Citrus is a wider name for several species such as pomelo, lemon, citron, Tangerine, mandarin among others. Citrus remains a vital horticultural crop in Kenya. They can thrive well under wider area, from low altitudes at sea level to highlands at 2100m above sea level. Sweet oranges, mandarin, and pixie orange are the main citrus species that are grown commercially.

Citrus is widely cultivated in tropical as well as subtropical African countries. While fresh fruit for the market is produced preferably in subtropical climates (e.g. South Africa) and Mediterranean climates (e.g. Tunisia, Egypt, Morocco, Libya), citrus for juice is predominant in tropical climates because of the possibility for higher sugar content. The most important species of citrus fruits are sweet oranges (Citrus sinensis), limes (C. aurantifolia), grapefruits (C. paradisi), lemons (C. limon) and mandarins (C. reticulata), often called tangerines.

Citrus Farming In Kenya

Orange farming in Kenya does well in the arid and semi-arid lands (ASALs), predominantly in the Ukambani regions (Makueni and Machakos) and some coastal parts such as Voi. Wangithi[9]notes that the area under citrus was relatively higher in Makueni County at 13,482Kg/Ha as compared to 9692Kg /Ha in Machakos County.

Orange growers are mainly small-scale and characteristically attain 4 -10 tonnes per acre. Oranges also do well in central regions of Kenya such as Murang’a and Nyeri and some parts of Western Kenya. The main growing areas in Makueni Sub-county are Mumbuni, Wote, and Nzaui locations. In these areas, oranges are grown commercially and contributes hugely to household income. The fruits are sold locally in open markets or transported to Mombasa, Nairobi, and Nakuru, which are the largest target markets.

Common challenges related to citrus Farming in Kenya

> Inferior varieties – Most farmers rely on local varieties that are sometimes very susceptible to infections and low yields. New seedlings are generally raised directly from seeds, hence propagating the low yielding traits of the mother plants. Improved varieties are not easily accessible to farmers due to the limited availability of plant nurseries. As most improved varieties can only be propagated vegetatively by budding or grafting, farmers who lack this knowledge cannot do it themselves.

> Poor yields – Due to drought and poor management, poor yields often result. Most citrus farming in Kenya is done on small gardens mainly for the domestic market. The crops are not irrigated and in most cases suffer from drought stress, delayed flowering, affecting potential yields.

> Pests and diseases – Citrus is attacked by many diseases that cause serious losses (e.g. greening disease, anthracnose, damping off, phaeoramlaria leaf and fruit spot). Citrus is also very liable to infestation by pests like aphids, scales and white flies, some of which are vectors of the citrus tristeza virus or the greening disease.

> High postharvest losses – Harvesting of immature and overmature fruit, mechanical damage during harvest, transport and distribution, water loss (wilting) due to a poor handling system, and decay either due to blue or green mould and insect damage due to the Mediterranean fruit fly result in high postharvest losses.

To meet the above mentioned challenges and make citrus farming more sustainable and profitable, interventions are needed. This article introduces organic approaches, which can be adapted to local conditions and can help address some citrus production challenges.

Selection of good planting material for citrus farming in Kenya

Most citrus orchards consist of grafted trees that combine favourable attributes of the scion and the rootstock. However, the choice of the rootstock should depend on the adaptability to local conditions and resistance to common soil borne infections. Sour orange (Citrus aurantium L.) is the most widely planted rootstock and is an excellent rootstock for areas free of Citrus Tristeza Virus
(CTV). Rough lemon (Citrus jambhiri) is also a widespread rootstock, but should be avoided in areas known to have blight and nematodes.

When choosing cultivars for scion production, factors like disease resistance, drought resistance and quality as well as yield performance should be considered. Valencia is an important cultivar for orange juice and this cultivar is known to do well under organic management. Washington navel is used mainly as fresh fruit. Other varieties used in Africa include Hamlin, Tangelo, King Star ruby and
Red blush. There are many other local variants, some of which are good for organic production.

Although they may not be high-yielding, they may be adapted to local production conditions.
Purchased seedlings should be obtained from good nurseries like Fruit Africa Nurseries In Kenya, to make sure they are free of diseases (especially viruses) and pests and for which the authenticity of rootstock and scion cultivars is guaranteed.

Raising seedlings in the nursery The use of virgin sites for nurseries is very important in organic production. It reduces the risk of soil-borne diseases like Phytophthora, Pythium and pests like nematodes to which citrus seedlings are very susceptible. The site can also be treated to make it safe by covering it with a black polythene sheet for at least two days of full sun or by burning dead plant material over the site.

Citrus trees are normally propagated by grafting (budding) a preferred citrus tree onto an appropriate rootstock. This ensures that the new tree has the same characteristics as the mother plant. T-budding is the most common method of grafting oranges. However, budding should be done during warm months (not during cold periods or during dry conditions). Budded plants are normally ready for transplanting 4 to 6 months after budding. Citrus rootstocks are ready for grafting 6 to 7 months from pricking. If budding is to be done, seedlings are budded 9 to 10  months from pricking.

