- Email: [email protected]
Alley-cropping system increases vegetation heterogeneity and moderates extreme microclimates in oil palm plantations
Agricultural and Forest Meteorology 276–277 (2019) 107632
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Alley-cropping system increases vegetation heterogeneity and moderates extreme microclimates in oil palm plantations
T
Mohamad Ashrafa,b, Ruzana Sanusib,c, , Raja Zulkiflia, Kamil A. Tohirana, Ramle Moslima, Adham Ashton-Buttd, Badrul Azharb,e ⁎
a
Division of Integration Research and Extension, Malaysian Palm Oil Board, No 6, Persiaran Institusi, Bandar Baru Bangi, 43000, Kajang, Selangor, Malaysia Department of Forest Management, Faculty of Forestry, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia c Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia d School of Biological Sciences, University of Southampton, Southampton, SO17 1BJ, United Kingdom e Institute of Biosciences, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia b
ARTICLE INFO
ABSTRACT
Keywords: Agriculture Biodiversity Crop Ecosystem Monoculture Sustainable
Forest conversion to oil palm plantation is causing a major loss of biodiversity in Southeast Asia and other tropical regions. Oil palm plantations have less biodiversity because of their simplified vegetation, human disturbances, and extreme microclimate conditions. Alley-cropping system incorporates a secondary crop in the alleys between the main crops. In some cases alley-cropping can result in a greater vegetation structural complexity, thus potentially providing agricultural and ecological benefits, including: buffering against weather extremes, reduction in soil erosion, increased biodiversity, and increased nutrient and water-use efficiency. In this study, we compared vegetation structure (height and cover of vegetation), microclimate (air temperature, relative humidity, light intensity and wind speed), and soil conditions (soil surface temperature, soil pH and soil moisture) across a range of alley-cropping systems and two ages of monoculture oil palm. We found that alleycropping system had varied structural complexity across different crops when compared to oil palm monoculture system. Careful selection of crops was essential, with black pepper and cacao having the largest impact on improving vegetation heterogeneity and microclimate regulation when incorporated into an alley-cropping system. In particular, we found that systems intercropped with black pepper had air and soil surface temperatures up to 1.3 °C and 2.1 °C cooler than those in oil palm monoculture. In contrast, systems intercropped with bactris and bamboo had increased air temperatures. Our findings show that some alley-cropping systems have great potential as a climate-smart practice in sustainable oil palm agriculture. This study also shows that careful selection of crops is important in the planning and management of future alley-cropping system to optimise the ecosystem benefits that can be gained from this management system.
1. Introduction The establishment of oil palm plantation, especially for large-scale production, involves massive land clearing either using heavy machinery or fire before the planting of young oil palms (Butler, 2011; Dislich et al., 2017). This practice leads to a reduction in the structural complexity of vegetation (Corley and Tinker, 2003; Fischer and Lindenmayer, 2007; Chung et al., 2000). This simplification of vegetation structure affects the microclimate of the converted area. Conventional oil palm plantations use a monoculture management system, experiencing higher temperatures and reduced humidity than forest habitat (Sabajo et al., 2017). Greater canopy openness in oil palm plantations results in greater penetration of sunlight to the ground thus ⁎
leading to a hotter and drier ground (Yaap et al., 2010). Sustainable management practices to enhance vegetation structure in order to ameliorate these extreme microclimates could benefit oil palm yield, biodiversity and ecosystem functioning in oil palm plantations. The alley-cropping system offers an opportunity to improve the vegetation structure and related ecosystem functions. Alley-cropping incorporates a main crop species intercropped with another plant species that are cultivated in several horizontal strips in an adjacent manner (Gold and Garrett, 2009). Alley-cropping can provide greater vegetation structural complexity than monocultures with varied crop plants, trees, ground vegetation cover and plant canopy; thus increasing soil fertility (depending on the species used), water quality and carbon cycling (Fahrig et al., 2011; Torralba et al.,
Corresponding author at: Department of Forest Management, Faculty of Forestry, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia. E-mail address: [email protected] (R. Sanusi).
https://doi.org/10.1016/j.agrformet.2019.107632 Received 11 June 2018; Received in revised form 30 May 2019; Accepted 20 June 2019 Available online 04 July 2019 0168-1923/ © 2019 Elsevier B.V. All rights reserved.
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
2016). Alley-cropping also functions as a potential adaption strategy for the mitigation of climate change effects through its ecological benefits such as buffers for weather extremes, soil erosion reduction and improvement of biodiversity, nutrient and water-use efficiency (Wolz et al., 2018). Ashraf et al. (2018) found that alley-cropping in oil palm improved biodiversity indicating that the alley-cropping system could act as a key management strategy in conserving and promoting biodiversity within oil palm production landscapes. Harvey and Villaloboz (2007) have observed higher richness and abundance of bird and bat species in cacao and banana alley-cropping systems compared to monocultures and arthropod diversity can be increased by incorporating alley-cropping into agricultural practices (Jose, 2012; Asmah et al., 2017; Ghazali et al., 2016; Novais et al., 2016; Ashraf et al., 2018). Our study compares vegetation structure, microclimate, and soil conditions of oil palm plantations incorporating the alley-cropping system into a conventional monoculture system in a large-scale oil palm production landscape. The findings of this study provide recommendations for sustainable farming practices and climate-smart agriculture i.e. through the introduction of alley-cropping and selection of suitable crops to intercrop with oil palm.
with five other crops. The alley-cropping system incorporated double-row avenue planting (Ismail et al., 2009) and has been used in experimental plots by the Division of Integration Research and Extension of MPOB since 2006. In this system, the alley-cropping species were planted in between oil palm trees and were arranged parallel to each other in strips or alleys with a length of 70–100 m and width of 15.2 m (Fig. 3). The planting distances between oil palms in the same row and between rows were 6.1 m and 9.1 m, respectively (Ismail et al., 2009). The planting distances in intercropping and monoculture were slightly different. For the monoculture oil palm plantation system, the planting distances between oil palms in the same row and between rows were 7.8 m and 9 m, respectively. Both crops and oil palm were managed following Good Agriculture Practises in terms of fertilization and pest/disease control (Ismail et al., 2009). 2.2. Study design Data was collected between July and November 2017. We used a systematic sampling design with a random starting point adopted from Morrison et al. (2008) where the first sampling point was randomly established at any location in each treatment alley and the following points were systematically distanced from the starting point. This design ensures randomization (Krebs, 1989). A total of seven treatments were established that comprised of five treatments of the alley-cropping system and two treatments of the monoculture oil palm system (Fig. 2). In alley-cropping system, oil palm (aged seven years old) was intercropped with: (i) pineapple (Ananas comosus), (ii) bactris (Bactris gasipaes), (fruit producing, spiny palms), (iii) bamboo (Gigantochloa albociliata), (iv) black pepper (Piper nigrum), and (v) cacao (Theobroma cacao). In monoculture oil palm, the oil palm stands were aged (vi) seven-years old and (vii) 15-years old. Each treatment was represented by three alleys (100 m each). Ten
2. Methodology 2.1. Study area This study was conducted on experimental plots in an oil palm plantation (607 ha) operated by the Malaysian Palm Oil Board situated in Keratong, Pahang, Peninsular Malaysia (2′47′1″ N, 102, 55′22″ E) (Fig. 1). The oil palm plantation is 60 m above sea level with flat terrain and no notable differences in elevation. The experimental plots were grouped into two categories: monoculture and alley-cropping agriculture systems. The monoculture oil palm was divided into two areas of different ages while the alley-cropping system incorporated oil palm
Fig. 1. Treatment plots within an oil palm plantation. Each plot had three alleys with 30 measurement points (10 points per alley). 2
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Fig. 2. Seven treatments including those intercropped with cacao (A), black pepper (B), pineapple (C), bactris (D), and bamboo (E). Two conventional oil palm monoculture of seven- (F) and 15- (G) year old crops were used as control treatments (Adopted from Ashraf et al., 2018).
measurement points were established at each alley. Thirty points per treatment were established within a period of four months with a total of 210 sampling points set up simultaneously in all the seven treatments per month. For each treatment, measurement points were assigned randomly on the harvesting path 5 m away from each other and 5 m away from the edge of the cropping lane at each treatment. The distance between different alley-cropping plots and between the monoculture and alley-cropping plots was at least 300 m.
non-grass species in a 1 m × 1 m quadrat, (iv) % non-grass species in a 2 m × 5 m quadrat (v) height of grass cover in a 1 m × 1 m quadrat, (vi) height of grass cover in a 2 m × 5 m quadrat, (vii) height of nongrass cover in a 1 m × 1 m quadrat, and (viii) height of non-grass cover in a 2 m × 5 m quadrat. All these characteristics were measured 1 m north, east and west, from the sampling point.
2.3. Vegetation structure
Five parameters were measured: (i) soil surface temperature, (ii) air temperature, (iii) wind speed, (iv) relative humidity, and (v) light intensity. Soil surface temperature was recorded three times per sampling point and averaged. Wind speed and light intensity parameters were recorded ten times per sampling point and averaged. The relative humidity and air temperature were recorded once per sampling point. All the microclimatic measurements were conducted at solar noon time (between 1 p.m. and 2.30 p.m.) in both alley-cropping and monoculture systems. The measurement at solar noon was selected as when the sun reaches its zenith, the sun is at the highest point of the day where at this time period, the area receives the greatest insolation. Most importantly, the vegetation structure of all treatments does not change in relation to daily time scale, however the solar radiation does vary depending on the sun orientation. Therefore, to look solely at the influence of
2.4. Microclimate
Two different scales of measurements were used for vegetation structure to provide a more accurate evaluation: small scale of 1 m2 to ensure vegetation was measured without duplication or omission; and a larger scale of 10 m2 to ensure accurate representation of vegetation in the measured area. This is because weeding was done mechanically (throughout the alley) and chemically (circular spraying around oil palm trees and selective spraying elsewhere) in the alley-cropping system. In order to consider the effects of circular and selective spraying on the vegetation structure, these two scales were necessary to be included in this study. A total of eight vegetation structural characteristics were measured at each sampling point: (i) % grass cover in a 1 m × 1 m quadrat, (ii) % grass cover in a 2 m × 5 m quadrat,(iii) %
Fig. 3. Planting distance used in the oil palm alley-cropping system. 3
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
vegetation structure on microclimate, the measurement at solar noon is important to minimise the influence from the variation of sun orientation according to the time of the day. Air temperature, wind speed and relative humidity were measured using a digital anemometerthermometer-hygrometer from Skywatch-Atmos (accuracy: air temperature, ± 0.4 °C (to 25 °C); wind speed, ± 3% FS; relative humidity, ± 3% rH (20 to 80% rH)) while light intensity was measured using a light meter from ISO-TECH ILM 1332A (accuracy: ± 4% + 10). The surface temperature was taken by using a Fluke infrared 59 MAX thermometer (accuracy: ± 2 °C or ± 2% of reading, whichever is greater).
