General Information and Agronomic Aspects
In Kenya tea ranks as the second most important cash crop in terms of foreign exchange earnings and is grown both in large estates (total hectares in 2005: 48,800) and by small holders (total hectares 2005: 88,000) with a total production in 2005 of 324,700 tons at a price of 12,696 KSh per 100 kg bag of black tea.
Tea is used worldwide as a beverage after infusion of the leaves in hot water. Primarily, tea is drunk as black tea. But in East Africa tea is mixed with milk and commonly referred as white tea. Recently, organic green tea and instant tea are manufactured in increasing quantities.
The ideal growing conditions for tea are average annual temperatures of 18-20°C, an average daily amount of sunshine of 4 hours per day, as well as an optimum of 2000-2200 mm of rainfall distributed evenly throughout the year. Higher rainfall causes erosion through soil run off especially on steep slopes. A minimum of 1400 mm of rain is required but tea can grow adequately with less rainfall in areas with frequent mists and low clouds or under irrigation. Relative humidity should lie between 70 and 90%. Tea is grown in an altitude range of 1500-2200 m above sea level. Below 1500 m yields increase but the tea flavour decreases.
In regions with extensive dry seasons, shading trees play an important role in providing and maintaining sufficient humidity. Additionally, tea plantations in windy regions should also be protected by windbreaks (see below), to reduce the intensity of evapo-transpiration.
Tea performs best in soil of volcanic origin. Areas with bracken (ferns) are indicators of suitable ecology. The soil should be deep (1.8-2.0m), well-drained and aerated. Nutrient-rich and slightly acidic soils are best (optimum pH-value 4.0-6.0). Outside this range, basic nutrients are rendered immobile, i.e. above pH 6, calcium restricts the uptake of potassium and below pH 4, phosphorus is fixed (locked in).
Sufficient drainage and aeration of the soil can be lastingly and economically achieved with the combination of shading trees and deep-rooting green manure plants. China tea (C. sinensis var. sinensis) is especially suited to hilly regions. It is resistant to drought, and can tolerate short periods of frost (yet has a low tolerance of shade). Contrastingly, Assam tea (C. sinensis var. assamica) is a purely tropical crop, and reacts sensitively to drought and cold (yet has a high tolerance of shade). With a slope of above 30°, expensive soil conservation measures will be necessary. If terraces are dug, they should be 1 m wide at 2 m vertical intervals and also have a 1:30 gradient for drainage.
Assam type of tea is grown in Kenya. New plants are selected vegetatively from exceptionally good clones. Vegetatively propagated plants are identical to the mother plant and thus will flush at the same time with the yields and quality being similar to the mother plant. Use of seed produces seedlings that are genetically variable.
- Old clones include: "6/8", "7/9", "12/12", "31/8", "100/5", "7/3", "11/4", "12/19", "31/11" and "108/82"
- 1986 releases include: "54/40", "303/178", "302/216"
- 1988 releases include: "31/27", "31/29", "55/56", "303/2592, "55/55", "30/199"
- others: clone "7" and "15/11"
Propagation and Planting
There are several methods, which can be used in the propagation of tea plants i.e.
- Tea seed production.
- Tea breeding.
- Tea seed nurseries.
- Clonal selection.
- Vegetative propagation.
Among these, only vegetative propagation is applied in Kenya for fast tea establishment and a uniform crop. The other 4 methods are long-term procedures, which are expensive and the crop may exhibit some variation. They are basically research oriented and the farmer may not have the required skills to carry out seed propagation.
1. Nursery site
- Site should be well sheltered from prevailing winds.
- Site should be exposed to sunlight for developing plants to benefit from the sun's warmth (i.e. in cold areas like Kericho and upper areas of Central Kenya).
- In hot areas site needs some protection from the full heat of the sun. Suitable shading trees include Crotalaria spp. and, Sesbania spp. (both fast growing and able to fix nitrogen).
- Avoid low lying areas which get very wet during rainy seasons or frost during dry months.
- Site should be near a reliable water source.
2. Nursery soil
- Site should be near suitable source of soil.
- Soil to be used in sleeves can be transported to the nursery.
- Top soil should have a pH of 5.5 while subsoil should have a pH of 5. Cuttings will not root in soil with a pH higher than 5.5. Test both topsoil and subsoil for pH if it is being used the first time.
- Avoid subsoil with a high clay content as it will have poor drainage.
- Rooting of cuttings is also hampered if the soil has a high organic matter content (humus).
- Cuttings should therefore be rooted in subsoil or in soil from below long established grass.
- After establishment roots should eventually get access to a more fertile soil.
3. Nursery fertiliser guidelines
- Cuttings should be planted in a layer of subsoil about 7.5 cm deep, containing 600g/m³ rock phosphate and 300-500 g/m³ wood ashes (containing potassium) or in polythene sleeves containing the same.
