Citrus species (Citrus sinensis) probably originated in North Eastern India, Burma and the surrounding areas from where the species crossed into China, the North East and to the Mediterranean region. From the Mediterranean, it was carried to other parts of the world. The subtropics and warm temperate regions of the world are the largest producers of citrus especially the sweet orange cultivars. Tropical areas are also producing sizeable quantities of other citrus cultivars (Davies et al., 1994).
Citrus is grown in several parts of the world, where minimum temperatures stay above – 4oC (Spiegel-Roy and Goldschmidt, 1996). The worldwide production of citrus, about 102 million metric tonnes per year, is much greater than that of other tropical and subtropical fruits, including banana, mango, apple, pear and peach. The majority of the world best quality fruits is produced in the subtropical region. Brazil and the United States account for up to 45% of the total world orange production; whereas the United States accounts for up to 40% of grapefruit production in the world (FAO, 2004). Around 80% of this total fruit production is processed into orange juice by more than 10 concentrated and frozen juice processing plants located in the state of Sao Paulo, which encompassed Brazil’s major citrus production region.
Citrus ranks among the foremost fruit trees cultivated in Nigeria along side mango, and it is industrially used mainly for the manufacture of soft drinks (Opeke, 2005). In Nigeria citrus production is more concentrated in the guinea and Sudan Savanna zones (Olaniyan, 2004), with Benue State giving the highest annual production of the commodity (Avav and Uza, 2002). Unfortunately, there have been little or no studies involving crucial aspects of the production in this important area.
Although citrus production extends over a wide range of soils, sandy to clay loam soils are best suited for the production of high quality fruits. Adequate soil drainage is an important factor for good tree growth. Citrus is planted on raised beds in high rainfall areas with fine textured soils, where drainage would not be a problem. Soil pH is an important factor that influences nutrient availability and other soil chemical and biological processes. Soil pH range of 5.5-7.5 can support adequate growth of citrus trees, depending on the rootstock used.
To underscore the importance of maintaining flourishing citrus industry, there is a need to establish sustainable production management system that would support optimal production of fruits with minimal negative impacts on the environment. The philosophy takes into account best management practices (BMPs) of agricultural resources to improve the efficiency of fertilizer inputs by minimizing the losses (Havlin et al., 1999). Therefore, BMPs for soil nutrients imply timing and placement of fertilizer, combined with optimal scheduling of irrigation.
There has been a steady rise in citrus production globally due mainly to increase in hectarage, consumer preference for more healthy or convenient food and rising incomes (UNCTAD, 2010). Although about 140 countries are known to be involved in citrus production year 2007 estimate indicates that the top 10 citrus producing countries are Brazil, China, United States, Mexico, India, Spain, Iran, Italy, Nigeria and Turkey (UNCTAD, 2010).
Citrus production in West Africa is on a small scale and unorganized (Opeke, 2005), the ranking of Nigeria on the 9th position among the world top 10 producers of the commodity signifies that the situation might be changing. This is in consideration of the fact that previous statistics did not feature Nigeria or any of the West African countries (FAO, 1991). In any case, most of the citrus fruits produced in the country are consumed locally (Opeke, 2005) and does not seem to feature in the international trade (UNCTAD, 2010). Another factor that could constitute considerable waste to citrus fruits is postharvest management (Samson, 1980; Davies and Albrigo, 1994). This is especially true of developing nations like Nigeria, where the necessary equipment do not seem to be in place and awareness is generally low.
Citrus fruits are rich sources of vitamin C, the deficiency of which results in scurvy (Davies and Albrigo, 1994). One glass of orange or mandarin juice is said to contain enough vitamin C to supply the daily requirement (Samson, 1980). Citrus fruits are consumed fresh, as juice or concentrate. The pulp and molasses are valuable as livestock feed particularly cattle, while the peel is a rich source of pectins and essential oils (Samson, 1980).
Due to the strategic position of Benue State in citrus production in Nigeria, this study surveyed the constraints and production status of citrus in Benue State; some agronomic and postharvest management strategies for the crop were evaluated.
The specific objectives of the study were:
- To survey and document the agronomic practices, cultivars grown, disease and pest prevalence and the postharvest management practices of citrus in Benue State;
- To evaluate the effects of previous farm management and five manure rates on the yield of citrus; and
- Determine the effects of previous farm management and the five manure rates on the quality of juice produced thereof.
Botany of citrus plant
Many types of citrus are believed to have moved West to various Arabian areas, such as Oman, Persia, Media (Iran) and even Palestine (Tolkowsky, 2002). Major types of edible citrus include citron, sour orange, Lime, lemon, sweet orange, shaddock, grape fruit, Mandarin and Kumquat (Opeke, 1992).
The commonly grown citrus species belong to the family Rutaceae which contains about 150 genera and nearly 200 species (Opeke, 1992). The genus citrus contains all the species widely cultivated in West Africa. Citrus species are evergreen trees of small to medium stature. They often have thorny (prickly) stems. The leaves are unifoliate, petiolated and quite often the petioles are winged. The flowers are perfect, usually in large numbers, fragrant, and mostly white. The leaves, twigs and rind of the fruit contain oil glands which secrete the rind oil (acid) of commerce (Opeke, 1992).
Citrus fruits are small to large plants with leathery rind, yellow to orange in colour when ripe. The pulp and juice may vary in taste from sweet to acid, the fruit segments may vary from 8 to 18, but usually are 10 to 14. Seeds may be many, few or absent as in the tangelo. Flowers are carried singly or in small clusters, sweet scented, and with five- membered parianth segments.
Agronomic Practices in Relation to Topicivity and Quality of Fruits
The principle of cultivating citrus follows the same pattern as for other tree crops. Although citrus trees can be grown over a wide range of latitudes, climatic regimes and edaphic conditions, proper site selection remains the key to successful commercial production (Grimm, 1994). Selection of the proper orchard design and layout and planting density would have a significant impact on future yields, cultural operation and net returns. The spacing may range from 7 x 7 m (205 tree ha – 1) to as wide as 9 x 9m (125 trees ha – 1) depending on individual species. The seedlings in the nursery are ready for transplanting for orchard establishment as from one year of budding (Odim, 2002).
Nitrogen and Potassium represent the largest component of the nutrients removed from the soil by the tree on an annual basis. Other nutrients for example Calcium, are present in large amounts in the structural framework of trees formed by woody tissue and old leaves (Mattos Jr et al., 2003). Nutrients removed by harvesting the fruit