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agronomy
Article
Sustainable Production of Robusta Coffee under a
Changing Climate: A 10-Year Monitoring of Fertilizer
Management in Coffee Farms in Vietnam
and Indonesia
Vivekananda Byrareddy * , Louis Kouadio , Shahbaz Mushtaq and Roger Stone
Centre for Applied Climate Sciences, Institute for Life Sciences and the Environment, University of Southern
Queensland, Toowoomba 4350, Queensland, Australia
*Correspondence: vivekananda.mittahallibyrareddy@usq.edu.au; Tel.: +61-7-4631-1169
Received: 29 July 2019; Accepted: 28 August 2019; Published: 30 August 2019
Abstract:
Assessing and prescribing fertilizer use is critical to profitable and sustainable coffee
production, and this is becoming a priority concern for the Robusta coffee industry. In this study,
annual survey data of 798 farms across selected Robusta coffee-producing provinces in Vietnam
and Indonesia between 2008 and 2017 were used to comparatively assess the fertilizer management
strategies in these countries. Specifically, we aimed to characterize fertilizer use patterns in the key
coffee-growing provinces and discuss the potential for improving nutrient management practices.
Four types of chemical (NPK, super phosphate, potassium chloride and urea) and two of natural
(compost and lime) fertilizers were routinely used in Vietnam. In Indonesia, NPK and urea were
supplemented only with compost. Farmers in Vietnam applied unbalanced quantities of chemical
fertilizers (i.e., higher rates than recommended) and at a constant rate between years whereas
Indonesian farmers applied well below the recommended rates because of poor accessibility and
financial support. The overuse of chemical fertilizers in Vietnam threatens the sustainability of
Robusta coffee farming. Nevertheless, there is a potential for improvement in both countries in terms
of nutrient management and sustainability of Robusta coffee production by adopting the best local
fertilizer management practices.
Keywords: Robusta coffee; smallholder farms; sustainability; chemical fertilizer; organic fertilizer
1. Introduction
Coffee is one of the top-traded agricultural commodities worldwide [
1
,
2
]. It is cultivated in over
50 countries and covers more than 11 million ha around the world [
3
]. Coffee plays a crucial role in the
economies of producing countries (e.g., the gross domestic product largely depends on coffee export
revenues with the sector employing an important proportion of the rural population [
3
,
4
]. The two
economically important coffee species—Arabica (Coffea arabica L.) and Robusta (C. canephora Pierre
ex A. Froehner)—account for about 99% of world coffee production [
3
,
5
,
6
] with Arabica representing
roughly 60%.
Producing healthy coffee plants throughout the growth cycle, particularly during sensitive
phenological stages (flowering, cherry development, and bean filling) requires sufficient levels of
mineral nutrients such as nitrogen (N), phosphorus (P) and potassium (K) in the soil to avoid
any nutrient stress [
7
,
8
]. This pre-supposes suitable environmental conditions (air temperature,
water availability, intensity of sunshine, soil type, wind and land topography) and other management
practices (such as pest and disease control and pruning) [
5
,
9
]. In perennial crops like coffee, fertilizers
are applied to replace the nutrients removed during the harvest and address the nutrient need during
Agronomy 2019,9, 499; doi:10.3390/agronomy9090499 www.mdpi.com/journal/agronomy
Agronomy 2019,9, 499 2 of 19
the following growth cycle. Coffee is harvested as cherry; this includes pulp and parchment which are
often not returned to the field and so are lost to the system [
10
]. It has been estimated that the major
nutrients removed in one ton of coffee green beans may be 33–63 kg N, 2–11 kg P
2
O
5
and 47–67 kg K
2
O
depending on soil type and fertilizer application [
7
,
8
,
10
–
12
]. In the Central Highlands of Vietnam, the
nutrient removal from Robusta coffee farms has been estimated to average 33 kg N, 1 kg P
2
O
5
and 30
kg K
2
O for each ton per hectare of green beans harvested (ignoring nutrient losses from leaching and
erosion) [13].
In the coffee industry, sustainability has become a paramount concern over the past several years.
Developing sustainable agricultural production systems involves dealing with various and interrelated
aspects including water management, land capability and use, biodiversity, energy, soil quality,
agricultural production and productivity, and socio-economic aspects [
14
,
15
]. Of particular interest for
coffee is the implementation of environmentally-friendly and sustainable production practices [
4
]. The
coffee industry’s growth in the major producing countries is expected to be fuelled over the next years
given an increased activity at both consumer and trade levels from both domestic and foreign players.
Given its economic importance and the environmental risks and vulnerabilities that its production
could pose or face, the coffee industry requires special attention.
The main purpose of this study was to provide a detailed characterization of one of the
most important management practices in coffee production—fertilizer application—for the top
coffee-producing countries in South-East (SE) Asia, namely Vietnam and Indonesia. Assessing
and prescribing fertilizer use is critical to ensure profitable and sustainable coffee production systems.
Vietnamese coffee production averaged 1.46 million metric tons during 2014–2017 for about
597,000 hectares harvested [
16
] while Indonesian production averaged 553,000 metric tons for
about 1 million hectares harvested over the same period [
17
,
18
]. Coffee production in both
countries is dominated by Robusta coffee—95% in Vietnam and about 85% in Indonesia [
16
,
17
,
19
].
The total production of both Vietnam and Indonesia represents about 60% of global Robusta coffee
production [20,21], and the two countries rank respectively second and fourth worldwide [20].
In Vietnam, a combination of factors including local institutional reforms in the 1980s,
state-sponsored migration, suitable land for production and infrastructure investment in irrigation,
have accelerated the expansion of coffee farms and led to an increase in coffee production over the
1990s and 2000s. The total coffee area has risen from around 22,000 ha in 1980 to around 665,000 ha by
2017 [
16
,
22
]. Although the total Vietnamese coffee area has increased by only 33% over the last 14 years
(2004–2017) [
16
], the trend is likely to be on expanding producing areas, but with the potential effect of
imbalanced fertilizer application [
13
,
19
]. Similar future prospects could be noted for Indonesian coffee
sector [23,24].
Using annual survey data of 798 farms across selected Robusta coffee-producing provinces in
Vietnam and Indonesia during the 2008–2017 period (with a total of 7980 observations), the main
objective of this study was to comparatively assess fertilizer management strategies in the two major SE
coffee-producing countries. Specifically, the paper aimed to address the following questions: (1) what
fertilizers (chemical and organic) were used in Robusta coffee farms in Vietnam and Indonesia over the
last ten years? (2) were there different fertilizer management practices between provinces in each of
the countries? (3) what are the potentials for improved sustainable fertilizer application in Robusta
coffee farms in Vietnam and Indonesia? Few papers or published reports have dealt with such topic in
both countries. As such, our findings will provide further insight into the fertilizer management in
Robusta coffee farms in these countries and could help in adopting environmentally-friendly coffee
management practices.
Agronomy 2019,9, 499 3 of 19
2. Materials and methods
2.1. Study Areas
2.1.1. Vietnam
The study areas in Vietnam were located in four provinces of the Central Highlands region—Dak
Lak, Dak Nong, Gia Lai and Lam Dong (Figure 1A). These are the main provinces producing Vietnamese
Robusta coffee, accounting for more than 90% of the national production [
16
]. Robusta coffee is typically
grown as an unshaded and clean-weeded monocrop in Central Highlands [25].
Agronomy 2019, 9, x FOR PEER REVIEW 3 of 20
Figure 1. Location of the study areas in Vietnam (A) and Indonesia (B). The boundaries of the study provinces
(red line) and districts (blue line) are shown. Source: GADM database of Global administrative areas
(https://gadm.org/).