- Beneath this subsoil (cap) or sleeve, enrich rooting medium by mixing with topsoil and additional fertiliser similar to above application. On grassland soil and exhausted soil, the site should be prepared with legumes 1 year ahead, e.g. with Crotalaria spp., Tephrosia candida that are afterwards mulched and worked into the subsoil and above cap added on top before planting.
- Do not compact the surface of the lower rooting medium to ensure transitional layer between it and the sub-soil cap or sleeve
- Soil used in the nursery may be heated to 60°C for killing the infective juveniles of root knot nematodes (see also "solarisation")
4. Sleeve Nurseries
They are easier to transfer to planting holes than uprooted plants. Size of sleeves depends on size of plants required by the grower - larger plants need larger sleeves.
Cuttings in large sleeves are more widely spaced and have better lateral shoot growth. Large sleeves imply fewer plants raised in each bed which is expensive. Sleeves should be spot sealed or stapled once in the middle of the bottom edge to help hold the soil and allow for drainage. Excess water is drained by punching a few holes near the bottom edge. Fill sleeves with soil mix described above, from which all roots, hard soil lumps and stones are removed up to a height of 17.5-18 cm. Pack soil firmly (not too hard) and let it be damp all the time, otherwise it will pour out of the sleeve. If soil in the sleeve is allowed to dry, it becomes difficult to wet later.
5. Nursery construction
Size of nursery depends on number of plants required by the grower and can range from 1000 plants to hundreds of thousands of plants. There are 2 types of nurseries (i) low shade nursery and (ii) high shade nursery. For details of construction please contact nearest Agriculture Extension Office.
6. Mother bushes
These should be pruned twice a year even if cuttings are needed only once a year in order to get highest quality material. Time of pruning depends on the time cuttings are to be propagated: for propagation in September, mother bushes should be pruned February to March.
New stems should never be allowed to remain on mother bushes for more than 7 months, as the material then gets too hard and produces poorly growing cuttings. Mother bushes should not be covered. If the mother bushes have aphids, these should be eliminated ahead of pruning for cuttings.
7. Preparation of cuttings
Prunings (cut branches) are wrapped in wet sacks and taken to a nearby shelter (shade) where they are watered immediately. They should be kept shaded at all stages thereafter. Cuttings are made from young shoots (5-7 months old), which are vigorously growing. Discard (trim off) the very soft tips (those that are smashed when pressed in between 2 open fingers and thumb) and the very hard lower parts of branch where bark is forming.
|© AIC, Kenya 2002|
Make cuttings consisting of a 1 leaf with 3-4 cm of stem below the leaf as shown on above diagram. Make 1 cut just above the bud and sloping away from bud with a sharp knife. Make second cut across the stem 3-4 cm below the bud and also a sloping cut.
Place cuttings immediately in a container full of water and let soak for about 30 minutes before planting. Place each cutting as in the drawing above making sure neither leaf nor bud is touching the soil. The bud should be just above the soil surface. Do not touch the top or buttom (ends) of the cutting as the sweat from the fingers may affect survival. Keep the cuttings moist during planting by regular light watering.
NB: Strong water jets displace cuttings. Shade the cuttings by spreading a clear polythene sheet over the nursery bed, forming a dome shape and tacking it into the soil.
After planting care: All beds should be inspected at least once a week. A heavy condensation should be found on the under surface of the polythene sheeting (enough to mar clear view). If there is only a little condensation, it means the soil in the sleeves is too dry or sheeting is torn or seal is poor. Such faults should be corrected immediately. Remove weeds by hand pulling and replace the shade. In hotter areas a more dense shade may be necessary.
Hardening off: Plants grown under polythene sheeting and shade are soft and will be scorched to death if sheeting is removed too quickly. Hardening off starts as soon as new shoots are 20 cm (8") tall. During the first 4 weeks, the polythene is gradually opened and raised on the side away from prevailing winds. First week open polythene a bit every 3 m and support by a stake. Second week the vents are doubled by making similar vents every 1.5 m.
Soil in the sleeves should not be allowed to dry, so watering is done through the vents with a hosepipe. Third week the whole sheeting is completely rolled upon the vent side, leaving only 1 side of the bed covered and at the fourth week polythene is removed completely, washed thoroughly and stored away from sun and rodents for later use.
Two weeks after removal of polythene the shade frame is raised 30 cm (1 ft) on 1 side only and supported by stakes. After this it is raised 30 cm every week for 3 weeks and then completely removed. Plants must be watered as necessary and foliar feed applied weekly until they are transplanted.
NB: If the weather changes and gets suddenly dry and plants start scorching, hardening off should be postponed or beds recovered.
