Arabica coffee yields at various harvest seasons and altitudes in the Gayo Highlands, Aceh

Arabica coffee yields in the Gayo Highlands, Aceh, are limited by altitude. Areas suitable for coffee are an altitude of 1000-1600 m asl. Climate changes, especially rising temperatures, result in vulnerability to Arabica coffee yields. This study aims to study coffee yields at various locations based on altitudes and harvest seasons. This study used a split-plot design, with 3 replications. The main plot is two season harvests (S) (March-June Harvest and September-December Harvest), and the sub-plot is six locations based on altitudes in Bener Meriah (BM) and in Aceh Tengah (AT), i.e.: BM>1000-1200 m asl, BM>1200-1400 m asl, BM >1400-1600 m asl, AT>1000-1200 m asl, AT>1200-1400 m asl, and AT >1400-1600 m asl. The season harvests did not affect all coffee yield parameters. Altitudes significantly affected the average number of coffee cherries/plant, the average weight of 100 dry coffee beans, and the average weight of dry coffee beans/plant but did not affect the average weight of coffee cherries/plant. The combination of harvest seasons and altitudes (locations) shows that in the March-June harvest season, location BM>1200-1400 m asl results in a better average weight of 100 dry coffee beans than September-December harvest season, while in AT>1200-1400 m asl is the other way around.


Introduction
The sustainability of today's agricultural productivity is highly vulnerable to climate change, so agricultural practices should follow a more serious pattern of mitigation on the one hand and limiting adverse impacts on biodiversity and other ecosystem services on the other.Agroforestry systems, 1297 (2024) 012001 IOP Publishing doi:10.1088/1755-1315/1297/1/012001 2 cultivation patterns that include tree crops in a cropping system both spatially and temporally, are ideal candidates for sustainable and climate-smart intensive agricultural systems, as agroforestry systems are widely expected to improve soil fertility, regulate pest and disease balance, and buffer crops from the impacts of climate change.In addition, agroforestry systems also serve to mitigate climate change through carbon sequestration while maintaining biodiversity [1] [2].Agroforestry coffee systems, especially in cultivation systems that use shade crops as protection, are ideal systems to address the above issues, especially in sub-optimal environmental conditions, such as high temperatures, or sloping areas, as well as microclimate regulation and soil protection [3] [4].
Arabica coffee is Aceh's leading commodity, in addition to being an export product, it also plays an important role in the income of coffee farmers.Aceh's arabica coffee is known as speciality coffee and has gained international recognition through several certifications such as 'Fair Trade' and 'Organic'.Aceh's Arabica coffee area reached 100,590 hectares, spread across Central Aceh District (49,366 hectares) producing 31,597 tons, Bener Meriah District (46,294 hectares) producing 32,100 tons and Gayo Lues District (4,930 hectares) producing 1,425 tons.[5].In Aceh, arabica coffee yields are limited by altitude, with areas suitable for its development being those at 1000-1500 m above sea level [6].Studies on the effects of global warming on coffee production and carbon and energy footprints show that coffee production will not only decline markedly but will also be severely impacted [7][8].
Anhar, et al. [9] reported that coffee production in the Gayo Highlands (DTG), which is cultivated at lower altitudes of 900-1000 m above sea level (asl), experienced a significant decline in coffee quantity and quality compared to higher altitudes.Hifnalisa and Karim [10] have reported a significant correlation between altitude and variety in the quantity and quality of Ariba coffee in the Gayo Highlands.Unfortunately, information on adaptation patterns carried out by coffee farmers in the Gayo Highlands is still very limited.Arabica coffee yield is affected by temperature and is highly susceptible to and significantly reduces coffee yield even with a 1 °C increase in temperature.With the scenario that the general temperature will decrease by about 0.6 °C for every 100 m above sea level, there will be a decrease in temperature between 1.0-1.2°C for every 200 m above sea level.Temperatures tend to decrease in higher areas for every 200 m increase, namely >1000-1200 m asl, > 1200-1400 m asl, and >1400-1600 m asl.This decrease in temperature is thought to increase coffee yields.
Another important piece of information to research is environment-specific (harvest season) coffee productivity.There are two harvest seasons in DTG.March-June harvest season (intermediate season) and September-December harvest season (peak season).The intermediate or peak season is named because the coffee harvest in the intermediate season is much smaller than in the peak season.However, based on information from coffee actors, this condition is no longer absolute.This study aims to study coffee yields at various altitudes (locations) based on altitudes and harvest seasons
Bener Meriah District is in the category of Climate Type A (Q = <14.4%),namely the Very Wet Area, with the average annual rainfall amount for the 2009-2021 period in Bener Meriah District being 2633.3 mm/year.Aceh Tengah District is categorized as Climate Type B (Q = 14.3-33.3%),namely Wet Areas with an average annual rainfall amount (CH) for the period 2009-2021 of 2617.1 mm/year.In general, in both districts, the average temperature ranges from 25.8-27.5°C,and the average humidity ranges from 81.2-87.1% [11].
To obtain real field data on differences in air temperature and humidity at various altitudes of the place under study, direct observations were made using a temperature and humidity measuring device (Data logger) from March 2022 to September 2022.Digital temperature and humidity measuring devices were placed at 6 research sites at 2 heights at low altitudes (>1000-1200 m asl), 2 at medium altitudes (>1200-1400 m asl), and 2 at high altitudes (>1400-1600 m asl).Temperature and humidity were recorded at every 1-hour interval.The average daily air temperature at the study site was 20.40 (3.89) °C, with a minimum air temperature of 9.60 °C and a maximum air temperature of 34.30 °C.The recording results show that the average daily air temperature at low altitude (>1000-1200 m asl) is 22.34 °C with a minimum air temperature of 16.05 °C and a maximum air temperature of 31.55 °C, at medium altitude (>1200-1400 masl) is 21.10 °C, with a minimum air temperature of 14.25 °C and a maximum air temperature of 31.85 °C.at high altitude (>1400-1600 m asl) is 18.75 °C, with a minimum air temperature of 11.20 °C and a maximum air temperature of 29.8 °C.The results show that there is an average temperature difference of -1.24 °C between low and medium altitude and -2.24 °C between medium and high altitude.The average daily air humidity at the study site was 87.58%, with a minimum air humidity of 37.20% and a maximum air humidity of 100%.
The soils in both study districts are dominated by Andisols characterized by highly porous, black soil, low specific gravity, and predominantly "amorphous" exchange complexes.Rapid weathering of porous parent material produces "allophanic compounds" (allophane and imogolite) [12].