The Central Highlands region is dominated by a humid tropical climate. Climate data over 30 years
(1985–2014) showed that the total annual rainfall ranged from 1800 to 3000 mm across the four study
provinces (Figure S1A). Maximum temperatures were normally above 24 °C, and the average monthly solar
radiation ranged from 428 to 698 MJ m−2. Two main soils in the Central Highlands region are reddish-yellow
acrisols and reddish-brown ferrosols, with coffee trees are cultivated mostly on the latter [13,26].
2.1.2. Indonesia
Robusta coffee is grown predominantly in Southern Sumatra provinces in Indonesia, namely in
Lampung, South Sumatra and Bengkulu provinces (Figure 1B). These provinces account for about 60% of
the national total coffee area and about 75% of the national Robusta production [17,24].
The total annual rainfall across the coffee-growing areas during 1985–2014 ranged from 3000 to 3249
mm (Figure S1B). Maximum and minimum temperatures are typically above 27 °C and 23 °C, respectively.
The dominant soils in coffee-growing provinces in Indonesia are rhodic ferrosols and orthic acrisols [27].
2.2. Study Design: Annual Monitoring of Fertilization Management–Farmers Survey
Data were collected within the Sustainable Management Services (SMS) programme implemented by
ECOM Agroindustrial Corporation since 2005 across coffee-producing countries in the Asia Pacific region
Figure 1.
Location of the study areas in Vietnam (
A
) and Indonesia (
B
). The boundaries of the
study provinces (red line) and districts (blue line) are shown. Source: GADM database of Global
administrative areas (https://gadm.org/).
The Central Highlands region is dominated by a humid tropical climate. Climate data over
30 years (1985–2014) showed that the total annual rainfall ranged from 1800 to 3000 mm across the four
study provinces (Figure S1A). Maximum temperatures were normally above 24
◦
C, and the average
monthly solar radiation ranged from 428 to 698 MJ m
−2
. Two main soils in the Central Highlands
region are reddish-yellow acrisols and reddish-brown ferrosols, with coffee trees are cultivated mostly
on the latter [13,26].
Agronomy 2019,9, 499 4 of 19
2.1.2. Indonesia
Robusta coffee is grown predominantly in Southern Sumatra provinces in Indonesia, namely in
Lampung, South Sumatra and Bengkulu provinces (Figure 1B). These provinces account for about 60%
of the national total coffee area and about 75% of the national Robusta production [17,24].
The total annual rainfall across the coffee-growing areas during 1985–2014 ranged from 3000 to
3249 mm (Figure S1B). Maximum and minimum temperatures are typically above 27
◦
C and 23
◦
C,
respectively. The dominant soils in coffee-growing provinces in Indonesia are rhodic ferrosols and
orthic acrisols [27].
2.2. Study Design: Annual Monitoring of Fertilization Management–Farmers Survey
Data were collected within the Sustainable Management Services (SMS) programme implemented
by ECOM Agroindustrial Corporation since 2005 across coffee-producing countries in the Asia Pacific
region including Vietnam and Indonesia. The main objective of the SMS programme is to promote
more sustainable coffee production and to strengthen traceability and transparency throughout the
coffee supply chain. Through the SMS programme, coffee farmers are regularly trained on various
aspects of farm management practices (such as balanced fertilization and soil nutrition improvement,
tree stock management, pest and disease control, irrigation, farm bookkeeping, farm diversification
and farm certification).
Coffee farm activities are monitored throughout every crop season, with three to four farm surveys
each year with farm data collected using designed questionnaires. Questionnaires were translated
into the local languages and local agronomists who speak these languages conducted the interviews.
Data were managed through the SMS database within ECOM. Farmers also keep their data using farm
books, given such information is also valuable in certification programmes.
Within the SMS programme, more than 5000 coffee farmers are enrolled in Vietnam and more
than 2000 in Indonesia (as of 2018). For this study, a representative random sampling was performed
to compile the data from the SMS database over the 2008–2017 period. The selection was based on
differences in climate, proportion of coffee areas, water resources and farm sizes. A total of 558 farmers
were selected across 18 districts in the four provinces in Vietnam; and 240 farmers were selected
across eight districts of the three main coffee-producing provinces in Indonesia (Table 1). Data of
the 2008–2017 period were collected during the last quarterly farms survey in 2017 from 798 farms
(7980 observations in total). All farm data were cross-checked with those of the SMS database to verify
their consistency.
Table 1. Sampling design: numbers of districts and participant farmers in Vietnam and Indonesia.
Vietnam Total
Province Dak Lak Dak Nong Gia Lai Lam Dong 4
Number of districts 6 4 3 5 18
Number of farmers 180 120 93 165 558
Total observation 1800 1200 930 1650 5580
Indonesia
Province Lampung South Sumatra Bengkulu 3
Number of districts 3 3 2 8
Number of farmers 90 90 60 240
Total observation 900 900 600 2400
Source: survey data 2008–2017.
The data collected consisted of farm characteristics (i.e., altitude, farm area, age of trees,
plant density, and yield) and the type and proportion of fertilizers applied. In Vietnam the differences
in management practices related to the irrigation methods, which were either manual or sprinkler.
The sampling was carried out in such a way that it represented both irrigation methods. In Indonesia
Agronomy 2019,9, 499 5 of 19
Robusta coffee is grown under rainfed conditions (i.e., without irrigation). All the data were anonymised
before any analysis was performed in this study.
2.3. Data Analyses
The rates of chemical fertilizers were expressed in total rate of each of the major nutrients
nitrogen (N), phosphate (P
2
O
5
) and potassium (K
2
O) in order to have a common basis for comparisons.
The recommended fertilizer rates for Robusta coffee in Vietnam and Indonesia were from the Western
Highlands Agriculture and Forestry Science Institute (WASI) [
26
,
28
–
30
], and the Indonesia Coffee and
Cocoa Research Institute [
31
], respectively. Although sulphur (S) and magnesium (Mg) are important
nutrients for Robusta coffee, few farmers reported these nutrients during the surveys. These nutrients
were therefore discarded in our analyses.
We assessed first the year-to-year variability of fertilizer application at the selected provinces over
the 10-year period for each country. Then, the differences in fertilizer application within province and
between provinces were compared using a one-way ANOVA (significance level =0.05). The analyses
were done according to the farm size. Two groups of farm size were defined for Vietnamese and
Indonesian Robusta coffee farms: ‘small-scale’ and ‘large-scale’ farms corresponding to farms with
area
≤
1 ha, and area >1 ha, respectively. These thresholds were based on those adopted by [
30
,
32
]
when classifying coffee smallholders.
Further, we assessed the potential for improved fertilization management strategies, i.e., reducing
nutrient rates while maintaining the current levels of Robusta coffee yields. Based on the ranges of
observed coffee yields and recommended nutrient rates, the surveys data were analysed under three
scenarios of nutrient rates in all provinces.
All the data and statistical analyses were carried out using the R Language and Environment for
Statistical Computing [33] and Microsoft®Office Excel (Redmond, WA, USA).
3. Results
3.1. Background Information from the Survey
3.1.1. Vietnam
Overall the area of coffee farms ranged from 0.1 to 11.2 ha, with 60% being of size >1 ha (Table 2).
The planting density ranged from 1000 to 1100 plants ha
−1
. The farms surveyed were predominantly
(67%) located between 500 and 900 m A.M.S.L. with only 18% of the farms below 500 m A.M.S.L. and
15% above 900 m A.M.S.L. (Table 2). The age of coffee farms varied between 3 and 29 years in 2008 (start
year of the study period), with 89% of the farms being under 20 years old. Fertilizers were applied
four times throughout the crop season. The first application occurred during the blossoming/setting
(March–April); the second at the onset of the monsoon (generally in June); the third application
occurred during the cherry development stage (August–September); and the last round of application
taking place during the bean filling and bud wood development stage (October–November).
