OCL 2025, 32, 31DOI: 10.1051/ocl/2025022© D.E. Munévar-Martínez et al., Published by EDP Sciences, 2025

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Review

Sustainable intensification of oil palm production through integration with other crops: a review☆

Intensification durable de la production d'huile de palme par intégration d'autres cultures : une revue

Daniel Eduardo Munévar-Martínez orcid, Elizabeth Ruiz-Álvarez orcid, María Celina Estupiñán-Villamil and Mauricio Mosquera-Montoya* orcid

Research Results Validation Unit, Colombian Oil Palm Research Center – Cenipalma, Colombia

* Corresponding author: mmosquera@cenipalma.org

Received: 23 December 2024 Accepted: 20 June 2025 Published online: 1 October 2025

Abstract

Unsustainable monoculture systems practices, driven by global demand for agricultural commodities like palm oil, contribute to deforestation, biodiversity loss, and soil degradation, compromising livelihoods and environmental health. With increasing land scarcity, sustainable practices maximizing productivity and minimizing ecological impact, such as intercropping, are crucial. This review of over 116 publications examines global oil palm intercropping systems, analysing their technical, economic, environmental, and social implications. While companion crop productivity is relatively well-studied, long-term effects on adult palms require further investigation. Crop design (species selection, type of oil palm used and spatial arrangement) and crop management are key to mitigating interspecific competition and optimizing productivity, given diverse intercropping patterns. Economic performance varies, with benefit-cost ratios from 0.26 (palm with onion) to 2.86 (palm with corn/pepper). Intercropping offers socio-environmental benefits: enhanced food security through integrating food crops, diversified income, increased biodiversity (birds, arthropods), and efficient resource use. Land equivalent ratios (LERs) range from 0.98 to 4.10, indicating more efficient land use than monocultures. However, research gaps remain regarding long-term intercropping impacts on palm cultivation, particularly fertilization and pest/disease management, water use, pollinators, yields, and environmental impacts.

Résumé

Les pratiques de monoculture non durables, motivées par la demande mondiale de produits agricoles comme l'huile de palme, contribuent à la déforestation, à la perte de biodiversité et à la dégradation des sols, compromettant les moyens de subsistance et l’environnement. Avec raréfaction des terres cultivables, les pratiques durables maximisant la productivité et minimisant l'impact écologique, comme les associations de cultures, sont cruciales. Cette revue de plus de 116 publications examine les systèmes d’associations avec le palmier à huile à l'échelle mondiale, analysant leurs implications techniques, économiques, environnementales et sociales. Bien que la productivité des cultures associées soit relativement bien étudiée, les effets à long terme sur les palmiers adultes nécessitent des investigations supplémentaires. La mise en place de la culture (choix des espèces, type de palmier à huile utilisé et arrangement spatial) et les techniques culturales sont essentielles pour atténuer la compétition interspécifique et optimiser la productivité, compte tenu des divers schémas d’association. La performance économique varie, avec des ratios coût-bénéfice allant de 0,26 (palmier avec oignon) à 2,86 (palmier avec maïs/poivre). L’association offre des avantages socio-environnementaux : une sécurité alimentaire améliorée grâce à l'intégration de cultures vivrières, des revenus diversifiés, une biodiversité accrue (oiseaux, arthropodes) et une utilisation efficace des ressources. Les Land equivalent ratios (LERs) varient de 0,98 à 4,10, traduisant une utilisation plus efficace des terres que les monocultures. Cependant, des lacunes subsistent concernant les impacts à long terme des associations sur la culture du palmier, en particulier la fertilisation, la gestion des ravageurs/maladies, l'utilisation de l'eau, les pollinisateurs, les rendements et les impacts environnementaux.

Key words: sustainability / production systems / equivalent land index / profitability / ecosystem services

Mots clés : durabilité / systèmes de production / land equivalent ratio / rentabilité / services écosystémiques

☆

Contribution to the Topical Issue: “Innovative Cropping Systems / Systèmes innovants de culture oléoprotéagineux”.

Highlights

Unsustainable oil palm monoculture involves several environmental challenges. Intercropping offers a sustainable alternative, improving food security and biodiversity. Economic benefits vary, with some intercropping systems showing high yields. More research is needed on the long-term impacts of intercropping on mature palm plants.

1 Introduction

Technological advances in the 21st century have significantly improved the ability to meet the basic needs of much of the global population. However, persistent economic, political, health, and social challenges in the world's poorest countries have given rise to two critical and urgent issues: hunger and poverty. Despite progress in reducing poverty indicators over the past decade, it is currently estimated that 828 million people are at risk of malnutrition and 648 million live in poverty (Harari, 2018; Organización Mundial del Comercio, 2010; World Bank, 2022).

The problem of how to adequately feed and supply a growing population has led to the intensification of agricultural production systems, in a process that has been characterized by the increase in production yields through the use of technology, the globalization of agricultural markets, the intensive use of agrochemicals, the exploitation of large areas in monoculture, the concentration of land tenure and asymmetries in the governance of agricultural value chains between small, medium and large-scale farmers (Baccar et al., 2019; Lamine & Marsden, 2023; Reisman and Fairbairn, 2020). The inefficient use of land in agri-food systems, both by underutilization and overutilization, has led to complex socio-environmental conflicts that have impacted on the quality of life of communities and the ecosystems that host them (Petrescu-Mag et al., 2018). Conflicts over land use lead to negative environmental impacts such as erosion of the topsoil, loss of biodiversity, reduction in the supply of water resources, and forced displacement, among others, which affect the sustainability of rural areas (Kangas et al., 2022; Pacheco et al., 2014; Petrescu-Mag et al., 2018; Rodrigues et al., 2019).

Oil crops play a significant role in global agricultural markets, accounting for approximately 27.2% of total crop production. Among these, oil palm is the most productive, with palm oil serving as a key commodity for the food, energy, and industrial sectors (Adade, 2022; Mesa, 2016). In 2023, global oilseed production exceeded 667 million tonnes, with soybeans (59.09%), rapeseed (13.37%), and sunflower (9.39%) being the most prominent (USDA FAS, 2024). However, in terms of oil production, oil palm has reported a productivity of 2.88 t oil/ha, while soybean, rapeseed and sunflower can be 84%, 72% and 73% less productive, respectively.

Oil palm is cultivated commercially in tropical regions, with Indonesia (59.3%), Malaysia (23.97%), Thailand (4.35%), Colombia (2.27%), Nigeria (1.77%), and Guatemala (1.16%) leading global production in 2023 (USDA, 2022). In these countries, the palm agroindustry has contributed to economic development, improved quality of life and increased income for palm growers (Escobar et al., 2010; Meijaard and Sheil, 2019; Mosquera and Beltrán, 2017; Santika et al., 2019). The Asian and American countries also leaded the global crude oil palm exports with Indonesia (35.7%) and Malaysia (35.2%) heading the list in 2023 (World Integrated Trade Solution, 2024a). The main destinations of these exportations were India (48.04%), European Union (15.53%) and the Netherlands (7.93%) (World Integrated Trade Solution, 2024b)

Oil palm monoculture is the most common production system of this crop globally. It seeks to maximize crop yields through the homogeneity of the agroecosystem, the intensive use of agrochemicals (chemical fertilizers and pesticides) and increasing mechanization (Emanuelli et al., 2011; Liu et al., 2018). However, there are challenges related to phytosanitary problems and the decrease in biological diversity inside and outside the plantation (Dhandapani et al., 2020; Gebru, 2015; Salaheen and Biswas, 2019).

