ABSTRACT                                                                          

Two field experiments were conducted in 2008 and 2009 cropping seasons at the linkage farm of the University of Nigeria, Nsukka to evaluate growth and yield response of (Taro) Colocasia esculenta  to plant spacing and NPK fertilizer on the plains of Nsukka with the objectives of identifying best performing cultivar, optimum plant spacing and NPK fertilizer rate. Experiment one was laid out  in a 3x5 factorial in Randomized Complete Block Design (RCBD) in which Factor A is plant spacing comprising 0.3m x 1.0m, 0.4m x 1.0m and 0.5m x 1.0m levels while Factor B is taro cultivars consisting of Nkpong, Odogolo, Nworoko, ugwuta and Nachi. Experiment two was laid out in a 5x6 factorial in RCBD in which Factor A is taro cultivars as mentioned above and Factor B NPK fertilizer with 6 levels among which are : Okg/ha, 100kg/ha, 150kg/ha, 200kg/ha, 250kg/ha, and 300kg/ha with three replications in each of the two experiments. F-LSD was applied to detect significant differences at 5% probability level. The result showed that the mean rainfall for 2009 planting season was higher than that of 2008. The soil was texturally clayey and moderately acidic with a PH of 5.0 .Cultivar diferences in cormel and corm yield were not significant, however Nworoko produced the highest yield of 11.0 t/ha among the cultivars. Plant spacing produced significant effect (P=0.05) in the tuber yield in both 2008 and 2009. Planting at 0.3m x 1.0m significantly gave the highest tuber yield/ha among the three plant spacing. NPK fertilizer showed significant effect (P=0.05) on the measured traits with 200kg/ha and 150kg/ha producing the highest yield of 43.0 t/ha and 3.0 t/ha respectively, in both 2008 and 2009.

INTRODUCTION

            Cocoyam is a monocotyledonous crop that has (the character of being) an underground stem. It differs from yam as it is not a tuber but a corm. Eatable cocoyam belongs to the family of plants called Araceae or Aroids with two genera- taro (Colocasia) and Tania (Xanthosoma) (Uguru, 1996).

            Colocasia esculenta is believed to have originated in South-East Asia while Xanthosoma   sagittifolium  is indigenous to tropical America and the West Indies (Uguru, 1996).  The mode of attachment of the long petiole to the large lamina forms the main difference between these two species of cocoyam. The petiole in Colocasia esculenta attaches the lamina at some point about the middle of the lamina whereas in Xanthosoma, the petiole is attached to the edge of the lamina at a deep indentation that tends to partition the base of the lamina into two lobes (Okpul  et al., 2002).

            Cocoyam is one of the four most important staple foods in Nigeria, ranking third after yam and cassava, the fourth being sweet potato (Knipscheer and Wilson, 1980). Normally, cocoyam is grown for the corms and cormels, although the leaves, petioles and flowers are also eaten as vegetables in soup during the vegetable-lean periods. Alternatively the leaves can be fed to cattle and pigs as browse or used for wrapping processed food like “akpu” and sliced cooked oil bean seed (Ezedinma, 1987); paste called “foo-foo” or “akpu. Cocoyam leaves are equally used for wrapping and preserving of colanuts, bitter cola, etc. Cocoyams are of great importance as they are subsistence staple food for the aged (Okwuowulu, 2000). Plucknett (1970) also stated that cocoyam is food for the children with allergy and for persons with intestinal disorder. It has high content  of pentosans and digestible crude proteins when compared with other root crops (Oyenuga, 1968) and is a source of pharmaceutical and industrial alcohols (Villanueva, 1986). Parkinson (1981) stated that cocoyams contain significant quantities of amino acids. Ohiri et al (1996) stated that only 24% of the croppable land for cocoyams in Nigeria is under cultivation. Taro (colocasia esculenta) is the fourteenth most consumed vegetable worldwide and comprises the diet of 300 million people (Brown, 1998). About a million metric tonnes of taro is produced globally from an estimated area of 2 million ha. (FAO, 2006).

            Taro is a staple food for many people in developing countries in Africa, Asia and the Pacific (Agueguia et al., 1992). It is produced mainly in Africa (especially in Nigeria) and Asia (mainly China), but it is most important per capita in oceanic (Howeler et al., 1993; Onwueme, 1999). The cultivated species of taro may be distinguished into two main groups; the “eddoes” and the “dasheen” types (Ki-zerbo,1990; Onwueme, 1994; Valerior, 1988; IPGRI, 1999). The eddoes types have cormels that may be 5-20 in number and become as big as the mother corm. The cormels are usually absent in the dasheen types and it is the mother corm which is the main storage organ (IPGRI, 1999). The corm and cormel which are the major economic part have a nutritional value comparable to potato (Wang, 1983), while the young leaves and petioles which are occasionally used for food contain about 23% protein on a dry weight basis. It is also rich source of calcium, phosphorus, iron, vitamin C, thiamine, riboflavin and niacin, which are important constituents of human diet (Onwueme, 1999; Ndon et al., 2003). Where grown in Uganda, Taro corms have a high economic value in urban markets. Its production provides employment to many people and the crop maintains ground cover in the fields (Talwana et al., 2009)

            In spite of the advances made in cocoyam research, several factors remain as challenges to sustained cocoyam production in Nigeria. The ignorance of the nutritive value and diversities of food forms from cocoyam by a large percentage of the populace is a major limiting factor to general acceptability and extensive production of the crop. The notion that cocoyam is a poor man’s crop is still prevalent and needs to be dispelled through the extension of proper information about the crop.

            Colocasia esculenta (L.) Schott has not been researched upon in respect to plant spacing and NPK fertilizer rates in the ecological zone of Nsukka. In view of the above reason, this study was undertaken with the following objectives:

i To identify best performing cultivar of Colocasia esculenta

ii To determine optimum plant spacing

iii To determine optimum NPK fertilizer rate.

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