Four types of chemical (urea, blended NPK, super phosphate, and potassium chloride) and two
types of natural (compost and lime) fertilizers were recorded during the 10-year period across the four
study provinces in Vietnam (Table 2). Most farmers applied all the four chemical fertilizers: 79% for
blended NPK, 98% for super phosphate and potassium chloride, and 100% for urea. The common
nutrient content N–P2O5–K2O for blended NPK fertilizer during the survey was 16–8–16 (Table 3).
Agronomy 2019,9, 499 6 of 19
Table 2.
Characteristics of coffee farms surveyed during the 2008–2017 period in selected provinces in
Vietnam and Indonesia. The total number of monitored farms per year was 558 in Vietnam and 240
in Indonesia.
Vietnam Indonesia
min max average min max average
Farm size (ha) 0.1 11.2 1.72 0.3 8 1.54
Small
(≤1 ha)
Large
(>1 ha)
Small
(≤1 ha)
Large
(>1 ha)
Farm size group (%) 40 60 55 45
min max average min max average
Age of tree (years) 3 29 13.2 3 48 13
≤10 years 10–20 years >20 years ≤10 years 10– 20 years >20 years
Trees (%) 28 61 11 44 37 20
≤500 m 501–900 m >900 m ≤500 m 501–900 m >900 m
Farm altitude (%) 18 67 15 28 45 27
Chemical Organic Chemical Organic
Fertiliser users (%) NPK (79%)
Super phosphate (98%)
Potassium chloride (98%)
Urea (100%)
Compost (81%)
Lime (19%)
NPK (68%)
Urea (80%)
Triple super
phosphate (5%)
Compost
(96%)
Source: Survey data 2008–2017.
3.1.2. Indonesia
Coffee farms in Indonesia were predominantly small-scale (55%; Table 2) but densely planted
with 2000–2500 plants ha
−1
. In terms of elevation, 45% of the coffee farms were located between 500
and 900 A.M.S.L. with 28% below 500 m and 27% above 900 m. Regarding the age of coffee trees,
44% were young as
≤
10 years in 2008, 37% aged between 10 and 20 years; the remaining 20% were
older than 20 years (Table 2). Fertilizers were applied in two rounds throughout the crop season;
the first application during initial cherry development stage (October–November) and the second
during cherry development and bean filling stage (February–March).
The farmers surveyed across the study provinces in Indonesia during 2008–2017 used three
chemical fertilizer types (urea, blended NPK and triple super phosphate), with the proportions of
users being 80%, 68% and 5%, respectively. The common nutrient content N–P
2
O
5
–K
2
O for blended
NPK fertilizer during the survey was 15–15–15 (Table 3). Compost was the only organic fertilizer type
recorded in the farms surveyed, with 96% of farmers using it (Table 2).
Table 3.
Fertilizer types recorded in surveyed Robusta coffee farms in Vietnam and Indonesia and their
nutrient contents. The recommended nutrient rates for two targeted yield levels in Vietnam [
26
,
28
–
30
]
and mature trees (i.e., bearing fruits) in Indonesia [31] are provided.
Vietnam
N (%) P2O5(%) K2O (%)
NPK 16 8 16
Urea 46
Super phosphate 16
Potassium chloride 60
N (kg ha−1) P2O5(kg ha−1) K2O (kg ha−1)
Recommendation #1 (2.5–3.0 ton ha−1)192 88 261
Recommendation #2 (3.0–4.0 ton ha−1)248 116 317
Indonesia
N (%) P2O5(%) K2O (%)
NPK 15 15 15
Urea 46
Triple super phosphate 36
Potassium chloride 60
N (kg ha−1) P2O5(kg ha−1) K2O (kg ha−1)
Recommendation 135 35 145
Agronomy 2019,9, 499 7 of 19
3.2. Year-To-Year Variability of Fertilizer Use in Robusta Coffee Farms in Vietnam and Indonesia
The spatial distributions of the 10-year average of the chemical fertilizers as applied during
2008–2017 in Vietnam (urea, blended NPK, super phosphate, and potassium chloride) and Indonesia
(urea, NPK and triple super phosphate) are provided in Figures S2 and S3. For comparison purposes
the observed rates of chemical fertilizers were expressed in total rate of each of the major nutrients
nitrogen (N), phosphate (P2O5) and potassium (K2O) using the values provided in Table 3.
3.2.1. N, P2O5and K2O Uses in Vietnam During 2008–2017
In Vietnam, urea and blended NPK, which contributed to total N rates, were included in fertilizer
management strategies of most of the surveyed farmers every year (Table 2), with their respective rates
varying between 1000 to 1400 kg ha
−1
and 400 to 800 kg ha
−1
(Figure S2). The dominant nutrients
provided through the chemical fertilizers during 2008–2017 in all provinces were N and K
2
O, regardless
of the farm size (Figure 2). For example in Dak Nong, the amounts of K
2
O were among the highest
compared to the three remaining provinces Dak Lak, Gia Lai and Lam Dong. For all nutrients and in
all provinces, 2014 was the year with lower rates applied (Table 4and Table S1).
Agronomy 2019, 9, x FOR PEER REVIEW 8 of 20
Figure 2. Year-to-year variations of nutrient rates in large- and small-scale Robusta coffee farms for each of
the study provinces in Vietnam during the 2008–2017 period. The rates of nitrogen (N), phosphate (P2O5,
referred to as P) and potassium (K2O, referred to as K) were calculated based of the nutrient contents of each
the chemical fertilizers recorded (see Tables 2 and 3). In the boxplot, upper and lower borders of the box
represent the 3rd and 1st quartiles, respectively. The line within the box represents the median value. Bars
extend to the minimum and maximum values. Outliers are represented by black circles. Small-scale farms
have area ≤1 ha; large-scale farms have area >1 ha.
3.2.2. N, P2O5 and K2O Uses in Indonesia During 2008–2017
In Indonesia, farmers across Lampung applied more urea and blended NPK than those in South
Sumatra and Bengkulu (Figure S3). Very little triple super phosphate fertilizer was used, averaging from 50
to 100 kg ha−1 yr−1 over the 10-year period (Figure S3). Thus, the rates of N, P2O5 and K2O during 2008–2017
(Figure 3) were lower compared to those observed in Vietnam over the same period. P2O5 and K2O rates
were on average <50 kg ha−1 yr−1, irrespective of the farm size (Figure 3).
The comparisons of the average rates of each nutrient N, P2O5 and K2O within a given province over
the 10-year survey showed that these rates were not statistically significant (p > 0.05) from year to year in
Bengkulu and S outh Sumatra, regardless of the farm siz e (Table S2). I n Lampung, s uch similarit y was foun d
for K2O rates in both small- and large-scale Robusta coffee farms, and for P2O5 in small-scale farms. For N
rates, small-scale farmers applied relatively high and similar annual rates (on average 93 kg ha−1) in the
majority of years, except in 2011 and 2014 where lower rates (on average 66–68 kg ha−1) were applied. In
large-scale farms, lower and statistically different (p < 0.05) N rates were applied in only 2011 (Table S2).
Figure 2.