The global oil palm industry faces challenges to ensure its sustainability, an increasingly important aspect for the global consumer. The expansion of this crop has led to environmental impacts such as loss of biodiversity, environmental pollution, waste discharge into water sources, effects on soil regeneration and greenhouse gas emissions, among others. (Dhandapani et al., 2019; Qaim et al., 2020; Ramírez-Contreras et al., 2020; Shahputra and Zen, 2018). At least 50% of the planted oil palm area has developed through the clearing of forests, especially in the Southeast Asia (in Malaysia, 60% of oil palm land replaced the native forests), while the rest of the oil palm plantation area, however, was a replacement for former crops or poorly preserved natural ecosystems, especially in America (21% of oil palm expansion occurred through deforestation, in Ecuador, Peru, Guatemala and Brazil) (Lesage et al., 2021; Qaim et al., 2020). Some authors relate the expansion of cultivation with negative social impacts on issues such as public health, food insecurity, conflicts between communities, labor formalization and social inequity (Hamann, 2018; Morand and Lajauni, 2020; Ordway et al., 2019; Sibhatu, 2023).

The requirement for environmental certifications, the institutional strengthening of the management of sustainability, the design of environmental policies for the planning and regulation of agribusiness and the improvement of technical processes are some of the strategies that have been implemented to improve the sustainability of the sector and contribute to the achievement of the Sustainable Development Goals (Purwanto et al., 2020).

Intercropping is understood as the planting and management of two or more crops in the same space and under a defined temporal arrangement. It is recognized as an agronomic practice that can promote the sustainability of agricultural activity through improved ecosystem services such as the provision of resources (raw materials) and the regulation of natural processes (Duchene et al., 2017; Glaze-Corcoran et al., 2020). Carbon sequestration, efficient soil use, assurance of food security and stabilization of productivity are some of the general benefits documented in relation to the implementation of intercropped production systems (Glaze-Corcoran et al., 2020; Yang et al., 2021).

In oil palm, crop intercropping is expected to optimize land and resource use, especially during the early years of the plantation development. This technique has been adopted mainly by independent smallholders as a strategy to improve the profitability of their production systems. In addition, some farmers have considered intercropping as an option to strengthen the food security of their households. In Africa, the place of origin of the oil palm, smallholder production systems have traditionally included the integrated oil palm-based intercropping; although this practice is less popular in more technical production systems (Nkongho et al., 2015). In countries in which the oil palm has been recently introduced, agroforestry and intercropping practices have been adapted over monoculture systems, which are the most widely adopted. In Indonesia, for example, agroforestry systems in rubber have been more popular than in oil palm (Drescher et al., 2016).

The adoption of intercropping in oil palm-based systems can be considered as an opportunity to improve the sustainability of the palm oil sector. This has stimulated the interest of academia in answering questions about the feasibility and success of these production systems. Therefore, the purpose of this article is to describe the state of the art on the particularities of adopting a diversified production system. In the first section, we describe the various systems reported in the literature. In the second section, we describe the implications from the point of view of the productivity of the systems. Finally, we analyse the key factors for the improvement of environmental sustainability.

2 Methodology

This study conducted a comprehensive review of key literature, including both peer-reviewed scientific articles (white literature) and grey literature such as institutional reports, master's and doctoral theses, and official websites. The review focused on the productivity, economic, environmental, and social implications of adopting intercropping systems in oil palm cultivation.

The literature search was performed using keywords in Spanish, English, and French across academic databases and search engines, including Google Scholar and Scopus (Tab. 1). Boolean operators were employed to refine the search results. Articles that did not mention “oil palm" in their abstracts or were not aligned with the objectives of this study were excluded.

Although the review includes publications prior to 2018, these were selected based on the relevance and significance of their content. It is important to note that no quantitative bibliometric analysis was conducted. In total, 122 documents were selected for inclusion in this review.

Table 1

Terms of search.

3 Production systems for oil palm-based intercropping are heterogeneous

The concept of intercropping is closely related to several other practices such as agroforestry, mixed crops and polyculture. Masure et al. (2023) have identified four main types of intercropping or agroforest system in oil palm that are classified by the duration along the lifecycle of the oil palm and by the purpose of the system. Intercropping can be temporary at the beginning of the cycle of the oil palm, at the end, or permanent. Also, intercropping can have can be based on the planting designs following a regular pattern, or not (like the traditional oil palm agroforestry in Africa). Intercropping systems can also be associated with livestock production, adding more complexity to the agroecosystem (Ruiz-Álvarez et al., 2024).

A wide variety of species have been intercropped with oil palm. The choice of companion crops depends on several factors, including climate, soil conditions, the age of the oil palm, local food culture, market value, the farmer’s economic capacity, and the specific objectives of the intercropping strategy. (Khasanah et al., 2020; Salleh and Harun, 2015). The complexity of this kind of production system depends not only on the spatial arrangement (vertical and horizontal) but also for the time frame of the planting (Bybee-Finley and Ryan, 2018; Maitra et al., 2021; Yang et al., 2021). According to Costa et al. (2024), the effectiveness of these production systems depends on their level with respect to plant diversity (influences the resilience of the system), functionality (interactions strengthen the resilience and productivity of the system) and economic diversity (increases the economic benefits of the system and decreases the risks of loss).

Although intercropping is primarily practiced by smallholders, numerous initiatives have also emerged from researchers (Costa et al., 2024; de Castro and Futemma, 2021; Dhandapani et al., 2020; Feintrenie et al., 2008; Lee and Kasbi, 1978; Oomen, 2023; Yahya et al., 2017).

There are two main groups of crops usable for intercropping: food crops and cash crops, which can be rather annual or permanent. Food crops, such as maize and cassava, are planted due to their importance in the food security of the communities and the ease of marketing their surplus, and they are more frequent during the immature stage of the palm (ETA and TBI, 2021; FAO, 2001; Koussihouèdé et al., 2020; Okere et al., 2015; Orewa, 2008). Food crops are not usually highly mechanised, as their purpose is often to provide for subsistence and to increase household income, but in maize intercropping mechanisation can be possible (FENALCE, 2008; Nchanji et al., 2016).

Cash crops are species with high commercial value such as cocoa, timber, pineapple or pepper, that also are generally permanent or semipermanent crops. As they are grown in the long term, along with the oil palm often modification in the special distribution of the plant is made (ETA and TBI, 2021). Forestal species are also included into agroforestry-based production systems, and they are used as green barriers or for timber.

Literature shows that several crops, although not produced in a commercial scale, could be promising, such as watermelon, ornamental plants or medicinal herbs.

The association of crops with oil palm has been carried out in all the continents where it is planted and at different stages of its development, mainly in Asia and Africa. The experiences reported in the literature in the Americas are scarce, except for Brazil (Tab. 2 and Tab. 3).

Table 2

Main annual crops planted in intercropping with oil palm.

Table 3

Main semi-annual and permanent crops planted in intercropping with oil palm.

4 Intercropping systems can contribute to the economic sustainability of the palm sector

One of the economic objectives of palm production systems is to ensure competitiveness, which can be measured, among other indicators, through productivity and production costs. In intercropping systems, productivity is a central concern and often a limiting factor in adoption.

