POST HARVEST MANAGEMENT STRATEGIES AMONG YAM FARMERS IN AKWA IBOM NORTH WEST SENATORIAL DISTRICT FOR INCREASED PRODUCTIVITY
1.1 Background of the Study
Yam production has been and is still one of the most lucrative and highly practiced aspects of crop production in Akwa Ibom State, especially in Akwa Ibom North West Senatorial District due to its general acceptance and consumption. Yam (Dioscorea species of the family Dioscureaceae) is multi-specie polyploidy. It is clonally propagated crop that is cultivated for its starchy tubers. It is important for food, income, socio-cultural events (example: New Yam Festivals) and industrial use (starch making). It is a dioecious plant with leaves which are small, net veined and devoid of hair with opposite or alternate leaf arrangement on the stem with Dioscorea rotundata, Dioscoreaalata, Dioscoreacayensis,Dioscoreadumentorum, Dioscorea esculenta and Dioscoreabulbifera being the major edible species with different origins.
Nsa, Agba and Anangbor (2014), stated that yam is propagated vegetatively by tuber fragments (setts, mini-setts, and seed yams) of 200-600g taken from near the collar of the main stream at the upper (proximal) part of the mature tubers where several eyes are located but growth of the tuber fragments varies with their sizes. Yam stem is thin and twinning structure, with or without spines. The direction of the stem twinning around a support depends on the yam specie; thus, most twine anti-clockwise but Dioscorea dumentorum, Dioscorea esculenta and Dioscorea bulbifera twine clockwise. Yam stem is more or less circular in a cross section and has a fibrous root system confined mostly to the top soil (i.e. 30cm). Mainly grown in the tropics, it thrives best at temperatures of 25-300 C with a well distributed rainfall of about 1,500mm per annum with a dry season of 2-5 months.
Osunde (2013) stated that the causes of storage losses of yam tubers include sprouting, transpiration, respiration, rot due to mould and bacteriosis, and attack by insects, nematodes and mammals. Sprouting, transpiration and respiration are physiological activities which depend on the storage environment (mainly temperature and relative humidity). These physiological changes affect the internal composition of the tuber and result in destruction of edible material and changes in nutritional quality. Storage losses in yam of the order of 10-15% after the first three months and approaching 50% after six months storage have been reported. A number of treatments and techniques have been developed to reduce these physiological activities and also to protect the tuber from post-harvest diseases which could lead to losses of tubers. These include treatment with chemicals, plant extracts, palm wine and gamma irradiation; storage techniques used include cold storage, improved underground storage and improved yam barns and others.
In view of these highlighted problems faced by yam farmers in the course of production, there exist a multiplicity of strategies which were and are still in use today all in a bid to arrest the situation of losses of tubers after harvest to the lowest thresh-hold, provide / project to yam farmers an array of suitable, affordable and practicable management strategies suitable for yam tubers. Such include handling, transport and packaging, curing of yam tuber and storage.
Handling, according to Atanda, Pessu, Agoda, Isong and Ikotun (2011) should be carefully done since mechanical injury provides sites for pest attack and increases physiological losses. Therefore, mechanical injury to the crop should be avoided while handling. Because of their soft texture, all agricultural products should be handled gently to minimize bruising and breaking of the skin. Bruising renders the product unsalable to most people although it usually has minor effect upon the nutritional value. The skin of agricultural products is an effective barrier to most of the opportunistic bacteria and fungi that cause rotting of the tissues.
However, transporting and packaging is another sure way of reducing post harvest losses. McGregor (2010) stated that after harvest, yam tubers are traditionally placed into woven baskets made from parts of the palm tree or coconut fronds. These are ideal for transporting small quantity of tubers over short walking distances. The basket is carried on the head, shoulder, or tied to a bicycle and transported to the market or storage facility. Compression damage is reduced since the basket is able to bend and thereby reduce the amount of force acting on individual tubers. However, when large quantities of tuber are harvested, these baskets are not suitable because of their limited size. Packaging tubers in full telescopic fireboard cartons with paper wrapping or excelsior reduces bruising and enables large quantity of tuber to be transported over long distances.
Furthermore, curing of root crops according Coursey to (2005) allows suberisation of surface injuries and reduces subsequent weight loss and rotting in root crops. Curing of yams is recommended before storage so as to “heal” any physical injury, which may have occurred during harvesting and handling. This can be accomplished under tropical ambient conditions or in a controlled environment. Traditionally, yams are cured by dying the tubers in the sun for a few days.
Osunde (2013) maintained that in the humid forest zone yam is stored in a yam barn which is the principal traditional yam storage structure in the major producing areas. Barns in the humid forest zone are usually located under the shade and constructed so as to facilitate adequate ventilation while protecting tubers from flooding, direct sunlight and insect attack. There are several designs, but they all consist of a vertical wooden framework to which the tubers are individually attached. Tubers are tied to a rope and hung on horizontal poles 1-2 m high; barns up to 4 m high are not uncommon. Depending on the quantity of tuber to be stored, frames can be 2 m or more in length. The ropes are usually fibrous; in south-eastern Nigeria they are made from the raffia obtained from the top part of the palm wine tree. Many farmers have permanent barns that need annual maintenance during the year’s harvest. In these situations, the vertical posts are often made from growing trees which are trimmed periodically. Palm fronds and other materials are used to provide shade. The vegetative growth on the vertical trees also shades the tubers from excessive solar heat and rain. The yams are heaped at different positions in the barn. Such barns are constructed every year and are situated near the house under a tree to protect the tuber from excessive heat. At the end of the storage period the barn is burnt down and in December/January a new structure is built for the next harvest.
POST-HARVEST MANAGEMENT STRATEGIES AMONG YAM FARMERS IN AKWA IBOM NORTH WEST SENATORIAL DISTRICT FOR INCREASED PRODUCTIVITY