Year-to-year variations of nutrient rates in large- and small-scale Robusta coffee farms for each
of the study provinces in Vietnam during the 2008–2017 period. The rates of nitrogen (N), phosphate
(P
2
O
5
, referred to as P) and potassium (K
2
O, referred to as K) were calculated based of the nutrient
contents of each the chemical fertilizers recorded (see Tables 2and 3). In the boxplot, upper and lower
borders of the box represent the 3rd and 1st quartiles, respectively. The line within the box represents
the median value. Bars extend to the minimum and maximum values. Outliers are represented by
black circles. Small-scale farms have area ≤1 ha; large-scale farms have area >1 ha.
Comparing the average rates of each nutrient N, P
2
O
5
and K
2
O within a given province over
the 10-year survey, our analyses revealed that there was no statistical difference between the rates of
P
2
O
5
and K
2
O applied every year, irrespective of the province and farm size (Table S1). With regard to
the average rates of N, small-scale farmers in each of the provinces applied similar N rates (i.e., not
statistically different, p>0.05) in the majority of the study years, except in 2014 (Table 4), though there
seemed an alternate use of low and high N rates from year to year after 2011. This alternate trend was
also found in large-scale farms across all provinces. Large-scale farmers in Lam Dong were among
Agronomy 2019,9, 499 8 of 19
those applying different (statistically significant, p<0.05) N rates from year to year. In the remaining
provinces Dak Lak, Dak Nong or Gia Lai, similarities between years with lower N rates or between
years with higher N rates were found (Table 4).
Table 4.
Comparison of nitrogen rates (N kg ha
−1
) between years according to the farm size in
Vietnamese Robusta coffee-producing provinces. Number with similar letter in a given row are not
statistically different (p>0.05). SF: small-scale farms; LF: large-scale farms.
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Dak
Lak SF 379a 379a 402a 402a 379a 402a 351b 402a 379a 402a
LF 388ab 388ab 411a 411a 388ab 411a 365b 411a 388ab 411a
Dak
Nong SF 435ab 435ab 477a 477a 435ab 477a 408b 477a 435ab 477a
LF 435ab 435ab 480a 480a 435ab 480a 407b 480a 435ab 480a
Gia
Lai SF 369ab 369ab 403a 403a 369ab 403a 347b 403a 369ab 403a
LF 381ab 381ab 398a 398a 381ab 398a 359b 398a 381ab 398a
Lam
Dong SF 464ab 464ab 504a 504a 464ab 504a 422b 504a 464ab 504a
LF 475b 475b 511a 511a 475b 511a 438c 511a 475b 511a
3.2.2. N, P2O5and K2O Uses in Indonesia During 2008–2017
In Indonesia, farmers across Lampung applied more urea and blended NPK than those in South
Sumatra and Bengkulu (Figure S3). Very little triple super phosphate fertilizer was used, averaging
from 50 to 100 kg ha
−1
yr
−1
over the 10-year period (Figure S3). Thus, the rates of N, P
2
O
5
and K
2
O
during 2008–2017 (Figure 3) were lower compared to those observed in Vietnam over the same period.
P2O5and K2O rates were on average <50 kg ha−1yr−1, irrespective of the farm size (Figure 3).
Agronomy 2019, 9, x FOR PEER REVIEW 9 of 20
Figure 3. Year-to-year variations of nutrient rates in large- and small-scale Robusta coffee farms for each of
the study provinces in Indonesia during the 2008–2017 period. The rates of nitrogen (N), phosphate (P2O5,
referred to as P) and potassium (K2O, referred to as K) were calculated based of the nutrient contents of each
of the chemical fertilizers recorded (see Tables 2 and 3). In the boxplot, upper and lower borders of the box
represent the 3rd and 1st quartiles, respectively. The line within the box represents the median value. Bars
extend to the minimum and maximum values. Outliers are represented by black circles. Small-scale farms
have area ≤1 ha; large-scale farms have area >1 ha.
3.3. Comparisons of Fertilizer Use in Robusta Coffee Farms Between Provinces
3.3.1. Vietnam
Generally, small-scale farm holders in Dak Lak and Gia Lai applied similar N rates during the study
period (p > 0.05; Table 5). The average rates ranged from 369 to 403 kg ha−1, and were lower and statistically
different from those applied in Dak Nong and Lam Dong. Across these latter provinces, homogenous
patterns of N rates were observed (i.e., not statistically different, p > 0.05; Table 5), with average values
ranging from 408 to 504 kg ha−1. Likewise, in large-scale farms in Dak Lak and Gia Lai, similar N
management strategies were adopted. A difference was found in large-scale farms between Dak Nong and
Lam Dong was observed, with those in the Lam Dong applying higher N rates (438–511 kg ha−1) (Table 5).
Regarding P2O5 and K2O, small-scale farmers in Dak Lak behaved differently from those in Dak Nong,
Gia Lai and Lam Dong. Lesser rates of P2O5 and K2O were applied, with average values ranging from 177
to 195 kg ha−1, and 400 to 418 kg ha−1, respectively (Table 5). The respective rates of P2O5 and K2O in the
other provinces ranged from 190 to 224 kg ha−1, and from 496 to 558 kg ha−1, on average. In large-scale farms,
P2O5 and K2O management strategies were similar across Gia Lai and Lam Dong in all years, i.e., no
statistically different rates applied (p > 0.05; Table 5). The common pattern between these provinces and
Dak Lak was only found for P2O5 management. In Dak Nong, large-scale farmers behaved differently from
their counterparts in the three other provinces, applying higher rates of P2O5 and K2O in all years.
Figure 3.
Year-to-year variations of nutrient rates in large- and small-scale Robusta coffee farms for
each of the study provinces in Indonesia during the 2008–2017 period. The rates of nitrogen (N),
phosphate (P
2
O
5
, referred to as P) and potassium (K
2
O, referred to as K) were calculated based of
the nutrient contents of each of the chemical fertilizers recorded (see Tables 2and 3). In the boxplot,
upper and lower borders of the box represent the 3rd and 1st quartiles, respectively. The line within the
box represents the median value. Bars extend to the minimum and maximum values. Outliers are
represented by black circles. Small-scale farms have area ≤1 ha; large-scale farms have area >1 ha.
Agronomy 2019,9, 499 9 of 19
The comparisons of the average rates of each nutrient N, P
2
O
5
and K
2
O within a given province
over the 10-year survey showed that these rates were not statistically significant (p>0.05) from
year to year in Bengkulu and South Sumatra, regardless of the farm size (Table S2). In Lampung,
such similarity was found for K
2
O rates in both small- and large-scale Robusta coffee farms, and for
P
2
O
5
in small-scale farms. For N rates, small-scale farmers applied relatively high and similar annual
rates (on average 93 kg ha
−1
) in the majority of years, except in 2011 and 2014 where lower rates (on
average 66–68 kg ha
−1
) were applied. In large-scale farms, lower and statistically different (p<0.05) N
rates were applied in only 2011 (Table S2).
3.3. Comparisons of Fertilizer Use in Robusta Coffee Farms Between Provinces
3.3.1. Vietnam
Generally, small-scale farm holders in Dak Lak and Gia Lai applied similar N rates during the
study period (p>0.05; Table 5). The average rates ranged from 369 to 403 kg ha
−1
, and were lower and
statistically different from those applied in Dak Nong and Lam Dong. Across these latter provinces,
homogenous patterns of N rates were observed (i.e., not statistically different, p>0.05; Table 5),
with average values ranging from 408 to 504 kg ha
−1
. Likewise, in large-scale farms in Dak Lak and
Gia Lai, similar N management strategies were adopted. A difference was found in large-scale farms
between Dak Nong and Lam Dong was observed, with those in the Lam Dong applying higher N rates
(438–511 kg ha−1) (Table 5).
Table 5.
Comparison of fertilizer use between provinces in small- and large-scale farms in Vietnam
during 2008–2017. For a given farm size group, numbers with similar letter in a given row are not
statistically different (p>0.05).