4.1 How intercropping affects productivity

The integration of crops with oil palm generates impacts on the yields of the system; the literature records more frequently only the yields associated with integrated cultivation (Tab. 4). Reports are more frequent in semi-annual crops. For example, in the palm-watermelon system, the yield of intercropped palms was 6.8% lower than that of monoculture (Oomen, 2023). In a soybean and corn plot intercropped with immature oil palms, yields varied –51.8% and –4.16%, respectively, compared to monoculture (Rizki et al., 2020). In cassava and maize, yield can diminish as oil palms grow and are lower than their respective monoculture, but the total performance of the production system is higher than a typical oil palm monoculture, given that oil palm productivity is not affected (Agele et al., 2019).

Despite these findings, there is a notable gap in understanding the long-term effects of intercropping on oil palm yield dynamics. The results showed in Tables 4 and 5 don’t explain what the impact of intercropping in the productivity of the production system in the long term is, and what is the response in the yield curve of oil palm, given that most of these researches have focused on the yields of intercropped species. However, the productivity of intercropping systems should be understood as the sum of the partial contributions of all the crops that comprise it, so that as a whole, it can be greater than monoculture (Bybee-Finley and Ryan, 2018). Productivity relies on the quality of the agronomic management that is performed (George, 2014; Giller et al., 2021).

Adopting an intercropping approach requires a shift in how production systems are planned and managed. One of the key factors influencing this system is the planting density and spatial arrangement of the crops, as these factors directly affect both inter- and intraspecific competition within the agroecosystem (ETA and TBI, 2021; Khomphet et al., 2021). In oil palm intercropping systems, the spatial arrangement is generally designed to accommodate the agronomic requirements of the secondary crops (i.e. those that accompany oil palm), rather than altering the standard planting density of the oil palm. Companion crops are typically established in inter-row spaces or non-harvest zones, ensuring that their presence does not interfere with palm maintenance or its harvesting operations, also promoting efficient land use.

The spatial arrangement of oil palm in intercropping systems influences both the agronomic response both palm and companion crops. Some intercropping models retain the classical staggered planting density (approximately 143 palms per hectare) allowing for the integration of crops without altering the traditional layout. In contrast, other systems, such as those reported involve modifications to the spatial configuration of the palms—such as increased spacing or rectangular planting patterns—to reduce competition. Some growers have reported changes in palm planting design, shifting from traditional staggered layouts to rectangular ones (Oomen, 2023) or altering palm planting density by increasing the space between palms (Ahmad and Diniyati, 2022; Perez et al., 2024).

The type of oil palm involved in production systems should also be considered. Although the literature is not specific about the characteristics of palms suitable for intercropping, the selected materials such as Tenera are the most used, due to their productive attributes. Regarding Elaeis oleifera x Elaeis guineensis hybrids, only one case has been reported, in which pineapple and passion fruit were planted in association with oil palm (López, 2021). The slow growth of these species and the planting distance used (116–128 palms per hectare) could favor the intercropping of crops in the first years of the palm (Romero et al., 2023).

The literature provides different arrangements depending on the type of crop to be integrated and shows various examples of planting arrangements depending on the companion crop. For instance, cassava is typically planted at the end of the non-productive phase of palm plantations, with densities of up to 3200 plants per hectare annually (Carvalho Rocha et al., 2020). Maize is mainly established with young palm crops in all alleys, with planting densities of 50,000 plants/ha. (Danso et al., 2020; FENALCE, 2008; Koussihouèdé et al., 2020; Nuertey, 1999; Nuertey et al., 2010). For pineapple, as for maize, the integration in early stages of palm crops is common with planting densities of 30,000 plants per hectare (Van Leeuwen, 2019). The integration of palm with other perennial crops makes it necessary to modify traditional planting densities: in cocoa, there is evidence of systems where one row of palm and one row of cocoa are planted, while others plant quintuple rows (one row of palm and five rows of cocoa), with planting distances of 2.5 × 10 m and 2.5 × 3 m, respectively (Afolami and Ajobo, 1983; Lee and Kasbi, 1978).

In most cases it has not been found that the integration of palm with crops such as corn, peanuts, vegetables, soybeans, cocoa, chili, watermelon, pineapple, harms the development of oil palm. (Koussihouèdé et al., 2020; Nurjannah et al., 2021; Oomen, 2023). In corn-palm systems, the selection of cultivars tolerant to conditions such as drought or low soil fertility has made it possible to make fertilization more efficient (Danso et al., 2020; Louarn et al., 2021; Nuertey et al., 2010; Rizki et al., 2020). In cassava, the adoption of creeping cultivars is preferred, since they do not interfere with the development of the palm canopy (Leihner, 1983; Nuertey et al., 2010) Generally, there is no negative effect on palm productivity or development in the short term, but this can do occur in the intercropped specie compared to its monoculture (Amalia et al., 2024; de Maijer, 2023; Firmansyah and Umami, 2021; Obi et al., 2023; Rizki et al., 2020). In some cases intercropping can favor greater palm height or fronds etiolation and can have physiological effects on intercropping, such as increased chlorophyll content, increased stomata density, or a change in plant architecture, because of light competition (Hariyadi et al., 2019; Hidayat et al., 2019, 2021; Jeki Daisa et al., 2024; Jurusan et al., 2023; Oomen, 2023; Perez et al., 2024; Rizki et al., 2020; Treetaruyanont et al., 2014). Leaf area index is clue to determinate the optimal distance between plants (Ahmad and Diniyati, 2022).

The integration of crops with oil palm requires differentiated nutrient management strategies (Khomphet et al., 2021; Tanaka et al., 2009) since nitrogen and potassium nutritional imbalances have been recorded mainly in integrated systems (Essono et al., 2023; Rafflegeau et al., 2010). Good nutrition management is crucial in plantations where intercropping has been carried out to compensate for the nutritional imbalances that are generated in young palms, given that macronutrient content may be depleted more rapidly as nutritional demand increases, and that can affect productivity in the long term (Essono et al., 2023; Nuertey et al., 2010; Rizki et al., 2020). In fact, Koussihouèdé et al., 2020, highlight that prioritizing fertilizer application for one crop, and waiting for the other to take advantage of nutrients that were not used, does not meet the nutritional needs of both. In a system of intercropping with young palm, this can cost oil palm productivity in the long term (Koussihouèdé et al., 2020; Rafflegeau et al., 2010).

Root development patterns also play a significant role in minimizing competition between oil palm and companion crops. When crops occupy different soil strata, they are less likely to compete for the same resources, which can enhance overall system efficiency (Erhabor et al., 2002; Erhabor and Filson, 1999; Khomphet et al., 2021; Oluwatobi, 2020a; Oomen, 2023; Putra et al., 2012; Rizki et al., 2020). This principle has been particularly well demonstrated in systems that incorporate leguminous cover crops, which not only improve soil fertility through nitrogen fixation but also contribute to erosion control and organic matter accumulation. These benefits make leguminous species among the most widely used in oil palm intercropping systems (Al Manar et al., 2023; Ruiz and Molina, 2014).