seven-years and 15-years (5.77 cm and 5.63 cm, respectively) and was significantly different from oil palm intercropped with bactris and bamboo that had the lowest height of grass (1 m2) with 5.08 cm and 5.10 cm, respectively. For height of grass (10 m2) and non-grass (1 m2 and 10 m2), oil palm intercropped with cacao was highest and were significantly different from most of the other treatments. 3.2. Microclimate and soil characteristics between alley-cropping and monoculture systems in oil palm production landscape We found that air temperature, soil surface temperature, relative humidity, light intensity, wind speed, soil pH and soil moisture were significantly different (p < 0.001) between conventional monoculture and some of the crops in the alley-cropping systems (Table 2; Fig. 5). For air temperature, oil palm intercropped with black pepper and cacao had the lowest air temperatures (33.2 °C and 33.3 °C, respectively) whereas oil palm intercropped with bamboo (36.4 °C) and bactris (37.0 °C) had significantly higher air temperature compared to most of the other treatments. Similarly, only oil palm intercropped with black pepper and cacao had significantly lower soil surface temperatures (33.0 °C and 33.1 °C, respectively) compared to all treatments including both of the monoculture oil palm treatments aged seven- and 15-years (34.4 °C and 35.1 °C, respectively) and bamboo was significantly had the highest surface temperature (37.7 °C). The light intensity in oil palm intercropped with bamboo was the highest, with 521.2 lx and cacao had a significantly lower light intensity with 197.24 lx compared to other treatments. Oil palm intercropped with black pepper had the highest relative humidity (60.53%) among the treatments whereas oil palm intercropped with bamboo had the lowest relative humidity compared to most of the other treatments (55.85%). The wind speed was highest in oil palm intercropped with black pepper treatment (2.17 m/s) and lowest in oil palm intercropped with cacao (1.55 m/s). Most importantly, the air temperature of oil palm intercropped with black pepper and cacao were 1.3 °C and 1.2 °C cooler, respectively, than the monoculture treatment aged 15-years and the soil surface temperature were 2.1 °C and 2.0 °C cooler, respectively. Oil palm intercropped with cacao also had the greatest light intensity reduction with up to 97.2 lx compared to the monoculture treatments (Table 3). Mean soil pH was the most acidic in oil palm intercropped with pineapple and the least acidic in oil palm intercropped with black pepper although all treatments can be characterised as slightly acidic to neutral with pH value ranging from 6.79 to 7.05. The soil moisture was highest in oil palm intercropped with cacao and black pepper (2.7% and 2.6%, respectively) and lowest in oil palm intercropped with bamboo (1.4%).
2.5. Soil characteristics For soil characteristics, a Moon City 3-in-1 Soil Meter for moisture (range: 1–10 (1–3 DRY, 4–7 NOR, 8–10 WET), light (range: 0–2000 lux (0–200 LOW, 200-500LOW+, 500–1000 NOR 1000–2000 HGH)), and pH (range: 3.5–8 pH (3.5–6.5 ACID, 7 NOR, 7–8 ALKALI)) was used to measure (vi) soil moisture and (vii) soil pH. We recorded all measurements on a monthly basis. 2.6. Data analysis To compare vegetation structure, microclimate and soil characteristics between monoculture oil palm and alley-cropping systems, a oneway analysis of variance (ANOVA) with blocking was used. Sampling week was included as the experimental block in this analysis. All 15 variables were tested with a Shapiro-Wilk’s test to detect deviation from normality. All variables were log-transformed to improve the linearity of the data. Tukey’s test was used as a post hoc comparison to detect significance between treatments. Analyses were performed using Genstat version 15 software (VSNI, Hemel, Hempstead, UK). 3. Results 3.1. Vegetation structure of alley-cropping and oil palm monoculture systems Our results revealed that grass cover (1 m2, grass cover (10 m2), non-grass cover (1 m2), non-grass cover (10 m2) height of grass (1 m2), height of grass (10 m2), height of non-grass (1 m2), and height of nongrass (10 m2) were significantly different (p < 0.05) between conventional monoculture and some of the crops in the alley-cropping systems (Table 1; Fig. 4). For grass cover (1 m2), oil palm intercropped with black pepper had the highest (51.2%), followed by oil palm intercropped with bactris (43.9%) and cacao (43.4%) where these three treatments were significantly greater than both oil palm monoculture aged 15-years (39.7%, at p < 0.05) (Table 1). However the conventional monoculture treatments did not differ with the oil palm intercropped with bamboo as this treatment had the lowest grass cover (39.4%). Similarly, grass cover (10 m2) for oil palm intercropped with black pepper and bactris (52.1% and 46.6%, respectively) were significantly greater compared to oil palm monoculture treatments. Meanwhile, the conventional monoculture treatments were not significantly different with the oil palm intercropped with pineapple (39.7%) and bamboo (41.9%). Non-grass vegetation cover (1 m2) for oil palm intercropped with bactris had the highest percentage (24.3%) followed by pineapple (22.9%). These two treatments were significantly different from the conventional monoculture treatments while the other crops were not. On the other hand, for non-grass vegetation cover (10 m2), oil palm intercropped with pineapple had highest non-grass vegetation cover with 24.5% followed by bactris with 24.3% and these two treatments were significantly different from the other treatments. The height of grass (1 m2) was highest in oil palm monoculture
4. Discussion 4.1. Conventional monoculture system vs. alley-cropping system Our results show that the oil palm monoculture system had less vegetation structure in some of the crops in the alley-cropping system. Both oil palm monocultures aged seven and 15-year had lower grass and non-grass ground vegetation cover, when compared to the majority of the alley-cropping treatments. Low vegetation cover in the oil palm monoculture system might be explained by the fact that in general, oil palm surroundings have sparse undergrowth vegetation due to constant herbicide usage and weeding (Dislich et al., 2017). Oil palm monocultures have a much hotter and drier microclimate than the original forest land use (Luskin and Potts, 2011). However, some alley-cropping treatments significantly ameliorated the extreme microclimate in plantations. For instance, oil palm intercropped with black pepper showed significantly greater relative humidity as well as lower air temperature than both oil palm monoculture treatments. Lack of undergrowth vegetation in the oil palm monoculture allows 4
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Table 1 The mean values of vegetation structural characteristics across seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alleycropping. The means that do not differ share an identical letter. Variable
Treatment
Grass cover (%) within 1 m2
Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil
Grass cover (%) within 10 m2
Non-grass cover (%) within 1 m2
Non-grass cover (%) within 10 m2
Height of grass (cm) within 1 m2
Height of grass (cm) within 10 m2
Height of non-grass (cm) within 1 m2
Height of non-grass (cm) within 10 m2
palm + bamboo palm monoculture aged palm monoculture aged palm + pineapple palm + cacao palm + bactris palm + black pepper palm + pineapple palm monoculture aged palm + bamboo palm monoculture aged palm + cacao palm + bactris palm + black pepper palm + black pepper palm monoculture aged palm monoculture aged palm + bamboo palm + cacao palm + pineapple palm + bactris palm + black pepper palm monoculture aged palm + cacao palm + bamboo palm monoculture aged palm + bactris palm + pineapple palm + bactris palm + bamboo palm + pineapple palm + black pepper palm + cacao palm monoculture aged palm monoculture aged palm + bactris palm + bamboo palm + pineapple palm monoculture aged palm monoculture aged palm + black pepper palm + cacao palm + bamboo palm monoculture aged palm monoculture aged palm + bactris palm + pineapple palm + black pepper palm + cacao palm + bamboo palm + pineapple palm + bactris palm monoculture aged palm monoculture aged palm + black pepper palm + cacao
15-years seven-years
15-years seven-years
seven-years 15-years
15-years seven-years
15-years seven-years
seven-years 15-years
15-years seven-years
15-years seven-years
greater sunlight penetration under the tree canopy and exposing the soil, resulting in rapid evapotranspiration loss of water (Azhar et al., 2013). Furthermore, loss of soil moisture from evaporation process that dries the soil may further decrease the evaporative latent heat cooling resulting in greater air temperature under oil palm monocultures (Comte et al., 2012; Henson and Harun, 2005). This interaction of hydrology, microclimate and vegetation shows the importance of these components in influencing the water condition of an area (Comte et al., 2012; Henson and Harun, 2005). The amelioration of harsh microclimatic effects in some of the crops the alley-cropping system is possibly due to the greater leaf area, increased transpiration, lower light penetration and reduced wind speed experienced in the majority of alley-cropping treatments. Fifteen year
Mean
Tukey
d.f.
Variance ratio
p
39.35 39.72 40.27 41.30 43.35 43.85 51.17 39.72 41.49 41.88 42.95 44.77 46.56 52.12 19.68 19.72 19.91 20.04 20.23 22.91 24.27 20.65 21.23 21.73 21.93 22.08 24.32 24.49 5.08 5.10 5.33 5.42 5.55 5.63 5.77 7.60 7.89 8.14 8.15 8.51 8.70 8.74 6.68 6.92 6.99 7.04 7.18 7.25 8.16 9.86 9.91 10.30 10.37 10.81 10.99 11.09
a a ab ab b b c a ab ab ab bc c d a a a a a b b a a a a a b b a a ab ab b b b a ab bc bc cd d d a ab ab ab ab b c a a ab abc bcd cd d
6
19.48
< 0.001
6
22.36
< 0.001
6
12.87
< 0.001
6
9.32
< 0.001
6
5.94
< 0.001
6
14.02
< 0.01
6
11.78
< 0.001
6
10.41
< 0.001
old oil palm is likely to have a higher relative humidity due to the closed canopy, whereas seven year old oil palm experiences greater sunlight penetration due to the more open canopy structure (Corley and Tinker, 2003). Luskin and Potts (2011) stated that young oil palm trees experienced greater fluctuations in local climate condition compared to mature trees due to their less complex canopy and lower leaf area index, explaining the greater light intensity in seven year old oil palm monoculture. This highlights the potential benefits of applying the alley cropping system in young oil palm stands as it can ameliorate these effects. In addition, some alley-cropping treatments improved soil moisture, which is a limiting factor on oil palm yield (Tao et al., 2017).
5
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Fig. 4. The vegetation structural characteristics in seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alley-cropping (oil palm intercropped with pineapple denoted by OP-Pin, black pepper denoted by OP-BP, cacao denoted by OP-Cac, bactris denoted by OP-Bac and bamboo denoted by OP-Bam) treatments.