Year Small-scale Large-scale
Dak Lak Dak Nong Gia Lai Lam Dong Dak Lak Dak Nong Gia Lai Lam Dong
N (kg ha−1)
2008 379b 435a 369b 464a 388c 435b 381c 475a
2009 379b 435a 369b 464a 388c 435b 381c 475a
2010 402b 477a 403b 504a 411c 480b 398c 511a
2011 402b 477a 403b 504a 411c 480b 398c 511a
2012 379b 435a 369b 464a 388c 435b 381c 475a
2013 402b 477a 403b 504a 411c 480b 398c 511a
2014 351b 408a 347b 422a 365c 407b 359c 438a
2015 402b 477a 403b 504a 411c 480b 398c 511a
2016 379b 435a 369b 464a 388c 435b 381c 475a
2017 402b 477a 403b 504a 411c 480b 398c 511a
P2O5(kg ha−1)
2008 181b 216a 202ab 191ab 193b 215a 184b 183b
2009 181b 216a 202ab 191ab 193b 215a 184b 183b
2010 195b 224a 216ab 201ab 205ab 225a 199b 191b
2011 195b 224a 216ab 201ab 205ab 225a 199b 191b
2012 181b 216a 202ab 191ab 193b 215a 184b 183b
2013 195b 224a 216ab 201ab 205ab 225a 199b 191b
2014 177b 215a 202a 190ab 187b 214a 184b 182b
2015 195b 224a 216ab 201ab 205ab 225a 199b 191b
2016 181b 216a 202ab 191ab 193b 215a 184b 183b
2017 195b 224a 216ab 201ab 205ab 225a 199b 191b
K2O (kg ha−1)
2008 402b 549a 509a 496a 423c 557a 471bc 473b
2009 402b 549a 509a 496a 423c 557a 471bc 473b
2010 418b 558a 525a 515a 440c 574a 486bc 486b
2011 418b 558a 525a 515a 440c 574a 486bc 486b
2012 402b 549a 509a 496a 423c 557a 471bc 473b
2013 418b 558a 525a 515a 440c 574a 486bc 486b
2014 400b 547a 509a 495a 419c 556a 471b 472b
2015 418b 558a 525a 515a 440c 574a 486bc 486b
2016 402b 549a 509a 496a 423c 557a 471bc 473b
2017 418b 558a 525a 515a 440c 574a 486bc 486b
Agronomy 2019,9, 499 10 of 19
Regarding P
2
O
5
and K
2
O, small-scale farmers in Dak Lak behaved differently from those in Dak
Nong, Gia Lai and Lam Dong. Lesser rates of P
2
O
5
and K
2
O were applied, with average values ranging
from 177 to 195 kg ha
−1
, and 400 to 418 kg ha
−1
, respectively (Table 5). The respective rates of P
2
O
5
and
K
2
O in the other provinces ranged from 190 to 224 kg ha
−1
, and from 496 to 558 kg ha
−1
, on average.
In large-scale farms, P
2
O
5
and K
2
O management strategies were similar across Gia Lai and Lam Dong
in all years, i.e., no statistically different rates applied (p>0.05; Table 5). The common pattern between
these provinces and Dak Lak was only found for P
2
O
5
management. In Dak Nong, large-scale farmers
behaved differently from their counterparts in the three other provinces, applying higher rates of P
2
O
5
and K2O in all years.
3.3.2. Indonesia
Overall, there was no statistical difference (p>0.05) in P
2
O
5
and K
2
O uses on small-scale Robusta
coffee farms between Bengkulu, South Sumatra and Lampung during 2008–2017 (Table 6). For N
use, a clear statistical difference (p<0.05) was found between Bengkulu (lower N rates applied) and
Lampung (higher N rates applied) in small-scale farms. For large-scale farms, N use was found to be
similar between Bengkulu and South Sumatra, but clearly different from that of Lampung. Regarding
P
2
O
5
and K
2
O, the difference in nutrient use between Lampung and South Sumatra was statistically
significant (p<0.05) in the majority of years, except 2011 (for P
2
O
5
) and 2011 and 2014 (for K
2
O)
(Table 6).
Table 6.
Comparison of fertilizer use between provinces in small- and large-scale farms in Indonesia
during 2008–2017. For a given farm size group, numbers with similar letter in a given row are not
statistically different (p>0.05).
Year Small-scale Large-scale
Bengkulu Lampung South Sumatra Bengkulu Lampung South Sumatra
N (kg ha−1)
2008 44b 93a 75ab 44b 97a 53b
2009 44b 93a 75ab 44b 97a 53b
2010 44b 93a 75ab 44b 97a 53b
2011 38b 66a 58ab 34b 68a 46b
2012 44b 93a 75ab 44b 97a 53b
2013 44b 93a 75ab 44b 97a 53b
2014 36b 68a 62a 33b 71a 46b
2015 44b 93a 75ab 44b 97a 53b
2016 44b 93a 75ab 44b 97a 53b
2017 44b 93a 75ab 44b 97a 53b
P2O5(kg ha−1)
2008 14a 16a 16a 11ab 15a 11b
2009 14a 16a 16a 11ab 15a 11b
2010 14a 16a 17a 14ab 20a 11b
2011 8a 10a 10a 7a 10a 8a
2012 14a 16a 17a 14ab 20a 11b
2013 14a 16a 17a 14ab 20a 11b
2014 9a 12a 12a 12ab 16a 8b
2015 14a 16a 17a 14ab 20a 11b
2016 14a 16a 17a 14ab 20a 11b
2017 14a 16a 17a 14ab 20a 11b
K2O (kg ha−1)
2008 14a 16a 16a 11ab 15a 11b
2009 14a 16a 16a 11ab 15a 11b
2010 14a 16a 16a 11ab 15a 11b
2011 8a 10a 10a 7a 10a 8a
2012 14a 16a 16a 11ab 15a 11b
2013 14a 16a 16a 11ab 15a 11b
2014 9a 12a 11a 9a 10a 8a
2015 14a 16a 16a 11ab 15a 11b
2016 14a 16a 16a 11ab 15a 11b
2017 14a 16a 16a 11ab 15a 11b
Agronomy 2019,9, 499 11 of 19
3.4. Organic Fertilizers Use in Robusta Coffee Farms in Vietnam and Indonesia
In Vietnam, compost and lime were the natural fertilizers used in the surveyed farms. Compost
was prepared from coffee husks, cuttings from orchards and fields and animal manure. These materials
were composted using microbial solutions and were applied once decomposed. Given the lack of
adequate materials, and its time-consuming preparation, farmers used to divide their farms in two and
applied compost in alternate years. All Robusta coffee farmers surveyed in Dak Lak were applying
compost in the same years (Table S3) at between 8 and 20 ton ha
−1
, higher rates than applied in the
other provinces (Figure S4). In Dak Nong and Lam Dong, most of the farmers followed the same
pattern while applying compost in alternate years. The lowest average compost rates were recorded at
Lam Dong (~10 ton ha
−1
). Lime was applied at 1–2 ton ha
−1
across the four provinces with the lowest
rates observed in Lam Dong (Figure S4).
In Indonesia, compost was the only organic fertilizer used in Robusta coffee farms. It was made
of animal manure and dried leaves and branch cuttings. Unlike in Vietnam, compost was applied
every crop season and to all trees on the farm once all the materials were decomposed. The total rates
varied between 0.5 and 2 ton ha
−1
(Figure S4), with highest rates in Bengkulu, then in South Sumatra
and Lampung.