The effects of intercropping on the phytosanitary status of the oil palm plantations are not yet clear. While some evidence suggests that intercropping may reduce pest and disease pressure, the overall impact appears to depend on the specific crop combinations and management practices employed (Blessing et al., 2022; Saravanan et al., 2022). In general, pest and disease management in intercropped systems follows similar protocols to those used in monocultures (Firmansyah and Umami, 2021; Oluwatobi, 2020b, 2020c; Saravanan et al., 2022; Van Leeuwen, 2019). However, in systems such as palm-cacao, there are shared phytosanitary problems. (Afolami and Ajobo, 1983; Bourgoing and Todem, 2010; Dhileepan, 1991; Saravanan et al., 2022). Particularly in the case of plantations in the Americas, Phytophthora palmivora, a causal agent of diseases in the two crops, could limit their association, although it is still necessary to clarify which pathovars are involved. (Afolami and Ajobo, 1983; Perrine-Walker, 2020; Torres et al., 2016). Modifying planting distance and layout and including host species of natural enemies can help manage pests and diseases. In cocoa, disease incidence may be higher in the intercropping system than in monoculture. In palm, there may be a decrease in the incidence of Ganoderma (Afolami and Ajobo, 1983; Boudreau, 2013; Shameer et al., 2018; Suwandi et al., 2024). Taro intercropped with oil palm can reduce root necrosis caused by Ganoderma in a 82%-96%, thanks to the allelochemical exudated by the tuber (Suwandi et al., 2024).

Water resource management in this type of system has not been widely studied either. Intercropping, in general, can improve water use due to the spatiotemporal distribution of water demand by the different crops and to the conservation of soil moisture, thanks to the decrease in evaporation (Yin et al., 2020). Intercropping oil palm with yam and pineapple has been shown to favor a higher soil moisture content, compared to palm monoculture (Dhandapani et al., 2020). Although water consumption is higher in intercropped systems, due to the water requirements of all crops, there is greater conservation of water in the soil but separate irrigation systems may be required for palm and other crops (Dhandapani et al., 2020; Khasanah et al., 2020; Reddy et al., 2004; Yin et al., 2020). Van Oosterhout et al. (2023) found that infiltration rate of the soil in an oil palm agroforest is similar to that of a natural forest, but higher than a soil of a monoculture, highlighting that agroforestry can improve soil water parameters.

Table 4

Reported yields in intercropping systems with young palm.

Table 5

Reported yields in intercropping systems with adult palm.

4.2 Profitability of intercropping with oil palm

The profitability of intercropping systems in oil palm cultivation depends on several interrelated factors, including total productivity, market prices, and production costs. Total productivity encompasses the combined yields of both the oil palm and the associated crops, and this aggregate output plays a crucial role in determining the economic viability of the system. However, profitability is also highly sensitive to fluctuations in market prices, which are often influenced by environmental, political, and economic variables. This volatility is particularly relevant in agri-food systems, where commodity prices can shift rapidly and unpredictably (Doporto Miguez and Michelena, 2011; Komarek et al., 2020).

In terms of production costs, intercropping has been shown to reduce certain expenses associated with oil palm maintenance. For example, tasks such as weed control and mulch application may be required less frequently in intercropped systems, thereby lowering labor and input costs. In some cases, the frequency of these tasks can be reduced from five to three times per year (Dissanayake and Palihakkara, 2019; López, 2021; Oluwatobi, 2020c). However, in watermelon, the development of weeds can increase herbicide use costs (Oomen, 2023).

On the other hand, intercropping requires a greater use of workforce to attend to the maintenance and harvesting of all the crops in the system, which means that the cost of labour has a greater share in the cost of production per hectare. (Adri and Yardha, 2022; Khasanah et al., 2020; Slingerland et al., 2019). In pineapple, maize and cassava intercropped systems, labour can represent up to 40% of operational costs (Carvalho Rocha et al., 2020)

Several studies have concluded that the intercropping of transitory crops with palm can become a profitable business, presenting favourable benefit/cost ratios, as shown in (Tab. 6) and (Tab. 7). However, the reports of the studies considered do not necessarily include the cost associated with oil palm cultivation, especially for short-cycle crops, which makes it difficult to estimate economic indicators for intercropping systems.

Certain crops, such as maize, pineapple, cassava and vegetables can generate profits high enough to pay for their own production costs and help to finance part of the production costs of the palm crop during its unproductive stage. (Carvalho Rocha et al., 2020; Carvalho Rocha, Lobato Rodrigues, Texeira, et al., 2007; Koussihouèdé et al., 2020; Leeuwen et al., 2019). For example, Carvalho Rocha et al (2020) estimated that agroforest system with pineapple, cassava or banana could cover between 64.5% and 100% of the production system costs. It is higher than the 13.5% of the cost of oil palm maintenance in the unproductive stage (up to 36 months after planting), reported by Sitorus and Zasari (2023), for a maize-oil palm system.

In long-term crops, such as cocoa, the seasonality of commodity prices may contribute to cushioning declines in oil palm yields, compared to monocropping (Khasanah et al., 2020). Although pepper has been mentioned as a potential crop for association with palm because of its price, yields may affect the profitability of the system (Migeon, 2018; Tengoua and Bakoumé, 2005; Zulkifli et al., 2016). Other aspects to be considered include the fact that the integration of semiannual crops allows for profits to be made while the palm begins to produce bunches (Slingerland et al., 2019; Van Leeuwen, 2019). This contributes to generate an early economic entry compared to monoculture palm plantations. (Kosová and Prášil, 2011; Norman, 1979; Trevellan, 2017).

Table 6

Benefit/cost ratio of different production systems intercropped with young oil palm.

5 Intercropping can boost environmental sustainability of the oil palm agroecosystem

Intercropping has emerged as a promising strategy for enhancing the environmental sustainability of oil palm production systems. This approach contributes to a range of ecosystem services that are essential for maintaining ecological balance and supporting long-term agricultural productivity (Tab. 8) (Abubakar et al., 2023; Masure et al., 2023).

One of the main benefits of intercropping is the increase of the biodiversity of the productive units without affecting (Meijaard and Sheil, 2019). In palm, these biodiversity increases have been found for arthropods, birds and microorganisms (Ashraf et al., 2018; Sapalina et al., 2022; Yahya et al., 2017). This brings on the provision of other ecosystem services such as natural pest and disease control, due to the enrichment of interspecific predation and parasitism relationships. (Ashraf et al., 2018; Ghazali et al., 2016; Saravanan et al., 2022).

Another environmental contribution of intercropping is the regulation of the atmosphere, mainly due to the modification of microclimates (Ashraf et al., 2019; Dhandapani et al., 2020) and the capture of greenhouse gases. It has been found that the practice of intercropping increases carbon sequestration in the form of biomass in crops such as pineapple, corn, cocoa and turmeric (Ahirwal et al., 2022). However, the impact on greenhouse gas emissions can vary depending on the crop combination and site conditions. According to Hariyadi et al. (2019) emissions (t CO₂ /ha*year) are higher in an eggplant intercrop (10.28) and lower in a chili bell pepper intercrop (8.66), compared to the palm monoculture (8.78). In the palm-pineapple system, methane emissions have been reported to be higher than those of the palm monoculture, related to soil drainage conditions (Dhandapani et al., 2020).

GHG emissions depend on environmental conditions: the rate of CO₂ emission in the soil is higher when the soil is wet, since the respiration of roots and soil microorganisms is stimulated by the decomposition of accumulated leaf litter during the dry period and after a period of water stress (Dhandapani et al., 2020; Linn and Doran, 1984; Rodrigues et al., 2016; Zanchi et al., 2009). In addition, the size of the plant root system influences the carbon content accumulated in the soil.

