In Tanzania tea (Camellia sinensis L.) is the fifth largest export crop, providing an annual foreign exchange revenue of over 30 m. US$ The total area cultivated with tea is estimated at 23,300 ha, more than half of which is owned by large estates in the Southern Highlands (Mufindi, Njombe and Tukuyu districts).
Sprinkler irrigation – by which the water is distributed in the air as droplets over a circular area – is the traditional method on irrigated tea estates in Tanzania. About 19% of Tanzania’s total tea area is irrigated by overhead sprinklers, while production in the remainder depends entirely on rainfall.
Most systems consist of a permanent pumping unit and main pipeline and portable submains, laterals, risers and sprinklers.
Poor design, excessively wide sprinkler spacing and irrigation at high wind speed were reported to have led to low application uniformities, as expressed by the Christiansen Coefficient of Uniformity of CU=31–72%.
Since the early 1990s, increased pressure on water resources and limited supplies of irrigation water has restricted the expansion of commercial tea estates in parts of East and Central Africa. Hence, applied research on a potentially more efficient irrigation method like drip is of high interest to the large estate tea growers and the local community, since it could help to secure employment and increase yield of made tea and profits.
Drip irrigation, one form of localized or micro-irrigation enables applications of water and fertilizers directly to the plant root zone at frequent intervals, low flow rates, small operating pressures achieving high application & distribution efficiencies. Provision of data on yield and economic aspects of commercial drip irrigation of C. sinensis for future investment decisions would be useful for estate managers, research agencies and equipment manufacturers alike.
In order to investigate potential options for more efficient water use, the first commercial drip irrigation system was established in 2000 at Kibena Tea Limited in the Southern Highlands of Tanzania. The goal was to measure and calculate irrigation uniformity and efficiency of the drip irrigation system versus sprinkler irrigation, to review the scheduling of water and fertilizer at Kibena Tea Ltd and to determine benefits and problems with drip irrigation. Additional goals were to provide recommendations for improved system management, to evaluate economics of the drip and overhead sprinkler irrigation systems and to estimate the achieved gross margin with drip in relation to tea price, yield and fertilizer rate.
Agro-industrial crop & forex earner for Tanzania Rising water scarcities restricting the expansion of commercial tea estates Low irrigation uniformities (CU= 50 to 70%) & application efficiencies by sprinkler irrigation due to high wind velocities, low systems pressures, poor designing, mechanical problems etc Low irrigation application efficiencies under overhead sprinkler irrigation Leaching of nutrients Low fertilizer use efficiency Low tea yields & quality Need for drip Economic importance of tea as forex earner in Tanzania To conserve water, increase water & fertilizer use efficiency and optimize tea yields
Kibena Tea Limited
Location: Kibena Tea Limited (9°12′S, 34°45′E, 1860 m above msl) is located in the Southern Highlands of Tanzania 15 km north of Njombe district town
Area: Drip – 55 ha and Overhead sprinkler – 635 ha
Crop variety: Clone 6/8 and BBT-133
Crop spacing: Row to row – 1.2 m and Plant to plant – 0.75 m
Plant density: 11111 plants/ha
Planting time: Between 1989 to 1998
Drip system: Commissioned in July 2000 Fertilizer dose:
Climate: Sub-humid with dry winter & warm summer;
Maximum temperature: 17.4 – 25.8°C;
Minimum temperature: 10.0 – 15.7°C; Vapour pressure deficit: 0.66 – 1.73 kPa;
Wind speed: 13 – 179 km/day;
Day length: 11.33 – 11.38 hours;
Solar radiation: 12.7 – 19.9 MJ m2/day;
Total rainfall: 1027 mm/year: Effective
rainfall: 724 mm;
Runoff: 186 mm/year;
Aridity index: 0.94;
Moisture index: 6%; and Reference crop evapotranspiration: 1086.98 mm/year.
Soil physical properties: Deep clay loam texture; soil reaction strongly acid (pH = 4.4 – 5.5); steady state infiltarton rate 132 mm/hour; and bulk density – 1.6 g/cm3; Water table below 6 m
Water source: Reservoir/Lake
Power source: Electric pump
Agro-solution: What has been done
Subsurface drip irrigation system: It consisted of a pump unit, the mainline, the head control including filtration and fertiliser injection unit, the sub-mains, block valves, the manifolds at the head of each irrigation block and the laterals; Ram Integral dripline (ID 16.7 mm) laid out on the surface with a lateral spacing of 1.2 m on 15 ha & 2.4 m on 40 ha serving one or two rows of tea bushes, respectively with an emitter spacing of 0.75 m and emitter flow rate 1.6 Litres/hour. Year of drip system installation: 2000 Drip system cost: US$ 2171/ha Agronomic & Technical support: Crop water requirement & irrigation scheduling (depth and frequency of water application; water quality consideration, measurement of applied water) & fertigation scheduling (soil & water analysis, estimation of nutrient dose, selection of fertilizers & compatibility, application skill via drip system, foliar diagnosis for nutrient deficiencies etc); System operation (pressure reading & maintenance, valves operation, measurement of applied water) & maintenance (cleaning of filters, fertilizer tank, acid treatment, chlorination etc). Training & capacity building: Soil water plant relationships, drip irrigation & fertigation principles, benefits, limitations & utility; water quality & herbicide usage.
Improved made tea yield: 3-Year old bushes: Surface drip increased yield by 13.7% (Clone 6/8 – 1656 kg/ha) to 25.4% (Clone BBT133 – 1639 kg/ha) in comparison to Conventional overhead sprinkler irrigation average yield of 1457 kg/ha by Clone 6/8 & BBT133 4-Year old bushes: Surface drip increased yield by 66.1% (Clone 6/8 – 2999 kg/ha) to 47.9% (Clone BBT133 – 2670 kg/ha) in comparison to Conventional overhead sprinkler irrigation average yield of 1805 kg/ha by Clone 6/8 & BBT133 5-Year old bushes: Surface drip increased yield by 52.1% (3500 kg/ha) in comparison to Conventional overhead sprinkler irrigation yield of 2300 kg/ha Water requirement of 3-year old bushes: Conventional overhead sprinkler irrigation – 4985 m3/ha & Subsurface drip – 3569 m3/ha Water saving by drip over overhead sprinkler: 1416 m3/year/ha (28.4%).
Additional area irrigated by saved water: 0.397 ha.
Irrigation uniformity: CU varied between 90 – 95%
Irrigation application efficiencies: Ranged between 86.6 – 98.3%
Irrigation adequacy: More than 95%
Saving in power: Surface drip enabled 15.7% saving in power (4.45 kWh/ha-mm) in comparison to overhead sprinkler (5.28 kWh/ha-mm)
Saving in labour: Surface drip enabled 47.7% saving in labour (34 US$/ha) in comparison to overhead sprinkler (65 US$/ha)
Economic indices: Higher net returns (2882.3 US$/ha in 3rd year and 3601 US$/ha in 4th year) by surface drip.
Other benefits: Management flexibility – Drip allows other field operations like harvesting, tipping, infilling, & weeding while irrigation the crop; improvement in fertilizer use efficiency, less weed growth, uniform irrigation of tea on undulated terrains etc
Drip irrigation of tea in Tanzania is a feasible eco-technological and economically viable technology Use of scarce water resources sustainably in tea cultivation enables expansion of tea plantations over a larger area Higher productivity, forex earner and increased income to estates & growers Tea estates are willing to expand the drip irrigation to the remaining tea area Tea best management practices – Subsurface Drip Irrigation & Fertigation scheduling
Grow More: 50% made tea yield
With Less: Water saving 28%