3.5. Potential for Reducing Nutrient Rates in Robusta Coffee Farms
Since the nutrients applied in Robusta coffee farms in Indonesia during the study period were low
and less than recommended (see Table 3for recommended N, P
2
O
5
and K
2
O rates), we limited this
analysis to Vietnam. Different yield levels (<2.5 ton ha
−1
, between 2.5 and 3 ton ha
−1
, and >3 ton ha
−1
)
were analysed under three different rates for each of the nutrients N, P
2
O
5
and K
2
O. With the aim of
investigating as to whether those nutrient rates can be reduced while maintaining current yield levels,
the recommended rates of N, P
2
O
5
and K
2
O for attaining 2.5–3 ton ha
−1
(recommendation #1 in Table 3)
were chosen to define the different categories of nutrient rates used in our analysis (Tables 7and 8).
Small-farmers in Dak Nong and Lam Dong applied predominantly >384 kg ha
−1
of N,
with corresponding yields up to 2.95 ton ha
−1
(Table 7, blocks B and D). In Dak Lak and Gia
Lai the majority applied between 192 and 384 kg ha
−1
, with corresponding yield up to 2.89 ton ha
−1
(Table 7, blocks A and C). In those provinces, there were small-scale farmers who applied >384 kg ha
−1
of N, while achieving similar yield levels than those applying up to 50% less, suggesting that a reduction
of N rates in these farms is possible. In large-scale farms across all provinces, however, the majority
of farmers applied >384 kg ha
−1
N, with varying yield levels achieved depending on the province
(Table 8). Although there were large-scale farmers applying between 192–384 kg ha
−1
, only a very
limited number achieved yields >2.5 ton ha−1.
In P
2
O
5
management, there are opportunities to reduce the current rates and maintain the current
coffee yield levels for small-scale farmers in provinces like Gia Lai and Lam Dong. In three out of four
provinces most small-holders farmers applied >176 kg ha
−1
: 85%, 74%, 77% of farmers in Dak Nong,
Gia Lai and Lam Dong, respectively (Table 7, blocks B1, C1 and D1), with corresponding respective
yields up to 2.87, 2.89 and 2.95 ton ha
−1
. In Gia Lai and Lam Dong, particularly, similar yield levels
were reported for P
2
O
5
rates varying between 88 and 176 kg ha
−1
, suggesting a potential for reducing
P
2
O
5
rates. In large-scale farms such potentials existed in Dak Lak and Gia Lai. In these provinces,
although the majority of large-scale farmers applied between 88–176 kg ha
−1
, with corresponding
yields up to 3.3 ton ha
−1
(Table 8, blocks A and C), farmers who were applying >176 kg ha
−1
and
were achieving in some instance <2.5 ton ha
−1
, could have improved their management strategies and
achieved better yield levels while reducing P2O5rates.
Regarding K
2
O management, K
2
O was predominantly applied between 261 and 522 kg ha
−1
in
both small and large-scale Robusta coffee farms across Dak Lak, Gia Lai and Lam Dong (Tables 7and 8).
In Dak Nong the dominant category was >522 kg ha
−1
(62% and 63% for small- and large-scale farms,
respectively) with corresponding coffee yields of up to 3.45 ton ha
−1
on average (Tables 7and 8, blocks
B1–2). For this latter province, some farmers 12% and 20% of the sample in small-and large-scale farms,
Agronomy 2019,9, 499 12 of 19
respectively—reported similar yield levels (up to 3.29 ton ha
−1
) while applying 261 to 522 kg ha
−1
,
suggesting the potential for reducing K
2
O rates. However, for the remaining three provinces, no
conclusive indication can be drawn from our dataset regarding the potential of reducing K
2
O rates
while achieving satisfactory yield levels.
Table 7.
Variations of Robusta coffee yields under different categories of N, P
2
O
5
and K
2
O rates in
small-scale farms for each of the study provinces in Vietnam. Pct. sample: sample distribution from all
the 2008–2017 dataset (expressed in %); Avg. yield: average coffee yield (ton ha−1).
N (kg ha−1) P2O5(kg ha−1) K2O (kg ha−1)
Levels ≤192 192–384 >384 ≤88 88–176 >176 ≤261 261–522 >522
A. Dak Lak
A1. Pct. sample
<2.5 - 34 30 1.9 34 28 2 59 3
2.5–3.0 - 15 15 0.1 17 13 1 27 2
>3.0 - 3 3 - 3 3 - 6 0
A2. Avg. yield
<2.5 - 2.11 2.14 2.01 2.12 2.14 2.17 2.11 2.29
2.5–3.0 - 2.81 2.84 2.56 2.84 2.82 2.86 2.82 2.87
>3.0 - 3.6 3.45 - 3.4 3.62 - 3.47 4.21
B. Dak Nong
B1. Pct. sample
<2.5 - 9 57 1 8 57 - 26 40
2.5–3.0 - 2 23 1 3 22 - 8 17
>3.0 - 2 7 1 1 6 - 4 5
B2. Avg. yield
<2.5 - 2.13 2.13 2.03 2.16 2.13 - 2.14 2.13
2.5–3.0 - 2.85 2.86 2.92 2.82 2.87 - 2.84 2.87
>3.0 - 3.19 3.41 3.13 3.34 3.39 - 3.26 3.45
C. Gia Lai
C1. Pct. sample
<2.5 - 25 20 - 12 33 - 27 18
2.5–3.0 - 22 15 - 10 27 - 19 18
>3.0 - 9 9 - 4 14 - 7 11
C2. Avg. yield
<2.5 - 2.28 2.22 - 2.31 2.23 - 2.26 2.24
2.5–3.0 - 2.89 2.86 - 2.86 2.89 - 2.89 2.87
>3.0 - 3.43 3.35 - 3.35 3.41 - 3.35 3.42
D. Lam Dong
D1. Pct. sample
<2.5 - 3 34 - 10 28 - 26 11
2.5–3.0 - 4 29 - 8 25 - 23 10
>3.0 - 2 28 - 5 24 - 16 14
D2. Avg. yield
<2.5 - 2.14 2.19 - 2.21 2.18 - 2.19 2.17
2.5–3.0 - 2.96 2.95 - 2.96 2.95 - 2.95 2.95
>3.0 - 3.36 3.46 - 3.44 3.46 - 3.43 3.48
Agronomy 2019,9, 499 13 of 19
Table 8.
Variations of Robusta coffee yields under different categories of N, P
2
O
5
and K
2
O rates in
large-scale farms for each of the study provinces in Vietnam. Pct. sample: sample distribution from all
the 2008–2017 dataset (expressed in %); Avg. yield: average coffee yield (ton ha−1).