4.2. Effects of crop choice on vegetation structure in the alley-cropping system
speed reduction, more moderate temperatures (due to lower radiation intensities) and an improved water regulation system (higher air and soil moisture, and reduced evaporation losses from the soil surface) (Quinkenstein et al., 2009). In this study, the air temperature and surface temperature were strongly affected by vegetation cover in the different alley-cropping treatments. Oil palm intercropped with black pepper and cacao had lower air and surface temperatures compared to other treatments. When compared to monoculture oil palm treatment, the oil palm intercropped with black paper and cacao reduced 1.3 °C and 1.2 °C of air temperature, respectively. Moreover, both treatments also had 2.1 °C and 2.0 °C lower surface temperature compared to the monoculture oil palm, respectively. Both black pepper and cacao plants have diversified vegetation structure with a high ground vegetation cover; such as grass or ground litter, greater canopy height for black pepper (Sivaraman et al., 1999) and a wider canopy cover for cacao (Somarriba and Beer, 2011). These vegetation structure characteristics influence not only the air temperature, but also the interception of solar radiation to the ground. Ground vegetation also absorbs solar radiation, reducing the surrounding air and surface temperature (Hardwick et al., 2015). In addition, physical characteristics of black pepper and cacao such as, higher and wider canopy cover will act as a wind barrier and reduces the vertical mixing of warm air due to the longer distance for the wind to reach the ground surface (Hardwick et al., 2015). Therefore, increasing relative humidity and lowering air temperature. On the other hand, when bamboo was selected in the oil palm alleycropping system, bamboo showed the highest light intensity, air temperature, surface temperature and a lower relative humidity when compared to other treatments. This may be due to the traits and morphology of bamboo as it grows in a small clustered stem with extensive branches and leaves, but with large gaps from one cluster to another cluster, leading to less ground vegetation cover (Soderstrom and Calderon, 1979). Furthermore, the small and thin leaves of bamboo create sparse canopy cover allowing more light penetration and low levels of transpiration (Soderstrom and Calderon, 1979). These results were similar to the vegetation structure findings where although there were differences between the monoculture and intercropping systems,
The findings indicated that vegetation structure in majority of the alley-cropping treatments were more complex compared to the monoculture oil palm system. Although there were differences between monoculture and intercropping systems, it is important to note that within the alley-cropping system itself, proper selection of crop is an important factor for enhancing the vegetation heterogeneity of an area. Grass vegetation cover of 1 m2 and 10 m2 were both greatest in oil palm intercropped with black pepper compared to the other treatments. This result may be explained by the fact that black pepper crops require mulching to prevent the roots of black pepper from drying during the dry season and to avoid soil erosion during the rainy season (Sivaraman et al., 1999). Therefore, natural cover or planting cover crops in black pepper landscape is necessary for a higher yield and to prevent diseases or infections (Sivaraman et al., 1999). In the non-grass vegetation cover (1 m2), oil palm intercropped with bactris had the highest percentage while for non-grass vegetation cover (10 m2), oil palm intercropped with pineapple had the highest cover. Both results can be associated with the presence of Imperata brasiliensis on the harvesting path in both plantations (Agamuthu and Broughton, 1985). Manual weeding was carried out every two or three months to prevent damage to the crops and destruction of other plant species (Ismail et al., 2009). In contrast, height of grass (10 m2) was highest in oil palm intercropped with cacao. Cacao plants provide shade by a large canopy cover and ground litter below the trees. In this respect, the management regime of alley-cropping system differs with the conventional oil palm system as the alley-cropping system does not rely on chemical herbicides to the same degree (Ismail et al., 2009; Ashraf et al., 2018). 4.3. Effects of crop choice on the microclimate and soil characteristics in the alley-cropping system Alley-cropping systems usually typified by a high structural diversity and recognized to influence microclimatic parameters (Quinkenstein et al., 2009). The microclimatic benefits include wind 6
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Table 2 The mean values of microclimate and soil characteristics across seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alleycropping. The means that do not differ share an identical letter. Variable
Treatment
Mean
Tukey
d.f.
Variance ratio
p
Air temperature (°C)
Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil
33.19 33.27 33.57 34.51 34.59 36.39 36.98 197.24 239.88 288.40 294.44 310.46 316.23 521.19 55.85 56.23 56.62 58.61 59.02 59.16 60.53 1.55 1.57 1.65 1.65 1.70 1.73 2.17 1.40 1.89 1.92 1.94 2.12 2.59 2.68 6.80 6.94 6.99 7.01 7.03 7.04 7.05 32.96 33.11 34.35 34.43 34.51 35.07 37.67
a a a b b c c a b c c c c d a a a b b b c a a ab ab ab b c a b b b c d d a b bc cd cd cd d a a b b b b c
6
105.96
< 0.001
6
60.70
< 0.001
6
30.0
< 0.001
6
22.71
< 0.001
6
186.85
< 0.001
6
40.73
< 0.001
6
61.20
< 0.001
Light intensity (Lux)
Relative humidity (%)
Wind speed (m/s)
Soil moisture (%)
Soil pH
Soil surface temperature (°C)
palm + black pepper palm + cacao palm monoculture aged palm monoculture aged palm + pineapple palm + bamboo palm + bactris palm + cacao palm monoculture aged palm + black pepper palm monoculture aged palm + pineapple palm + bactris palm + bamboo palm + bamboo palm monoculture aged palm + pineapple palm + bactris palm + cacao palm monoculture aged palm + black pepper palm + cacao palm monoculture aged palm + bactris palm + pineapple palm monoculture aged palm + bamboo palm + black pepper palm + bamboo palm monoculture aged palm + pineapple palm monoculture aged palm + bactris palm + black pepper palm + cacao palm + black pepper palm monoculture aged palm + bactris palm + cacao palm monoculture aged palm + bamboo palm + pineapple palm + black pepper palm + cacao palm + pineapple palm monoculture aged palm + bactris palm monoculture aged palm + bamboo
seven-years 15-years
15-years seven-years
15-years
seven-years seven-years 15-years
15-years seven-years
seven-years 15-years
seven-years 15-years
the microclimate conditions in the alley-cropping system were influenced by the crop choice. This therefore highlights the importance of proper selection of crops within the alley- cropping system in moderating extreme microclimate conditions in oil palm plantation.
19%–37% in yield compared to maize conventional mono-cropping (Bertomeu, 2012). However, the maize-timber intercropping significantly reduced 70%–80% less labour thus can optimally maximise land use with limited labour (Bertomeu, 2006). On the other hand, according to Ismail et al. (2009), the alleycropping system did not reduce oil palm yield where the alley-cropping system produced 15.38 t ha-1 yr-1 of average fresh fruit bunch (FFB) while conventional triangular planting system produced 15.28 t ha-1 yr-1 in the first four years. Properly planted and managed alley-cropping system following good agriculture practices through application of good quality planting materials, implementation of best planting technique, right fertilization and efficient pest and disease control ensure vegetation in this system grows well together without having to compete for the resources providing optimum yield (Ismail et al., 2009). Moreover, several factors correlated with crop yield such as soil moisture, shading and competition for resources are important and need to be taken consideration during establishment of alley-cropping system plot (Ong et al., 1991; Chirko et al., 1996). Our study shows that alley-cropping can in certain configurations
4.4. Alley-cropping system as an alternative for sustainable agricultural practice Declining oil palm prices have had an adverse impact on smallholders’ livelihoods (Kubitza et al., 2018). The alley-cropping practice was intentionally introduced to increase the income of oil palm smallholders and to improve food security by adapting and building resilience to climate change (Ismail et al., 2009; Azhar et al., 2017; Ashraf et al., 2018; Wolz et al., 2018). Alley-cropping system was reportedly to have reduced the annual crop yield. For instance, the intercropping of corn and soybean crops with silver maple tree in Northeast Missouri showed reduction of 24%–86% in crop yield (Udawatta et al., 2014). In addition, in Philippines, timber tree and maize integrations have caused reduction of 7
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Fig. 5. The microclimate and soil characteristics in seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alley-cropping (oil palm intercropped with pineapple denoted by OP-Pin, black pepper denoted by OP-BP, cacao denoted by OP-Cac, bactris denoted by OP-Bac and bamboo denoted by OP-Bam) treatments.
optimal condition for the growth of natural predator (Staver et al., 2001). Further research should be conducted on selecting suitable crop species to encourage ecosystem service delivery to oil palm, such as attracting predators of common pests. Crops with suitable physical traits such as having canopy cover, wider leaf area index and undergrowth vegetation can provide optimum conditions for natural predators to survive (Nurdiansyah et al., 2016). Furthermore, the alleycropping system increases arthropod biodiversity in oil palm plantations (Ashraf et al., 2018).
improve the microclimate and vegetation structure of an oil palm plantation. In terms of microclimate moderation, we identified black pepper as the most suitable crop to be integrated with oil palm, followed by cacao. Our data indicated that bactris and bamboo may not be appropriate to be intercropped with oil palm because of increased air temperature caused by the crop integration. With proper crop selection in the alley-cropping system, it could play an important role in sustainable land management through moderating the climate impacts from landscape change in the agricultural production landscape and could serve as a key strategy in mitigating the effects of climate change (Jose et al., 2008, 2004). The type of canopy cover, leaf size and the presence of ground cover are among the essential characteristics that have been observed influencing the presence of fauna and microclimate properties in oil palm plantations. Alley-cropping could also reduce pest outbreaks by increasing the crop and other plant diversity within a plantation (Ratnadass et al., 2012). Plant species selection can also modify the microclimate properties in ways that constrain pest growth by creating
5. Conclusion Overall, this study shows that oil palm alley-cropping system can promote greater vegetation heterogeneity and improve microclimate compared to the monoculture system depending on the crop selection in the alley-cropping system. Alley-cropping practice can increase vegetation cover, reduce sun exposure, reduce drying and buffer extreme
Table 3 The differences in means of: air temperature, light intensity, relative humidity, wind speed, soil surface temperature and soil moisture between the oil palm monoculture treatments aged seven- and 15-years to alley-cropping treatments. Variable
Air temperature (°C) Light intensity (Lux) Relative humidity (%) Wind speed (km/h) Soil surface temperature (°C) Soil moisture (%) ‡
Oil Palm monoculture age (year)
Treatment Oil palm + black pepper
Oil palm + cacao
Oil palm + bactris
Oil palm + pineapple
Oil palm + bamboo
7 15 7 15 7 15 7 15 7 15 7 15
0.38 ‡ 1.32 ‡‡ 6.04 ‡ −48.52 −1.37 −4.30 −0.6 −0.47 1.47 ‡ 2.11 ‡‡ −0.65 −0.70
0.3 ‡ 1.24 ‡‡ 97.2 ‡ 42.64 ‡‡ 0.14 ‡ −2.79 0.02 ‡ 0.15 ‡‡ 1.32 ‡ 1.96 ‡‡ −0.74 −0.79
−3.41 −2.47 −21.79 −76.35 0.55 ‡ −2.38 −0.08 0.05 ‡‡ −0.08 0.56 ‡‡ −0.18 −0.23
−1.02 −0.08 −16.02 −70.58 2.54 ‡ −0.39 −0.08 0.05 ‡‡ 0.08 ‡ 0.72 ‡‡ 0.02 ‡ −0.03
−2.82 −1.88 −542. 98 −281.31 3.31 ‡ 0.38 ‡‡ −0.16 −0.03 ‡‡ −3.24 −2.60 0.54 ‡ 0.49 ‡‡
Represents a lower value in the alley-cropping treatment compared to the oil palm monoculture aged seven-years. Represents a lower value in the alley-cropping treatment compared to the oil palm monoculture aged 15-years.
