Root and tuber crops

ROOT AND TUBER CROPSCOCOYAM (Xanthosoma saggittifolium) CASSAVA (Manihot esculenta)Identify the items

petiolecormcormelCocoyam's (Colocasia and Xanthosoma spp.) are stem tubers that are widely cultivated in both the tropical and subtropical regions of the world. the two species mostly grown in West Africa are Colocasia esculenta and Xanthosoma sagittifoliumCocoyam's can be processed into several industrial inputs, food and feed products, similar to products from potatoes in the Western world. The processing of the crops include boiling, roasting, frying in oil, pasting, milling and conversion into fufu, soup thickeners, flour for baking, chips, beverage powder, porridge, and special food for gastro-intestinal disorders usesCocoyam leaves are used in many homes as a leafy vegetable (pot herb) and can also be fed to poultry as greens It is also reported to be one of the most promising forages because of its re-growth capacity, high yield and palatability. leaves could be fed to growing pigs, while the petioles are considered to be more appropriate for feeding to pregnant sows, which need lower levels of protein in the diet and are able to tolerate bulky feeds as wellusesThe Neat Food Company, uses cocoyam to make fufu flour Akwaba Food Company which exports chopped cocoyam leaves and chips to EuropeNutritional valueThe young leaves and petioles which are occasionally used for food contain about 23% protein on a dry weight basis. They are also rich a source of calcium, phosphorus, iron, Vitamin C, thiamine, riboflavin and niacin, all of which are important constituents of the human ImportanceIn Ghana the crop is grown on a small scale and usually as an intercrop together with cocoa, plantains, oil palm and cassava.

Evidence exists that although cocoyam is cultivated on a small scale, it has been able to contribute significantly to the national food baskets. They also serve as a source of income for many families adaptationXanthosoma Sagittifolium is a tropical rain forest plant and requires an annual rainfall of about 1800mm per annum. It prefers a well drained soil with pH 5.5 6.5 (Owueme, 1991). Although in their natural habitat they grow under the forest canopythey can be cultivated in areas with full exposure to sunlight (Owueme, 1991). Most tuber crops including cocoyam grow and yield well in soils that are ploughed to a depth of about 20-40cm especially on clay soils. Cultivation of the cropPlanting materialsThe major planting material for cocoyam is the main stem (corm), although cormels can also be used. Selected corms are cut into pieces of about 100 to 200 grams with each piece having at least a bud (Karikari,1971). For rapid field multiplication, fresh, healthy cocoyam corms and cormels are cut into pieces of about 5 to 10 grams (microsetts

treated with (fungicide) and nursed in black polybags containing steam-sterilized 2:1 top soil: sand potting mixture Plantlets developed by the rapid field technique are kept under shade for about three months before they are planted out in their permanent fields. Planting materials raised from microsetts during the dry season and planted at the onset of the rains yield about twice more than plants grown from 100-200g cut corms at the beginning of the rainy season (Osei, 2003).Fertilizer applicationWhen cocoyam's are grown in high moisture regimes, fertilizers applied to them are subjected to leaching and should therefore be applied in split doses. The first application is done at planting whiles the second application is done three or four months after planting (Owueme and Sinha, 1991).

Fertilizer applicationMost farmers in tropical Africa cultivate cocoyam without applying any chemical fertilizers. They rely mostly on the native fertility of the soil, which is very high when virgin forest is used to establish cocoyam. They may sometimes place compost or farmyard manure in the planting holes before plantingHarvesting and storageCocoyam is ready for harvesting after 9-11 months after planting. Maturity indicator for cocoyam is yellowing of the leaves. For. X saggitifolium, multiple harvesting is done thus only the cormels are removed at each harvest while the corm is left to produce new generations of cormels, which will be harvested latter. Harvesting is usually by hand or hand tools. Alternatively the crop may be ploughed out after which the corm and cormels are picked manually.

Harvesting and storageCocoyam can be stored for up to four months when kept under 7oC at a relative humidity of 85% (Owueme and Sinha, 1991). Storage under high temperatures increases respiration, rotting and sprouting, shortening storage life of cocoyam's. Too low temperatures also cause corm decay (Owueme and Sinha, 1991). Traditional storage methods include storage in underground pits or on open platforms. Some farmers also leave the crop in the field and harvest it as neededprocessingCocoyam chipsCocoyam flourFufuChopped leaves dried petioles for silageCassava grater

Cassava (Manihot spp.)

