Coffee is being cultivated under shade as well as without shade depending upon the environmental and cultural practices in various countries. In countries like Brazil, where the temperature does not exceed 24°C to 30°C, the intensity of daylight is low, the rainfall is well spread over through out the year without having long gap (not exceeding 15 days) between two rainfalls, no shade is provided for coffee. Whereas, in the countries where high light intensity, high temperature and prolonged drought exist, coffee is cultivated under shade and the best example for this category is our country. The coffee growing regions in South India receive rainfall influenced either by South-West monsoon or North-East monsoon or both, followed by a long dry spell of 3 to 6 months. Therefore, the coffee plants experience various weather conditions like continuous wetness, heavy winds and followed by prolonged drought. Despite these favourable and unfavourable conditions, the coffee has to be cultivated for more than 40 years with economically viable yields and here lies the importance of shade in Indian coffee plantations.

Shade is more essential to Arabica coffee for the reasons that high light intensity, high temperature and low soil moisture affect the growth by reducing the leaf area, net photosynthesis and extension growth and also induce over-bearing, enervation and 'Die-back' which refers to death of young tertiary branches.

Arabica coffee is very sensitive to high light intensity and high temperature and so suffers due to the oxidative stress. This results in the early senescence of leaves and defoliation (Fig. 1).

Light Requirement
The studies conducted using various light intensities in India as well as in other countries showed that high light intensities reduce the net photosynthesis in arabica coffee. Tio (1962) reported that the saturation on apparent photosynthesis was reached at 2000 foot -candles and maintained the rate up to 6000 footcandle intensity (60% daylight) after which it decreased. Venkataramanan and Govindappa (1987) found that the dry matter production will not be maximum at full daylight especially in arabica coffee and the optimum light requirement will be 70% of daylight (Photosynthetically Active radiation (PAR): 1356 micro Einstein). The recent studies on the photosynthetic efficiency under various light intensities have also indicated that high light intensity reduced the photosynthetic efficiency in arabica coffee compared to robusta coffee. The saturation of efficiency was observed at the PAR of 750 to 920 and 650 to 750 p moles m z s ' in arabica cultivations of Sln.9 and S1n.12 respectively, whereas it was at 1000 to 1100 and 1300 to 1600 p moles m' s-' respectively in robusta cultivars of S.274 and C X R (Ananymous,2002). These results showed clearly that Robusta coffee was able to tolerate more high light intensity compared to Arabica coffee.

Why Shade
Under tropical conditions as in South India, shade is very much essential to prevent over-bearing, suppress weed growth, reduce the intensity of sunlight and temperature, combat drought effects, increase the moisture input and to protect from low temperature, wind velocities and damage caused by hail stone. Adequate shade improves soil fertility, aeration of root system, nitrogen fixation and retains soil moisture. Shade limits the incidence of pest such as white stem borer and leaf rust disease in Arabica coffee. The incidence of white stem borer, which can cause death of plants, will be more in arabica coffee grown under less shaded condition (Subramaniyam 1941). During the current season, high incidence of white stem borer has been reported from most of the Arabica plantations on account of unprecedented low rainfall experienced for the past 2 to 3 seasons in South India. The non adoption of control measures for curtailing the incidence and also extraction of timber to tide over the situation caused by low price scenario for coffee aggravated the problem. The incidence of stem borer will be at minimum, if shade is maintained adequately. Similarly the incidence of leaf rust will be more in Arabica coffee grown in open condition compared to shaded condition. Heavy incidence of leaf rust results in defoliation, which is found to be a predisposing factor for stem borer build up. The shade was also found to improve the coffee quality. Hence shade management is as important as the main crop.