‡‡
8
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
temperature in certain configurations. These effects are also desirable to create the habitat that is required to enhance biodiversity and ecosystem functions. We found that there were significant differences in microclimate and vegetation structure between alley-cropping and monoculture oil palm agriculture. Although the oil palm alley-cropping system can enhance vegetation complexity and mitigate extreme microclimates in oil palm plantations, careful selection of crops was essential. Cacao and black pepper were the best option for intercropping with oil palm as these crops have essential vegetation characteristics such as a wider canopy cover and presence of undergrowth vegetation. We suggest that alley-cropping system with properly selected crops can provide an alternative income with the secondary crops, increase biodiversity and benefit microclimate within oil palm agriculture; thus, it should be considered as a key strategy in sustainable oil palm production.
landscapes. Ecol. Lett. 14, 101–112. Fischer, J., Lindenmayer, D.B., 2007. Landscape modification and habitat fragmentation: a synthesis. Glob. Ecol. Biogeogr. 16 (3), 265–280. Ghazali, A., Asmah, S., Syafiq, M., Yahya, M.S., Aziz, N., Tan, L.P., et al., 2016. Effects of monoculture and polyculture farming in oil palm smallholdings on terrestrial arthropod diversity. J. Asia Pac. Entomol. 19, 415–421. Gold, M.A., Garrett, H.E., 2009. Agroforestry nomenclature, concepts, and practices. North American Agroforestry: An Integrated Science and Practice, 2nd edition. pp. 45–56 (northamericanag). Hardwick, S.R., Toumi, R., Pfeifer, M., Turner, E.C., Nilus, R., Ewers, R.M., 2015. The relationship between leaf area index and microclimate in tropical forest and oil palm plantation: forest disturbance drives changes in microclimate. Agric. For. Meteorol. 201, 187–195. Harvey, C.A., Villalobos, J.A.G., 2007. Agroforestry systems conserve species-rich but modified assemblages of tropical birds and bats. Biodivers. Conserv. 16, 2257–2292. Henson, I.E., Harun, M.H., 2005. The influence of climatic conditions on gas and energy exchanges above a young oil palm stand in north Kedah, Malaysia. J. Oil Palm Res. 17, 73–91. Ismail, S., Khasim, N., Zulkifli, R., 2009. Double-row Avenue System for Crop Integration with Oil Palm. MPOB Information Series No. 424. Bangi, Malaysia. . Jose, S., Gillespie, A.R., Pallardy, S.G., 2004. Interspecific interactions in temperate agroforestry. Agrofor. Syst. 61 (1-3), 237–255. Jose, S., Allen, S.C., Nair, P.R., 2008. Tree-crop interactions: lessons from temperate alleycropping systems. Ecol. Basis Agrofor. 15–36. Jose, S., 2012. Agroforestry for conserving and enhancing biodiversity. Agrofor. Syst. 85, 1–8. Krebs, C.J., 1989. Ecological Methodology (No. QH541. 15. S72. K74 1999.). Harper & Row, New York. Kubitza, C., Krishna, V.V., Alamsyah, Z., Qaim, M., 2018. The economics behind an ecological crisis: livelihood effects of oil palm expansion in Sumatra, Indonesia. Hum. Ecol. 46 (1), 107–116. Luskin, M.S., Potts, M.D., 2011. Microclimate and habitat heterogeneity through the oil palm lifecycle. Basic Appl. Ecol. 12 (6), 540–551. Morrison, M.L., Block, W.M., Strickland, M.D., Collier, B.A., Peterson, M.J., 2008. Wildlife Study Design. Springer Science & Business Media. Novais, S., Macedo-Reis, L.E., DaRocha, W.D., Neves, F.S., 2016. Effects of habitat management on different feeding guilds of herbivorous insects in cacao agroforestry systems. Rev. Biol. Trop. 64, 763–777. Nurdiansyah, F., Denmead, L.H., Clough, Y., Wiegand, K., Tscharntke, T., 2016. Biological control in Indonesian oil palm potentially enhanced by landscape context. Agr. Ecosyst. Environ. 232, 141–149. Ong, C.K., Corlett, J.E., Singh, R.P., Black, C.R., 1991. Above and below ground interactions in agroforestry systems. For. Ecol. Manage. 45 (1-4), 45–57. Quinkenstein, A., Woellecke, J., Böhm, C., Gruenewald, H., Freese, D., Schneider, B.U., Huettl, R.F., 2009. Ecological benefits of the alley cropping agroforestry system in sensitive regions of Europe. Environ. Sci. Policy 12, 1112–1121. Ratnadass, A., Fernandes, P., Avelino, J., Habib, R., 2012. Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review. Agron. Sustain. Dev. 32 (1), 273–303. Sabajo, C.R., Le Maire, G., June, T., Meijide, A., Roupsard, O., Knohl, A., 2017. Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia. Biogeosciences 14 (20), 4619. Sivaraman, K., Kandiannan, K., Peter, K.V., Thankamani, C.K., 1999. Agronomy of black pepper (Piper nigrum L.) – a review. J. Spices Aromat. Crop. 8 (1), 1–18. Soderstrom, T.R., Calderon, C.E., 1979. A commentary on the bamboos (Poaceae: bambusoideae). Biotropica 161–172. Somarriba, E., Beer, J., 2011. Productivity of Theobroma cacao agroforestry systems with timber or legume service shade trees. Agrofor. Syst. 81 (2), 109–121. Staver, C., Guharay, F., Monterroso, D., Muschler, R.G., 2001. Designing pest-suppressive multistrata perennial crop systems: shade-grown coffee in Central America. Agrofor. Syst. 53 (2), 151–170. Tao, H.H., Snaddon, J.L., Slade, E.M., Caliman, J.P., Widodo, R.H., Willis, K.J., 2017. Long-term crop residue application maintains oil palm yield and temporal stability of production. Agron. Sustain. Dev. 37 (4), 33. Torralba, M., Fagerholm, N., Burgess, P.J., Moreno, G., Plieninger, T., 2016. Do European agroforestry systems enhance biodiversity and ecosystem services? A meta-analysis. Agric. Ecosyst. Environ. 230, 150–161. Udawatta, R.P., Motavalli, P.P., Jose, S., Nelson, K.A., 2014. Temporal and spatial differences in crop yields of a mature silver maple alley cropping system. Agron. J. 106 (2), 407–415. Wolz, K.J., Lovell, S.T., Branham, B.E., Eddy, W.C., Keeley, K., Revord, R.S., et al., 2018. Frontiers in alley cropping: transformative solutions for temperate agriculture. Glob. Chang. Biol. 24 (3), 883–894. Yaap, B., Struebig, M.J., Paoli, G., Koh, L.P., 2010. Mitigating the biodiversity impacts of oil palm development. Cab Rev. Perspect. Agric. Vet. Sci. Nutr. Nat. Resour. 5 (19), 1–11.
Acknowledgments This research was funded by Putra Graduate Initiative Grant (IPS) from Universiti Putra Malaysia (Grant No: GP-IPS/2016/9513900). We would like to thank Sapari Mat and Nur Hidayatul Akma for their comments and suggestions on an earlier version of the manuscript. Mohamad Ashraf was funded by the MPOB Graduate Students Assistantship Scheme (GSAS). We also thank all the MPOB Kratong staff, particularly Fathil Kamil and Jamaludin Bokhari for providing logistical support during data collection in the field. References Agamuthu, P., Broughton, W.J., 1985. Nutrient cycling within the developing oil palmlegume ecosystem. Agric. Ecosyst. Environ. 13 (2), 111–123. Ashraf, M., Zulkifli, R., Sanusi, R., Tohiran, K.A., Terhem, R., Moslim, R., et al., 2018. Alley-cropping system can boost arthropod biodiversity and ecosystem functions in oil palm plantations. Agric. Ecosyst. Environ. 260, 19–26. Asmah, S., Ghazali, A., Syafiq, M., Yahya, M.S., Peng, T.L., Norhisham, A.R., et al., 2017. Effects of polyculture and monoculture farming in oil palm smallholdings on tropical fruit-feeding butterfly diversity. Agric. For. Entomol. 19, 70–80. Azhar, B., Lindenmayer, D.B., Wood, J., Fischer, J., Manning, A., Mcelhinny, C., Zakaria, M., 2013. The influence of agricultural system, stand structural complexity and landscape context on foraging birds in oil palm landscapes. Ibis 155, 297–312. Azhar, B., Saadun, N., Prideaux, M., Lindenmayer, D.B., 2017. The global palm oil sector must change to save biodiversity and improve food security in the tropics. J. Environ. Manage. 203, 457–466. Bertomeu, M., 2006. Financial evaluation of smallholder timber-based agroforestry systems in Claveria, Northern Mindanao, the Philippines. Small-Scale For. Econ. Manag. Policy 5 (1), 57–81. Bertomeu, M., 2012. Growth and yield of maize and timber trees in smallholder agroforestry systems in Claveria, northern Mindanao, Philippines. Agrofor. Syst. 84 (1), 73–87. Butler, R., 2011. In Brazil, palm oil plantations could help preserve Amazon. Yale Environment. pp. 360. Chirko, C.P., Gold, M.A., Nguyen, P.V., Jiang, J.P., 1996. Influence of direction and distance from trees on wheat yield and photosynthetic photon flux density (Qp) in a Paulownia and wheat intercropping system. For. Ecol. Manage. 83 (3), 171–180. Chung, A.Y.C., Eggleton, P., Speight, M.R., Hammond, P.M., Chey, V.K., 2000. The diversity of beetle assemblages in different habitat types in Sabah, Malaysia. Bull. Entomol. Res. 90 (6), 475–496. Comte, I., Colin, F., Whalen, J.K., Grünberger, O., Caliman, J.P., 2012. Agricultural practices in oil palm plantations and their impact on hydrological changes, nutrient fluxes and water quality in Indonesia: a review. Advances in Agronomy 116. Academic Press, pp. 71–124. Corley, R.H.V., Tinker, P.B., 2003. The Oil Palm Fourth Edition. World Agriculture Series. Blackwell. Dislich, C., Keyel, A.C., Salecker, J., Kisel, Y., Meyer, K.M., Auliya, M., et al., 2017. A review of the ecosystem functions in oil palm plantations, using forests as a reference system. Biol. Rev. 92 (3), 1539–1569. Fahrig, L., Baudry, J., Brotons, L., Burel, F.G., Crist, T.O., Fuller, R.J., et al., 2011. Functional landscape heterogeneity and animal biodiversity in agricultural
9
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Alley-cropping system increases vegetation heterogeneity and moderates extreme microclimates in oil palm plantations
T
Mohamad Ashrafa,b, Ruzana Sanusib,c, , Raja Zulkiflia, Kamil A. Tohirana, Ramle Moslima, Adham Ashton-Buttd, Badrul Azharb,e ⁎
a
Division of Integration Research and Extension, Malaysian Palm Oil Board, No 6, Persiaran Institusi, Bandar Baru Bangi, 43000, Kajang, Selangor, Malaysia Department of Forest Management, Faculty of Forestry, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia c Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia d School of Biological Sciences, University of Southampton, Southampton, SO17 1BJ, United Kingdom e Institute of Biosciences, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia b
ARTICLE INFO
ABSTRACT
Keywords: Agriculture Biodiversity Crop Ecosystem Monoculture Sustainable
Forest conversion to oil palm plantation is causing a major loss of biodiversity in Southeast Asia and other tropical regions. Oil palm plantations have less biodiversity because of their simplified vegetation, human disturbances, and extreme microclimate conditions. Alley-cropping system incorporates a secondary crop in the alleys between the main crops. In some cases alley-cropping can result in a greater vegetation structural complexity, thus potentially providing agricultural and ecological benefits, including: buffering against weather extremes, reduction in soil erosion, increased biodiversity, and increased nutrient and water-use efficiency. In this study, we compared vegetation structure (height and cover of vegetation), microclimate (air temperature, relative humidity, light intensity and wind speed), and soil conditions (soil surface temperature, soil pH and soil moisture) across a range of alley-cropping systems and two ages of monoculture oil palm. We found that alleycropping system had varied structural complexity across different crops when compared to oil palm monoculture system. Careful selection of crops was essential, with black pepper and cacao having the largest impact on improving vegetation heterogeneity and microclimate regulation when incorporated into an alley-cropping system. In particular, we found that systems intercropped with black pepper had air and soil surface temperatures up to 1.3 °C and 2.1 °C cooler than those in oil palm monoculture. In contrast, systems intercropped with bactris and bamboo had increased air temperatures. Our findings show that some alley-cropping systems have great potential as a climate-smart practice in sustainable oil palm agriculture. This study also shows that careful selection of crops is important in the planning and management of future alley-cropping system to optimise the ecosystem benefits that can be gained from this management system.
