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Agricultural practices in oil palm plantations and their impact on hydrological changes, nutrient fluxes and water quality in Indonesia: a review
Abstract
Rapid expansion of oil palm (Elaeis guineensis Jacq.) cultivation in Southeast Asia raises environmental concerns about deforestation and greenhouse gas emissions. However, less attention was paid to the possible perturbation of hydrological functions and water quality degradation. This work aimed to review :
i) the agricultural practices commonly used in oil palm plantations, which potentially impact hydrological processes and water quality, and ii) the hydrological changes and associated nutrient fluxes from plantations. Although many experimental trials provide clear recommendations for water and fertilizer management, we found that few studies investigated the agricultural practices actually followed by planters. Our review of hydrological studies in oil palm plantations showed that the main hydrological changes occurred during the first years after land clearing and seemed to dissipate with plant growth, as low nutrient losses were generally reported from plantations. However, most of those studies were carried out at the plot scale and often focus on one hydrological process at a single plantation age. So, there is insufficient information to evaluate the spatio-temporal fluctuations in nutrient losses throughout the entire lifespan of a plantation. Furthermore, few studies provided an integrated view at the watershed-scale of the agricultural practices and hydrological processes that contribute to nutrient losses from oil palm plantations and the consequences for surface and ground water quality. Future research efforts need to understand and assess the potential of oil palm plantations to change hydrological functions and related nutrient fluxes, considering agricultural practices and assessing water quality at the watershed-scale.
Introduction
Oil palm (Elaeis guineensis) is one of the most rapidly expanding crops in the tropics. Since the early 1980s, the global land area under oil palm production has more than tripled, reaching almost 15 million hectares in 2009 and accounting for almost 10 % of the world’s permanent crop land (FAOSTAT, 2011 ; Sheil et al., 2009) Most of this increase has taken place in Southeast Asia. Together, Malaysia and Indonesia account for almost 85 % of the 46.5 million tonnes of crude oil palm produced in the world, Indonesia being the top producer since 2007 (Oil World, 2011; USDA, 2007). The area covered by smallholder plantations in Indonesia increased nearly 1000-fold between 1979 and 2008, reaching almost 3 million ha, i.e. 39 % of current total Indonesian oil palm plantations, the remaining 4.5 million ha being large private (53 %) and government owned (8 %) plantations (IMA, 2010).
Although oil palm cultivation is a strong driver of economic development in Indonesia, providing jobs and incomes to millions of people (USDA, 2007), it is strongly denigrated for its environmental impacts. Many media and NGOs accuse oil palm plantation development in Southeast Asia of triggering deforestation, loss of biodiversity, peatland degradation and high greenhouse gas (GHG) emissions (Greenpeace, 2011; WWF, 2011). In the scientific community, there is controversy about the positive and negative aspects of the expanding oil palm cultivation and potential environmental risks, which has been discussed at length in the scientific literature (Basiron, 2007; Lamade and Bouillet, 2005; Nantha and Tisdell, 2009; Sheil et al., 2009). The development of oil palm plantations, which frequently cover tens of km2 in Southeast Asia, involves land clearing, roads and drainage network construction, and sometimes earthworks such as terracing on undulating areas. The use of agro-chemicals, such as fertilizers and pesticides might represent a potential risk for the sustainability of aquatic ecosystem and hydrological functions, when agricultural practices are not optimized. In particular, oil palm growers usually apply large amounts of commercial fertilizer, and thus are among the largest consumers of mineral fertilizers in Southeast Asia (Härdter and Fairhurst, 2003). However, hydrologica l processes within oil palm plantations are still not fully understood and few studies have examined the impacts of agricultural practices on terrestrial hydrological functions and water quality in nearby aquatic ecosystems (Ah Tung et al., 2009), although “ aspects that impact on water quality are by far the largest component of an environmental risk register accounting for nearly 50 % of all entries in oil palm plantations” (Lord and Clay, 2006).
This review aims to document the current state-of-knowledge of agricultural practices in oil palm plantations that potentially impact hydrological functions and water quality in surface waters, with a focus on nutrient loading of surface waterways, and to highlight research gaps in the understanding of these processes. This work focuses on the situation in Indonesia, with examples from other oil palm producing countries in the humid tropics as appropriate. First, the expansion of oil palm cultivation in Indonesia, relevant environmental issues and polemics will be presented. Next, typical agricultural practices in industrial and smallholder oil palm plantations will be discussed, focusing on nutrient, soil and water management. Finally, the last section gives the state-of-the-art knowledge of hydrological changes and associated nutrient fluxes from oil palm plantations compared to tropical rainforests, which were the dominant natural ecosystem prior to oil palm plantation establishment. Relevant processes in the hydrological cycle, their magnitude and relevance in oil palm plantations will be explained in this section, but we do not provide an in-depth discussion of hydrological processes in rainforests, as a number of reviews were already published on this topic (Bruijnzeel, 1991; Bruijnzeel, 2004; Elsenbeer, 2001).