Two Tier Shade Canopy
For these reasons two tier of shade canopy is recommended especially for Arabica coffee. For the lower shade canopy, Dadap (Erythrina lithosperma) has to be planted at closer spacing initially along with coffee in new clearings and the population of Dadap will be thinned out later based on the requirement. For better establishment of dadap, soil drenching of 1 or 2 litres of HORMONOL SOLUTION (200m1 of HORMONOL per 200 litres of water) could be given around the dadap stake immediately after planting. Three to four weeks later, 25 grams of superphosphate per dadap stake could be applied to the soil for boosting the growth. The branches of dadaps have to be lopped once or twice in a year to regulate the light requirements. Generally the lopping of dadap is advocated immediately after the on set of monsoon.

As temporary shade tree, the exotic species of Grevillea robusta (Silver oak) can be grown in coffee plantation. Initially, it can be planted with a spacing of 6 m X 6 m and later it can be thinned out based on light requirement and silviculture specification. However, providing monoculture shade of Silver oak for Arabica coffee has to be curbed, since it does not provide the required shade. Further, the fall off silver oak leaves covering the coffee plants during the monsoon period leads to the high incidence of black rot. The fallen leaves will also take longer period to decompose. For these reasons the number of Silver oak trees could be at minimum for Arabica plantations.

The permanent shade trees such as Ficus spp, Albizzia spp, Terminalia spp, Artocarpus integrifolia (Jack fruit) and other jungle trees can be planted at a distance of 12 m to 14 m apart. A list of shade trees commonly grown in coffee plantations of South India is available in Coffee Guide Book (Anonymous, 2003). The canopy of these permanent shade trees has to be regulated by undertaking the operations such as shade lopping, shade thinning and shade lifting depending upon the necessity and requirement to maintain optimum shade for the coffee plants. These operations have to be carried out in such a way that in course of time, the shade canopy has to be about 10 to 14 m above the coffee. As such the shade regulation will not cause any harm to the trees but facilitates the new growth. Thus the shade regulation practice could be comparable to pruning of any horticultural crops, which does not cause substantial damage to the trees.

To maintain the BEANEY (Best Annual Efficient Yield) of arabica coffee, it is very much essential to retain the leaves on the plants for a longer period by providing adequate optimum shade with two-tier shade canopy especially to minimize the incidences of white stem borer and leaf rust. The mixed shade canopy is always found to be very advantageous in maintaining the higher productivity with low dosage of fertilizers due to recycling of nutrients.

Similarly, the Robusta coffee requires shade especially for the un-irrigated field on account of its susceptibility to drought, although it has tolerance to high light intensity and temperature to some extent. Hence a medium shade pattern is required for sustainable production in rain fed conditions. To overcome the effects of drought and also to maximize the crop production in robusta coffee, irrigation is being given for blossom and backing. These fields could be maintained with thin and minimum shade under intensive cultivation.

Effects of High Shade
The coffee plant requires shade during dry weather period to protect the plants from adverse micro and macro climatic conditions. During monsoon months the shade should be at minimum by lopping the dadap and regulating the permanent shade canopy to allow the full daylight, which will be less during the monsoon period. The heavy shade during this period increases the disease incidence of black rot, stalk rot etc. and also cause premature fruit drop due to prolonged wet conditions. Further, high shade induces excessive production of plant hormone `gibberellic acid' which in turn triggers more vegetative growth and less induction of flower buds. This ultimately results in low productivity. Production of more black beans was also observed under high shaded conditions. Hence shade regulation during pre-monsoon period is very much essential for improving the productivity of coffee.

Thus, cultivation and regulation of shade will vary with type of coffee grown, altitude, aspect, soil conditions, slope, irrigation etc. In addition to this, the pattern of shade, choice of trees and their spacing will vary from region to region and also from field to field. Monoculture of shade trees is not preferred to coffee plantations for the reasons like pest and disease attacks. Keeping this in view, the mixed shade canopy is advocated to get average good crop yield every year, to minimize the pest and disease incidences and also to tide over the situation caused by long drought, high light intensity and high temperature.

The importance of shade under South Indian conditions especially for Arabica coffee has been appreciated from a very long time. The extent of shade canopy retained is again born out of experience. What one may call 'thick' in one place may become 'thin' in another place and vice versa.

