By Bernard Okafor
Citrus is a commonly cultivated tree crop in Nigeria. It is in high demand because of its nutritional, economic and industrial values. Citrus cultivation in Nigeria is mainly under rainfed conditions in rainforest/derived guinea savanna zones of the country with the Sahel and Sudan savanna being drier parts and not very favorable for citrus production except under irrigation. Common citrus varieties grown in Nigeria include Citrus sinensis, Citrus paradisi, Citrus limon, Citrus grandis and Citrus reticulata (see Table 1).
Intercropping (growing crops among plants of a different kind, in the space between rows) before canopy closure in orchards is carried out to generate extra income for the farmers before the trees reach economic yield and maturity. The crops intercropped are often used to improve family food and nutritional security and to enhance livelihood with the crops harvested used as soil amendments. Other reasons for intercropping include pest/disease and erosion control.
Citrus is produced under multiple tree cropping systems mainly as intercrops. It is produced in homesteads, open space and orchards. Orchards are more common in Central Nigeria.
Citrus is planted at a conventional spacing of 7 meters by 7 meters. However, it is planted at 6 meters by 6 meters or 5 meters by 5 meters in some situations.
A high percentage of citrus in Nigeria is produced under multiple tree cropping systems. This involves intercropping with Theobroma cacao, Musa spp., Mangifera indica, Irvingia spp., Chrysophyllum albidum, Elaeis guineensis, Anacardium occidentale, Dacryodes edulis and other economic tree crops depending on the agro ecology. In these conditions, there is no regular spacing, and soil fertility depends mainly on decomposition of leaf litter. Intercropping of citrus with vegetables is also commonly practiced (Figure 1).
The intercropping model varies with the climate and agricultural practice in the agro ecology of the country. The savanna zone is more vulnerable to drought and drier soils with low organic matter and nitrogen due to high temperatures and lower vegetation cover. The intercropping models or combinations common in the agro ecologies of Nigeria are presented in Table 2.
Although intercropping is a common practice in citrus production in Nigeria, its use can have a negative impact on fruit yield if not properly managed. Intercropping of citrus with maize can lead to lower fruit set and reduced yield. Intercropping with cassava and some other root and tuber crops can also lead to yield decline due to their heavy soil nutrient requirement and disturbance of citrus tree roots. The effect of intercropping citrus with cassava, pineapple, spices, vegetables, legumes and some root/tuber crops are presented in Tables 3, 4 and 5.
Research efforts in Nigeria have advocated intercropping of vegetables and some spices in juvenile citrus orchards. It is recommended that they should be planted close to the trees with a spacing of 2 to 4 meters from the tree; closer spacing hinders the performance of citrus. Intercropping should be discontinued between six to seven years after establishment of orchards. Intercropping with legumes and vegetables is recommended for more profits and soil management with up 50 percent profit margin in some cases. Crops with heavy nutrient requirements or those that can affect citrus roots are often not recommended as intercrops with citrus.
Bernard Okafor is a citrus research program scientist at the National Horticultural Research Institute in Nigeria.