Expansion of oil palm cultivation in Indonesia and environmental stakes
Expansion of oil palm cultivation
Palm oil utilization
Palm oil is derived from the plant’s fruit, which produces two types of oils: crude palm oil (CPO), which comes from the mesocarp of the fruit, and palm kernel oil, which comes from the seed in the fruit. Most CPO is used for food products, while most palm-kernel oil is used in non-edible products such as detergents, cosmetics, plastics, as well as a broad range of other industrial and agricultural chemicals (Wahid et al., 2005). The oil palm is the highest productive oil crops in terms of oil yield per hectare and resource use efficiency due to its high efficiency at transforming solar energy into vegetable oil. The average yield of palm oil is approximately 4.2 t ha-1 yr-1, with yields exceeding 6.0 t ha-1 yr-1 in the best managed plantations, greatly exceeding vegetable oils such as rapeseed and soybean that produce only 1.2 and 0.4 t ha-1 yr-1, respectively (Fairhurst and Mutert, 1999). In addition, little fossil fuel energy is used, as most of the energy required by the oil palms mill for processing of the fruits is provided by burning the palm by-products (shells and fibers). Consequently, the energy balance, expressed as the ratio of outputs to inputs, is higher for oil palm (9.6) than other commercially grown oil crops (e.g. rapeseed : 3.0; soybean : 2.5), making oil palm the most attractive candidate for biofuel production (Fairhurst and Mutert, 1999).
1.3.1.2. Extent of oil palm cultivation in Indonesia: 1911 to present
The first commercial plantation was developed in Sumatra in 1911 and the area planted in Indonesia increased from about 31600 ha by 1925 to 7.3 million ha by 2008 (Corley and Tinker 2003; IMA, 2010). Since 2007, Indonesia has been the world’s largest and most rapidly growing producer. Its production rose from 168 000 tonnes in 1967 to 22 million tonnes by 2010 (IMA, 2010). Crude palm oil and kernel oil prices have been rising, encouraging investors to develop plantations on the large areas of suitable land in the islands of Sumatra, Indonesia (Figure 1.1) then, new developments occurred, mainly on the island of Borneo (USDA, 2007).
Expected future expansion of oil palm cultivation
Continued expansion of oil palm plantations is forecast due to growing global demand for palm oil as a source of fats and oil for human consumption, non-edible products and biofuel to keep pace with human population growth, expected to reach 8.9 billion in 2050 (Bangun, 2006; Tan et al., 2009; UN, 2004). Present plans are to increase production up to 40 million tonnes of CPO by 2020 (IMA, 2010; Rist 2010). According to USDA (2007), the availability of land in Indonesia, coupled with other factors – high seed sales, record energy prices, and high vegetable oil prices – ensure that Indonesia w ill continue to lead the world in palm oil production for years to come. However, few developments generate as much controversy as the rapid expansion of oil palm in developing countries such as Indonesia (Koh and Wilcove 2008; Nantha and Tisdell, 2009). Negative consequences reported by environmental groups include deforestation, loss of biodiversity, peatland degradation, GHG emissions and water pollution.
Environmental stakes
Deforestation and loss of biodiversity
The most contentious environmental issue facing the oil palm industry is deforestation as huge tracts of tropical rainforest are converted to plantations (Germer and Sauerborn, 2008; Wakker, 1999). Indonesian tropical forested area ranks third behind Brazil and the Democratic Republic of Congo, and harbors numerous endemic or rare species (Koh and Wilcove, 2008; WRI, 2002). Many sources are claiming that virgin tropical forests are being cleared for oil palm plantations, leading to natural habitat loss for many endangered species and biodiversity reduction. For instance, it was reported that Sumatran orangutans (Pongo abelii) and Bornean orangutans (Pongo pygmaeus) face extinction due to plantation expansion (Nantha and Tisdell, 2009; Nelleman et al., 2007; Tan et al., 2009). Herds of elephants, tigers and rhinos are reported to be critically threatened due to this expansion (Danielsen et al., 2008; WRI, 2002). Studies in oil palm frontier areas on the island of Sumatra concluded that oil palm plantations result in a significant reduction in biodiversity if plantations replace natural forests, secondary forests, agroforests, or even degraded forests and scrubby unplanted areas (Gillison and Liswanti, 1999; Sheil et al., 2009). However, others mentioned that the expansion of oil palm plantations is only one of the factors contributing to herd displacement and local extinction, as other anthropogenic activities like illegal logging, forest fires and illegal hunting ar e also problematic for large mammals (Nelleman et al., 2007; Tan et al., 2009). According to Koh and Wilcove (2008), at least 56 % of the oil palm expansion in Indonesia during the period 1990-2005 occurred at the expense of primary, secondary, or plantation forests, and 44 % was on cropland area. Deforestation in Southeast Asia cannot be attributed solely to oil palm production. According to the World Rainforest Movement (WRM, 2002), the immediate causes of rainforest destruction in Southeast Asian countries are logging by commercial companies, shifting agriculture, monoculture plantations (e.g. rubber in Thailand), cattle ranching, fuelwood harvesting, hydro-electric dams, mining and oil exploitation, and colonization schemes.
