilizers are applied during the growing season at a rate of N 160, P2O5 80, K2O 160 kg of active substance per hectare. With late cabbage varieties, fertilizers are applied at a rate of N 240, P2О5 120, K2О 240 kg of active substance per hectare. In this case, the yield is 10–12 kg/m2 (100–120 ton/ha). 50% of the total amount of fertilizer is applied during basic soil preparation as nitroammophoska (500 g per 10 m2 with early cabbage varieties and 750 g per 10 m2 with late cabbage varieties), the remainder being given as supplementary fertilizing (ammonium and potassium nitrate) during the growing season. Fertilizer application rates are adjusted according to the nutrient status of the soil.
Systematic irrigation is a crucial factor in the cultivation cycle. No less than 5–8 irrigations should be given to early cabbage varieties and 8–12 irrigations – to late ones. The water application rate is 350–400 l per 10 m2 (350–400 m3/ha) per irrigation prior to the head formation and 400–450 l per 10 m2 (400–450 m3/ha) after the formation. Combining drip irrigation with application of water-soluble fertilizers through the drip irrigation system (fertigation) is a highly efficient technique resulting in a more uniform moisture and fertilizer distribution in the root zone, more efficient water use, less soil compaction, and no soil crust formed. Readily soluble mineral fertilizers are given with each water application.
During the growing season, numerous pests, such as blue fleas, cabbage aphid, cabbage white butterfly and looper, cabbage moth, and thrips attack cabbage. Therefore, chemical control is an essential component of cabbage production technology.Control measures : on discovering the first signs of infestation, sprays with insecticides such as Actara, Zolone, Sumi-alpha, Sherpa, Fastac, Nomolt, etc. should be made systematically in cycles of 7–10 days. Considering the fact that the cabbage leaf has a thick wax coating, it is good practice to admix adhesives (Trend, Silvet, skimmed milk, or household soap in amounts of 30–50 g per 10 l of water) into the spray solution.
The cabbage root fly which is the most harmful insect pest attacking cabbage plants deserves special mention. It starts to fly in mid- or late April when the soil has warmed up to 12–13˚С. The fly lays eggs on the root neck or in the soil around it. The hatching larvae penetrate the roots and gnaw passages in them. As a result, the plants begin to wilt (especially in dry, hot weather), the leaves turn leaden-blue, the growth is retarded or completely arrested and, not infrequently, the affected plants die.Control measures: good cultural practices, strict adherence to the crop sequence, preventive insecticide sprays (at the beginning of flight of moths), prophylactic pre-plant soaking of transplant roots in Actara suspension (1.5 g per 1 l of water per 250 plants) for 90–120 minutes at a temperature of 18–23˚C. Hilling-up of plants is another measure which prevents larvae from reaching the root crown and promotes adventitious root formation.
Among the diseases attacking brassicas, the most harmful are Back rot, Soft rot and Fusarium wilt. Control measures: use of resistant varieties, seed treatment, strict adherence to the crop sequence and good cultural practices. In recent years, both cabbage transplants and adult plants have been attacked by downy mildew. To prevent outbreaks of this disease, it is desirable to carry out preventive treatment of plants with chemicals controlling downy mildew.