Land is a fundamental factor of production for the existence of agricultural activity and its access is a determining factor in the human development of rural communities (de Vos, 2016). Intercropping is a production alternative that makes land use more efficient, since it achieves higher productivity per unit area compared to monoculture systems. The Table 9 shows the estimated values of the equivalent land ratio or LER, i.e., the relative area required by a monoculture to produce the same as its intercropping system (Bitew et al., 2019; Bybee-Finley and Ryan, 2018; El-Ghobashy et al., 2018; Hong et al., 2020; Khasanah et al., 2020; Mead and Willey, 1980; Petrie and Bates, 2017). Semi-annual and semestral intercrops seem to be more efficient than their monoculture homologue, as their LER is higher than 1. It is important to mention that the data are referred to a same area unit, given that intercropped crops don’t occupy the same extension than its monocrop equivalent. Of course, these results aren’t enough to support a decision-making process, given that few of those reports are including a long-term vision of oil palm production system and have focused more on the intercropped specie, as productivity data are faster to collect.

Table 7

Benefit/cost ratio of different production systems intercropped with adult oil palm.

Table 8

Environmental services provided by the palm production system with intercropping.

Table 9

Land equivalent ratio (LER) reported for intercropping with palm.

6 The adoption of oil palm intercropping systems is influenced by the perception of their effectiveness

Intercropping has a positive impact on rural communities by promoting food security, generating well-being in productive units and strengthening the social fabric. This is particularly important among small-scale producers, who, depending on the mix of crops they choose to grow, may use the production to supply household food or to sell all or part of it. In Indonesia, for example, 80% of the daily diet of households comes from their own crops. (Ahirwal et al., 2022; Cheyns and Rafflegeau, 2005; Hervas, 2021; Koczberski et al., 2012, 2018).

However, the perception of usefulness that producers have is decisive in the adoption of crop intercropping, despite its possible benefits. This perception is dynamic and is conditioned by factors inherent to the producer (such as their socioeconomic and cultural profile) and by external factors (such as the environmental and economic context) (Susanti et al. 2021; Hendrawan and Musshoff 2024).

Intercropping with palm is seen as a more complex system, difficult to manage and more labour-intensive (Madjid et al., 2023; Susanti, et al., 2021; Susanti et al., 2021). An oil palm + cocoa system may require 338 additional man-days per hectare, compared with sole oil palm (Rao et al., 2019). In small producers, the cultivation work is generally carried out by the members of the family nucleus, so intercropping could increase the costs of hiring external workers (Adri and Yardha, 2022; Okere et al., 2015; Orewa, 2008). This perception is not only observed among producers who have monoculture palm systems, but also among producers who already have agroforestry systems without oil palm (Perez Braga et al., 2024). Intercropping is also not easily adopted in industrial plantations with mechanized labor, as it reduces work efficiency (Dhandapani et al., 2020).

Palm growers have also considered crop intercropping as a production system with high uncertainty regarding profitability since it is thought that crop integration causes a detriment to palm productivity due to interspecific competition (Hendrawan and Musshoff, 2024; Perez Braga et al., 2024; Susanti et al., 2020). The positive financial results of the monoculture system, the management recommendations made by the technical assistants of the oil extraction companies and the lack of knowledge about the management of interleaving reinforce this idea. However, the possible income left by integration, whether with species with high commercial value or with easy marketing, also make these systems attractive, especially to face fluctuations in commodity prices (Madjid et al., 2023; Salleh and Harun, 2015; Susanti et al., 2020)

The gaps can be overcome through better agronomic practices that have been developed from the traditional knowledge and experiences of the communities that have adopted these production systems, but also, in an incipient way, from the scientific development of the institutions (de Castro and Futemma, 2021; Sagna et al., 2019). Particularly in Brazil, de Castro and Futemma (2021) have described the SAFTA (Sistema Agroflorestal De Tomé-Açu) system as a success story in the adoption of agroforestry systems with oil palm, which has allowed the exchange of indigenous knowledge, scientific knowledge and commercial knowledge, improving the relationship between the different actors in the community. In addition, SAFTA has made it possible to strengthen peasant identity and local empowerment.

The sustainability of intercropping systems implies that producers have adequate training to enable good agronomic management, which is especially important for small producers who, for the most part, rely on empirical knowledge for decision making (Hong et al., 2020; Okere et al., 2015). Likewise, educational level, having another economic activity and whether or not the farmer lives near the oil palm crop, determine the decision to implement intercropping systems with oil palm (Susanti et al., 2021).

Women's participation is important in palm agroforestry systems, especially in the planning and management of production units. Koczberski et al. (2018) also reported that men tend to work in the palm while women tend to do the work of the intercropped species, especially, when they are food crops. Although each community has its own dynamics, intercropping could reduce women's vulnerability to food insecurity and lack of income.

7 Summary and perspective

Intercropping is a means of sustainable intensification that increases the overall productivity of a production unit and improves the efficiency of resource use - such as water and soil nutrients - even though the yields of the crops involved may be lower than those reported if they were planted under monoculture (Martin-Guay et al., 2018; Oluwatobi, 2020a; Rizki et al., 2020; Sun et al., 2021; Yin et al., 2020). Additionally, intercropping favors the resilience of agricultural systems to scenarios such as climate change, since the diversity of species in the agroecosystem reduces the use of pesticides, attracts the natural enemies of pests and provides them with refuge (Khatun et al., 2020; Petrie and Bates, 2017). They also strengthen the food sovereignty and security of the communities that adopt and adapt them to their conditions and culture. (Knörzer et al., 2009; Maitra et al., 2021; Santika et al., 2019).

The adoption of intercropping as a complementary piece on the road to sustainability in the palm sector requires adequate technical, financial and training bases for producers. The adoption of this practice is easier for small-scale palm growers, who account for at least 40% of the area planted in Malaysia and 27% in Indonesia. (RSPO, 2023). In Ivory Coast, at least 70% of palm growers are small-scale. (Solidaridad, 2022). In Colombia, they represent 75% of the total number of palm growers, but only 10% of the total area. (Fedepalma, 2022).

However, this vision of the oil palm cropping breaks with the current paradigm on crop management. Perceptions on the management of palm plantations differ among the various actors of the crop, according to their interests, but putting in the debate the dichotomy of instrumental - relational value of production (Lusiana et al., 2023; Susanti et al., 2021). The transition from monocultures to more complex agroforestry systems may not be seen as necessary, due to the risk of loss of competitiveness of the plantations, the socioeconomic benefits derived from the status quo, and the fact that the implementation of Good Agricultural Practices already classify them as equal or similar to agroforestry systems (Rivera-Mendez and Romero Angulo, 2018). In contrast, the arguments in favor of the paradigm shift focus and the need to increase food security in farming families, income diversification, the perceived generation of environmental impacts of poor monoculture management, the weaknesses of crop governance, among others (Purwanto et al., 2020; Rival and Chalil, 2023; Susanti et al., 2020).

The heterogeneity of agroecological conditions implies an agronomic management of intercropping that is different from that of monoculture and that has not yet been standardized. Given that each crop combination has an inherent management, it is necessary to deepen the knowledge of which are the optimal species, materials and planting distances to implement these systems, as well as the ecophysiology, pollinator dynamics and phytosanitary behaviour of these crops (Budiadi et al., 2019).