1. Introduction The establishment of oil palm plantation, especially for large-scale production, involves massive land clearing either using heavy machinery or fire before the planting of young oil palms (Butler, 2011; Dislich et al., 2017). This practice leads to a reduction in the structural complexity of vegetation (Corley and Tinker, 2003; Fischer and Lindenmayer, 2007; Chung et al., 2000). This simplification of vegetation structure affects the microclimate of the converted area. Conventional oil palm plantations use a monoculture management system, experiencing higher temperatures and reduced humidity than forest habitat (Sabajo et al., 2017). Greater canopy openness in oil palm plantations results in greater penetration of sunlight to the ground thus ⁎
leading to a hotter and drier ground (Yaap et al., 2010). Sustainable management practices to enhance vegetation structure in order to ameliorate these extreme microclimates could benefit oil palm yield, biodiversity and ecosystem functioning in oil palm plantations. The alley-cropping system offers an opportunity to improve the vegetation structure and related ecosystem functions. Alley-cropping incorporates a main crop species intercropped with another plant species that are cultivated in several horizontal strips in an adjacent manner (Gold and Garrett, 2009). Alley-cropping can provide greater vegetation structural complexity than monocultures with varied crop plants, trees, ground vegetation cover and plant canopy; thus increasing soil fertility (depending on the species used), water quality and carbon cycling (Fahrig et al., 2011; Torralba et al.,
Corresponding author at: Department of Forest Management, Faculty of Forestry, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia. E-mail address: [email protected] (R. Sanusi).
https://doi.org/10.1016/j.agrformet.2019.107632 Received 11 June 2018; Received in revised form 30 May 2019; Accepted 20 June 2019 Available online 04 July 2019 0168-1923/ © 2019 Elsevier B.V. All rights reserved.
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
2016). Alley-cropping also functions as a potential adaption strategy for the mitigation of climate change effects through its ecological benefits such as buffers for weather extremes, soil erosion reduction and improvement of biodiversity, nutrient and water-use efficiency (Wolz et al., 2018). Ashraf et al. (2018) found that alley-cropping in oil palm improved biodiversity indicating that the alley-cropping system could act as a key management strategy in conserving and promoting biodiversity within oil palm production landscapes. Harvey and Villaloboz (2007) have observed higher richness and abundance of bird and bat species in cacao and banana alley-cropping systems compared to monocultures and arthropod diversity can be increased by incorporating alley-cropping into agricultural practices (Jose, 2012; Asmah et al., 2017; Ghazali et al., 2016; Novais et al., 2016; Ashraf et al., 2018). Our study compares vegetation structure, microclimate, and soil conditions of oil palm plantations incorporating the alley-cropping system into a conventional monoculture system in a large-scale oil palm production landscape. The findings of this study provide recommendations for sustainable farming practices and climate-smart agriculture i.e. through the introduction of alley-cropping and selection of suitable crops to intercrop with oil palm.
with five other crops. The alley-cropping system incorporated double-row avenue planting (Ismail et al., 2009) and has been used in experimental plots by the Division of Integration Research and Extension of MPOB since 2006. In this system, the alley-cropping species were planted in between oil palm trees and were arranged parallel to each other in strips or alleys with a length of 70–100 m and width of 15.2 m (Fig. 3). The planting distances between oil palms in the same row and between rows were 6.1 m and 9.1 m, respectively (Ismail et al., 2009). The planting distances in intercropping and monoculture were slightly different. For the monoculture oil palm plantation system, the planting distances between oil palms in the same row and between rows were 7.8 m and 9 m, respectively. Both crops and oil palm were managed following Good Agriculture Practises in terms of fertilization and pest/disease control (Ismail et al., 2009). 2.2. Study design Data was collected between July and November 2017. We used a systematic sampling design with a random starting point adopted from Morrison et al. (2008) where the first sampling point was randomly established at any location in each treatment alley and the following points were systematically distanced from the starting point. This design ensures randomization (Krebs, 1989). A total of seven treatments were established that comprised of five treatments of the alley-cropping system and two treatments of the monoculture oil palm system (Fig. 2). In alley-cropping system, oil palm (aged seven years old) was intercropped with: (i) pineapple (Ananas comosus), (ii) bactris (Bactris gasipaes), (fruit producing, spiny palms), (iii) bamboo (Gigantochloa albociliata), (iv) black pepper (Piper nigrum), and (v) cacao (Theobroma cacao). In monoculture oil palm, the oil palm stands were aged (vi) seven-years old and (vii) 15-years old. Each treatment was represented by three alleys (100 m each). Ten
2. Methodology 2.1. Study area This study was conducted on experimental plots in an oil palm plantation (607 ha) operated by the Malaysian Palm Oil Board situated in Keratong, Pahang, Peninsular Malaysia (2′47′1″ N, 102, 55′22″ E) (Fig. 1). The oil palm plantation is 60 m above sea level with flat terrain and no notable differences in elevation. The experimental plots were grouped into two categories: monoculture and alley-cropping agriculture systems. The monoculture oil palm was divided into two areas of different ages while the alley-cropping system incorporated oil palm
Fig. 1. Treatment plots within an oil palm plantation. Each plot had three alleys with 30 measurement points (10 points per alley). 2
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Fig. 2. Seven treatments including those intercropped with cacao (A), black pepper (B), pineapple (C), bactris (D), and bamboo (E). Two conventional oil palm monoculture of seven- (F) and 15- (G) year old crops were used as control treatments (Adopted from Ashraf et al., 2018).
measurement points were established at each alley. Thirty points per treatment were established within a period of four months with a total of 210 sampling points set up simultaneously in all the seven treatments per month. For each treatment, measurement points were assigned randomly on the harvesting path 5 m away from each other and 5 m away from the edge of the cropping lane at each treatment. The distance between different alley-cropping plots and between the monoculture and alley-cropping plots was at least 300 m.
non-grass species in a 1 m × 1 m quadrat, (iv) % non-grass species in a 2 m × 5 m quadrat (v) height of grass cover in a 1 m × 1 m quadrat, (vi) height of grass cover in a 2 m × 5 m quadrat, (vii) height of nongrass cover in a 1 m × 1 m quadrat, and (viii) height of non-grass cover in a 2 m × 5 m quadrat. All these characteristics were measured 1 m north, east and west, from the sampling point.
2.3. Vegetation structure
Five parameters were measured: (i) soil surface temperature, (ii) air temperature, (iii) wind speed, (iv) relative humidity, and (v) light intensity. Soil surface temperature was recorded three times per sampling point and averaged. Wind speed and light intensity parameters were recorded ten times per sampling point and averaged. The relative humidity and air temperature were recorded once per sampling point. All the microclimatic measurements were conducted at solar noon time (between 1 p.m. and 2.30 p.m.) in both alley-cropping and monoculture systems. The measurement at solar noon was selected as when the sun reaches its zenith, the sun is at the highest point of the day where at this time period, the area receives the greatest insolation. Most importantly, the vegetation structure of all treatments does not change in relation to daily time scale, however the solar radiation does vary depending on the sun orientation. Therefore, to look solely at the influence of
2.4. Microclimate
Two different scales of measurements were used for vegetation structure to provide a more accurate evaluation: small scale of 1 m2 to ensure vegetation was measured without duplication or omission; and a larger scale of 10 m2 to ensure accurate representation of vegetation in the measured area. This is because weeding was done mechanically (throughout the alley) and chemically (circular spraying around oil palm trees and selective spraying elsewhere) in the alley-cropping system. In order to consider the effects of circular and selective spraying on the vegetation structure, these two scales were necessary to be included in this study. A total of eight vegetation structural characteristics were measured at each sampling point: (i) % grass cover in a 1 m × 1 m quadrat, (ii) % grass cover in a 2 m × 5 m quadrat,(iii) %
Fig. 3. Planting distance used in the oil palm alley-cropping system. 3
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
vegetation structure on microclimate, the measurement at solar noon is important to minimise the influence from the variation of sun orientation according to the time of the day. Air temperature, wind speed and relative humidity were measured using a digital anemometerthermometer-hygrometer from Skywatch-Atmos (accuracy: air temperature, ± 0.4 °C (to 25 °C); wind speed, ± 3% FS; relative humidity, ± 3% rH (20 to 80% rH)) while light intensity was measured using a light meter from ISO-TECH ILM 1332A (accuracy: ± 4% + 10). The surface temperature was taken by using a Fluke infrared 59 MAX thermometer (accuracy: ± 2 °C or ± 2% of reading, whichever is greater).