Recommendations to farmers regarding preparation of rootstocks for citrus farming in Kenya:

• Choose seeds from healthy and vigorously growing mother trees, which are not grafted or budded. Extract the seeds and subject them to hot water treatment at about 55 °C for 10 minutes.
• Sow the seeds immediately in seedbeds, mixed with well-prepared compost.
• Water the seeds regularly, preferably twice a day until they germinate. Seeds germinate in 2 to 3 weeks. If seedlings appear congested, thin them out so as to produce sturdy and vigorous plants. Thinning also reduces chances of disease outbreaks.
• Seedlings are ready for picking and potting in polybags when they have 2 pairs of leaves and a bud.
• Seedlings are normally ready for budding when they reach pencil thickness or about 6 to 8 months after germination.
• Dumping off is the most serious disease favoured by wet soil, dense shading, and humid environment due to overcrowding. To prevent dumping off,
• shelter the seedlings to keep rain off. This reduces leaf wetness also and can reduce fungal infections such as cercospora leafspot. Pests like aphids, leaf miners and orange dogs are likely to attack. These can be controlled by applying plant extracts, for example, from neem or tephrosia.

Recommendations to farmers regarding budding of rootstocks:

• Select healthy trees from which to obtain bud graft branches (bud sticks). Cut a number of branches, about 30 cm long, using a very sharp knife.
• Select the seedlings onto which the grafting will be done. They should be above 30 cm tall in order to ensure that the budding takes place at about 30 cm above the ground, not higher. The closer to the ground you insert the graft, the more the graft receives nutrients, water and sap that are undiluted. The higher up you place the graft, the greater the chance is of it either dying off or taking too long to become a strong branch. Before budding, it is good to check if the bark peels easily. A bark that is peeling indicates that the seedling is undergoing active growth and is ready for budding.
• Make a 1½-inch cut in the shape of a ‘T’ at the grafting location using a sharp knife, opening the bark of the stem. Continue to cut well below the bark into the seedlings wood.
• Pick up the first bud stick and choose the biggest bud. With a sharp knife, gently slice the bud together with the bark and a thick portion of the wood to which it is attached. Take care not to touch the cut side of the bud with your fingers as this may impair the connection of the bud to the rootstock.
• Uncover the wood underneath the ‘T’ cut in your orange tree by gently lifting up the bark and gently insert the bud into the open wood under the ‘T’ slice, starting at the top of the ‘T’ and moving downwards. The bud will be held in place by the wood of the main seedling. Ensure that the bud is put exactly in the same direction as it was oriented on the bud stick.
• Wrap budding tape underneath and above the graft in order to prevent any movement that might hinder the integration of the bud into the actual wood of the orange seedling. The tape also avoids moisture loss and callousing (tissue overgrowth) at the grafting site. The bud should also be entirely covered.
• Remove the budding tape when the buds start sprouting, in about 2 to 3 weeks, and continuously remove all rootstock sprouts (including the terminal bud of the seedling). The new bud will then be able to grow to take over the entire crown of the orange tree.

The objective of budding is to align the cambium layer of both rootstock and bud as closely as possible. Thus, it is important that the bud is removed from the bud stick with a smooth cut, and the bud and rootstock to be tightly pressed together. Farmers can start by practising the budding process on branches of older trees. After they gain experience, then they can do it on young seedlings.

Selecting suitable growing conditions for citrus farming in Kenya

Citrus farming can be grown in a wide range of climatic and soil conditions. But proper site selection remains the key to successful organic production. Climate has a significant effect on nearly all aspects of citrus growth and quality development:

• Extremely hot temperatures that exist in some African countries are damaging to citrus. Ideal temperatures range from 13 °C to 38 °C. At higher temperatures, flowers and leaves drop prematurely.
• Rainfall or irrigation throughout most of the year is necessary for citrus, however, dry and hot temperatures during the day and cool temperatures at night are favourable conditions for good colour development.

Although citrus grows in a wide variety of soils all over Africa, it grows best in deep soils of medium texture and moderate depth, with good drainage and high fertility. Moderate pH conditions between 5 and 7 are preferable for citrus, as they generally allow adequate availability of nutrients.

Adequate drainage is also needed, as tree growth is reduced in poorly drained soils or where compacted soil layers are present in the root zone. Furthermore, poor drainage causes problems with Phytophthora and other soil borne diseases. Yields in subtropical climates peak at 20 to 25 years, while yields in tropical regions reach a maximum at 10 to 15 years already because of the higher pest and disease pressure in these regions.

Transplanting

Some months before planting citrus seedlings, farmers can sow vigorous legumes which are then slashed and mulched shortly before planting the citrus trees. Then the soil will be enriched with organic matter and nitrogen, both stimulating soil microbial activity.

