Vietnam is well-known as the second largest global coffee producer and the largest worldwide exporter of Robusta coffee. However, the Robusta coffee sector in Vietnam is facing many problems, including low quality, high external inputs and water shortages as a result of shade tree eradication. A six-month research project was conducted that focused on effects of shaded tree types on variation of light intensity and aspects of Robusta production. Three shade tree species at different planting densities and shade provision were investigated, including 46 trees of Durian ha –1 (14% shade), 35 trees of Sennaha –1 (17% shade), and 60 trees of Leucaena ha –1 (34% shade), and unshaded site (Open) was used as a control. The study found that light intensity declined 50% with Durian, 58% with Senna and 60% with Leucaena compared with the Open site (2096 μmol ?m –2 ?s –1). Within the coffee canopy, a significant decline in light intensity was observed from the top of the canopy to the bottom. The percentage of light at the middle (90 cm above ground) and bottom (30cm) levels of the coffee canopy was declined by 81% and 88% respectively for the Open site, and 86% and 92% for the Leucaena site. There were no differences in the number of flowers branch –1 tree –1 and fruit set between shaded and unshaded coffee sites. However, a significant difference in first fruit drop was observed.
Coffee is well-known as an understory bush, and early coffee plantations are grown under shade trees or forest canopy. However, in the modern coffee cultivation, opinions differ on whether or not shade is beneficial for coffee production.
Scientists who support shaded coffee cultivation highlight the positive effects of shade trees on yield improvement [
Two coffee species in Vietnam are 95% of Coffea canephora (Robusta) and 5% of Coffea arabica L. (Arabica). They are an important economic commodity and significantly contributing to socio-economic development. Vietnam, which has 653,000 ha of coffee in 2014, is the second largest global coffee producer, accounting for 19.4% of total production, additionally, is the world’s biggest Robusta producer with 47.7% share of worldwide Robusta production [
Traditionally, the practice of growing coffee in Vietnam involves planting coffee under shade trees. However, since the 1990s, worldwide coffee demand has increased sharply and this has led to a dramatic expansion in coffee growing areas along with shade abandonment to exploit maximum yield [
Therefore, understanding the influence of shade trees on coffee cultivation is critical to future coffee production, and in order to make it, researches should focus specifically on regions (climate and soil), coffee cultivars, shade tree species and density, and producer’s objectives. The general aim of research was to investigate the effect of different shade tree types (Durian, Leucaena and Senna) on light variation and Robusta coffee production in the Western Highland province of Gia Lai, Vietnam in order to evaluate the effect of shade trees on available light for the coffee tree canopies, and the effect of shade on coffee production (flowering, fruit set and fall proportions).
Ia Grai, as a west mountainous and border district of Gia Lai, has the largest both coffee area (16,615 ha) and yield (3.000 kg green bean ha−1) of province [
Four treatment sites included coffee farms shaded by either Senna siamea (Lam.). Irwin and Barneby (Senna), Leucaena leucocephala (Lam.) de Wit (Leucaena), Durio zibethinus L. (Durian), and one unshaded farm (Open), were used to determine the influence of different shade tree types on light intensity, flowering, fruit set, and fruit fall in Robusta coffee. Measurements were taken during December 2014 (the harvesting period) to the end of May 2015 (the pinhead stage of fruit). These three shade tree species are evergreen and long-lived with an open canopy and good drought tolerance [