Peatland degradation
Peatland formation
Southeast Asia has an estimated 27.1 million ha of peatlands, most of which are located in Indonesia (22.5 million ha), representing 12 % of its land area (Hooijer et al., 2006). Peatlands develops in depressions or wet coastal areas when the rate of biomass deposition from adapted vegetation (i.e., mangroves, swamp forest) is greater than the rate of decomposition. The accumulation of organic matter that degrades very slowly, over a period of hundreds of years, makes peat soil. This is due to the presence of a permanently high water table that prevents aerobic microorganisms from decomposing the plants debris (Mutert et al., 1999; Wieder et al., 2006). A soil is considered to be peat when it includes an organic layer thicker than 40-50 cm (USDA, 2006). In Southeast Asia, all low-lying peatlands are naturally forested with an average canopy height of 40 m and emergent trees of up to 50 m (WI, 2010). In the Eastern coast of the island of Sumatra, Indonesia, peat deposits are usually at least 50 cm thick but can form a deep profile that extends up to 20 m (CAAL, 2011).
Peatland ecological functions
Peatlands regulate water flow by capturing rainwater during the wet season and slowly releasing it, over a period of months, during the dry season. Consequently, peatlands help to prevent floods and droughts (Clark et al., 2002; Tan et al., 2009). In addition, peatlands are an important carbon (C) sink in the global C cycle because they cover nearly 3 % (some 4 million km2) of the earth’s land area and store about 528 000 Mt C, which is equivalent to one-third of global soil C and 70 times annual global emissions from fossil fuel burning (Hooijer et al., 2006; Tan et al., 2009). Peatland attributes also include biological diversity, since tropical peatlands are important genetic reservoirs of certain animals and plants. Tropical peatlands have long provided goods and services for local communities to fulfill their daily, basic requirements, for example, hunting grounds and fishing areas, food, medicines, and construction materials (Rieley, 2007).
Peatland conversion to oil palm
Peat swamp forests have remained relatively undisturbed until recently, as they were unattractive for agriculture. But the increasing international demand for biofuel and the current lack of available land on mineral soils has accelerated the conversion of peatlands to oil palm plantations especially in Indonesia (Kalimantan, Sumatra and West Papua) where nearly 25 % of all oil palm plantations are located on peatlands (Sheil et al., 2009; Tan et al., 2009). However, oil palms cannot survive in undrained waterlogged peatlands. Drainage for oil palm growth in peatlands is installed between 40 and 80 cm, but the water table could recede below 80 cm during an extended drought (WI, 2010). Many authors reported that there is a direct relationship between the depth of the water table and the rate of peat subsidence and thus the sustainability of the peat (Strack and Waddington, 2007; Wösten et al., 1997; Wösten e t al., 2008). Drainage results in rapid peat subsidence and compaction, leading to various changes in its physical properties including greater bulk density and less total porosity, oxygen diffusion, air capacity, available water volume and water infiltration rate (Rieley et al., 2007). Drainage ultimately destroys the sponge effect of peat swamps and their reservoir function (Andriesse, 1988). In addition, the exploitation or removal of the overlying forest resource further reduces the ability of the ecosystem to hold rainfall and water is flushed more quickly into the rivers, increasing flooding in the rainy season and drought in the dry season (Rieley, 2007; Rieley and Page, 1997). Moreover, the drainage of C-rich peatlands leads to aeration of the peat material and hence to the oxidation (or aerobic decomposition) of peat material resulting in massive CO2 gas emissions to the atmosphere (Schrevel, 2008; Hooijer et al., 2006). Although the exploitation of peat swamp forests also provides employment, local income, new jobs and business opportunities, contributing to poverty alleviation of the country, it is at the expense of the ecosystem and the environment (Rieley et al., 2007).