An optimum plant density that permits optimal light interception and aeration is achieved at a tree spacing of around 8 m by 8 m. This leaves some space for intercropping. The citrus seedlings should be planted well, making sure that the budding point remains above the ground to avoid exposing the scion to root rot diseases and to make sure it does not start rooting itself. It is recommended to apply compost into the planting holes to encourage quick establishment of the
plants.

Depending on the planting season, supplementary watering or irrigation may be required to support the growth of the young seedlings. Shoots that grow below the budding union must be removed. These shoots, if not removed, will retard growth or kill the scion part of the budded shoot.

Field layout of a new citrus orchard

Establishing a new orchard has the advantage that the farmer can create an optimal organic system by applying the following strategies:

• Creating diversity – In the citrus orchard, diversity can be created by mixing different cultivars in the same orchard, growing specific cover crops in the alleyways and under the trees, as well as planting hedges and wild flower fallow plots around and in the orchard.
• Intercropping – For smallholder farmers, relying on citrus production alone is not sufficient. Citrus in Kenya is in most cases intercropped with annual crops, for example maize and beans at establishment stage for about two seasons or with fruit trees such as mangoes or any other long-term trees at a much wider spacing. The space to grow additional crops is limited to alleyways. Successful examples are intercropped beans and maize for subsistence supply, as it is practiced in Kenya, or intercropped with Aloe vera, as practiced in South Africa. The orchard can also be intercropped with legume cover crops in the later stages of growth.
• Plant density – Using a plant density that permits optimal light interception and good aeration is necessary to control fungal infections. Citrus trees need wide spacing of about 8 m to 8 m to offer enough space for intercropping as well as allowing good aeration of the orchard. Sufficient spacing is also necessary to allow for application of compost and management of pests and diseases.

Improving an existing citrus orchard

Citrus growing is a long-term investment. Orchards can be productive for up to 50 years or more. The useful economic life span of the plantation depends on climatic and management conditions. Organic farmers aim to achieve tree longevity as part of their sustainable land use strategy.
Almost every orchard can be improved back to full production by applying organic methods. However, these practices also apply to newly established citrus orchards.

Ensure proper pruning

As the trees grow, the inner and lower branches become shaded. This leaves fruiting to the outer periphery of the canopy whereas the inner parts have poor or no fruit set at all. This problem can become especially severe in high-density orchards. Annual pruning maintains light and air penetration through the canopy of the citrus trees and reduces the humidity around the plants  contributing to pest and disease prevention. The tree height should be maintained at less than twice the planting distance in the row.

Three major types of pruning include:

• Heading back to control size and form of the tree
• Thinning out to improve aeration
• Selective pruning to cut off infested parts of the tree, especially after Phytopthora infections or citrus greening Pruning should be done during the vegetative phase (before flowering) of the trees.

Recommendations to farmers regarding proper pruning:

• Maintain a single stem up to a height of 3 feet (100 cm), and pinch or break the main shoot to encourage side branching
• Allow 3 to 4 main branches to form the framework of the tree
• Remove any extra side branches including those growing inwards
• Ensure all diseased and dead branches are removed regularly

Improving soil fertility

The building up and maintenance of a fertile soil is a central goal in organic citrus growing. Careful soil management is especially important in the humid tropics, where heavy rainfall and strong solar radiation accelerate soil degradation, leaching of nutrients and erosion.

The basic tools of organic soil management are interdependent and influence tree health, tree development, fruit yield and quality. Relevant soil management techniques for organic citrus orchards include:

• Soil erosion control
• Use of cover crops (understorey plants) or mulching
• Agroforestry and intercropping methods
• Application of compost

a. Soil erosion control

Especially in sloping areas, soil erosion control structures are very important. Water conservation structures like terraces should be constructed to prevent the loss of topsoil and organic matter.

b. Soil cover systems

A permanent soil cover is an important component of the organic orchard cultivation system. Locally adapted leguminous crops, such as beans to help restore degraded soils very fast. They successfully suppress weeds, fix nitrogen and prevent erosion. To avoid strong competition between the cover crop and the citrus trees, the cover crop should be regularly cut.

c. Application of compost

Most tropical soils are low in organic matter. To improve soil organic matter content at least 20 kg or 1 bucket of well-rotted cattle manure or compost should be applied to each tree every year. If possible, a handful of rock phosphate should be added. Compost should be added especially 2 to 4 weeks before flowering to encourage good fruit formation and development. According to citrus farmers, application of manure or compost also makes fruit sweeter.

Proper weed management

Noxious perennial grasses such as Panicum spp., Paspalum spp., Amaranthus spp., couch grass (Cynodon dactylon) and spear grass (Imperata cylindrica) are suppressed by sowing cover crops.
Cover crops must be slashed when they start to compete with citrus trees. Hand weeding may be necessary when specific weeds start to dominate.

If tools or machines are used, injuries on the tree trunks and roots must be avoided, as they may become entry points for soil-borne diseases.

In orchards with newly planted citrus trees, the soil is best when covered with mulch.

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