Sustainable specialty coffee production: An agronomy perspective (A review)

Indonesia has several specialty coffee that have been marketed domestically and exported to foreign countries. The current focus of specialty coffee development is increasing production and quality of domestic coffee by paying attention to aspects of local wisdom. This review article was aimed to discuss several agronomical measures should be applied by coffee farmers in Indonesia. It is hoped that this effort will enrich the variety of high-value specialty coffees from various regions. To obtain specialty coffee products with good quality, coffee cultivation techniques that are in accordance with good agricultural practices (GAP), environmentally friendly, as well as adaptive to climate change, need to be supported. Therefore, it is necessary to apply sustainable coffee cultivation by 1) replanting and rejuvenating of coffee plantations using novel resilient cultivars, 2) planting shade trees, 3) pruning, 4) using organic fertilizer and biofertilizer, 5) rainwater harvesting and irrigation systems, 6) integrated pest, desease, and weed management, and 7) selective cherry harvest.


Introduction
Indonesia is one of the leading coffee producing countries in the world, behind Brazil, Columbia and Vietnam.In 2019.Coffee plantations in Indonesia covering of 1,245,358 ha of land with which producing of green coffee beans of 752,511 tons, so that the productivity was only 803 kg/ha.This figure was much lower than the coffee production of Brazil, Vietnam and Colombia which reached 3,492,660; 1,829,220; and 846,000 tons, respectively [1,2].This condition was affected by various factors, including low adoption of superior varieties, the technical application of plant cultivation that was not in accordance with good agricultural practices (GAP), the adverse effects of climate change, and the lack of government policy support for coffee development [3].
On the other hand, Indonesia has great potential to produce coffee products that are highly competitive in the international market.Geographical landscape and agro-climatic conditions are very diverse, ranging from lowlands to mountainous highlands, which are widespread from the island of Sumatra to Papua.Several regions in Indonesia has been produce high quality coffee products through a series of processes, starting from selection of suitable planting materials until post-harvest handling with special cares.High quality coffee products which were later known as "specialty coffee" can be sold at high prices compared to regular coffee (regular products).Specialty coffee has unique flavor and aroma with which high score (≥80) of cup quality according to SCAA protocol.Each region (from Aceh 1230 (2023) 012067 IOP Publishing doi:10.1088/1755-1315/1230/1/012067 2 to Papua) in Indonesia produces specialty coffee that has a distinctive taste according to environmental conditions.
The term specialty coffee is still strongly associated with Arabica coffee products, although some robusta coffee products have begun to be promoted as having special quality [4,5].The specialty coffee category quantitatively refers to the Specialty Coffee Association of America (SCAA) protocol [6]: the final score of cupping test of <80.0 = below specialtynot specialty; 80 -84.99 = very goodspecialty; 85 -89.00 = excellentspecialty; and 90 -100 = outstandingspecialty.
Specialty coffee is usually consumed singly (without being mixed with other coffees), in consequence it is very important to ensure the authenticity and purity of specialty coffee in an effort to maintain the quality of specialty coffee traded.To maintain the authenticity of specialty coffee, the government of Indonesia provides a Geographical Indication (IG) certificate for the coffee producers [7].
Despite of high potential for specialty coffee production in Indonesia, its sustainability is very challenging because there are many potential threats related to global climate change.A future warmer climate is projected to have negative effects, both directly and indirectly, on the coffee crop [8].Coffee grown in warmer area would yielding lower quality bean.Land suitable for growing Arabica coffee could be narrower as the temperature rises [9].Pressure from coffee plant pests and diseases would also get worse [10].This paper attempts to summarize various efforts to mitigate various constraints in specialty coffee production from an agronomic point of view.