Thus shade management has to be practiced systematically depending on elevation, location, aspects etc. So as to protect coffee from the ill effects of drought and direct exposure to sunlight. However even today, many growers adopt shade practices to exploit the plants without considering the long range effects of less shade on coffee plants. Hence the suggestions on package of practices for shade management under intensive cultivation as well as for sustainable coffee production of Arabica and Robusta coffee are given in Table 1.

Table1: Shade management package for intensive and sustainable production of Arabica and Robusta coffee.
Plant material	Package for Intensive cultivation	Package for Sustainable production
Arabica Coffee	Maintain a two tier shade canopy consisting of temporary and permanent shade trees. Tree density to be maintained 100-120 per ha. At high altitudes temporary shade trees may be phased out once the coffee is well established, if there is no open patch. Retention of lower shade canopy in Western aspect is essential. Regulate shade every year instead of once in 3-4 years to minimize the damage to coffee bushes. Indiscriminate timber extraction should be avoided. Maintain adequate foliage on coffee plants by adopting required measures to control the disease incidence, to improve the longevity of the leaves and vegetative growth and also restrict the centering to 6" from the main stem for minimizing the incidence of white stem borer.	Maintain a two tier shade canopy consisting of temporary and permanent shade trees. Tree density to be maintained 120-140 per ha. At high altitudes temporary shade trees may be phased out once the coffee is well established, if there is no open patch. Retention of lower shade canopy in Western aspect is essential. Regulate shade every year instead of once in 3-4 years to minimize the damage to coffee bushes. Indiscriminate timber extraction should be avoided. Maintain adequate foliage on coffee plants by adopting required measures to control the disease incidence, to improve the longevity of the leaves and vegetative growth and also restrict the centering to 6" from the main stem for minimizing the incidence of white stem borer.
Robusta coffee	Maintain optimum shade by regulating the population of shade trees to 75 - 100 per ha. Light shade regulation every year after harvest and before blossom irrigation.	Maintain a medium shade with a tree population of 100 - 120 trees per ha. A medium shade comprising of mixed canopy should be encouraged as an insurance against long dry spells and erratic blossom showers.

Conclusion

During the current year, open patches are more in the plantations due to lack of adequate shade canopy, which might have been due to the tree fall on account of heavy wind and removal of trees. Developing lower canopy shade in all the open patches is very much essential to restrict the further incidence of white stem borer. Planting of Dadap or Gliricidia can be undertaken during the current season itself, as the soil moisture is adequate on account of good rainfall received in most of the coffee zones. For the better establishment and to boost the growth of shade plants, hormone and nutrient applications could be given as per the schedule. Wherever replanting programme is undertaken in the timber extracted fields, planting of Indigofera and Maesopsis eminii could be opted along with the Dadap and Gliricidia, since these trees will be very quick in achieving the required shade pattern. Retention of leaves on the plants for a longer period is a must to maintain BEANEY in Arabica coffee. This could be achieved by providing the required shade pattern of two tier shade canopy in addition to all other cultural operations carried out in time. This pattern of shade will also minimize the biennial bearing habit of plants, which refers to the high and low yield obtained alternately. Further, it is also essential to maintain adequate shade in the plantations under the present irregular weather conditions.

References

Anonymous, 2002. Fifty Fifth Annual Report of Coffee Board Research Department for 2001-02. pp 110.

Anonymous, 2003. Coffee Guide. Coffee Board Research Department. pp. 200.

Subramaniam,T.V.1941.The coffee stem borer. Entomological series Bulletin. No.II.pp;1-29.

Tio"M.A.1962. Effect of light intensity on the rate of apparent photosynthesis in coffee leaves. J. Agri. University, Puerto Rico. Vol. XLVI.pp:159165.

Venkataramanan, D and D.A. Govindappa.1987. Shade requirement and productivity of coffee. J.Coffee Res. 17(2) pp: 16-39.