seven-years and 15-years (5.77 cm and 5.63 cm, respectively) and was significantly different from oil palm intercropped with bactris and bamboo that had the lowest height of grass (1 m2) with 5.08 cm and 5.10 cm, respectively. For height of grass (10 m2) and non-grass (1 m2 and 10 m2), oil palm intercropped with cacao was highest and were significantly different from most of the other treatments. 3.2. Microclimate and soil characteristics between alley-cropping and monoculture systems in oil palm production landscape We found that air temperature, soil surface temperature, relative humidity, light intensity, wind speed, soil pH and soil moisture were significantly different (p < 0.001) between conventional monoculture and some of the crops in the alley-cropping systems (Table 2; Fig. 5). For air temperature, oil palm intercropped with black pepper and cacao had the lowest air temperatures (33.2 °C and 33.3 °C, respectively) whereas oil palm intercropped with bamboo (36.4 °C) and bactris (37.0 °C) had significantly higher air temperature compared to most of the other treatments. Similarly, only oil palm intercropped with black pepper and cacao had significantly lower soil surface temperatures (33.0 °C and 33.1 °C, respectively) compared to all treatments including both of the monoculture oil palm treatments aged seven- and 15-years (34.4 °C and 35.1 °C, respectively) and bamboo was significantly had the highest surface temperature (37.7 °C). The light intensity in oil palm intercropped with bamboo was the highest, with 521.2 lx and cacao had a significantly lower light intensity with 197.24 lx compared to other treatments. Oil palm intercropped with black pepper had the highest relative humidity (60.53%) among the treatments whereas oil palm intercropped with bamboo had the lowest relative humidity compared to most of the other treatments (55.85%). The wind speed was highest in oil palm intercropped with black pepper treatment (2.17 m/s) and lowest in oil palm intercropped with cacao (1.55 m/s). Most importantly, the air temperature of oil palm intercropped with black pepper and cacao were 1.3 °C and 1.2 °C cooler, respectively, than the monoculture treatment aged 15-years and the soil surface temperature were 2.1 °C and 2.0 °C cooler, respectively. Oil palm intercropped with cacao also had the greatest light intensity reduction with up to 97.2 lx compared to the monoculture treatments (Table 3). Mean soil pH was the most acidic in oil palm intercropped with pineapple and the least acidic in oil palm intercropped with black pepper although all treatments can be characterised as slightly acidic to neutral with pH value ranging from 6.79 to 7.05. The soil moisture was highest in oil palm intercropped with cacao and black pepper (2.7% and 2.6%, respectively) and lowest in oil palm intercropped with bamboo (1.4%).
2.5. Soil characteristics For soil characteristics, a Moon City 3-in-1 Soil Meter for moisture (range: 1–10 (1–3 DRY, 4–7 NOR, 8–10 WET), light (range: 0–2000 lux (0–200 LOW, 200-500LOW+, 500–1000 NOR 1000–2000 HGH)), and pH (range: 3.5–8 pH (3.5–6.5 ACID, 7 NOR, 7–8 ALKALI)) was used to measure (vi) soil moisture and (vii) soil pH. We recorded all measurements on a monthly basis. 2.6. Data analysis To compare vegetation structure, microclimate and soil characteristics between monoculture oil palm and alley-cropping systems, a oneway analysis of variance (ANOVA) with blocking was used. Sampling week was included as the experimental block in this analysis. All 15 variables were tested with a Shapiro-Wilk’s test to detect deviation from normality. All variables were log-transformed to improve the linearity of the data. Tukey’s test was used as a post hoc comparison to detect significance between treatments. Analyses were performed using Genstat version 15 software (VSNI, Hemel, Hempstead, UK). 3. Results 3.1. Vegetation structure of alley-cropping and oil palm monoculture systems Our results revealed that grass cover (1 m2, grass cover (10 m2), non-grass cover (1 m2), non-grass cover (10 m2) height of grass (1 m2), height of grass (10 m2), height of non-grass (1 m2), and height of nongrass (10 m2) were significantly different (p < 0.05) between conventional monoculture and some of the crops in the alley-cropping systems (Table 1; Fig. 4). For grass cover (1 m2), oil palm intercropped with black pepper had the highest (51.2%), followed by oil palm intercropped with bactris (43.9%) and cacao (43.4%) where these three treatments were significantly greater than both oil palm monoculture aged 15-years (39.7%, at p < 0.05) (Table 1). However the conventional monoculture treatments did not differ with the oil palm intercropped with bamboo as this treatment had the lowest grass cover (39.4%). Similarly, grass cover (10 m2) for oil palm intercropped with black pepper and bactris (52.1% and 46.6%, respectively) were significantly greater compared to oil palm monoculture treatments. Meanwhile, the conventional monoculture treatments were not significantly different with the oil palm intercropped with pineapple (39.7%) and bamboo (41.9%). Non-grass vegetation cover (1 m2) for oil palm intercropped with bactris had the highest percentage (24.3%) followed by pineapple (22.9%). These two treatments were significantly different from the conventional monoculture treatments while the other crops were not. On the other hand, for non-grass vegetation cover (10 m2), oil palm intercropped with pineapple had highest non-grass vegetation cover with 24.5% followed by bactris with 24.3% and these two treatments were significantly different from the other treatments. The height of grass (1 m2) was highest in oil palm monoculture
4. Discussion 4.1. Conventional monoculture system vs. alley-cropping system Our results show that the oil palm monoculture system had less vegetation structure in some of the crops in the alley-cropping system. Both oil palm monocultures aged seven and 15-year had lower grass and non-grass ground vegetation cover, when compared to the majority of the alley-cropping treatments. Low vegetation cover in the oil palm monoculture system might be explained by the fact that in general, oil palm surroundings have sparse undergrowth vegetation due to constant herbicide usage and weeding (Dislich et al., 2017). Oil palm monocultures have a much hotter and drier microclimate than the original forest land use (Luskin and Potts, 2011). However, some alley-cropping treatments significantly ameliorated the extreme microclimate in plantations. For instance, oil palm intercropped with black pepper showed significantly greater relative humidity as well as lower air temperature than both oil palm monoculture treatments. Lack of undergrowth vegetation in the oil palm monoculture allows 4
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Table 1 The mean values of vegetation structural characteristics across seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alleycropping. The means that do not differ share an identical letter. Variable
Treatment
Grass cover (%) within 1 m2
Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil
Grass cover (%) within 10 m2
Non-grass cover (%) within 1 m2
Non-grass cover (%) within 10 m2
Height of grass (cm) within 1 m2
Height of grass (cm) within 10 m2
Height of non-grass (cm) within 1 m2
Height of non-grass (cm) within 10 m2
palm + bamboo palm monoculture aged palm monoculture aged palm + pineapple palm + cacao palm + bactris palm + black pepper palm + pineapple palm monoculture aged palm + bamboo palm monoculture aged palm + cacao palm + bactris palm + black pepper palm + black pepper palm monoculture aged palm monoculture aged palm + bamboo palm + cacao palm + pineapple palm + bactris palm + black pepper palm monoculture aged palm + cacao palm + bamboo palm monoculture aged palm + bactris palm + pineapple palm + bactris palm + bamboo palm + pineapple palm + black pepper palm + cacao palm monoculture aged palm monoculture aged palm + bactris palm + bamboo palm + pineapple palm monoculture aged palm monoculture aged palm + black pepper palm + cacao palm + bamboo palm monoculture aged palm monoculture aged palm + bactris palm + pineapple palm + black pepper palm + cacao palm + bamboo palm + pineapple palm + bactris palm monoculture aged palm monoculture aged palm + black pepper palm + cacao
15-years seven-years
15-years seven-years
seven-years 15-years
15-years seven-years
15-years seven-years
seven-years 15-years
15-years seven-years
15-years seven-years
greater sunlight penetration under the tree canopy and exposing the soil, resulting in rapid evapotranspiration loss of water (Azhar et al., 2013). Furthermore, loss of soil moisture from evaporation process that dries the soil may further decrease the evaporative latent heat cooling resulting in greater air temperature under oil palm monocultures (Comte et al., 2012; Henson and Harun, 2005). This interaction of hydrology, microclimate and vegetation shows the importance of these components in influencing the water condition of an area (Comte et al., 2012; Henson and Harun, 2005). The amelioration of harsh microclimatic effects in some of the crops the alley-cropping system is possibly due to the greater leaf area, increased transpiration, lower light penetration and reduced wind speed experienced in the majority of alley-cropping treatments. Fifteen year
Mean
Tukey
d.f.
Variance ratio
p
39.35 39.72 40.27 41.30 43.35 43.85 51.17 39.72 41.49 41.88 42.95 44.77 46.56 52.12 19.68 19.72 19.91 20.04 20.23 22.91 24.27 20.65 21.23 21.73 21.93 22.08 24.32 24.49 5.08 5.10 5.33 5.42 5.55 5.63 5.77 7.60 7.89 8.14 8.15 8.51 8.70 8.74 6.68 6.92 6.99 7.04 7.18 7.25 8.16 9.86 9.91 10.30 10.37 10.81 10.99 11.09
a a ab ab b b c a ab ab ab bc c d a a a a a b b a a a a a b b a a ab ab b b b a ab bc bc cd d d a ab ab ab ab b c a a ab abc bcd cd d
6
19.48
< 0.001
6
22.36
< 0.001
6
12.87
< 0.001
6
9.32
< 0.001
6
5.94
< 0.001
6
14.02
< 0.01
6
11.78
< 0.001
6
10.41
< 0.001
old oil palm is likely to have a higher relative humidity due to the closed canopy, whereas seven year old oil palm experiences greater sunlight penetration due to the more open canopy structure (Corley and Tinker, 2003). Luskin and Potts (2011) stated that young oil palm trees experienced greater fluctuations in local climate condition compared to mature trees due to their less complex canopy and lower leaf area index, explaining the greater light intensity in seven year old oil palm monoculture. This highlights the potential benefits of applying the alley cropping system in young oil palm stands as it can ameliorate these effects. In addition, some alley-cropping treatments improved soil moisture, which is a limiting factor on oil palm yield (Tao et al., 2017).
5
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Fig. 4. The vegetation structural characteristics in seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alley-cropping (oil palm intercropped with pineapple denoted by OP-Pin, black pepper denoted by OP-BP, cacao denoted by OP-Cac, bactris denoted by OP-Bac and bamboo denoted by OP-Bam) treatments.