Table of contents :
GENERAL INTRODUCTION
CHAPTER 1. AGRICULTURAL PRACTICES IN OIL PALM PLANTATIONS AND THEIR IMPACT ON HYDROLOGICAL CHANGES, NUTRIENT FLUXES AND WATER QUALITY IN INDONESIA: A REVIEW
1.1. Abstract
1.2. Introduction
1.3. Expansion of oil palm cultivation in Indonesia and environmental stakes
1.3.1. Expansion of oil palm cultivation
1.3.1.1. Palm oil utilization
1.3.1.2. Extent of oil palm cultivation in Indonesia: 1911 to present
1.3.1.3. Expected future expansion of oil palm cultivation
1.3.2. Environmental staked
1.3.2.1. Deforestation and loss of biodiversity
1.3.2.2. Peatland degradation
1.3.2.3. Greenhouse gas emissions and carbon storage
1.3.2.4. Water pollution
1.3.2.5. Agricultural policies
1.3.2.6. Implications for future research
1.4. Oil palm cultivation
1.4.1. Climate and soil conditions
1.4.2. Production systems: industrial versus smallholder plantations
1.4.3. Land clearing and site preparation
1.4.4. Water and soil management
1.4.5. Nutrient demand assessment
1.4.6. Fertilizer management
1.4.6.1. Chemical fertilizer
1.4.6.2. Organic fertilizer
1.4.7. Synthesis
1.5. Hydrological processes and associated nutrient transfers in oil palm plantations
1.5.1. Precipitation in Indonesia
1.5.2. Interception
1.5.3. Evapotranspiration
1.5.4. Soil infiltration, leaching and ground water quality
1.5.4.1. Soil infiltration
1.5.4.2. Leaching and ground water quality
1.5.5. Surface runoff and erosion
1.5.6. Stream flow and stream water quality
1.5.6.1. Stream flow
1.5.6.2. Stream water quality
1.5.7. Synthesis
1.6. Conclusion
CONNECTING PARAGRAPH TO CHAPTER 2
CHAPTER 2. LANDSCAPE-SCALE ASSESSMENT SOIL RESPONSE TO LONG-TERM ORGANIC AND MINERAL FERTILIZER APPLICATIONS IN AN INDUSTRIAL OIL PALM PLANTATION IN INDONESIA
2.1. Abstract
2.2. Introduction
2.3. Materials and methods
2.3.1. Site description
2.3.1.1. Study area
2.3.1.2. Preliminary soil classification
2.3.1.3. Fertilizer management
2.3.2. Landscape-scale approach: description and assumptions
2.3.2.1. Attributing a soil class to each block
2.3.2.2. Calculation of the fertilizer application sequence value for each block
2.3.2.3. Construction of nested subsets within each soil
2.3.2.4. Soil fertility survey and soil analysis
2.3.2.5. Statistical analysis
2.4. Results
2.4.1. Overall soil fertility status
2.4.2. Effect of organic versus mineral fertilizer on soil fertility in uniform fertilizer application sequences
2.4.3 Effect of organic versus mineral fertilizer on soil fertility in mixed fertilizer Sequences
2.5 Discussion
2.5.1. Effect of organic fertilizer application on soil fertility parameters in Sandy-loam uplands and loamy lowlands
2.5.1.1. Soil pH
2.5.1.2. Organic C and total N
2.5.1.3. Cation exchange capacity and base saturation
2.6. Conclusion
CONNECTING PARAGRAPH TO CHAPTER 3
CHAPTER 3. MULTI-SITE ASSESSMENT OF WATER QUALITY IN OIL PALM AGROECOSYSTEMS AND INFLUENCE OF SOIL TYPES AND FERTILIZER MANAGEMENT ON NUTRIENT FLUXES TO STREAMS
3.1. Abstract
3.2. Introduction
3.3. Material and Methods
3.3.1. Description of the study area and watershed delineation
3.3.2. Fertilizer management and nutrient inputs
3.3.3. Groundwater and watershed monitoring
3.3.4. Water sample analysis
3.3.5. Estimation of water flow, nutrient concentrations and fluxes
3.3.5.1. Annual water yields from water budget
3.3.5.2. Water flow estimation
3.3.5.3. Annual nutrient fluxes in streams
3.3.6. Data analysis
3.4. Results
3.4.1 Hydrological behavior
3.4.2. Stream water quality and nutrient fluxes in the landscape
3.4.2.1. Water quality
3.4.2.2. Nutrient fluxes to streams
3.4.3. Influence of the soil and fertilizer management on water chemistry and nutrient transfers
3.4.3.1 Nutrient inputs
3.4.3.2. Influence at the local-scale: groundwater hydrochemistry
3.4.3.3. Influence at the watershed-scale: nutrient inputs and nutrient fluxes
3.5. Discussion
3.5.1. Streams mainly fed by shallow groundwater
3.5.2. Low concentrations and low fluxes exported in the landscape
3.5.2.1. Overall stream water quality in the landscape
3.5.2.2. Overall nutrient fluxes to streams in the landscape
3.5.3. Soil characteristics and fertilizer management influenced groundwater chemistry and nutrient fluxes
3.5.4. Agronomic and environmental implications
3.6. Conclusion
GENERAL CONCLUSIONS
FUTURE RESEARCH DIRECTIONS
REFERENCES