Although the agronomic practices that are implemented in this type of production systems have been generated from the knowledge of the producer, there is currently interest from academia to transform current production systems into more sustainable, participatory and technically viable ones. Therefore, of the research referenced in this document, 31% of the results (58 documents) come from trials carried out by researchers. Initiatives such as the TRIAL Project, the SAFTA Project or are examples of mature innovations on sustainable oil palm production at a commercial level: species diversification, knowledge exchange between producers and researchers and monitoring of palm productivity are key elements of their success/implementation (Braga et al., 2024; de Castro and Futemma, 2021; Rival et al., 2022; Rival and Chalil, 2023). The application of models to simulate the agronomic behaviour of these systems is another strategy by academia to promote the adoption of intercropping, offering producers tools for decision-making (Khasanah et al., 2020; Slingerland et al., 2019).

In economic terms, oil palm monocultures face challenges related to competitiveness and profitability. The investment and maintenance costs of the crop during the unproductive period - which, in the case of oil palm, can take between 2 to 3 years to start producing fruit - can range from USD 61.47 to USD 201.5 per tonne. (LMC, 2022). Also, palm oil is a commodity characterized by volatile prices, which in turn depend on the dynamics of oil prices (due to its use in biodiesel) and palm oil inventories in Southeast Asia (Arshad et al., 2012; LMC International, 2022). Intercropping can help to reduce the financial risk of a production system by diversifying income sources. Economic benefit, of course, depends on the market prices of each crop, but commodities such as cocoa and pepper may be interesting due to their high value. Nevertheless, the transition from a monoculture to a polyculture implies higher investment costs, labour costs and access to information, so financing and the purchasing power of producers play an important role in the adoption of intercropping.

Workforce scarcity is a reality that oil palm growers are facing and so conditionate the will to adopt. In monocropping system, a worker can be assigned to at least eight hectares, so an intercropping system would not be efficient if the production unit is not able to supply enough workers by area unit (Azman et al., 2015; Ruíz Álvarez et al., 2022). Studying how work productivity can be increased is challenging, especially if it is considered that mechanization can be restrained in some cases. Gaps of information in this area represents a great opportunity for further research, particularly in the design of new machines of new planting patterns.

Intercropping contributes to the fact that less land is needed to achieve similar productivities to those of monoculture systems, of course, per unit area. Efficient land use reduces pressure on natural resources. Specifically, it reduces the need to expand the agricultural frontier or to convert forest into cropland. The association of palm with corn, cassava, plantain or cocoa can be an alternative with higher productivity than monoculture. However, it is important to analyse the negative environmental impacts, especially those that may have an impact at the river basin level. Aspects such as water consumption, impact on erosion, waste and pollutant management and territorial planning require greater attention. Likewise, regional socioeconomical impact must be considered, given that intercropping can have difficulties in adapting to economies of scale, as they are highly site-specific, more complex to manage and productive uncertain.

Finally, institutional and public infrastructure support must be sufficient to enable producers, especially small producers, to access marketing channels for their products (Susanti et al., 2021). The promotion of the association of oil palm crops requires strong institutional support from both the public and private sectors to enable the definition of comprehensive environmental and agricultural public policies. For example, in Indonesia, Ministerial Decree Permen LHK No. 9/2021 and specific environmental regulations in Brazil set a political precedent for transforming oil palm production systems (Costa et al., 2024; Madjid et al., 2023).

8 Conclusion

The adoption of intercropping in the palm sector represents a critical step towards sustainability, offering numerous benefits such as increased productivity, improved resource efficiency, and enhanced resilience to climate change. The potential for greater food security, income diversification, and environmental benefits makes it a promising alternative, despite the challenges posed by the transition from monoculture to intercropping, such as higher initial investment costs, need for specialized knowledge, and potentially unpredictable environmental impacts. Successful implementation requires robust technical, financial, and training support for producers, particularly smallholders.

Funding

This study was funded by Fondo de Fomento Palmero.

Conflicts of interest

The authors have no conflicts of interest to declare that are relevant to the content of this article.

Author contribution statement

All authors contributed to the study conception and design. Daniel Eduardo Munévar Martínez made the conceptualization, data curation, methodology, visualization and writing of the paper. María Celina Estupiñán Villamil made the conceptualization and writing of the paper. Elizabeth Ruiz Álvarez made conceptualization, editing and supervision of the paper. Mauricio Mosquera Montoya made the reviewing of the paper.

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Cite this article as: Munévar-Martínez DE, Ruiz-Álvarez E, Estupiñán-Villamil MC, Mosquera-Montoya M. 2025. Sustainable intensification of oil palm production through integration with other crops: a review. OCL 32: 31. https://doi.org/10.1051/ocl/2025022

All Tables

Table 1

Terms of search.

In the text

Table 2

Main annual crops planted in intercropping with oil palm.

In the text

Table 3

Main semi-annual and permanent crops planted in intercropping with oil palm.

In the text

Table 4

Reported yields in intercropping systems with young palm.

In the text

Table 5

Reported yields in intercropping systems with adult palm.

In the text

Table 6

Benefit/cost ratio of different production systems intercropped with young oil palm.

In the text

Table 7

Benefit/cost ratio of different production systems intercropped with adult oil palm.

In the text

Table 8

Environmental services provided by the palm production system with intercropping.

In the text

Table 9

Land equivalent ratio (LER) reported for intercropping with palm.

In the text

Table 1

Terms of search.

Topic | Descriptor | Registers retrieved
General aspects | (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) | Google Scholar: 2250; Scopus: 339
Economics aspects | (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND “yield” | Google Scholar: 64; Scopus: 61
| (intercrop* OR agroforest* or “intercalado”) AND AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND profit* | Google Scholar: 39; Scopus: 24
Social aspects | (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND (“work” OR “labor”) | Google Scholar: 55; Scopus: 41
| (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND wom* | Google Scholar: 11; Scopus: 6
| (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND (“food” OR “food security”) | Google Scholar: 15; Scopus: 62
Environmental aspects | (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND (“environmental” OR “biodiversity” OR “ecosystem*) | Google Scholar: 69; Scopus: 184
| (intercrop* OR agroforest* OR “intercalado”) AND (“oil palm” OR “palmier a’huile” OR “palma de aceite” OR “Elaeis guineensis”) AND “carbon” | Google Scholar: 49; Scopus: 86

Table 2

Main annual crops planted in intercropping with oil palm.

