Coffee tracts in India receive both South-West and North-East monsoon rains from June to August and from October to December respectively. In some years the North-East monsoon tapers off by the end of October itself leading to extension of dry period in this area. Hence, in India coffee areas encounter a dry spell of 4 to 6 months in a year. Therefore, the coffee plants experience fluctuating weather conditions like continuous wet condition, hail stone, heavy winds, as well as prolonged drought and dry periods. These conditions have forced our coffee farmers to grow coffee under shade.
Shade trees essentially help in providing congenial micro climatic conditions to the plant growth and prevent large variation in soil temperature and moisture levels. They reduce the intensity of sunlight and temperature, combat drought effects and maintain soil moisture levels to provide adequate water to the coffee plants tissues and protect the plants from high temperature. Shade trees also protect the coffee plants from damage by hailstorm, high wind velocities and prevent overbearing of the plants. Adequate shade improves soil fertility by returning large amounts of leaf litter improves the organic matter in the soil thus increasing the amount of useful micro-organisms in the soil. A properly maintained shade also helps in limiting the incidence of coffee pests and diseases. Coffee grown under shade is always found to be of superior quality and taste. Shade trees are therefore recommended as a protective measure in areas of harsh environmental conditions such as high temperatures, extended drought, heavy rainfall, high winds and occurrence of hail storm. In India, two tier shade is necessary for growing coffee, especially Arabica. All trees provide shade but some are planted with well-defined objectives to provide desired shade. Therefore while selecting the shade trees, it must be ensured that selected trees species has the following properties:
• Fast growth
• Shed leaves during the rainy season but should rapidly put forth fresh shoots immediately after the rainy season.
• Resistance top high winds and hailstorms.
• Have a deep rooting system so that they so not compete for applied nutrients and soil surface moisture.
• Not harbor/host pest and diseases affecting coffee.
• Provide filtered shade.
Arabica coffee requires 50% to 60% filtered shade and Robusta coffee requires 40% to 50% (Unirrigated) and 30% to 40% shade for irrigated blocks to maintain consistent production. The shade tree branches have to be regulated properly in order to provide desired shade to coffee plants. Shade regulation should be done only when sufficient moisture is present in the ground soil. The permanent shade trees can be regulated every year by lopping the branches up to a height of 9 m to 12 m to provide required filtered light and air circulation in the field. In Arabica plantations situation at higher elevations (more than 1100 m) having two tier shade canopy of dadap (lower) and permanent (upper) shade trees, the shade regulations can be done during February or March. In irrigated Robusta fields, the shade regulation can be undertaken immediately after the harvest. While in plantations, under rainfed conditions, the shade regulation should be done only after the receipt of 100 to 125 mm of rain. Dadap looping should be undertaken immediately after the onset of monsoon and all the stakes should be finely chopped and returned to the field along with the leaf mass.
Labor scarcity is one of the major problem in coffee plantations and availability of skilled workers for shade regulation is limited. Therefore, while choosing new shade trees, preference should be given to those shade trees which shed their leaves during the monsoon. Atthi and havalige (Balanji) belong to this category of trees. Timber extraction in Arabica fields should be done only after establishing the permanent shade trees along with required number of dadap trees. The shade trees should be established 2 to 3 years before planting coffee. Silver oak trees can be extracted when they reach the age of 30 to 35 years. Maintenance of mono culture shade especially silver oak should be strongly discouraged in coffee plantations. The atmospheric temperature and soil temperature in such plantations is generally higher than other fields. The incidence of white stem borer, leaf rust and black rot disease is also found more in silver oak-shaded plantations.
Measurement of shade intensity
The studies on photosynthesis light saturation curve revealed the optimum light intensity is in the range of 700 to 900 umol photon m-2 s-1 and 1000 to 1200 umol photon m-2 s-1 for Arabica and Robusta coffee needs to be maintained. However, there is no easy method to measure light intensity of shade. Hence, correlation studies of the LUX with light intensity have been carried out.
Based on these studies it is possible to measure light intensity with the help of LUX meter. For optimum shade for Arabica and Robusta coffee plantations the recommended LUX is as follows
Recommended range of LUX
· Arabica =55,000 to 70,000 LUX
· Robusta =75,000 to 90,000 LUX
Time of measurement
To assess the shade requirement, the LUX measurements need to be recorded between noon and 2 PM, above the canopy of coffee bushes. A minimum of 50 readings per acre have to be taken during the peak dry period at random points.
Management of shade trees
The high light intensities and temperature experienced during the drought period are not conductive for normal and healthy growth of coffee plants. Therefore, it is necessary to protect the coffee plants during this period by providing both temporary (lower canopy) and permanent (upper canopy) shade trees. This is particularly the case for Arabica coffee, which needs more shade for optimal growth under south Indian conditions than Robusta coffee. Dadap (Erythromycin lithosphere) is used as lower canopy shade in India. It is planted along with coffee in new clearings. When stakes are planted in June, they grow quickly since sufficient moisture is there in the soil. In areas where the establishment of dadap cuttings, application of 1 to 2 liter of hormonal solution (1 ml per liter of water ) on the same day of planting and 25 g of super phosphate to the soil around the cuttings after 3 to 4 weeks of planting helps in rooting and promoting profuse branching with proper foliage.
The dadaps are lopped two or three times a year to regulate the light requirements according to the season. Dadps are lopped at the commencement of the South-West monsoon to allow more light and regulated during the post-monsoon period when the dry weather begins to provide the filtered light.
Next to dadap, silver oak (Grevillea robusta) is the most commonly used tree for temporary shade. It grows easily and rapidly in new clearings but does not give much leaf mulch. The most popular permanent shade trees belong to the Indian fig and legume families. From the fig family, shade trees are atthi (ficus glomerata), mitli (ficus retusa), mallegargathi (Fircut tsiela) and Albizzia stipulate, A. moluccana and A. sumatrana from the legume family. Other common shade trees are rosewood (Dalbergia latifolia), jack (Artocarpus integrifolia), and gandha garage (Cendrellatoona).
Permanent shade trees are generally planted about 12 m to 14 m apart. It is advisable to plant a large number initially and thin them out as the trees grow and spread out. The trees have to be regulated in such a way that in the course of time, they have their canopy about 10 m to 14 m above the coffee. The most convenient time to do so is just before the monsoon. Shade regulation by lopping temporary shade trees could be done more than once a year depending upon the requirement of light intensity for growth.