N (kg ha−1) P2O5(kg ha−1) K2O (kg ha−1)
Levels ≤192 192–384 >384 ≤88 88–176 >176 ≤261 261–522 >522
A. Dak Lak
A1. Pct. sample
<2.5 - 24 36 0.6 30 30 7 47 6
2.5–3.0 - 9 24 0.3 17 16 3 26 5
>3.0 - 2 5 0.1 3 3 - 5 1
A2. Avg. yield
<2.5 - 2.18 2.19 2.14 2.18 2.19 2.13 2.19 2.21
2.5–3.0 - 2.74 2.77 2.71 2.76 2.76 2.75 2.75 2.82
>3.0 - 3.27 3.23 3.06 3.27 3.22 - 3.24 3.23
B. Dak Nong
B1. Pct. sample
<2.5 - 5.7 44 - 8 42 - 17 33
2.5–3.0 - 4 36 - 6 34 - 16 24
>3.0 - 0.3 10 - 1 9 - 4 6
B2. Avg. yield
<2.5 - 2.24 2.19 - 2.21 2.2 - 2.24 2.18
2.5–3.0 - 2.83 2.8 - 2.81 2.8 - 2.8 2.8
>3.0 - 3.29 3.31 - 3.27 3.31 - 3.29 3.32
C. Gia Lai
C1. Pct. sample
<2.5 - 23 29 - 27 25 - 35 17
2.5–3.0 - 14 20 - 18 15 - 23 10
>3.0 - 7 7 - 6 9 - 9 6
C2. Avg. yield
<2.5 - 2.16 2.12 - 2.12 2.16 - 2.12 2.18
2.5–3.0 - 2.79 2.82 - 2.8 2.82 - 2.81 2.79
>3.0 - 3.26 3.28 - 3.3 3.25 - 3.29 3.24
D. Lam Dong
D1. Pct. sample
<2.5 - 2 24 0.2 8 18 - 19 7
2.5–3.0 - 3 35 0.6 12 25 - 28 10
>3.0 - 3 33 0.2 11 25 - 25 11
D2. Avg. yield
<2.5 - 2.24 2.24 2.39 2.26 2.23 - 2.24 2.24
2.5–3.0 - 2.88 2.83 2.79 2.82 2.83 - 2.83 2.83
>3.0 - 3.34 3.32 3.28 3.31 3.33 - 3.32 3.33
4. Discussion
4.1. Were Coffee Farmers Following the Fertilizer Recommendations in Both Countries?
In Indonesia, the recommended nutrient rates for N, P
2
O
5
and K
2
O were 135, 35 and 145 kg ha
−1
yr
−1
, respectively [
31
]. Thus Indonesian farmers across the surveyed provinces were applying less
nutrients than recommended, irrespective of the province and farm size group (Figure 3and Table 6).
Various factors can explain this. Traditional farming practice does not depend on the use of external
inputs such chemical fertilizers and pesticides. Indonesian coffee farmers apply fewer agri-chemical
inputs than other major coffee producers such as Columbia, Brazil and indeed Vietnam. Also the
price of fertilizers (which are imported) is regulated by the Indonesian government. For example,
the price of blended NPK fertilizer has followed the same trend as green coffee prices over the last
10 years (Figure 4B), and farmers therefore may not be keen to increase the input of fertilizers. Also,
the importance of coffee in Indonesia’s agricultural commodities exports has decreased over the last
Agronomy 2019,9, 499 14 of 19
decade (5.1% in 2005 to 3.8% in 2015) whereas exports of commodities such as palm oil or tobacco have
more than tripled [
24
]. Low use of fertilizers in Robusta coffee farms could be because farmers are
increasingly turning towards Arabica coffee where possible, given its relatively higher price on the
global market.
In Vietnam the recommended rates of N, P
2
O
5
and K
2
O in Robusta coffee farms vary according
to the targeted yield (Table 3). Unlike farmers in Indonesia, the rates of nutrients applied in Robusta
coffee farms in Vietnam during the 10-year survey were generally higher than those recommended.
Compared to countries such as Thailand, or Philippines [
32
], coffee farmers in Vietnam are applying
noticeably higher rates of fertilizers. The general trend of overusing fertilizers found in this study was
in line with the conclusions from previous studies [
13
,
19
,
26
,
32
,
34
], although in these studies only one
or two provinces were involved.
One of the findings of this study by assessing all the major coffee-producing provinces in Vietnam
indicates that farmers were generally following similar practices in terms of the rates of fertilizers
applied across those provinces. The monitoring also revealed that Vietnamese Robusta coffee farmers
tended to follow an “aggressive” approach while applying fertilizers—“the more fertilizers you can
apply, the better your plants stay nutrient-stress free throughout the growth cycle and increase your
capacity to maintain the same yield performance from year to year”. However, the relationships
between the coffee yields and fertilizer rates showed no strong correlation between the yield and
fertilizer rate (Figure S5). The high use of fertilizers in Vietnam could also be explained, in part, by the
affordability of fertilizers to most coffee farmers through governmental subsidies [
35
–
37
]. In addition,
the price of coffee beans has been satisfactory to farmers over the last decade (despite its volatility)
(Figure 4A).
Agronomy 2019, 9, x FOR PEER REVIEW 16 of 20
Figure 4. Average prices of the top three fertilizers and green Robusta coffee in Vietnam (A) and Indonesia
(B) during the 2008–2017 period. Coffee prices were sourced from the International Coffee Organization
(http://www.ico.org/new_historical.asp). VND: Vietnam Dong. IRD: Indonesia Rupiah. NPK: blended NPK;
SP: super phosphate; KCl: potassium chloride.
4.2. Challenges for a Sustainable Management of Fertilizers in Vietnam and Indonesia
Robusta coffee farmers in Vietnam were applying high rates of chemical fertilizers at constant rates
from year to year whereas Indonesian farmers applied well below the recommended rates. More chemical
fertilizers are being used in coffee production than in other crops in Vietnam [38,39]. Although intensive
fertilizer use in Robusta coffee farms has led to increased yields during the previous decades [40,41], the
dependence on chemical fertilizers may not be sustainable in the long term. Such intensive use of chemical
fertilizer can reduce soil fertility through increased soil acidity, reduction of beneficial microorganisms,
increased unstable aggregates leading to erosion and degradation [22,42]. Intensive use of fertilizer can also
impact water quality, thereby leading to sustainability issues. Chemical fertilizers such blended NPK when
applied intensively over long periods could also cause the depletion, or accumulation, of other plant
nutrients in the soil [43]. This could lead to reduced yields and production [13,44,45].
Investigating the potential for reducing nutrient rates in coffee farms in Vietnam based on our dataset
showed that there are opportunities for reducing the higher rates observed during the study period by up
to 50% in some instances, depending on the nutrient and farm size, while achieving current yield levels
(Tables 7 and 8). However, for nutrients like K2O, no conclusive indication can be drawn from our dataset
regarding the potential of reducing the current rates while achieving satisfactory yield levels. This is because
there were few or no reports in the majority of the selected provinces of such patterns. An optimum
management of fertilizers involving lower rates than those recorded during the survey could still maintain
satisfactory yields. For example, Bruno et al. [46] reported that a routine nitrogen fertilizer rate of 600 kg ha-
1 could be reduced by one-third without decreasing the production of coffee beans in commercial Arabica
coffee farms in Brazil. Similar conclusions were drawn in Costa Rica [47]. Further research is therefore
needed to investigate fertilizer use efficiencies in farm conditions, especially in Vietnam, and improve
current fertilizer management practices for a sustainable production.
Figure 4.
Average prices of the top three fertilizers and green Robusta coffee in Vietnam (
A
) and
Indonesia (
B
) during the 2008–2017 period. Coffee prices were sourced from the International Coffee
Organization (http://www.ico.org/new_historical.asp). VND: Vietnam Dong. IRD: Indonesia Rupiah.
NPK: blended NPK; SP: super phosphate; KCl: potassium chloride.
In Indonesia, the recommended rate for compost was 5 ton ha
−1
year
−1
[
31
], but, as with
chemical fertilizers, the recommended rate of organic fertilizer was not reached on most Robusta coffee
Agronomy 2019,9, 499 15 of 19
farms throughout the monitoring years. In Vietnam, the recommended rates of lime and compost
were 1 ton ha
−1
year
−1
and 5–8 ton ha
−1
year
−1
, respectively (depending on the targeted yield of
2.5–4.0 ton ha−1) [29]. The rates recorded were generally greater than those recommended, but given
the alternate application might not be sufficient to meet the requirement each season. It was not clear
whether the alternations of low and high applications of N, P
2
O
5
and K
2
O observed, at least between
2012 and 2017, could be related to the alternate use of organic fertilizers during these particular years.
