CHAPTER ONE INTRODUCTION
Citrus is a genus of flowering plants in the Rutaceae family; it is the most economically important genus of this family. This genus includes species such as limes, lemons, citrons, pomelos and mandarins (New World Encyclopedia, 2008). Citrus are evergreen trees that grow to a height of 183-914cm depending on the variety and rootstock selected. Most varieties are self-pollinated (Lazaneo, 2008).
Citrus grows on a wide range of soils but perform well on soils with good drainage, good fertility and good aeration; soils with pH between 6 – 6.5 are ideal (DARSA, 2009). Orange production accounts for over 50% of the world citrus production with consumption growing at a rate of 3.5% over the past thirty years. Within the same period production and exportation of processed orange products have increased by 4.4% (Sawe, 2017).
In Ghana, citrus is grown mostly by smallholders in the forest regions mainly in the Eastern, Ashanti and Central regions where rainfall amounts exceed 1000mm and is distributed in a bimodal fashion (Ofosu-Budu et al., 2007). The crop serves as income for farmers in these regions thereby contributing to reduction of rural poverty. Close to 90% of the total yearly production is consumed fresh while about 10% is processed into juice and sometimes concentrate for the local market. The nation also exports orange juice to the European markets (GEPC, 2006). In the year 2010, 10,729 metric tons of fresh orange fruits were exported, generating foreign exchange of US$ 654,000 for the country (MoFA, 2011). In 2016, total production reached 690,130 tons which proportionally generated higher foreign exchange for the country (FAOSTAT, 2016).
In West Africa, Ghana and Nigeria together produce 91.13% of about 891,535MT of citrus produced in the region contributing significantly to vitamin C, minerals and dietary fibre requirement for over 250 million peoples in the sub region (FAOSTAT, 2010).
The most widely grown citrus crop in Ghana is the sweet orange especially the Late Valencia cultivar. The late Valencia fruit is succulent and juicy, with a is yellow rind when ripe. The fruits are medium to large in size and have thin rinds (Maurer and Bradley, 1998). There has been significant increase in the cultivation of citrus in terms of acreage in the past decade in the country most of which is concentrated in the Ashanti, Eastern, Brong Ahafo, Western and Volta Regions of Ghana (Asare-Bediako et al., 2013). Based on maturity times, we have the following orange varieties in Ghana: Early maturing (August – October) Ovaletto, Sikkan; Mid-season (October – January) Obuasi, Mediterranean sweet and Red Blood; Late maturing (March – April) Late Valencia, Olando and Frost Valencia (AILAP, 2006). The rootstock determines various factors in the plant’s life ranging from maturity to disease resistance. Rangpour lime as a root stock was promoted for the cultivation of sweet oranges in the forest region of Ghana because of its quick adaption to the soil (Ofosu-Budu et al., 2007).
Currently the citrus industry has been plagued with some production constrains which have caused it to plummet along with its economic importance to communities which produce the crop and the country at large. Notable among the production constraints is low yields (Asare- Bediako et al., 2013), caused by pests, disease and declining soil fertility. The decline in soil fertility due to continuous cultivation without soil replenishment in sub-Saharan Africa is a major cause of food insecurity and poverty; yields continue to decline on smallholder farmers’ fields leading to loss of profit and income (Yeboah et al., 2009). At the core of good yield of any crop is the state of the soil, and currently the Citrus Growers and Marketing Association of Ghana (CIGMAG), have observed low soil fertility in many fields (Brentu, 2016). It is important to ensure that the soil is properly maintained, to ensure fertility. Adoption of organic
and inorganic soil fertility management approaches is considered as the most viable way of addressing the challenge of soil degradation (Agyekum, 2016).
Citrus serves as a major source of income for farmers. Even though it is not a food security crop, it is an important cash crop for some farmers in the forest zones of Ghana. Regardless of the importance of this crop to the economy of the country (Ghana), its decline in yield and fruit quality has received little attention. Continuous harvesting without replenishing soil nutrients, has led to soil nutrient mining, which has consequently resulted in low yields of citrus in Ghana (Ofosu-Budu, 1998). Poor soil fertility leads to many nutrient deficiencies which render the crop susceptible to diseases coupled with poor postharvest handling to reduce the quality of fruits. The poor returns of orange farmers make the venture unlucrative resulting in massive cutting of large areas of citrus plantations (Adofo, 2009). Thus, without addressing this problem of soil fertility, the country may end up importing oranges to meet market demand depriving those in the production chain of their livelihoods.
