Coffee is primarily cultivated as a rained crop worldwide. In equatorial regions such as South and Central America, where there are no well defined alternations between wet and dry periods, coffee is generally not irrigated. But in the regions of single rainfall region such as East and Central Africa and India, coffee is irrigated during the 4 to 6 month dry spell. This substantially boosts growth and productivity. Coffee, being an evergreen plant, requires maintenance of soil moisture during dry months. In the coffee tracts of South India, the South-West monsoon provides more than 60% of the rain during June to September and the rest is during the North-East monsoon period in October to December. The dry period usually consists of 4 months from December on wards. In some years the North-East monsoon tapers off by the end of October itself leading to an extension of the dry period. The most important factor which limits the production of coffee even in well managed estates is the long dry period. Besides this, if blossom rains are delayed beyond March then the production of coffee receives a major set back. In coffee, irrigation is mainly used as an insurance against failure of good blossom and backing showers and for overcoming long dry period.
Sprinkler irrigation is the most versatile method of irrigation to supplement the natural rainfall for the growth and flowering of coffee. In sprinkler irrigation the water is sprayed under pressure through small orifices or nozzles all over the plant and land surface. System are designed, type of soil, location of water source, topography of land, wind velocity and infiltration rate.
For successful establishment of young plantations, coffee should be irrigated during the dry months to a depth well below the root zone and the intervals between irrigation should be long enough to allow the soil to dry out without causing serious wilting. This encourages deep rooting as a protection against drought, responds well to irrigation must commence 20 to 25 days after the cessation of monsoon. Irrigation up to 25 mm once in 20 to 25 days till the end of December is a must. Later blossom irrigation at 25 to 40 mm is to be given during the second fortnight of February followed by backing irrigation of 25 mm water within a gap of 15 to 20 days after blossom.
Preparing Coffee for Overhead Irrigation
This is essential for effective irrigation. Overcrowded plantations and old coffee under thick shade should be avoided. Preference should be given to younger and more responsive coffee. Shade should be well regulated and pruned every year after harvest. Shot-hole borer affected plants, dead twigs and whippy wood are to be removed. Weed growth has to be checked.
Beneficial Effects of Sprinkler Irrigation in Coffee
Sprinkler irrigation results in a two fold increase in length of laterals due to increase in number of nodes and intermodal length, increase in leaf area by 45% retention of foliage in unirrigated plants, improved nutrient uptake, and uniform ripening of berries. Providing blossom and backing irrigation alone improved yields by 48 to 57% and continuous irrigation throughout dry period gave a yield increase of 85 to 95% over un-irrigated plots in Robusta coffee.
The drip or trickle irrigation has assumed considerable importance in recent years in view of the greater need for economy in water use. In drip method, water is distributed by a network of tubing which bring water directly to each plant near the root system. Water is provided daily or on alternate days based on the water requirement of crops. Thus the water losses during conveyance and due to seepage, evaporation etc., are avoided. Besides, the water is not applied to the unwanted areas like inter-spaces between the rows of plants. Thus drip irrigation system include saving in labour, increase yields, better quality of produce, less weed growth, increased fertilizer efficiency, possibility of fertilizer application through irrigation water and reduced incidence of foliar pests. However, the initial cost of drip equipment is a limitation for large scale adoption. Cost of the unit per hectare depends mainly on the spacing of the crop. The main item of expenditure is the lateral pipe line which is run all along the rows. The wider the row spacing lesser the cost.
Components of Drip Irrigation System
The drip irrigation system consists of a pump, fertilizer injector, filters, distribution lines, emitters/drippers and other control and monitoring equipment. Distribution lines are made up of a network of graduated pipelines starting with a main line followed by smaller sub-main lines are made of PVC and are burried in the soil. Lateral lines are main and sub-main line. Emitters/drippers which discharge water in droplet form are fixed on lateral line near the root system of the plants. The main control station for the drip irrigation system is organized to measure and filter the water and to regulate pressure and time of water application. The control station includes the pump, back-flow prevention device, primary filter, pressure regulator, pressure gauge, water meter, chemical gauge, and chemical injection equipment.
Beneficial Effects of Drip irrigation in Coffee
Results obtained with drip irrigation in coffee for the last few years have revealed that this method is most suited for sustenance irrigation of coffee plants during the dry period. Establishment of young coffee is much better with drip irrigation compared to sprinkler irrigation as there is less weed growth. Application of 3 to 4 l of water once a week was found to be ideal for establishment of young coffee. in established plantations, application of 8 l of water per plant on alternate days to cauvery and daily to Robusta during dry months from November to May could increase the crop yield by 28% and 48% respectively. Drip irrigation in Arabica (cauvery) coffee allowed for natural blossom showers while in Robusta, blossom could be induced by applying around 200 l of water per plant during February-March through drippers or micro-sprinklers. This blossom irrigation needs to be given at a stretch, after withholding daily drip irrigation for about 15 days prior to blossom irrigation.
The studies on drip irrigation in cauvery coffee were initiated during 1988 as a part of the project ‘drip irrigation’. The trial was modified during 1994 to study the response of cauvery coffee to graded doses of fertilizers under drip irrigation system. The results from the field experiment indicated that over the six cropping years, the yield was significantly highest in single dripper per plant treatment (4 l per day with yield of 1014 kg ha-1)followed by two drippers per plant treatment (8 l per day with yield of 942 kg ha-1). The increase in yield due to drip irrigation was 16 to 24% over the yield of un-irrigated control block.
The growth parameters studied with different levels of fertilizers, revealed that the girth of the primary branch, number of nodes per branch as well as number of bearing nodes per branches was significantly higher in both the treatments under drip irrigation when compared to un-irrigated control. The yield was significantly high in both the drip irrigation when compared to un-irrigated control treatment. A field experiment to compare different irrigation methods for Robusta coffee was initiated during 1996-97 on s.274 in coffee plantation (planted during the year 1978) at CCRI. Among the irrigation were found to be superior to drip irrigation during dry months. The micro sprinkler irrigation for winter, blossom and backing gave significantly high yields (1777 kg cc ha-1). The micro sprinkler irrigation during winter followed with blossom and backing irrigation (1545 kg cc ha-1) was found to be on par with overhead sprinkler irrigation for blossom and backing only (1512 kg cc ha-1). The percent yield increase over un-irrigated control was highest with sprinkler for winter, blossom and backing (109%) followed by micro sprinkler for winter, blossom and backing (82%), sprinkler for blossom and backing (78%) and drip irrigation during dry months(40%). It was concluded that sprinkler for blossom and backing is suitable for large areas with limited water supply, in small holdings with limited water supply. In small holdings with water scarcity, micro-sprinkler or drip irrigation method could be adopted.