When tea is to be cultivated on terraces, the soil should be protected against drying out by green manure plants (such as weeping love grass Eragrostis curvula). New tea plantations, especially those planted on slopes, are at the greatest risk of erosion taking place, which will lead to soil degradation and nutrient losses. Although trials in various regions have shown that there is no particular optimum spacing, the need for soil conservation has led to closer planting (60 cm) in the rows, with sufficient space (120 cm) between the rows to allow pluckers to walk and work. To further check erosion and provide some shade for the young plants, Tephrosia candida, Crotalaria anagyroides or C. usaramoensis are often sown between the rows of tea.
The cuttings of these leguminous plants or those of Guatemala grass (Tripsacum laxum) placed alongside the tea plants also serve to provide mulch for moisture conservation and to control erosion and weed growth.
Other crops, which can be used in a young tea plantation, include oats, Napier grass or maize stalks. The mulch should not touch the stems of the tea, as this will encourage weevils and dusty brown beetles. Another advantage of mulching is the release of nutrients during decomposition of the mulch. The use of shade trees is restricted to low altitudes; the most important are Falcataria moluccana (syn. Albizia falcata, A. falcataria, Paraserianthes falcataria), Leucaena leucocephala and the December tree Erythrina subumbrans.
Mature tea is mulched with its own prunings.
Planting of wind breaks: Wind breaks should be put in place facing the prevailing wind. A row of tea could also be allowed to grow up as a wind break, or depending on the size of the field, tall or short trees can be planted about 3 m apart. Useful tall trees include pine, cypress and grevillea. Shorter windbreaks include bananas, and the willow-leaved Hakea (Hakea salign).
- On level ground, the distance between adjacent belts should be 10 times the effective height above the tea (e.g. the effective spacing of trees which are 10 m tall planted to protect tea plants which are 1,5 m tall will be 8.5 m (10-1.5) multiplied with 10 i.e. 85 m (8.5x10) or 85 m apart.
- On sloping ground the distance between adjacent belts should be less than this, but if the belts become too close the yields will be reduced by shading and also by competition with shelter trees
Husbandry and harvesting
In new plantings, weeding has to be done by hand until the canopy closes. It is recommended that a circle of at least 40 cm diameter around each tea plant must be kept weed free. The uprooted weeds are left between the rows as mulch. In mature tea weeds are slashed and left on the ground before they produce seed. Overhead irrigation during the dry season gives economic yield increases in many cases and is becoming increasingly popular with tea growers who have a nearby water supply.
Older plantations may have depleted the soil of certain nutrients. If a soil analysis shows very low calcium levels, an application of gypsum is recommended, as this will provide calcium without increasing the pH. Also rock phosphate is an allowed fertiliser in organic systems; apply about 30 g/bush per year (2 tablespoons) as well as light sprinkling of any wood ashes available.
Bringing tea into bearing: During establishment of tea in an estate or smallholding, there is a period when financial returns may depend on the speed and efficiency with which the young tea is brought into bearing. Any operation designed to form a permanent branch system, from the time the plants are in the nursery to the time they are tipped in to form a plucking table in the field is defined as 'bringing tea into bearing'.
Frame formation: The lower parts of the bush will form the permanent frame which remains unchanged throughout the life of the bush or until the bush is cut down or 'collar- pruned' to rejuvenate it. This frame must be low, strong and have a good spread. In tea, a wide frame of branches is needed for the plucking table. The tea plant is cut back to 15 cm after being in the field for 12 months. When the new shoots reach height of 60-75 cm they are pegged down (when the reddish bark starts to develop near the main stem).
|© AIC, Kenya 2002|
Pegging: The shoots that develop from a stump (explained above) or after the first light pruning of a sleeved plant are bent downwards and pegged so that they radiate outwards and upwards from the main stem. Pegged branches form the base of a permanent frame, which is an addition to the vertical shoots that develop from auxiliary buds among the branches. Development of these buds is encouraged by pegging the branches, so that they slope uniformly and slightly upwards. If pegging is done such that branches are horizontal or slope downwards, development of auxiliary buds is retarded or even stopped. Auxiliary bud development is further encouraged when two terminal leaves and buds are removed from the pegged branches during pegging. This activity removes growth inhibitors from the plant tip, which promote terminal growth and suppresses or inhibits lateral or auxiliary bud growth.
This phenomenon is known as "apical dominance".
Plucking table formation: After the frame is formed shoots are allowed to grow for 3 months, and then their growth is checked by tipping (removing 3 leaves and bud from each shoot above the desired height). Plucking table should be 50 cm from the ground and tipping should be done 4-5 times before plucking starts.
