Nigeria is a country endowed with enormous food and agricultural resources such as yam, cassava, cocoa, rice, sugar cane, maize and millet. In the early years of Nigeria's independence, cash crops such as rubber, cashew, groundnut and oil palm were the major crops around which the economy revolved. Today, there is a shift to alternatives for biofuel, pharmaceutical starch and derivatives using root and tuber crops, which have continued to play a significant role in the agricultural revolution of the country. The current agricultural transformation agenda in Nigeria is intended to engineer the bulk of root and tuber crops in the country into value-added products to match the increasing new tastes and demands for products across the globe. It is also intended to provide job opportunities and to generate additional income for low-income earners, especially in the rural areas. There is, therefore, the need to intensify research efforts aimed at exploring the potentials of major and minor root and tuber crops to ensure food security. In this review, six (6) major root and tuber crops, namely cassava (Manihot esculenta Crantz), yam (Dioscorea spp.), sweet potato (Ipomoea batatas (L.) Lam), potato (Solanum tuberosum L.), cocoyam (Xanthosoma sagittifolium Schott) and ginger (Zingiber officinale L.) as well as three (3) minor ones, namely the Hausa potato (Solenostemon rotundifolius (Poir) J. K. Morton), Livingstone potato (Plectranthus esculentus N.E.Br.) and the Polynesian arrowroot (Tacca leontopetaloides (L.) Kuntze) were examined. In spite of the numerous benefits derivable from these crops in terms of nutrition and medicinal values, some have been neglected to the extent that they are classified as orphan crops. Therefore, much more attention should be accorded to these crops, which have the potentials to contribute to food security in Nigeria.

An experiment was carried out during the 2006 growing season, between June and November, to investigate the growth and yield responses of four varieties of maize (SUWAN-1-Y, TZSR-Y, DMESR-W and ACROSS-97 TZL) to time of fertilizer application (2,4 and 6 weeks after planting). The experiment was laid out in a 3 x 4 factorial in a randomized complete block design with four replications. The results indicated that the mean number of leaves per plant, leaf area index (LAI), plant height, mean number of rows per ear, ear weight, shelling %, kernel weight and total grain yield significantly (P<0.05) increased when fertilizer was applied at two weeks after planting. The mean number of days to 50% tasseling and 50% silking decreased when fertilizer was applied at six weeks after planting. The mean number of barren plants increased with delay in fertilizer application at six weeks after planting. The interactions of variety and time of fertilizer application on the number of rows per ear, mean ear weight, kernel weight and shelling % were significant. The study revealed that the yield of maize could be enhanced by the early application of fertilizer at two weeks after planting. These results are discussed in the light of time of fertilizer application on growth and yield attributes of maize.

The improvement of the fresh bulb and the economic dry matter yields of onion is dependent on the morphogenetic variability and the interrelationships amongst morphological attributes which can be used to determine the quality or performance of the crop. This research was aimed to study the morphogenetic characteristics of ten genotypes of onion (Ares, Violet de Galmi, Red Creole, &ldquo;Wase&rdquo;, &ldquo;Dan Zaria&rdquo;, &ldquo;Dan Garko&rdquo;, &ldquo;Dan Giyawa&rdquo;, &ldquo;Bahaushe&rdquo;, &ldquo;Bakana&rdquo; and &ldquo;Yar Aleiro&rdquo;) in Jos, Plateau State. Using the seedlings raised in the nursery, the genotypes were laid out in a completely randomized design (CRD) with four replicates. Results showed that morphological attributes differed amongst the genotypes, except the number of leaves per plant, neck thickness and horizontal bulb diameter. The study concludes that morphological differences, which are responsible for differences in fresh bulb and dry matter yields, exist amongst the different genotypes of onion. These attributes could be used as selection indices in the improvement of the onion.

This work was carried out in collaboration between both authors. Author OATN initiated the project, designed the study, wrote the protocol and supervised the study and project report. Author SAO collected field data, performed statistical analysis, wrote the first draft of the manuscript and managed the literature search. Both authors read and approved the final manuscript.

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