Shade tree layout in regard to coffee bushes and the location of light measurements are provided in
The position at the stem of the shade tree was marked as 0 m and the distance from this to the nearest coffee bush, in both directions, was 1.5 m. The distance between coffee bushes was 3 m and hence the distance from the stem of the shade tree to the farthest coffee bush was 7.5 m. The positions of the three coffee bushes, ranging from the nearest to farthest from the shade tree, were therefore labeled 1.5, 4.5 and 7.5 m respectively. At the Open site, five plots with six coffee bushes per plot were randomly allocated. For each coffee bush, measurements were also taken in the vertical plane on both the north and south side of each plant. These were taken from three levels, branches on the top, middle and bottom (
An Electric Calibration Line Quantum2 sensor (model MQ-306 with 6 Sensors, Apogee Instruments) was used to measure light intensity (μmol∙m−2∙s−1). Readings were taken at between 11:00 am and 1:30 pm on clear, sunny days once the sun was at a right angle (90˚) to the ground [
Five coffee bushes were selected from under the canopy of the shade trees at Leucaena and five bushes at Open to determine light variation caused by coffee self-shading and shade trees. At Leucaena, coffee bushes located at
4.5 m on the north side of the shade tree were used. Because the height of trees was consistent at 180 cm, each coffee bush was measured at six locations every 30 cm starting at and above 30 cm above the ground (
Counts were conducted 3 - 5 days after watering. The total number of flowers per branch was calculated. Measurements were taken from coffee bushes chosen to measure light intensity (three bushes each on the north and south side of the shade tree) (
The percentage fruit set and fruit fall was calculated from branches also used for measuring number of flowers per branch. Fruit set was measured in March when flowers had finished the pollinating process; approximately one month after blossoming. First fruit drop was measured during May at the “pinhead” stage; 3 - 4 months after the first stage of fruiting [
Analysis of variance (ANOVA) was used to assess the effects of shade treatments on light and plant variables using R version 3.1.1 [
Shade trees caused a significant decrease (P = 2e−16) in available light with closer proximity to the tree’s stem (
The vertical variation in light reaching different parts of the coffee bush was measured at the Leucaena and Open sites. Despite different light intensities at the top of coffee bushes grown without shade (100% light, 2,096 μmm−2∙s−1) compared to those grown under Leucaena (52% of open conditions, 1089 μmm−2∙s−1), the decline in light variation from the top to the bottom of the coffee canopy was no different between the two sites (P > 0.05). However, differences in light intensity for the different vertical positions within the coffee canopy were significant (P < 0.05). Compared to the top of the coffee bushes (180 cm) at the Leucaenasite, light decreased to around 13.4% (280 μmm−2∙s−1) at 90 cm aboveground (the middle) and 7.9% (166 μmm−2∙s−1) at 30 cm aboveground (the bottom), at the same positions in Open site, however, light intensity dropped to approximately 19.2% (402 μmm−2∙s−1) and 12.3% (258 μmm−2∙s−1) respectively (
shaded and unshaded sites. Coffee shaded by Durian which had 278 flowers branch−1 bush−1, tended to have a little higher than others sites.
In terms of vertical position, shaded and unshaded sites both produced the highest number of flowers at the top of coffee bush (336 and 327 flowers branch−1), followed by the middle (251 and 252 flowers branch−1) and the bottom (175 and 183 flowers branch−1). Furthermore, data indicated that there was a significant difference in the amount of flowers branch−1 bush−1 on the vertical positions (P < 2e−16).