Application of mineral fertilizers to sweet orange significantly increases fruit yield (Ofosu- Budu, 1998). Use of local organic waste (manure), including cocoa pod husk (CPH), poultry manure (PM), empty fruit bunches (EFB) have also been found to increase yield of sweet oranges significantly (Ofosu, 2005). Thus, effective integration of these organic wastes into soil fertility management to improve the fertility of the soil at a very low cost is of significant benefit to citrus production (MOFA, 2005). The combination of mineral and organic fertilizer can help improve yield and fruit quality of oranges (Amankwa, 2005). However, these are avenues that have not been explored extensively to improve the productivity of citrus in Ghana. This study aimed to develop an integrated soil fertility management options to increase the
productivity of citrus in Ghana. This experiment will lead to the creation of a local fertilizer module which CIGMAG can adopt to improve citrus production in Ghana.
OBJECTIVES
The main objective of the study was to determine the effect of inorganic and organic fertilizer and their combination on yield and fruit quality of sweet orange.
Specific objectives
- Determine the effect of organic and inorganic fertilizers on nutrient content of the leaves
- Determine the effect of organic and inorganic fertilizers on soil chemical properties
- Determine the effect of organic and inorganic fertilizers on the yield
- Determine the effects of organic and inorganic fertilizers on the fruit quality
CHAPTER 2
LITERATURE REVIEW
Origin and spread of Citrus
Citrus fruits found today are believed to have come from four promiscuous ancestors; the citron, the pomelo, the pepeda and mandarin (Graber et al., 2016). The origin of citrus spans through north-eastern India through the Malay Archipelago and south to Australia (Atta et al., 2012). Currently the fruit is grown worldwide in tropical and sub-tropical regions commercially (Ehler, 2011). Sweet orange was grown for many years in China and reached an advanced stage of cultivation before it was introduced to Europe. The first member of the citrus family was introduced to Europe around 310 B.C (WHW, 2005).
Citrus was introduced into North Africa in the late 4th century as depicted in ancient art from wall paintings in the Egyptian temple at Karnak. Other suggestions perpetuate that the Jews were probably familiar with citrus when they were enslaved in Babylon during the 6th century BC (Malcom, 2006).
In America, Christopher Columbus is credited with introducing citrus seeds there on his second voyage in 1493, whiles another Spanish explorer Ponce de Leon was also known to have planted the first orange tree in Florida between 1513 and 1565 (NRC, 2010). In Brazil, citrus was introduced into the country by the first colonizers in the 16th century from which it spread to other South American countries (BACE, 2010).
Sir Thomas Herbert recorded in his book “Travels” the finding of oranges, lemons and limes on the island of Mozambique in the mid 1600’s (Malcom, 2006). In Ghana citrus production began with the introduction of the West Indian lime in 1913 when an orchard was established at Asuansi Agricultural Research Station (Ofosu-Budu et al, 2007). Citrus orchards are now
widespread in the country and grow in the Eastern, Ashanti, central and some parts of the Volta region. Major categories of citrus cultivars are Mediterranean and Spanish oranges which are distinguished by fruit morphology and chemical constituents (Ehsani, 2007).
Sweet Oranges and Late Valencia variety
Important species of citrus include Late Valencia (Citrus sinensis) and Tangerine (Citrus reticulata). Others include Lemons (Citrus limon), Lime (Citrus aurantifolia), Tangors, Tangelos and Ortanique (AILAP, 2006). Sweet orange is the most grown citrus cultivar around the world. It originated from southern China and thrives in the tropical and semi-tropical regions (Ehler, 2011). Though, the origin of sweet orange is unknown, it is believed to have come from the hybridization of some primitive citrus species (Xu et al., 2013). Sweet orange varieties include common oranges (Late Valencia being the most popular), Navel oranges (The Washington navel is the best known of them), Blood oranges (distinguished by their red coloration and a tart taste). The Valencia orange was named by an agronomist William Wolfkill, after the Spanish city of Valencia known for massive orange productions (Ehsani et al., 2007). Among the numerous varieties of sweet orange, the late Valencia is the most sought after by farmers and consumers probably due to its sweet taste and its wide range of climatic tolerance (Alhassan, 2013).
The botany of the Citrus plant
Citrus is a long-lived perennial evergreen tree with a lifespan of about 50 years (Nicolosi et al., 2000). Most leaves of cultivated citrus have petioles that are winged or not and a single terminal leaflet. Leaves of many citrus plants are compound (ranging from trifoliate to palmately and pinnately compound) and are described as unifoliate (Citrus ID, 2011).