Current status of specialty coffee in Indonesia
Rencently, Indonesia has generated 17 specialty arabica coffee scattered from Aceh to Papua province.Mostly were arised on Sumatera Island (8), followed by Java island (3), Sulawesi island (2), Flores island (2), Bali island (1) and Papua island (1) (table 1).However, arabica coffe plantations which produce specialty coffee was covered only 24% out of the total area of arabica coffee plantations throughout Indonesia (figure 1).It means that the majority of arabica coffee production areas are produce of non specialty grade.In 2019, the area of Arabica coffee plants in Indonesia reached 360,703 ha with a production of 204,296 tons or equivalent to a productivity of 836 kg/ha/year [1].Thus, there is still wide opportunity to expand the proportion of specialty arabica coffee area as well as production in the future.Arabica coffee has naturally found in highland (950 -≥ 2,000 m asl) forest of East Africa.So, it is suitable for cultivation in high elevation areas of low latitude regions [11].Specialty coffee products had been gained from quite diverse range of elevation as well as micro-climatic conditions in Indonesia (table 1).Minimum altitudes for development of arabica coffee plantations is of 900 m asl.However, lowering the altitude below 900 m is very risky for arabica coffee plant as it could be severely damaged by pests and diseases, especially of coffee leaf rust of Hemileia vastatrix [12] and coffee berry borer of Hypothenemus hampei [13].Moreover, lower altitude at tropical regions would assosiated with higher temperature which has adverse effect on coffee beans quality [14].At low altitude, coffee cherries would rippening faster, unless the coffee plant are grown at understory of shade trees.Early ripening of coffee cherries would produce higher proportion of defected beans [15].Those condition would be exacerbated by climate change that promote rising temperature.On the other hand, many farmers tend to expand their arabica coffee plantation onto higher altitude of mountainous areas which is mostly covered by protected forest [16].It means there are serious threats on local biodiversity as well as environmental health and safety.Notes: a) from Sumatera island, b) from Java island, c) from Bali island, d) from Flores island, e) from Sulawesi island; and f) from Papua island.Source: [14].
In addition to diverse environmental conditions, all specialty arabica coffee plantations in Indonesia has composed by various arabica coffee cultivars, except for Baliem Wamena arabica coffee which composed by only single cultivar, i.e.Typica (table 2).Interestingly, early generation of recommended cultivars, such as Typica, USDA 762, and Kolombia are still widely grown and maintained by farmers.Those tall growing habit cultivars had relatively low yield and highly susceptible to leaf rust.However, the most cultivated cultivar is S 795 which has moderate yield and relatively more resistant to the disease.Modern high yielding cultivar, i.e.Sigarar Utang shows a wide spread at western part of Indonesia.Another high yielding cultivars, Andungsari has widely propagated in the eastern part of Indonesia.
Table 2. Scattered of various arabica coffee cultivars grown at each specialty arabica coffee plantation in Indonesia.

Name of Specialty Coffee
Coffee Cultivars

Replanting and rejuvenating coffee plant using improved planting materials
Various efforts have been made to improve the yield and quality of coffee in Indonesia.Coffee breeders have worked hard to develop new high yielding varieties with high yields, as well as being more resistant to pests and diseases.Several new superior varieties have been produced through hybridization and/or selection processes.Almost all of those novel varieties have compact growing habit and could produce more than 1 ton of coffee green bean per hectare [17].However, coffee farmers in Indonesia generally grow more than one cultivar of coffee in the same area.Some of them even grow more than one species.Such a cropping pattern in the long term may generate natural hybrid zones [11].Some creative farmers also carry out participatory selection activities which eventually lead to several local superior cultivars [18][19][20].Therefore, in term of cultivar type and composition, specialty coffee in Indonesia is quite dynamic.
To sustain the future arabica coffee production, it is important to generate novel cultivars highly resistance to pest and disease [21] as well as tolerance to elevated temperature and drought [22].Exploring hybrid vigour has been promising, even for C. arabica which is considered as autogamous species.Breeding for F1 hybrid cultivar was initiated in Kenya and subsequently followed by some other coffee producing countries [23].Combined with other agronomical measures describe below, resilient coffee cultivars would meet the need for sustainable specialty coffee [24].