Associated cultivation with palm
Palm stage
Country in which reported
Source

Corn (Zea mays)
Young
Colombia, Nigeria, Ghana, Benin, Cameroon, Uganda, Ivory Coast, India, Indonesia
Agele, (2019); Danso et al. (2020); Dissanayake and Palihakkara, (2019a); FENALCE, (2008); Koussihouèdé et al. (2020); Nuertey et al. (2010); Obi et al. (2023); Rizki et al. (2020); Erhabor et al. (2002); Hariyadi et al. (2019); Jurusan et al. (2023); Jeki Daisa et al. (2024); Nchanji et al. (2016); Orewa, (2008); Okyere, (2014)

Cassava (Manihot esculenta)
Young
Brazil, Nigeria, Benin, Cameroon, Uganda, Ivory Coast, Ghana, Indonesia
Agele, (2019); Koussihouèdé et al. (2020); Okyere, (2014); Carvalho Rocha et al. (2020); Nchanji et al. (2016); Nuertey et al. (2010); Obi et al. (2023); Orewa, (2008); Sapalina et al. (2022); Namanji et al. (2021); Cheyns and Rafflegeau, (2005)

Rice (Oryza sativa)
Young
Indonesia, Brazil, Ivory Coast
Perez et al. (2024); Alridiwirsah et al. (2019); Alves et al. (2013); Cheyns and Rafflegeau, (2005)

Sorghum (Sorghum bicolor)
Young
Indonesia
Sapalina et al. (2022)

Solanaceae (tomato, eggplant, chili, pepper, garden huckleberry)
Young
Nigeria, Benin, Cameroon, Indonesia, India
Agele et al. (2019); Koussihouèdé et al. (2020); Nurjannah et al. (2021); Obi et al. (2023); Oluwatobi, (2020b); Tengoua and Bakoumé, (2005); Hariyadi et al. (2019); Nchanji et al. (2016); Sapalina et al. (2022); Reddi et al. (2015); Bakeri et al. (2019)

Okra (Abelmoschus esculentus)
Young
Nigeria, India
Oluwatobi, (2020a); Reddi et al. (2015)

Taro, cocoyam (Colocasia sculenta)
Young, adult
Cameroon, Nigeria, Indonesia
Erhabor and Filson, (1999); Suwandi et al. (2024); Nchanji et al. (2016)

Yam (Dioscorea sp.)
Young
Malaysia, Nigeria, Cameroon, Indonesia
Dhandapani et al. (2020); Fadli et al. (2023); Nchanji et al. (2016); Orewa, (2008)

"Porang" (Amorphophallus muelleri).
Young
Indonesia
Amalia et al. (2024)

Legumes (beans, peanuts, soybeans)
Young, adult
Nigeria, Benin, Cameroon, India, Indonesia, Ivory Coast
Idawanni and Ferayanti, (2021); Marwoto et al. (2012); Putra et al. (2012); Rizki et al. (2020); Adri and Yardha, (2022); Erhabor et al. (2002); Hariyadi et al. (2019); Hidayat et al. (2019); Nchanji et al. (2016); Sapalina et al. (2022); Reddi et al. (2015); Yuliani et al. (2021): Agustira et al. (2018); Kusumawati et al. (2021); Koussihouèdé et al. (2020); Sitorus and Zasari, (2023); Cheyns and Rafflegeau, (2005)

Onion (Allium cepa)
Young
India
Reddi et al. (2015); Rethinam, (2017)

Indian mustard (Brassica juncea), cabbage (Brassica oleraceae)
Adult
Indonesia
Yanda, (2019); Yanda et al. (2018)

Edible fern (Displazium esculentum)
Adult
Indonesia
Yanda, (2019)

Aromatic, ornamental and medicinal plants
Adult
India, Thailand, Nigeria, Sri Lanka
Nwaogu et al. (2014); Rethinam, (2017); Treetaruyanont et al. (2014); Dissanayake and Palihakkara, (2023)

Watermelon (Citrullus lanatus)
Young
Indonesia, Cameroon
de Maijer, (2023); Oomen, (2023); Nchanji et al. (2016)

Cucumber (Cucumis sativus)
Young
Indonesia
Sitorus and Zasari, (2023)

Table 3

Main semi-annual and permanent crops planted in intercropping with oil palm.

Associated cultivation with palm | Palm stage | Country in which reported | Source
Musaceae (banana, plantain) | Young, adult | Nigeria, Ghana, Cameroon, Ivory Coast, Indonesia | ETA and TBI, (2021); Okyere, (2014); Oomen, (2023); Nchanji et al. (2016); Nuertey et al. (2010); Cheyns and Rafflegeau, (2005)
Coffee (Coffea arabica) | Adult | Indonesia | Firmansyah and Umami, (2021)
Cocoa (Theobroma cacao) | Adult | Nigeria, Cameroon, Ghana, India, Malaysia | Amoah et al. (1995); Lee and Kasbi, (1978); Bourgoing and Todem, (2010); Rethinam, (2017); Afolami and Ajobo, (1983); Ashraf et al. (2019); Rao et al. (2019); Adenikinju et al. (1991)
Pineapple (Ananas comosus) | Young, adult | Colombia, Brazil, Malaysia, Benin, Indonesia | López, (2021); R. N. Carvalho Rocha et al. (2007); Van Leeuwen, (2019); Ashraf et al. (2019); Koussihouèdé et al. (2020); Sapalina et al. (2022); Dhandapani et al. (2022); Bakeri et al. (2019)
Black pepper (Piper nigrum) | Adult | Malaysia | Ashraf et al. (2019); Khasanah et al. (2020); Zulkifli et al. (2016); Migeon, (2018)
Passion fruit (Passiflora sp) | Young | Colombia | López, (2021)
Pistachio (Pistacia vera) | Young | Cameroon, Ivory Coast | Cheyns and Rafflegeau, (2005)
Timber | Adult | Malaysia, Indonesia, Thailand | Ahmad and Diniyati, (2022); Khomphet et al. (2021); Rahmani et al. (2021); Tata et al. (2016); Budiadi et al. (2019)
Bamboo (Bambusa sp) | Adult | Malaysia | Ashraf et al. (2019)
Papaya (Carica papaya) | Young | India, Indonesia | Maryani et al. (2021); Rethinam, (2017)
Cinnamon (Cinnamomum verum) | Adult | India | Manorama et al. (2019)

Table 4

Reported yields in intercropping systems with young palm.

Production system | Palm average yield (t FBB/ha*year) | Intercropped average yield (t/ha*year) | Reported by
Cassava (Manihot esculenta) | 7,84 - 14,11 (calculated) | 25 – 33 | Agele et al. (2019)
Rice (Oryza sativa) | – | 3 | Alves et al. (2013)
| – | 3,48 - 4,47 | Alridiwirsah et al. (2019)
Corn (Zea mays) | – | 7 | Danso et al. (2020)
| 7,84 - 14,11 (calculated) | 5 – 10,5 | Agele et al. (2019)
| – |  |
Peanut (Arachis hypogaea) | – | 1,32 | Putra et al. (2012)
Corn + soybean (Glycine max) | – | Corn: 9.86 - 11.59 | Rizki et al. (2020)
| – | Soybean: 1 - 1.03 |
Tomato (Solanum lycopersicum) | – | 6 | Tengoua and Bakoumé, (2005)
| – | 2,7 | Reddi et al. (2015)
Onion (Allium cepa) | – | 0,26 | Reddi et al. (2015)
Okra (Abelmoschus esculentus) | – | 3,82 | Reddi et al. (2015)
Chili (Capsicum annuum) | – | 2,02 | Reddi et al. (2015)
| – | 0,35 | Tengoua and Bakoumé, (2005)
Black pepper (Piper niger) | – | 1 - 3 | Zulkifli et al. (2016)
Pepper (Capsicum annuum) | – | 0,7 | Tengoua and Bakoumé, (2005)
Watermelon (Citrullus lanatus) | 3,429 | – | Oomen, (2023)
| – | 5.6 - 8,4 | de Maijer, (2023)

Table 5

Reported yields in intercropping systems with adult palm.