Plot Selection
The coffee plant plot is the farmer's entire coffee farm, with a minimum land area of 0.50 ha, coffee age between 5 -25 years, and coffee plant population of at least 1000 plants/ha.The selected coffee plots must implement good coffee plant cultivation management, at least implementing 4 aspects of the six aspects of coffee cultivation, namely pruning, shading more than 100 trees/ha, weed control, fertilization, pest and disease control, and/or land conservation.The results of interviews with farmers, and direct observation of farm conditions, were used as the basis for determining coffee farm plots that would be used to observe coffee yield variables (number of coffee cherry/plant, weight of coffee cherry/plant, and weight of dry beans of coffee plants).The designated plot should be in one of the observed elevation intervals.The tools used were digital temperature and humidity meters, digital scales, buckets for soaking and sorting beans, drying plastic, coffee storage packaging, stationery, and others deemed necessary.

Harvest Season
Direct observation in farmers' fields through a plot approach was conducted for 1 year covering 2 harvest seasons (March-June intermediate harvest season and September-December peak harvest season).

Coffee Yield
Coffee yield is the weight of coffee fruit/plant and the weight of coffee dry beans/plant.a) Number of coffee cherry/plant (cherry), counted as the total number of coffee cherries/plant in the 1 month before harvest stadia; b) Weight of coffee cherry/plant (g), calculated by multiplying the number of coffee cherries/plant by the average weight of coffee cherries/cherry.c) Weight of coffee dry bean/plant (g), obtained by conducting post-harvest processes as carried out by most farmers in the research location.Coffee cherries weighing 12 kg harvested for each variety in one plot under study, were rambled into a container filled with water, to remove floating coffee cherries.The coffee fruit is sunk, and pulped to remove the skin from the beans, then the beans are washed.The sunken coffee beans are then dried in the sun for 2-3 days depending on the weather, until they reach a moisture content of 20%.The horn skin is then removed from the coffee beans using a huller machine, then dried in the sun until it reaches 15% moisture content; and d) the weight of 100 dried coffee beans, calculated by weighing 100 dried coffee beans.