The average proportion of fruit set branch−1 bush−1 for all treatments was above 82% (84.1%, 83.3%, 82.9% and 82.6% for Leucaena, Senna, Open and Durian, respectively) (
The effect of shade tree type on the first fruit drop for the four sites was highly variable, ranging between 2.4% to 4.7% (
In this study, reduction in light resulted by three different shade tree species common in Vietnam (Durian, Sennaand Leucaena), were compared. Light decreased by an average of 50%, 58% and 60% under the canopy ofDurian, Sennaand Leucaena, respectively, compared to unshaded. This finding is similar to the work of Saptono and Ernawati [
The small canopy diameter of Durian produced the least shade area and therefore allowed more light to be transmitted than other shade tree species. The small canopy in durian was partly the result of grower’s harvesting Durian fruits resulting in fewer branches, low crown density and shade area and intensity [
The observed decline in light intensity from the top to the bottom of the coffee canopy was a result of the combined effect of the shade trees and the coffee bush strata. A decrease in light intensity has been shown to be simultaneous with increasing thickness of the tree canopy [
[
In terms of flowering, there were no significant differences in the average number of flowers per branch per bush between shaded and unshaded coffee. This finding contrasts with previous work that found that shaded coffee produced fewer flowers as a result of fewer flower buds forming per branch, which related the reduction in light intensity [
A possible reason for the difference in our findings with the work of others, is that our study was conducted in Vietnam where light intensity is relatively high [
With respect to vertical position in the coffee canopy, both shaded and unshaded coffee followed the same trend, whereby the number of flowers per branch per bush was similar for the top and middle of the canopy, but these were significantly higher than for the bottom. This result is similar to Lin [
A decrease in light intensity was also shown to inhibited flower bud initiation by Can nell [
Fruit set is an important process in achieving good coffee yield. Studies recognised that coffee, in general, has a low proportion of fruit set, for example, in Brazil, fruit set of Arabica coffee has been reported at around 29% [
Whereas Arabica coffee is self-fertilising, Robusta requires cross-fertilisation, therefore, compared to Arabica coffee, the pollination process in Robusta coffee can be affected by many additional factors. The two main factors that strongly influence pollination are genetic and external conditions [
The different fruit set proportions observed for the different vertical branch positions (top, middle and bottom) was also found by Reis and Arruda cited by [
After pollination, fruit experiences many growth periods before finally forming a bean at the ripening stage. Depending on coffee cultivar and region, in Vietnam, fruit drop for Robusta is defined by three periods. The first period occurs 2 - 4 months after flowering and is commonly known as the pinhead drop. The second stage is endosperm filling at 3 - 5 months, and the last is fruit growth after 6 months [
Average fruit fall at the four sites in our study ranged between 2.4% and 4.7%, with less fruit fall in the shaded sites compared to the Open site. This contradicts the study of Campanha, Santos [
Because fruit fall is expected to be at its lowest in the first fruit fall period (pinhead drop), resulting from pollination failure [
This study has indicated that the light intensity in coffee declines under shade and that this depends on the shade tree species. Overall, more than 50% of light was intercepted by the canopies of Durian, Senna and Leucaena planted at densities between 35 and 60 shade trees ha−1 and that provided 14% - 34% shade cover, respectively. Closer to the shade tree, light intensity tended to be decreased. Significant decline in light intensity was also recorded from the top to the bottom of coffee canopy. The number of flowers branch−1∙bush−1 between the unshaded and shaded sites was similar; however, it was affected by their location in the canopy. Differences in fruit set were also insignificant for the shaded and unshaded coffee among the shaded sites. However, first fruit fall under shade was less than for coffee grown in full sun.
Because of the time limitation, our study had several shortcomings with regard to inability to explore impacts of light on berry yield and quality, and distribution and viability of flowers amongst the branches of the coffee bush. Further research should therefore be conducted to address these limitations in order to better understand production and mechanisms of growth in Robusta coffee in response to shade.
Firstly, I would like to thank Dr. Isa Yunusa and Dr. Paul Kristiansen who supervised me to do this research. Thank to Ms. Chris Fyfe for proof reading, and my co-workers Mr. Dung, Mr. Ngoc, for data measurement. Secondly, I would like to gratefully acknowledge the Australia Awards Scholarships and The University of New England for funding support and assistance and especially for giving me an opportunity to study in Australia. Finally, thanks to the Vietnamese Australia Award staff and my leaders for their great support, and to the Western Highland Agriculture and Forestry Science Institute.
Nguyen Van Long,Nguyen Quang Ngoc,Nguyen Ngoc Dung,Paul Kristiansen,Isa Yunusa,Chris Fyfe, (2015) The Effects of Shade Tree Types on Light Variation and Robusta Coffee Production in Vietnam. Engineering,07,742-753. doi: 10.4236/eng.2015.711065