4.2. Effects of crop choice on vegetation structure in the alley-cropping system
speed reduction, more moderate temperatures (due to lower radiation intensities) and an improved water regulation system (higher air and soil moisture, and reduced evaporation losses from the soil surface) (Quinkenstein et al., 2009). In this study, the air temperature and surface temperature were strongly affected by vegetation cover in the different alley-cropping treatments. Oil palm intercropped with black pepper and cacao had lower air and surface temperatures compared to other treatments. When compared to monoculture oil palm treatment, the oil palm intercropped with black paper and cacao reduced 1.3 °C and 1.2 °C of air temperature, respectively. Moreover, both treatments also had 2.1 °C and 2.0 °C lower surface temperature compared to the monoculture oil palm, respectively. Both black pepper and cacao plants have diversified vegetation structure with a high ground vegetation cover; such as grass or ground litter, greater canopy height for black pepper (Sivaraman et al., 1999) and a wider canopy cover for cacao (Somarriba and Beer, 2011). These vegetation structure characteristics influence not only the air temperature, but also the interception of solar radiation to the ground. Ground vegetation also absorbs solar radiation, reducing the surrounding air and surface temperature (Hardwick et al., 2015). In addition, physical characteristics of black pepper and cacao such as, higher and wider canopy cover will act as a wind barrier and reduces the vertical mixing of warm air due to the longer distance for the wind to reach the ground surface (Hardwick et al., 2015). Therefore, increasing relative humidity and lowering air temperature. On the other hand, when bamboo was selected in the oil palm alleycropping system, bamboo showed the highest light intensity, air temperature, surface temperature and a lower relative humidity when compared to other treatments. This may be due to the traits and morphology of bamboo as it grows in a small clustered stem with extensive branches and leaves, but with large gaps from one cluster to another cluster, leading to less ground vegetation cover (Soderstrom and Calderon, 1979). Furthermore, the small and thin leaves of bamboo create sparse canopy cover allowing more light penetration and low levels of transpiration (Soderstrom and Calderon, 1979). These results were similar to the vegetation structure findings where although there were differences between the monoculture and intercropping systems,
The findings indicated that vegetation structure in majority of the alley-cropping treatments were more complex compared to the monoculture oil palm system. Although there were differences between monoculture and intercropping systems, it is important to note that within the alley-cropping system itself, proper selection of crop is an important factor for enhancing the vegetation heterogeneity of an area. Grass vegetation cover of 1 m2 and 10 m2 were both greatest in oil palm intercropped with black pepper compared to the other treatments. This result may be explained by the fact that black pepper crops require mulching to prevent the roots of black pepper from drying during the dry season and to avoid soil erosion during the rainy season (Sivaraman et al., 1999). Therefore, natural cover or planting cover crops in black pepper landscape is necessary for a higher yield and to prevent diseases or infections (Sivaraman et al., 1999). In the non-grass vegetation cover (1 m2), oil palm intercropped with bactris had the highest percentage while for non-grass vegetation cover (10 m2), oil palm intercropped with pineapple had the highest cover. Both results can be associated with the presence of Imperata brasiliensis on the harvesting path in both plantations (Agamuthu and Broughton, 1985). Manual weeding was carried out every two or three months to prevent damage to the crops and destruction of other plant species (Ismail et al., 2009). In contrast, height of grass (10 m2) was highest in oil palm intercropped with cacao. Cacao plants provide shade by a large canopy cover and ground litter below the trees. In this respect, the management regime of alley-cropping system differs with the conventional oil palm system as the alley-cropping system does not rely on chemical herbicides to the same degree (Ismail et al., 2009; Ashraf et al., 2018). 4.3. Effects of crop choice on the microclimate and soil characteristics in the alley-cropping system Alley-cropping systems usually typified by a high structural diversity and recognized to influence microclimatic parameters (Quinkenstein et al., 2009). The microclimatic benefits include wind 6
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Table 2 The mean values of microclimate and soil characteristics across seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alleycropping. The means that do not differ share an identical letter. Variable
Treatment
Mean
Tukey
d.f.
Variance ratio
p
Air temperature (°C)
Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil
33.19 33.27 33.57 34.51 34.59 36.39 36.98 197.24 239.88 288.40 294.44 310.46 316.23 521.19 55.85 56.23 56.62 58.61 59.02 59.16 60.53 1.55 1.57 1.65 1.65 1.70 1.73 2.17 1.40 1.89 1.92 1.94 2.12 2.59 2.68 6.80 6.94 6.99 7.01 7.03 7.04 7.05 32.96 33.11 34.35 34.43 34.51 35.07 37.67
a a a b b c c a b c c c c d a a a b b b c a a ab ab ab b c a b b b c d d a b bc cd cd cd d a a b b b b c
6
105.96
< 0.001
6
60.70
< 0.001
6
30.0
< 0.001
6
22.71
< 0.001
6
186.85
< 0.001
6
40.73
< 0.001
6
61.20
< 0.001
Light intensity (Lux)
Relative humidity (%)
Wind speed (m/s)
Soil moisture (%)
Soil pH
Soil surface temperature (°C)
palm + black pepper palm + cacao palm monoculture aged palm monoculture aged palm + pineapple palm + bamboo palm + bactris palm + cacao palm monoculture aged palm + black pepper palm monoculture aged palm + pineapple palm + bactris palm + bamboo palm + bamboo palm monoculture aged palm + pineapple palm + bactris palm + cacao palm monoculture aged palm + black pepper palm + cacao palm monoculture aged palm + bactris palm + pineapple palm monoculture aged palm + bamboo palm + black pepper palm + bamboo palm monoculture aged palm + pineapple palm monoculture aged palm + bactris palm + black pepper palm + cacao palm + black pepper palm monoculture aged palm + bactris palm + cacao palm monoculture aged palm + bamboo palm + pineapple palm + black pepper palm + cacao palm + pineapple palm monoculture aged palm + bactris palm monoculture aged palm + bamboo
seven-years 15-years
15-years seven-years
15-years
seven-years seven-years 15-years
15-years seven-years
seven-years 15-years
seven-years 15-years
the microclimate conditions in the alley-cropping system were influenced by the crop choice. This therefore highlights the importance of proper selection of crops within the alley- cropping system in moderating extreme microclimate conditions in oil palm plantation.
19%–37% in yield compared to maize conventional mono-cropping (Bertomeu, 2012). However, the maize-timber intercropping significantly reduced 70%–80% less labour thus can optimally maximise land use with limited labour (Bertomeu, 2006). On the other hand, according to Ismail et al. (2009), the alleycropping system did not reduce oil palm yield where the alley-cropping system produced 15.38 t ha-1 yr-1 of average fresh fruit bunch (FFB) while conventional triangular planting system produced 15.28 t ha-1 yr-1 in the first four years. Properly planted and managed alley-cropping system following good agriculture practices through application of good quality planting materials, implementation of best planting technique, right fertilization and efficient pest and disease control ensure vegetation in this system grows well together without having to compete for the resources providing optimum yield (Ismail et al., 2009). Moreover, several factors correlated with crop yield such as soil moisture, shading and competition for resources are important and need to be taken consideration during establishment of alley-cropping system plot (Ong et al., 1991; Chirko et al., 1996). Our study shows that alley-cropping can in certain configurations
4.4. Alley-cropping system as an alternative for sustainable agricultural practice Declining oil palm prices have had an adverse impact on smallholders’ livelihoods (Kubitza et al., 2018). The alley-cropping practice was intentionally introduced to increase the income of oil palm smallholders and to improve food security by adapting and building resilience to climate change (Ismail et al., 2009; Azhar et al., 2017; Ashraf et al., 2018; Wolz et al., 2018). Alley-cropping system was reportedly to have reduced the annual crop yield. For instance, the intercropping of corn and soybean crops with silver maple tree in Northeast Missouri showed reduction of 24%–86% in crop yield (Udawatta et al., 2014). In addition, in Philippines, timber tree and maize integrations have caused reduction of 7
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
Fig. 5. The microclimate and soil characteristics in seven treatment levels of control (oil palm monoculture aged seven-years and 15-years) and alley-cropping (oil palm intercropped with pineapple denoted by OP-Pin, black pepper denoted by OP-BP, cacao denoted by OP-Cac, bactris denoted by OP-Bac and bamboo denoted by OP-Bam) treatments.
optimal condition for the growth of natural predator (Staver et al., 2001). Further research should be conducted on selecting suitable crop species to encourage ecosystem service delivery to oil palm, such as attracting predators of common pests. Crops with suitable physical traits such as having canopy cover, wider leaf area index and undergrowth vegetation can provide optimum conditions for natural predators to survive (Nurdiansyah et al., 2016). Furthermore, the alleycropping system increases arthropod biodiversity in oil palm plantations (Ashraf et al., 2018).
improve the microclimate and vegetation structure of an oil palm plantation. In terms of microclimate moderation, we identified black pepper as the most suitable crop to be integrated with oil palm, followed by cacao. Our data indicated that bactris and bamboo may not be appropriate to be intercropped with oil palm because of increased air temperature caused by the crop integration. With proper crop selection in the alley-cropping system, it could play an important role in sustainable land management through moderating the climate impacts from landscape change in the agricultural production landscape and could serve as a key strategy in mitigating the effects of climate change (Jose et al., 2008, 2004). The type of canopy cover, leaf size and the presence of ground cover are among the essential characteristics that have been observed influencing the presence of fauna and microclimate properties in oil palm plantations. Alley-cropping could also reduce pest outbreaks by increasing the crop and other plant diversity within a plantation (Ratnadass et al., 2012). Plant species selection can also modify the microclimate properties in ways that constrain pest growth by creating
5. Conclusion Overall, this study shows that oil palm alley-cropping system can promote greater vegetation heterogeneity and improve microclimate compared to the monoculture system depending on the crop selection in the alley-cropping system. Alley-cropping practice can increase vegetation cover, reduce sun exposure, reduce drying and buffer extreme
Table 3 The differences in means of: air temperature, light intensity, relative humidity, wind speed, soil surface temperature and soil moisture between the oil palm monoculture treatments aged seven- and 15-years to alley-cropping treatments. Variable
Air temperature (°C) Light intensity (Lux) Relative humidity (%) Wind speed (km/h) Soil surface temperature (°C) Soil moisture (%) ‡
Oil Palm monoculture age (year)
Treatment Oil palm + black pepper
Oil palm + cacao
Oil palm + bactris
Oil palm + pineapple
Oil palm + bamboo
7 15 7 15 7 15 7 15 7 15 7 15
0.38 ‡ 1.32 ‡‡ 6.04 ‡ −48.52 −1.37 −4.30 −0.6 −0.47 1.47 ‡ 2.11 ‡‡ −0.65 −0.70
0.3 ‡ 1.24 ‡‡ 97.2 ‡ 42.64 ‡‡ 0.14 ‡ −2.79 0.02 ‡ 0.15 ‡‡ 1.32 ‡ 1.96 ‡‡ −0.74 −0.79
−3.41 −2.47 −21.79 −76.35 0.55 ‡ −2.38 −0.08 0.05 ‡‡ −0.08 0.56 ‡‡ −0.18 −0.23
−1.02 −0.08 −16.02 −70.58 2.54 ‡ −0.39 −0.08 0.05 ‡‡ 0.08 ‡ 0.72 ‡‡ 0.02 ‡ −0.03
−2.82 −1.88 −542. 98 −281.31 3.31 ‡ 0.38 ‡‡ −0.16 −0.03 ‡‡ −3.24 −2.60 0.54 ‡ 0.49 ‡‡
Represents a lower value in the alley-cropping treatment compared to the oil palm monoculture aged seven-years. Represents a lower value in the alley-cropping treatment compared to the oil palm monoculture aged 15-years.