Data Analysis
The results of data normality analysis (Kolmogorov-Smirnov test) showed that the data of coffee yield, namely the number of coffee cherry/plant, the weight of coffee cherry/plant, the weight of coffee dry beans/plant and the weight of 100 coffee dry beans were normally distributed.So that the effect of altitude categories, in 2 harvest seasons is analyzed by a parametric test (Split-split Plot Design), with harvest season as the main plot and altitude as the subplot.If the results of the analysis showed a significant difference, then further tests were carried out using the Least Significant Difference Test (LSD Test) p < 0.05.Statistical analysis was carried out using SPSS software version 23.0.

Characteristics of Research Plot
The characteristics of the research plots for testing coffee yield variables (average number of coffee cherries/plant, average weight of coffee cherries/plant, weight of coffee dry beans/plant, and weight of 100 coffee dry beans) in the 2021 harvest are listed in Table 1.The average elevation is 1304.7 m above sea level (186.2) with a low of 1022 m above sea level and a high of 1600 m above sea level.The average plant age was 12.11 (2.94) years, with the youngest coffee plant at 6.33 years and the oldest at 17.00 years.The average number of coffee cherries/plant was 1385.9 (247.02), with the lowest number of coffee cherries/plant being 801.83 and the highest being 1849.1.The average weight of coffee cherry/plant was 1742.3 (755.5)g, with the lowest weight of coffee cherry/plant being 1479.3 g and the highest being 3609.0 g.The average weight of coffee dry beans/plant (15% moisture content; 7-8% triage) was 384.60 (62.77) g, with the lowest weight of coffee dry beans/plant being 233.92 g and the highest being 520.71 g.The average weight of 100 dry coffee beans was 28.17 (4.36) g, with the lowest weight of 100 dry coffee beans being 19.30 g and the highest being 40.85 g.

Harvest Season
The results of the analysis of variance showed that the harvest season did not affect the average number of coffee cherries/plant, the average weight of coffee cherries/plant, the average weight of dry coffee beans/plant, and the average weight of 100 dry coffee beans.The average number of coffee cherries/plant, average weight of coffee cherries/plant, average weight of coffee dry beans/plant, and average weight of 100 coffee dry beans in different harvest seasons can be seen in Table 2.  2 shows that the naming of the peak harvest season for the September-December harvest is not very fixed.This is because although the studied coffee yield variables, namely the average number of coffee cherry/plant, the average weight of coffee cherry/plant, the average weight of coffee dry beans/plant, and the average weight of 100 coffee dry beans showed higher results compared to the intermediate harvest season or the March-June harvest, the overall results of the variables in the two harvest seasons were not statistically significantly different.It is suspected that the pattern of rainfall and air temperature before the intermediate harvest season and the peak harvest season is not much different from the previous period.Global studies show that rainfall factors such as annual and seasonal rainfall are less important than temperature in determining coffee crop suitability [13] [14].Other studies suggest that heating may be less harmful to coffee suitability than previously thought, at least under conditions of adequate water supply [15].Coffee plants can cope with increased temperatures to a certain extent.However special attention needs to be paid to increased coffee pest pressure [16].