Managing the canopy of coffee plant and shade trees
Coffee plant has understory nature in its center of origin [25].Shades protect coffee plants against adverse environmental stresses such as high temperatures, dry climates, and low soil moisture.However, coffee plants grown in direct sunlight could have higher yield, but the plants are short-lived due to high evapotranspiration [26].In contrast, coffee plants under shade trees have high assimilate production which helps maintain high coffee yields in the long term.Reduced solar radiance in the coffee canopy triggered lower ambient temperature and causes a slowing down of coffee maturation.Flowering initiation is also affected by light.Fewer flowers developed under shade and immediate fruit set is lower.This less fruit leads to more seed filling [24,27,28].Moreover, increased photosynthesis and leaf area index of coffee plant under shade trees would be transformed into larger and heavier coffee berries with which ripen more synchronously.Finally, the bold-uniform coffee beans with better quality is obtained.Therefore, shade trees plays an important role in supporting the sustainability of specialty coffee production [28].
High quality coffee produced from shade grown coffee plant as positive attributes (appearance and preference) are increase, meanwhile negative attributes (bitterness and astringency) are decrease.Enhanced attributes of brewed coffee might came from uniform ripening of coffee berries and balance seed filling [27].The sensory attributes of the brewed coffee were assessed by seven trained panelists, producing a score for each attribute and a final/total score.Most of the attributes score higher in shade than in full sun.Thus, shading is positively correlated with all sensory variables.However, the acidity and balance attributes were less influenced by management or shade level [29].
Shade trees in agroforestry system could enhance functional biodiversity, carbon sequestration, soil fertility, drought tolerance as well as weed and biological pest control [30].The existence of coffee shade trees will increase soil fertility and reduce the rate of erosion, which in turn will ensure the sustainability of coffee farming [31].Apart from functioning as a shelter for coffee plants, shade trees can also act as an important source of organic matter through large amounts of litter input [32].Shade tree leaf litter that is easily decomposed will form a layer of humus.This will recover and recycle nutrients.Therefore, litter from shade trees plays an important role in sustainable coffee plantations because it is related to nutrient cycling [33].Moreover, biological nitrogen fixation is facilitated through the use of leguminous shade trees, such as Inga oerstediana [34].
In line with increasing economic needs, the shade plants used by farmers are increasingly diverse, ranging from timber-producing trees, plantation crops, to fruit-producing trees, and service trees [35].The level of shade needed by coffee plants is around 35%.However, shade trees need to be pruned periodically and adjusting the spacing or population size so that the incoming light intensity is suitable for coffee plants and does not have a negative effect on coffee plants [36,37].
Pruning coffee plants aims to increase the intensity of light entering the coffee plant canopy and improve air circulation as well as reduce humidity.Appropriate pruning would stimulate formation of new productive branches so that the stability of plant yield can be maintained [38,39].Orthotropic shoot should selectively removed to shift nutrients translocation from vegetatif to generative parts of coffee plant.In high dense of coffee plantation, pruning is essential in order to maximize the efficiency of photosynthesis and to reduce the risk of disease attacks.There is positive impact of pruning on arabica coffee yield [40,41].
Many coffee-producing countries apply pruning techniques to rejuvenate coffee plants, increase berry yields, and suppress coffee berry borer attacks [42].Under high density planting systems, coffee crop management through pruning is fundamental for renewal, revitalizing and yield stability in coffee plantations [43].In dense cropping systems, coffee plant management through pruning is essential to renew, revitalize and stabilize coffee yields [43].The average production of ripe berries on pruned plants was much higher than on unpruned plants over a two-year period.Pruning is also required early to help reduce infestation by the coffee berry borer.Good coffee plantation sanitation will reduce the breeding media for insect pests [44].

6
Farmers in Indonesia has been widely applied single stem pruning, consisting of canopy pruning, maintenance and rejuvenation.The advantage of the single-trunked system is that it is able to form secondary branches and maintain individual stems.Shape pruning is a clipping treatment especially for plants that have difficulty growing reproductive branches.Maintenance pruning or production pruning consists of off-harvest pruning, selective pruning (selective shoot removal) and coarse pruning (overall shoot removal).Selective pruning aims to prepare fruit-bearing branches for the next year's production.In principle, excess branches must be trimmed so that sunlight can enter the canopy and good air circulation, so that the growth process is good.Selective pruning is carried out twice a year.Rejuvenation pruning aims to renew the plant canopy by cutting diseased and/or unproductive branches, consisting of pruning old shoots or stems that are no longer productive using a saw as well as pruning young, diseased and unnecessary branches manually without using a tool [45,46].