‡‡
8
Agricultural and Forest Meteorology 276–277 (2019) 107632
M. Ashraf, et al.
temperature in certain configurations. These effects are also desirable to create the habitat that is required to enhance biodiversity and ecosystem functions. We found that there were significant differences in microclimate and vegetation structure between alley-cropping and monoculture oil palm agriculture. Although the oil palm alley-cropping system can enhance vegetation complexity and mitigate extreme microclimates in oil palm plantations, careful selection of crops was essential. Cacao and black pepper were the best option for intercropping with oil palm as these crops have essential vegetation characteristics such as a wider canopy cover and presence of undergrowth vegetation. We suggest that alley-cropping system with properly selected crops can provide an alternative income with the secondary crops, increase biodiversity and benefit microclimate within oil palm agriculture; thus, it should be considered as a key strategy in sustainable oil palm production.
landscapes. Ecol. Lett. 14, 101–112. Fischer, J., Lindenmayer, D.B., 2007. Landscape modification and habitat fragmentation: a synthesis. Glob. Ecol. Biogeogr. 16 (3), 265–280. Ghazali, A., Asmah, S., Syafiq, M., Yahya, M.S., Aziz, N., Tan, L.P., et al., 2016. Effects of monoculture and polyculture farming in oil palm smallholdings on terrestrial arthropod diversity. J. Asia Pac. Entomol. 19, 415–421. Gold, M.A., Garrett, H.E., 2009. Agroforestry nomenclature, concepts, and practices. North American Agroforestry: An Integrated Science and Practice, 2nd edition. pp. 45–56 (northamericanag). Hardwick, S.R., Toumi, R., Pfeifer, M., Turner, E.C., Nilus, R., Ewers, R.M., 2015. The relationship between leaf area index and microclimate in tropical forest and oil palm plantation: forest disturbance drives changes in microclimate. Agric. For. Meteorol. 201, 187–195. Harvey, C.A., Villalobos, J.A.G., 2007. Agroforestry systems conserve species-rich but modified assemblages of tropical birds and bats. Biodivers. Conserv. 16, 2257–2292. Henson, I.E., Harun, M.H., 2005. The influence of climatic conditions on gas and energy exchanges above a young oil palm stand in north Kedah, Malaysia. J. Oil Palm Res. 17, 73–91. Ismail, S., Khasim, N., Zulkifli, R., 2009. Double-row Avenue System for Crop Integration with Oil Palm. MPOB Information Series No. 424. Bangi, Malaysia. . Jose, S., Gillespie, A.R., Pallardy, S.G., 2004. Interspecific interactions in temperate agroforestry. Agrofor. Syst. 61 (1-3), 237–255. Jose, S., Allen, S.C., Nair, P.R., 2008. Tree-crop interactions: lessons from temperate alleycropping systems. Ecol. Basis Agrofor. 15–36. Jose, S., 2012. Agroforestry for conserving and enhancing biodiversity. Agrofor. Syst. 85, 1–8. Krebs, C.J., 1989. Ecological Methodology (No. QH541. 15. S72. K74 1999.). Harper & Row, New York. Kubitza, C., Krishna, V.V., Alamsyah, Z., Qaim, M., 2018. The economics behind an ecological crisis: livelihood effects of oil palm expansion in Sumatra, Indonesia. Hum. Ecol. 46 (1), 107–116. Luskin, M.S., Potts, M.D., 2011. Microclimate and habitat heterogeneity through the oil palm lifecycle. Basic Appl. Ecol. 12 (6), 540–551. Morrison, M.L., Block, W.M., Strickland, M.D., Collier, B.A., Peterson, M.J., 2008. Wildlife Study Design. Springer Science & Business Media. Novais, S., Macedo-Reis, L.E., DaRocha, W.D., Neves, F.S., 2016. Effects of habitat management on different feeding guilds of herbivorous insects in cacao agroforestry systems. Rev. Biol. Trop. 64, 763–777. Nurdiansyah, F., Denmead, L.H., Clough, Y., Wiegand, K., Tscharntke, T., 2016. Biological control in Indonesian oil palm potentially enhanced by landscape context. Agr. Ecosyst. Environ. 232, 141–149. Ong, C.K., Corlett, J.E., Singh, R.P., Black, C.R., 1991. Above and below ground interactions in agroforestry systems. For. Ecol. Manage. 45 (1-4), 45–57. Quinkenstein, A., Woellecke, J., Böhm, C., Gruenewald, H., Freese, D., Schneider, B.U., Huettl, R.F., 2009. Ecological benefits of the alley cropping agroforestry system in sensitive regions of Europe. Environ. Sci. Policy 12, 1112–1121. Ratnadass, A., Fernandes, P., Avelino, J., Habib, R., 2012. Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review. Agron. Sustain. Dev. 32 (1), 273–303. Sabajo, C.R., Le Maire, G., June, T., Meijide, A., Roupsard, O., Knohl, A., 2017. Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia. Biogeosciences 14 (20), 4619. Sivaraman, K., Kandiannan, K., Peter, K.V., Thankamani, C.K., 1999. Agronomy of black pepper (Piper nigrum L.) – a review. J. Spices Aromat. Crop. 8 (1), 1–18. Soderstrom, T.R., Calderon, C.E., 1979. A commentary on the bamboos (Poaceae: bambusoideae). Biotropica 161–172. Somarriba, E., Beer, J., 2011. Productivity of Theobroma cacao agroforestry systems with timber or legume service shade trees. Agrofor. Syst. 81 (2), 109–121. Staver, C., Guharay, F., Monterroso, D., Muschler, R.G., 2001. Designing pest-suppressive multistrata perennial crop systems: shade-grown coffee in Central America. Agrofor. Syst. 53 (2), 151–170. Tao, H.H., Snaddon, J.L., Slade, E.M., Caliman, J.P., Widodo, R.H., Willis, K.J., 2017. Long-term crop residue application maintains oil palm yield and temporal stability of production. Agron. Sustain. Dev. 37 (4), 33. Torralba, M., Fagerholm, N., Burgess, P.J., Moreno, G., Plieninger, T., 2016. Do European agroforestry systems enhance biodiversity and ecosystem services? A meta-analysis. Agric. Ecosyst. Environ. 230, 150–161. Udawatta, R.P., Motavalli, P.P., Jose, S., Nelson, K.A., 2014. Temporal and spatial differences in crop yields of a mature silver maple alley cropping system. Agron. J. 106 (2), 407–415. Wolz, K.J., Lovell, S.T., Branham, B.E., Eddy, W.C., Keeley, K., Revord, R.S., et al., 2018. Frontiers in alley cropping: transformative solutions for temperate agriculture. Glob. Chang. Biol. 24 (3), 883–894. Yaap, B., Struebig, M.J., Paoli, G., Koh, L.P., 2010. Mitigating the biodiversity impacts of oil palm development. Cab Rev. Perspect. Agric. Vet. Sci. Nutr. Nat. Resour. 5 (19), 1–11.
Acknowledgments This research was funded by Putra Graduate Initiative Grant (IPS) from Universiti Putra Malaysia (Grant No: GP-IPS/2016/9513900). We would like to thank Sapari Mat and Nur Hidayatul Akma for their comments and suggestions on an earlier version of the manuscript. Mohamad Ashraf was funded by the MPOB Graduate Students Assistantship Scheme (GSAS). We also thank all the MPOB Kratong staff, particularly Fathil Kamil and Jamaludin Bokhari for providing logistical support during data collection in the field. References Agamuthu, P., Broughton, W.J., 1985. Nutrient cycling within the developing oil palmlegume ecosystem. Agric. Ecosyst. Environ. 13 (2), 111–123. Ashraf, M., Zulkifli, R., Sanusi, R., Tohiran, K.A., Terhem, R., Moslim, R., et al., 2018. Alley-cropping system can boost arthropod biodiversity and ecosystem functions in oil palm plantations. Agric. Ecosyst. Environ. 260, 19–26. Asmah, S., Ghazali, A., Syafiq, M., Yahya, M.S., Peng, T.L., Norhisham, A.R., et al., 2017. Effects of polyculture and monoculture farming in oil palm smallholdings on tropical fruit-feeding butterfly diversity. Agric. For. Entomol. 19, 70–80. Azhar, B., Lindenmayer, D.B., Wood, J., Fischer, J., Manning, A., Mcelhinny, C., Zakaria, M., 2013. The influence of agricultural system, stand structural complexity and landscape context on foraging birds in oil palm landscapes. Ibis 155, 297–312. Azhar, B., Saadun, N., Prideaux, M., Lindenmayer, D.B., 2017. The global palm oil sector must change to save biodiversity and improve food security in the tropics. J. Environ. Manage. 203, 457–466. Bertomeu, M., 2006. Financial evaluation of smallholder timber-based agroforestry systems in Claveria, Northern Mindanao, the Philippines. Small-Scale For. Econ. Manag. Policy 5 (1), 57–81. Bertomeu, M., 2012. Growth and yield of maize and timber trees in smallholder agroforestry systems in Claveria, northern Mindanao, Philippines. Agrofor. Syst. 84 (1), 73–87. Butler, R., 2011. In Brazil, palm oil plantations could help preserve Amazon. Yale Environment. pp. 360. Chirko, C.P., Gold, M.A., Nguyen, P.V., Jiang, J.P., 1996. Influence of direction and distance from trees on wheat yield and photosynthetic photon flux density (Qp) in a Paulownia and wheat intercropping system. For. Ecol. Manage. 83 (3), 171–180. Chung, A.Y.C., Eggleton, P., Speight, M.R., Hammond, P.M., Chey, V.K., 2000. The diversity of beetle assemblages in different habitat types in Sabah, Malaysia. Bull. Entomol. Res. 90 (6), 475–496. Comte, I., Colin, F., Whalen, J.K., Grünberger, O., Caliman, J.P., 2012. Agricultural practices in oil palm plantations and their impact on hydrological changes, nutrient fluxes and water quality in Indonesia: a review. Advances in Agronomy 116. Academic Press, pp. 71–124. Corley, R.H.V., Tinker, P.B., 2003. The Oil Palm Fourth Edition. World Agriculture Series. Blackwell. Dislich, C., Keyel, A.C., Salecker, J., Kisel, Y., Meyer, K.M., Auliya, M., et al., 2017. A review of the ecosystem functions in oil palm plantations, using forests as a reference system. Biol. Rev. 92 (3), 1539–1569. Fahrig, L., Baudry, J., Brotons, L., Burel, F.G., Crist, T.O., Fuller, R.J., et al., 2011. Functional landscape heterogeneity and animal biodiversity in agricultural
9