Production system | Palm average yield (t FBB/ha*year) | Intercropped average yield (t/ha*year) | Reported by
Black pepper (Piper nigrum) | 15,5 | 3 | Migeon, (2018)
Cocoa (Theobroma cacao) | 13 | 1 | Bourgoing and Todem, (2010)
| 20- 28 | 0,138 - 0,795 | Amoah et al. (1995)
Cassava (Manihot esculenta) | 21,17 | 6,37 | Carvalho Rocha et al. (2020)
Pineapple (Ananas comosus) | 20,5 | 11,7 | Carvalho Rocha et al. (2020)
Banana (Musa paradisiaca) | 21,35 | 7,98 | Carvalho Rocha et al. (2020)

Table 6

Benefit/cost ratio of different production systems intercropped with young oil palm.

Production system | Data referred to¹ | Ratio B/ C | Time lapse² | Source
Corn (Zea mays) | IC | 2,86 | I | Manorama et al. (2019)
| IC | 1,43 | HC | Koussihouèdé et al. (2020)
| IC | 1,76 | Y | Agustira et al. (2018)
Soy (Glicine max) | IC | 1.51 | Y | Agustira et al. (2018)
Cassava (Manihot esculenta) | IC | 1,70 | HC | Koussihouèdé et al. (2020)
Pineapple (Ananas comosus) | IC | 2,14 | HC | Koussihouèdé et al. (2020)
Tomato (Solanum lycopersicum) | IC | 4,18 | HC | Koussihouèdé et al. (2020)
Okra (Abelmochus esculenta) | IC | 1,33 | I | Manorama et al. (2019)
Onion (Allium cepa) | IC | 0,26 | Y | Reddi et al. (2015)
Chili (Capsicum annuum) | IC | 1,78 | I | Manorama et al. (2019)
Heliconias (Heliconia spp.) | P + IC | 2,80 | Y | Ramachandrudu et al. (2014)
| P + IC | 2,38 | I | Manorama et al. (2019)
Cowpea bean (Vigna unguiculata) | IC | 1,28 | HC | Adri and Yardha, (2022)

¹

IC= values only for intercropped crop; P = values only for oil palm crop; P + IC = values considering palm + intercropping

²

HC =values per harvest cycle; Y = values per year; I =values for the duration of intercropping.

Table 7

Benefit/cost ratio of different production systems intercropped with adult oil palm.

Production system | Data referred to³ | Ratio B/ C | Time lapse⁴ | Source
Cocoa (Theobroma cacao) | P + IC | 2,78 | I | Manorama et al. (2019)
| P + IC | 1,21 – 2,08 | I | Rao et al. (2019)
| P + IC | 2,43 | Y | Ramachandrudu et al. (2014)
| P + IC | 2,4 - 3,3 | I | Khasanah et al. (2020)
Pepper (Capsicum annuum) | IC | 0,73 | Y | Tengoua and Bakoumé, (2005)
Black pepper (Piper nigrum) | P + IC | 1,9 - 2,2 |  | Khasanah et al. (2020)
Banana (Musa paradisiaca) | P + IC | 2,69 | I | Manorama et al. (2019)
Tomato (Solanum lycopersicum) | IC | 1,88 | Y | Tengoua and Bakoumé, (2005)
Timber | P + IC | 1,21 - 2,01 | I | Rahmani et al. (2021)
Bush pepper (Capsicum annuum) | P + IC | 2,86 | I | Manorama et al. (2019)
Ginger (Alpinia purpurata) | P + IC | 2,56 | Y | Ramachandrudu et al. (2014)
| P + IC | 2,58 | I | Manorama et al. (2019)

³

IC= values only for intercropped crop; P = values only for oil palm crop; P + IC = values considering palm + intercropping

⁴

HC =values per harvest cycle; Y = values per year; I =values for the duration of intercropping.

Table 8

Environmental services provided by the palm production system with intercropping.

Environmental service type
Environmental service description
Finding
Source

Provisioning
Terrestrial plants grown for nutrition, materials or energy.
The intercropping systems provide food, building materials, inputs for energy production and ornamentation.
Koczberski et al. (2012); Maitra et al. (2021); Okere et al. (2015); Sagna et al. (2019)

Regulating
Control of erosion rates
Cover crops (mainly legumes) provide protection against erosion and regulate runoff.
Erhabor et al. (2002); Satriawan et al. (2021)

Temperature and humidity control
The systems intercropped with black pepper showed a reduction in air and soil temperature of 1.3 and 2.1 °C.
Ashraf et al. (2019)

Regulation of the chemical composition of the atmosphere
Intercropping can increase capture of CO2 in the atmosphere and storage of carbon in soil reserves, up to 44%.Intercropping with pineapple can generate 30% more carbon stock compared to palm monoculture but generate methane emissions. Also, the system with cocoa can offer a lower carbon debt and have higher above and below ground carbon accumulation (116.7 Mg C/ha).
Ahirwal et al. (2022); Albrecht and Kandji, (2003); Besar et al. (2020); Budiadi et al. (2019); Chinade et al. (2015); Gomes et al. (2021); Khasanah et al. (2020); Lal and Kimble, (1997); Montagnini and Nair, (2004); Ramos et al. (2018); Tscharntke et al. (2011)

Decrease in CO emissions₂ due to increased photosynthetic activity per unit area and carbon sequestration in the soil. Emissions can decrease between 12.54% and 27.28% compared to bare soil.
Kusumawati et al. (2021).

Palm height and canopy diameter reduce understory tree growth and allow the oil palm to sequester 12 to 500 times more carbon.
Besar et al. (2020).

Pest and disease control
Increased number of predatory and parasitoid insects
Ashraf et al. (2018)

Reduction of damage generated by pathogens (Ganoderma boninense) on oil palm-cocoa system.
Fadli et al. (2023); Suwandi et al. (2024)

Supporting
Regulation of the hydrological cycle and water flow.
Intercropping palm oil with cocoa can replenish more groundwater compared to monoculture.
Khasanah et al. (2020)

Maintenance of populations and habitats
Increase in the abundance of bird species between 4 and 41% higher in the plots with polycultures than in the oil palm monoculture.
Yahya et al. (2017).

Increased richness and diversity of arthropods (predatory and decomposing insects).
Ashraf et al. (2018).

Three times higher mycorrhizal colonization in intercropping systems, especially in palm alleys.
da Silva Maia et al. (2021)

Cultural
Enjoyment activities
The value of the landscape and biodiversity may allow for passive recreation activities.
Yahya et al. (2017).

Table 9

Land equivalent ratio (LER) reported for intercropping with palm.

Intercropping | LER | Comparison monoculture | Reported by
Cassava (Manihot esculenta) | 1,38 | Cassava | Carvalho Rocha et al. (2020)
Pineapple (Ananas comosus) | 0,98 | Pineapple | Carvalho Rocha et al. (2020)
Banana (Musa paradisiaca) | 1,36 | Banana | Carvalho Rocha et al. (2020)
Corn (Zea mays) + soybean (Glicine max) | 1,14 - 1,76 | Corn and soybeans | Rizki et al. (2020)
Peanuts (Arachis hypogaea) | 4,10 | Peanuts | Putra et al. (2012)
Corn (Zea mays) | 1,32 | Corn | Agustira et al. (2018)
Soy (Glicine max) | 3,30 | Soy | Putra et al. (2012)
| 1,18 | Soy | Agustira et al. (2018)
Black pepper (Piper nigrum) | 0,77 | Palm | Migeon, (2018)
| 0,99 | Palm | Khasanah et al. (2020)
Cocoa (Theobroma cacao) | 1,44 | Palm | Khasanah et al. (2020)