Location (Altitude)
The results of the analysis of variance showed that the research location(altitude) had a very significant effect on the weight of coffee dry beans/plant, and the weight of 100 coffee dry beans, significantly affected the number of coffee cherries/plant, but had no significant effect on the weight of coffee cherry/plant.
The average number of coffee cherry/plant, average weight of coffee cherry/plant, average weight of coffee dry beans/plant, and average weight of 100 coffee dry beans due to location (altitude) can be seen in Table 3 Table 3.The average number of coffee cherries/plant, the average weight of coffee cherries/plant, the average weight of coffee dry beans/plant, and the average weight of 100 coffee dry beans at various altitudes (locations) Table 3 shows that the best average number of coffee cherry/plant was found in the location of BM >1200-1400 m above sea level, which was significantly different from the altitudes (locations) of AT >1000-1200 m above sea level, AT >1200-1400 m above sea level, and BM >1400-1600 m above sea level, but not significantly different from BM >1000-1200 m above sea level and AT >1400-1600 m above sea level.This shows that the number of coffee cherries/plant varies greatly by location and altitude.The high number of coffee cherries/plant at altitudes >1000-1200 m above sea level and >1400-1600 m above sea level is not positively correlated with the average dry bean weight of coffee/plant.The highest average dry bean weight of coffee/plant remained at BM >1200-1400 m asl and AT >1200-1400 m asl.This indicates that the ideal environmental conditions to support coffee development and yield are at altitudes >1200-1400 m asl, compared to altitudes >1000-1200 m asl and >1400-1600 m asl.The high number of cherries at the latter two heights may not all produce dry seeds, which may be damaged or hollow due to pest and disease attacks or due to incomplete physiological processes.The low weight of coffee dry beans/plant at altitudes (locations) >1000-1200 m above sea level and >1400-1600 m above sea level is thought to be due to the high loss or low ratio of coffee fruit/plant weight to coffee dry beans/plant at lower altitudes, as well as due to the physiological activities of coffee plants that are not optimal at higher altitudes (locations).DaMatta dan Ramalho [17] reported that coffee photosynthesis is very sensitive to temperatures above 20-25 °C.At high temperatures coffee growth is reduced especially in areas that have a warmer climate type, while the development and maturation of the coffee fruit is accelerated, resulting in a decrease in coffee quality due to incomplete bean filling.With increasing temperatures, coffee production tends to decrease at lower elevations, which also addresses the importance of shade/shade crops for adaptation to excessive solar radiation and temperature [18].Shade trees also function in the management of coffee plant pests and diseases.Coffee berry borer infestation and fungal pathogen spread rates are lower in shaded than in open cultivation systems [19].Reduced temperature around the shade will slow down the development of coffee berry borer larval stages (Jaramillo et al., 2009).In addition, shade trees can contribute to pest control by supporting pest control species such as birds and ants [21][22] Whereas at high altitudes, cooler temperatures, and clouds, reducing incoming radiation, can limit the yield component of coffee.The absence of a positive effect of increasing altitude on coffee yield was also found by similar studies in smallholder plantations in Costa Rica [23][9].De Bauw et al. [24] explained the absence of an effect of altitude, possibly due to the gradient of soil fertility present in the area, with more fertile soils in the lowlands.

Combination of Harvesting Season and Location (Altitude)
The results of the analysis of variance showed that the combination of harvest season and research location(altitude) had a very significant effect on the average weight of 100 dry coffee beans.The average weight of 100 dry coffee beans in various combinations of harvest season and location(altitude) can be seen in Table 4 Table 4 shows that the best average weight of 100 dry coffee beans in the Mar-Jun harvest season was found in the location of BM >1200-1400 m above sea level which was significantly different from the location of BM >1000-1200 m above sea level, although not significantly different from the location of AT >1000-1200 m above sea level, AT >200-1400 m above sea level, BM >1400-1600 m above sea level, AT >1400-1600 m above sea level.In the Sep-Dec harvest season, the best average weight of 100 dry coffee beans was found at the AT >1200-1400 location which was significantly different from the other altitudes (locations).This indicates that the altitude of 1200-1400 m above sea level produces a better average weight of 100 dry beans compared to locations at an altitude of >1000-1200 m above sea level in the Mar-Jun harvest season; while in the Sep-Dec harvest season, altitudes (locations) AT >1200-1400 m above sea level and BM >1400-1600 m above sea level produce a better average weight of 100 dry beans compared to other altitudes (locations).Description: Numbers in parentheses = standard deviation.Numbers followed by the same lowercase letter in the same row and the same capital letter in the same column are not different at LSD P<0.05.

Conclusions
The yield of coffee in Gayo Highland was not significantly different between the two harvest seasons.This also refutes the initial assumption that the peak harvest (September-December) produces higher coffee than the intermediate harvest (March-June).
Location (altitude) >1200-1400 m asl in general results in better coffee yield than location (altitude) >1000-1200 m asl and >1400-1600 m asl.This shows that the sustainability of coffee needs serious attention at lower altitudes (>1000-1200 m asl) and/or higher altitudes (>1400-1600 m asl).
The combination of harvest seasons and location (altitude)shows that in the March-June harvest season, location BM>1200-1400 m asl results in better the average weight of 100 dry coffee beans than September-December harvest season, while in AT>1200-1400 m the average weight of 100 dry coffee bean is the other way around.Therefore, the coffee yields are greatly influenced by environmental factors at the production stage.

Figure 2 .
Figure 2. Average number of coffee cherry/plant and average dry bean weight of coffee/plant, at various altitudes (locations)

Table 1 .
Characteristics of research plots and coffee yield variables in the 2021 harvest (n = 36 plots)

Table 2 .
The average number of coffee cherries/plant, the average weight of coffee cherries/plant, average weight of coffee dry beans/plant, and average weight of 100 coffee dry beans in different harvest seasons

Table 4 .
Average weight of 100 dry coffee beans (g) in different combinations of harvest season and location (altitude)