Using organic fertilizer and biofertilizer
Coffee plants require the major nutrients of N, P and K as well as minor nutrients, such as iron, copper, manganese, zinc, boron, sodium, molybdenum, and chlorine.Therefore, productivity and sustainability of specialty coffee production is highly dependent on good nutritional management.Coffee bean has high nutritional value with which requires a large amount of nutrient inputs such as organic fertilizers.Nutrient inputs derived from bilogical sources such as litter fall from coffee and shade tress as well as compost are essential for specialty coffee production in organic farming system in addition to that of the widely used source of biofertilizer.In addition, organic fertilizers could have other benefits as they can improve soil organic matter content as well as increase water infiltration and water holding capacity.Part of the nitrogen needed can be provided for by nitrogen fixing shade trees [47].
Organic fertilizers or organic matter added to the soil could enrich organic matter content of the soil while improving the physical and chemical properties of the soil in order to meet the needs of various types of microorganisms that play an active role in improving the quality of the topsoil [48].Soil was found to have higher macrofauna (31.4%), microbial population (34%), and microbial diversity indices when enriched by organic fertilizer compared to chemical fertilizer.In the long-term, organic fertilizer has better impact on soil properties compared to chemical fertilizer [49].
Coffee pulp and husk, by-products of coffee processing, are organic residues that can be used as fertilizer for coffee.Coffee husk and coffee pulp have been usually incubated for composting as the recycling of organic fertilizer in agriculture.Applying compost made from ground coffee and husks with different organic residues has been shown to significantly increase coffee yields.Compost made from the byproducts of coffee processing can provide many of the mineral nutrients needed by coffee trees for normal growth and sustainable yields and enable the production of organic coffee which is in world demand today.Most importantly, these practices are environmentally friendly and economical [48,50].The compost from coffee husk supplemented with cow manure, and fertilizers (phosphorus and urea) was used for coffee plant on the field with amount of 2.0-3.0 kg.plant-1.year-1during 3 years and reduced using from 20% to 30% chemical fertilizers.The results showed that fertility of soil, mineral nutrients in the coffee leaf and the growth of the coffee were improved in comparison with plots that no using this compost [51].
The use of compost fertilization supplemented green manure from Crotalaria juncea increased growth in height and diameter of the coffee canopy.In the first year, the percentage of N reached 8.5% at seven months and 4.1% at fifteen months after fertilization.In the second year, the percentage of N derived reached 17.9% N at the early harvest, five months after fertilization.The organic compound increases leaf N content in coffee trees [52].
Organic fertilizers produced through the decomposition of organic waste are known as vermicompost.The decomposition of organic waste is assisted by earthworms, which will then follow by microbes.The nutritional content is higher with a simpler structure and easily absorbed by coffee plants.Vermicompost has stabilized and neutral pH and free of seeds, pathogen, pesticides and heavy metals [53].It could have a significant effect on plant height and fresh weight, and had a very significant effect on the variables of dry weight of coffee seedlings in the main nursery.The use of vermicompost fertilizer from coffee husk waste can substitute NPK inorganic fertilizer for coffee nurseries in the main nursery [54].
Biofertilizers are organic fertilizers containing beneficial microorganisms with the potential to improve soil fertility and crop productivity, are valuable to the environment as they reduce dependency on chemical fertilizers [55].The results of greenhouse experiments showed that the biofertilizer product consortium enzymatic producing fungi gave significant effects on growth of coffee plants and increased the organic matter in soil.The biofertilizer product could provide a good choice to apply on coffee plants to decrease the application of chemical fertilizers [56].In Oaxaca, the production of organic coffee has increased with the practice of mycorrhizal inoculation [57].The use of the mycorrhizal consortium formed by the fungi Glomus claroides + Rhizophagus diaphanus + Paraglomus albidum increased the plant height, dry biomass, and phosphorus content compared with the non-inoculated plants [58].

Rainwater harvesting and irrigation systems
A lot of coffee plantation in Indonesia are grown under rainfed conditions [59].Rainwater harvesting in coffee plantations could maintain soil moisture content during drought periods.Rain water harvesting includes silt pit construction, reservoir development, and infiltration well construction (biopore).Making silt pit, silt pit is a dead-end channel constructed next to the coffee plant to collect and absorb surface runoff water into the soil, slowing the runoff rate and placing organic fertilisers.Building reservoir, water management with installation and setting up of irrigation techniques supported by technology in water saving irrigation and distribution techniques.Making biopore, biopore is infiltration wells to collect rainwater and seep it back into soil [60].
Rainwater harvesting treatments were able to increase the soil moisture storage.L-shape silt pit was able to increase water storage by 3.05 %, parallel silt pit was able to increase water storage by 2.32 %, and biopore was able to increase water storage by 1.54 % [61].Silt pit on coffee plantation increase nutrient content of N, P, K and soil pH as well as land productivity.Land using silt pit give yields 1047.61kg green bean / ha / year and land without rorak 683.89 kg green bean / ha / year [62].the amount of silt pit should be 50% of the number of coffee plants per hectare.It is necessary to add organic matter to increase the ability of the silt pit to bind water [63].
Drip irrigation is becoming a common technique for improving coffee yield in Brazil because it provides a more controlled production environment and avoids production losses due to soil water deficits.The adoption of drip irrigation causing increase in coffee plant height, crown diameter and stalk diameter.The irrigated coffee obtained the average yield of 2623 kg ha −1 , while the coffee without irrigation had anaverage yield of 1026 kg ha −1 .The irrigated treatments had greater root concentrations as compared to the non-irrigated treatments [64].
Basin and sprinkler irrigation are the two traditional irrigation methods in Vietnam.The source of irrigation water is mainly from the dug open wells at farms and/or nearby lakes [65].Coffee farms using the sprinkler system are more efficient than those using the basin irrigation technology [66].

