The Agronomic gist of cabbage
Cabbage is a leafy green (or purple for some varieties) biennial vegetable plat that is grown as an annual crop for its dense leaved heads. It is closely related to broccoli, Brussels sprouts, cauliflower and lettuce. Cabbage heads range from 0.5 to 4 kg and they can be green, purple or white. Cabbage belongs to the brassica genus and oleracae species. Smooth leafed green cabbages are the most common ones. Cabbages are known to be cool season crops that best suit a maritime climate with mild temperatures. Cabbages can grow at temperatures above 7oc. However, they grow best between temperatures of 15o c to 18oc. As temperatures increase, cabbages are prone to tip burn and at or beyond 27oc, they may bolt. But they have moderately high frost tolerance. For optimum growth, cabbage plants need constant water supply, sunshine and good soil aeration. Except for most temperate areas, light soils in which cabbage plants are cultivated must be irrigated in order to avoid poor development of the outer leaves and small heads. It is essential to avoid irrigating plants after drought because the sudden water supply will lead to splitting of cabbage heads due to rapid growth.
Cabbage seedlings have a thin taproot and a chordate cotyledon. It is usually noticed that the first leaves produced are ovate and with a lobed petiole (leaf stalk). While the colour spectrum of cabbage includes a range of greens and purples, it also has oblate, round and pointed shapes. Cabbage is selectively bred with keen interest to its shape, firmness, size, colour and other physical characteristics for head weight and morphological characteristics, frost hardiness, fast growth and storage ability. B. oleracae is mainly bred selectively to increase its resistance to insects, diseases and also to improve its nutritional content (Ernst, 2005). Scientific research has brought about the genetic modification of cabbages in order to achieve desired characteristics in bred cabbages. However, this is entail the biological alteration of the genetic content of the cabbages and as a result, not all agronomists agree with the idea of genetic modification of foods. United States and Europe are deeply involved in utilizing the genetic “modification” idea. Genetically modified cabbages are not known to be commercially available.
During the first year of the biennial cycle of cabbages, its densely leafed head is produced, which serves a great percentage of its culinary purpose. Different varieties have different preferences with re0spect to sunlight, soil type, oxygen and moisture. However, they all require fertile soils with high cation exchange capacity and pH of 6-7 and water requirements may vary from 380-500 mm per crop, depending on the climate (Department of Agriculture, 2008). Sufficient Nitrogen in soil is needed during early stages of growth and adequate amounts of Phosphorus and Potassium during early stages of expansion of the outer leaves. Temperatures for optimum growth can also be between 4oc-240c (International, 2016). But extended periods of low or high temperatures will result into premature flowering. Vernalization is induced when the plant is grown past its juvenile stage. This however does not occur in all areas. In most areas such as that of some parts of West Africa, vernalization does not occur. It is usually observed that the plant transits to adult stage from its juvenile stage when the stem is of 6mm (diameter). Generally, plants are started in protected locations for nesting before being transplanted on to the field. In most cases, seedlings are propagated till cabbage is due to be harvested. Seedlings usually emerge between 4-6 days when planted at a depth of about 1.3 cm in soil with temperature between 20-30oc. Most growers usually ensuring 30 to 61 cm spacing and we at Podiumfolks International think it is vital since closer spacing has proven to reduce the amount of available nutrients to plants and also increases the time for maturity. Some varieties only flower and so not produce heads. These varieties are therefore used for ornamental purposes. Early varieties take about 70 days to maturity while late varieties take about 120 days. When cabbages are firm and solid to touch, then they are mature. They are harvested by cutting the stalk from the bottom leaves with a blade or knife. The outer leaves are then trimmed and diseases, damaged and necrotic leaves are removed. Delay in harvest will result in splitting of cabbage head since the inner leaves would have fully developed. Growth in compacted soils as a result of “no tilling” farm practices, drought, waterlogging, disease incidence, insect infestation and nutrient suppression by weeds are factors that can lead to reduced size and weight of cabbage heads.
The incidence of pests and diseases cannot be overlooked just like with other agronomic crops. Fungal diseases include wire stem, which causes weak or dying transplants. Fasarium yellows results in stunted and twisted plants with yellow leaves, blackleg leads to sunken areas on stems and gray-brown spotted leaves. Bacterial diseases such as black rot (caused by xanthomonas campestris), results into chlorotic and necrotic lesion that starts at the leaf margins and wilting of plants. Club root is also a bacterial disease caused by soil borne slime mould (by plasmodiophora brassica), which results in swollen club-like roots. Parasitic diseases such as Downy mildew which is caused by an oomycete. Sometimes this disease is mistaken to be powdery mildew (which is caused by fungal disease). Pests are nit left out of the cabbage cycle. Root-knot nematodes and cabbage maggots which produce stunted and wilted plants with yellow leaves. Aphids also induce stunted plants with curled and yellow leaves, harlequin bugs also cause white and yellow leaves; Thrips which also lead to leaves with white bronze spots; stiped flea beetles, which riddle leaves with small holes and caterpillars which also leave behind large holes in leaves. The large white butterfly and diamond black moth are also well known pests that destroy cabbage plants. These insects can be effectively controlled with insecticides. Others may decide to go organic by using extracts from neem plant since azadirachtin in neem plants cause paralysis and eventually kill pests.
According to the Food and Agriculture Organization of UN, China is the leading producer of cabbage with productions of over 32,800,000 tonnes. For best nutritional value, cabbages are stored in temperatures ranging 1-2oc at 90-100 % humidity. When these conditions are met, they can last up to 6 months.
Cabbage is usually used for salad as a culinary way of utilizing it. It has a lot of nutritional values also. Researchers have identified 20 different flavonoids and 15 phenols in cabbage which all demonstrate antioxidant activities. These nutrients will help in reducing cardiovascular diseases when consumed. The presence anthocyanin in red-purple cabbages has upon research been found to provide cardiovascular protection and improved red blood cells. It reduces Low density lipoproteins in humans also. Cabbage’s one sulphur containing glucosinolates, sirigin is converted to ally-isothiocyanate which helps in the prevention of cancer. Consumption of cabbage also reduces risk of type 2 diabetes.
Even though cabbage has a lot of advantages with respect to its culinary use, it also has some disadvantages as well. When consumed in excessively large quantities, intestinal gas is increased, leading to bloating of the stomach and flatulence since trisaccharide raffinose will be produced (which the small intestine cannot digest). Also, cabbage can bring about outbreak of food-borne diseases when contaminated water is used in growing it. Cabbage contains small amounts of thyiocyanate, a compound associated with goiter when iodine is deficient.
Cabbage as vegetable plant is highly cultivated around the world. You can visit some cabbage farms around you to get a more practical experience. In place of consuming cabbage, other vegetables belonging to the brassica genus can be consumed since they have similar growth requirements and nutritional benefits.
Written by Alhassan Moses Joshua,
The Programs Coordinator,
Department of Agriculture, F. a. (2008). Production Guidelines for Cabbage. Pretoria: Directorate Agricultural Information Services.
Ernst, C. K. (2005). Cabbage. Kentucky: Corporate Extension Services.
Wolfersberger, M. (1987). Comparative Biochemistry andPhysiology. Philadelphia: Elsevier Inc.