CASSAVA(Manihot esculenta )

VarietiesVarietiesThe following varieties are recommended for their high yield and processing quality:ABASA FITAABOSOME INSIA TMS 30572, NR 8082, NR8083, TMS 4(2) 1425, TMS 81/00110, TMS 92/0326. ECT

VarietiesBankehema, Akabon, suitable for fufu, gari and cassava dough and starch Esam Bankye also good gari, agblema and starch.BOTANYEcology

Cassava is a tropical root crop, requiring at least 8 months of warm weather to produce a crop. It is traditionally grown in a savanna climate, but can be grown in extremes of rainfall. In moist areas it does not tolerate flooding. In droughty areas it looses its leaves to conserve moisture, producing new leaves when rains resumeEcology.It takes 18 or more months to produce a crop under adverse conditions such as cool or dry weather.

Cassava does not tolerate freezing conditions.

It tolerates a wide range of soil pH 4.0 to 8.0 and is most productive in full sun.Production Practices

Cassava is planted using 7-30 cm portions of the mature stem as propagules. The selection of healthy, disease-free and pest-free propagules is essential. The stem cuttings are sometimes referred to as 'stakes'. In areas where freezing temperatures are possible. Production PracticesThe cuttings are planted by hand in moist, prepared soil, burying the lower half.

When soils are too shallow to plant the cutting in an upright or slanted position,

the cutting are laid flat and covered with 2-3 cm soilMechanical planters have been developed in Brazil to reduce labor inputs.

Typical plant spacing is 1m by 1m. Cuttings produce roots within a few days and new shoots soon appear at old leaf petiole axes on the stem. Botanical seeds are used only for breeding purposes.

Early growth is relatively slow, thus weeds must be controlled during the first few months.

Although cassava can produce a crop with minimal inputs, optimal yields are recorded from fields with average soil fertility levels for food crop production and regular moisture availability.fertilizationResponses to macro-nutrients vary, with cassava responding most to P and K fertilization.

High N fertilization, more than 100 kg of actual N/ha may result in excessive foliage production at the expense of storage root development and a low harvest index.

Fertilizer is only applied during the first few months of growth.Crop maturityPlants are ready for harvest as soon as there are storage roots large enough to meet the requirements of the consumer. Under the most favorable conditions, yields of fresh roots can reach 90 t/ha while average world yields from mostly subsistence agricultural systems are 9.8 t/ha. Crop maturityTypically harvesting can begin as soon as eight months after planting.

In the tropics, plants can remain unharvested for more than one growing season, allowing the storage roots to enlarge further.

However, as the roots age, the central portion becomes woody and inedibleHarvesting

Most cassava is harvested by hand, lifting the lower part of stem and pulling the roots out of the ground, then removing them from the base of the plant by hand.

The upper parts of the stems with the leaves are removed before harvest.

Levers and ropes can be used to assist harvesting. A mechanical harvester has been developed in Brazil. It grabs onto the stem and lifts the roots from the ground.

Harvesting

Care must be taken during the harvesting process to minimize damage to the roots, as this greatly reduces shelf life.

During the harvesting process, the cuttings for the next crop are selected. These must be kept in a protected location to prevent desiccation.Processing

Toxicities

Cassava is famous for the presence of free and bound cyanogenic glucosides, linamarin and lotaustralin.

They are converted to HCN in the presence of linamarase, a naturally occurring enzyme in cassava. Linamarase acts on the glucosides when the cells are ruptured. All plant parts contain cyanogenic glucosides with the leaves having the highest concentrations. ToxicitiesIn the roots, the peel has a higher concentration than the interior. In the past, cassava was categorized as either sweet or bitter, signifying the absence or presence of toxic levels of cyanogenic glucosides.

Sweet cultivars can produce as little as 20 mg of HCN per kg of fresh roots, while bitter ones may produce more than 50 times as muchDISEASESThe diseases are;Cassava mosaicBacterial blight (Xanthomonas axonopodis)Tuber rot (Fusarium oxysporum) Brown leaf spot (Cercosporidium henningsii)Bacterial stem rot (Erwinia carotovora )AnthrancnoseArmillaria root rot(shoestring root rot0Black root and stem rot (scytalidium spp.)Blight Leaf spot(cercospora vicosae)Brown leaf spot(cercosporidium henningsii)

PESTThe major pests are;Cassava mealybug (Phenacoccus manihoti)Cassava green spider mite complex(Mononychellus tanajoa)Variegated grasshoppers(zonocerus variegatus)White flies(Bemissia tabaci)