Integrated pest, desease, and weed management
Pest and desease are among the different factors causing tremendous yield reduction in organic coffee.Pest and desease management strategies can be implemented in integrated approach of organic coffee system, including cultural methods, use of resistance variety, biological control, non synthetic chemicals application and mechanical management methods [47].The strategies aim not only to recover coffee productivity but also to escape from environmental and social risks caused by conventional agriculture practices as well as to reduce the dependency on external inputs such as pesticides [67].
Insects of coffee berry borer [CBB, Hypothenemus hampei (Ferr.)]become very damaging pests as it grows and breeds very fast inside the coffee berries.It causing a decrease in coffee production and yield quality significantly because it leaves the coffee beans with holes.The loss of coffee yield by CBB can reach more than 50% at high intensity of insect investation and proper pest control is not taken.Attacks on early phase of fruit development could cause fruit decay, whereas attacks on mature fruit (ripe) result in a decrease of coffee beans quality.Those damages directly affect coffee yield and quality [68].
An Integrated Pest Management used by coffee farmer in Indonesia consist of (1) sanitation of tree and ground raisins for areas with short growing seasons, and large estates, (2) pruning of both cofee and shade trees, (3) natural predators such as birds and ants, (4) parasitoids including the previously released Prorops nasuta and Cephalonomia stephanoderis, (5) sprays of the entomopathogenic fungus Beauveria bassiana, and (6) monitoring and control through mass trapping using alcohol-baited funnel traps.The main cultural practices for pest control in coffee crops are related to CBB and consist of harvesting dry overripe fruit on trees and cleaning up of abscised fruits on the ground to reduce CBB reservoir in the inter-crop season [10].Implementing good agriculture coffee cultivation including fertilization to improve plant health, pruning, and weed supression are related to CBB control [68].Pruning coffee plants can remove CBB until 70% because CBB is a type of lice which cannot stand the heat of the sun.The way to handle CBB was by doing sanitation, keeping the coffee farms clean, burying the fallen coffee berries, and planting shade trees [69].
The cultivation method is also one of the main disease control methods in organic coffee production systems.The method of controlling in cultivation is mainly done by keeping the coffee trees healthy and strong to reduce attacks.Hand weeding, cutting, increasing population density, intercropping with cash crops, and mulching are some of the cultural weed control methods for dealing with weed problems in organic coffee production.Certain fungi are used to control weeds as microbial herbicides [47].

Selective cherry harvest
Specialty coffee grade derived from uniform coffee bean size and quality.Producing uniform coffee beans needs carefull handling during cherry harvesting, i.e. select only ripe red or yellow cherries with which has the same and the right age of development.However, coffee beans derived from immature as well as overripe cherry has poor physical as well as beverage quality.Moreover, Ochratoxin A (OTA) contamination level is higher in coffee beans derived from immature and overripe cherry.Uniform coffee bean should also coming from single coffee cultivar or mixed cultivars with which has similar bean shape and size [70].Hand-picking ripe coffee cherry has been applied by many farmers in Indonesia

Conclusion
Many threats as well as challenging situations in the next decades should be able to anticipated and mitigated to guarantee supply of specialty coffee in global market.However, the sustainability of specialty coffee production is depend largely on many aspects of inter-related agronomical measures.Highly resilient cultivars combined with healthy and balance ecosystem is vital to be able to respond any future threats and challenges.

Figure 1 .
Figure 1.Distribution and proportion of specialty arabica coffee plantations in Indonesia.Sources: www.kopimat.com.

Table 1 .
Range of micro-climate and elevation of 17 specialty arabica coffee plantations developed in Indonesia