It was out of the scope of this study to determine the N, P
2
O
5
and K
2
O concentrations in compost in
the surveyed farms. Further investigations across the study areas on the combined use of chemical and
organic fertilizers, and on the farmers’ perceptions about such uses, would provide valuable guides in
the best fertilizer management practices in Vietnam and Indonesia.
4.2. Challenges for a Sustainable Management of Fertilizers in Vietnam and Indonesia
Robusta coffee farmers in Vietnam were applying high rates of chemical fertilizers at constant
rates from year to year whereas Indonesian farmers applied well below the recommended rates.
More chemical fertilizers are being used in coffee production than in other crops in Vietnam [
38
,
39
].
Although intensive fertilizer use in Robusta coffee farms has led to increased yields during the previous
decades [
40
,
41
], the dependence on chemical fertilizers may not be sustainable in the long term. Such
intensive use of chemical fertilizer can reduce soil fertility through increased soil acidity, reduction of
beneficial microorganisms, increased unstable aggregates leading to erosion and degradation [
22
,
42
].
Intensive use of fertilizer can also impact water quality, thereby leading to sustainability issues.
Chemical fertilizers such blended NPK when applied intensively over long periods could also cause
the depletion, or accumulation, of other plant nutrients in the soil [
43
]. This could lead to reduced
yields and production [13,44,45].
Investigating the potential for reducing nutrient rates in coffee farms in Vietnam based on our
dataset showed that there are opportunities for reducing the higher rates observed during the study
period by up to 50% in some instances, depending on the nutrient and farm size, while achieving current
yield levels (Tables 7and 8). However, for nutrients like K
2
O, no conclusive indication can be drawn
from our dataset regarding the potential of reducing the current rates while achieving satisfactory
yield levels. This is because there were few or no reports in the majority of the selected provinces
of such patterns. An optimum management of fertilizers involving lower rates than those recorded
during the survey could still maintain satisfactory yields. For example, Bruno et al. [
46
] reported that a
routine nitrogen fertilizer rate of 600 kg ha
−1
could be reduced by one-third without decreasing the
production of coffee beans in commercial Arabica coffee farms in Brazil. Similar conclusions were
drawn in Costa Rica [
47
]. Further research is therefore needed to investigate fertilizer use efficiencies
in farm conditions, especially in Vietnam, and improve current fertilizer management practices for a
sustainable production.
The optimal combined use of chemical and organic fertilizers to ensure satisfactory bean yields
is of great interest for Robusta coffee farms in Vietnam and Indonesia. The use of organic fertilizers,
such as compost, in coffee farms has been shown to improve soil texture, provide a better environment
for beneficial microorganisms and to increase water-holding capacity and efficient nutrient use [
7
,
38
].
Our survey noticed a lack of understanding about nutrient requirements and the role of a balanced
nutrient supply for coffee plants in the study provinces in Vietnam and Indonesia. In Vietnam,
particularly, a large proportion of N–P
2
O
5
–K
2
O fertilizers are blended locally by state-owned enterprises,
creating vested interests in the status quo [
48
]. Such challenges could be addressed by means such as:
(1)
capacity-building and training to shift farmers’ practices and raise their awareness on the potential
damages of fertilizer overuse to the environment;
(2)
establishing demonstration farms to increase the confidence of farmers for adopting best
management practices;
(3)
introducing policies and incentives encouraging farm diversification (such as agroforestry) to
help farmers not to rely solely on coffee for farm profit.
Agronomy 2019,9, 499 16 of 19
5. Conclusions
We documented the management of fertilizers (chemical and organic) in Robusta coffee farms across
selected provinces in Vietnam and Indonesia during the 2008–2017 period. Four types of chemical (urea,
blended NPK, super phosphate and potassium chloride) and two types of natural fertilizer (organic
compost and lime) were used routinely in Vietnam. In Indonesia, only compost was used as organic
fertilizer in addition to urea and blended NPK as chemical fertilizers. Because achieving high yields
and maintaining such levels are among the key drivers of fertilizer application in Robusta coffee farms
in Vietnam, chemical fertilizers were generally applied in unbalanced proportions, posing threats to the
sustainability of such farming activities, the environment and, more broadly, to the economies of this
country. In the studied provinces in Indonesia, Robusta coffee trees could not attain their potential since
the lower fertilizer rates might have restricted the soil nutrient balance. Our findings showed that there
is a potential for improvement in both countries in terms of fertilizer management and sustainability
of Robusta coffee production. Adopting integrated fertility management practices, increasing the
awareness of farmers regarding sustainable practices, and introducing policies to encourage farm
diversification are among the options to improve the profitability of coffee farming while ensuring
environmentally-friendly crop management practices in these two coffee-producing countries.
Supplementary Materials:
The following are available online at http://www.mdpi.com/2073-4395/9/9/499/s1,
Table S1: Average rates of phosphate (P
2
O
5
) and potassium (K
2
O) according to farm size in Vietnamese Robusta
coffee-producing provinces, Table S2: Comparison of nitrogen (N), phosphate (P
2
O
5
) and potassium (K
2
O) rates
according to farm size in Indonesian Robusta coffee-producing provinces, Table S3: Percentages of farmers
applying organic fertilizers during 2008–2017 in the study provinces in Vietnam; Figure S1: Total annual rainfall at
the study provinces in (A) Vietnam (Dak Lak, Gia Lai, Dak Nong, and Lam Dong) and (B) Indonesia (Lampung,
South Sumatra and Bengkulu) during the period 2008–2017, Figure S2: 10-year average (2008–2017) of the fertilizer
rates applied across the surveyed districts in Vietnam. (A) blended NPK; (B) super phosphate, SP; (C) potassium
chloride, KCl; and (D) Urea. The averages are expressed in kg ha
−1
, Figure S3: 10-year average (2008–2017) of the
fertilizer rates applied across the surveyed districts in Indonesia. (A) Urea; (B) blended NPK; and (C) triple super
phosphate, TSP. The averages are expressed in kg ha
−1
, Figure S4: Year-to-year variations of natural fertilizers
compost and lime in surveyed Robusta coffee farms in Vietnamese (Dak Lak, Dak Nong, Gia Lai and Lam Dong)
and Indonesian (Bengkulu, Lampung and South Sumatra) coffee-producing provinces during 2008–2017 (Note
differences on the y-axis.); Figure S5: Scatterplots of Robusta coffee bean yields versus annual total rates of nitrogen
(N), phosphate (P
2
O
5
, referred to as P) and potassium chloride (K
2
O, referred to as K) in the study provinces in
Vietnam (A–C) and Indonesia (D–F) during 2008–2017. All data of the 10-year period are presented according to
the farm size group (small- and large-scale farms). Source: Survey data 2008–2017.
Author Contributions:
Conceptualization, V.B. and L.K.; formal analysis, V.B.; writing—original draft preparation,
V.B.; writing—review and editing; V.B., L.K., S.M. and R.S. All authors have read and approved the final manuscript.
Funding:
The first author is supported by the University of Southern Queensland’s International Fees Research
and Research Training Program Stipend Scholarships. We also acknowledge the funding received from the
German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and
the World Meteorological Organisation (WMO) through the DeRISK project.
Acknowledgments:
We gratefully acknowledge the valuable support of ECOM’s field surveys team in collecting
and processing field data, as well as all the Robusta coffee farmers in Vietnam and Indonesia who participated in
the interviews and generously provided information about their production systems. We thank the anonymous
reviewers for their constructive comments.
Conflicts of Interest: The authors declare no conflict of interest.
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