Plucking: This is done to maintain the established tea, starting usually after 2 years. Routine picking is done at intervals of 5-10 days depending on growth. There are 4 types of plucking:
- Fine - plucking 1 or 2 leaves and a bud. A stick is placed on the tea table for guidance and shoots above it are picked (two leaves and a bud).
- Coarse - removal of 3 or more leaves and a bud.
- Light - pick leaving some new foliage above the previous plucking level.
- Hard - shoots are plucked right down to the previous plucking.
Plucked leaves must NOT be compressed in a basket as this will cause fermentation. Plucked leaves should be kept in the shade and taken to the factory as soon as possible and in good condition the same day. Leaf containers should NOT be placed on the soil. Dormant shoots with unopened central leaf are called Barijhi, they are hard and should be discarded. With correct plucking the plucking table rises some 10 cm every year. The finer the plucking, the better the quality of tea. Under plucking causes the table to rise very quickly and may render the plucking physically impossible by third year.
Pruning: This is the removal of a shoot from a tea plant. When soft apical shoots are removed as at tipping in to form a table, auxiliary buds are stimulated to develop for a distance of 10-12 cm below the cut. This development also occurs during hard pruning and during preparation of stumps from the nursery.
Any auxiliary shoot that develops outwards contributes to the spread of the bush. After 3 years, yields begin to decline and the plucking table becomes too high. It is then necessary to prune back. At each pruning the height should be increased by 5 cm above the previous pruning to avoid callous tissues.
After several prunings the bush should be cut right back to 45 cm. Pruning should be done parallel to the slope on steep land to avoid a step effect. In dry weather, prunings should be left on top of the bushes to protect the plants from sun scorch. Otherwise the prunings should be left between the rows to replenish the organic material and nutrients to the soil and to prevent erosion. It is best to prune only a third of the garden when due so as to keep up production.
The pruning cycle varies from every 2 years in tropical lowlands to every 3-5 years at higher altitudes. Pruning should preferably be done during a dormant period if there is one, e.g. immediately following dry weather in East Africa.
At the start of the conversion to an organic tea garden, the tea garden needs to be developed sequentially and in stages from a monoculture towards a diversified crop system. Alongside the tea crop, plants should be cultivated to improve soil fertility, provide a supply of nutrients (especially nitrogen), increase diversity (habitats for beneficial insects), supply wood (fuel and building material) and to provide feedstuff for on-farm animal husbandry. The main objective is to provide the soil with organic matter for the tea bushes. Spreading the organic matter over the site should be given preference to the more work-intensive practise of composting.
Organic fertilisation strategies
A. Litter fall and pruning material from shade trees
Litter is provided without any additional work. Additional working hours need to be calculated for pruning the shade trees (to create an ideal micro-climate, admit light and control the growth of the tea bushes). The pruning material should remain as mulch directly on the site, or, if applicable, be used as compost material. Yet if the pruning material is to be used as fuel, at least the ashes should be used as a compost supplement (e.g. to replace the potassium). Three aspects need to be heeded, in order to create the conditions necessary for the soil micro-organisms to efficiently decompose the pruned material: The material needs to be sufficiently chopped (2-5 cm pieces). The material must then be evenly spread around the tea bushes (avoid creating heaps of material). The carbon-rich material needs to be mixed with additional nitrogen-rich material (e.g. neem-press cakes, castor cake or green manure from crotalaria) in order to achieve a better soil environment for successful decomposition.
B. Green Manure (mulch)
The foliage from green manure plants, as well as that from the other crops, should remain as mulch material on the site. In the cases of tea gardens where integrated animal husbandry is practised, care should be taken to choose green manure plants that can also be used as fodder crops.
C. Composting and animal husbandry
The basic source of fodder for the animals comes from green manure plants (e.g. Guatemala grass) and vegetation in the tea garden's edges, which are not planted with tea, or from plants neighbouring the tea garden. The space available to grow fodder must be taken into consideration when calculating the number of cattle to acquire. If the nitrogen demand of the tea (on average around 60 kg) is to be met entirely from composted cattle manure, around 2 cattle per ha of cultivated tea are required. For this method, small ditches are dug between alternating plant rows every 3-4 years, and filled with pruning material, green manure plants, compost and cattle dung (the organic material must be well cut-up, and should not be buried too deep). Simultaneously, the tea bush roots are also cut to stimulate new growth. The disadvantage of this method is the high workload involved especially on older plantations with narrow gaps between the rows.
Annual yields of 1000 - 1300 kg/ha of processed tea or 5 times that amount of green leaf under good management are possible. An experienced plucker is able to pluck at least 30 kg of leaf per day. For tea bushes over 50 years old, it is necessary to monitor the yield level and percentage of gaps in individual fields. If yields are less than 1000 kg/ha of made tea in such a field it is a sign of stagnant production and call for rehabilitation. This can be done by rejuvenation pruning or replanting.