Modeling oil palm crop for Brazilian climate conditions
Graphical abstract
Introduction
The oil of the African palm (Elaeis guineensis Jacq.) is the vegetable oil with the highest production and commercialization volume in the world. According to the United States Department of Agriculture (USDA), the global production in 2019 was 74.60 million tons of processed oil, higher than the production of soy oil in the same period (56.85 million tons). The oil extracted from the palm fruit has several uses in the industry, such as in the production of food, detergents, cosmetics, and more recently in the production of biodiesel (Pirker et al., 2016). Most of the world's production comes from Southeast Asia. Indonesia is the main world producer, accounting for 57.19% of the world's production, followed by Malaysia (27.26%) and Thailand (3.99%), according to USDA. Together, these three countries account for almost 90% of the total palm oil production in the world.
Latin America has emerged as a feasible alternative to Southeast Asia to increase world palm oil production. Currently, Colombia is the main producer of palm oil in Latin America and the fourth-largest producer in the world. Brazil has a small contribution to the international market, ranking ninth and accounting for 0.72% of world production. However, the modest Brazilian oil palm production has been expanding. According to USDA, national production increased from 270 thousand tons in 2010 to 540 thousand million tons in 2019. This expansion is linked both to the creation of incentive governmental programs to increase palm oil production, such as Pronaf Eco Dendê (Monteiro de Carvalho et al., 2015), as well as the increase in domestic and international demand. The Pará state is the largest producer of palm oil in Brazil, accounting for 70% of the total planted area and 90% of national production.
In Brazil, more than 400 million ha are suitable for the cultivation of oil palm, but most of this area is currently covered by tropical forests, especially in the Amazon region (Pirker et al., 2016). The challenges imposed to the growth of oil palm production in Brazil due to competition by area with the Amazon Rainforest (Furumo and Aide, 2017; Vijay et al., 2016) and climate change (Almeida et al., 2017; Avila-Diaz et al., 2020; Da Silva et al., 2019; Paterson et al., 2017) require a deepening of knowledge about the plant's life cycle, including growth and yield in order to reduce the negative impacts of oil palm cultivation. Previous studies have shown how the environment and endogenous factors of the plant, such as age and reproductive cycle, affect the growth and yield of oil palm (Hoffmann et al., 2017; Woittiez et al., 2017). However, the contribution of climatic and meteorological conditions to carbon uptake and assimilation in oil palm is still unclear. Further, it is necessary to understand how these climatic conditions do affect crop yield.
Land surface models are a tool widely used in studies involving the relationship between agricultural production and the climate. These models are able to simulate crop yields under different climatic conditions, explicitly simulating processes such as photosynthesis, respiration, and phenology, as well as the exchange of carbon, water, and energy between the biosphere and the atmosphere (Sellers, 1997). In addition, modeling allows to assess the impact of management techniques on carbon assimilation and yield, as well as assessing the suitability of areas for the cultivation of different agricultural species, avoiding the deforestation of low-yield areas. Several models simulate oil palm yield currently, such as APSIM-Palm (Huth et al., 2014), ECOPALM (Combres et al., 2013), PALMSIM (Hoffmann et al., 2014), and CLM-Palm (Fan et al., 2015). However, most of these models represent biophysical processes in a simplified way, such as the coupling between photosynthesis and plant transpiration. Few models, such as CLM-Palm, are able of simulating growth, yield, and exchanges of carbon, water, energy, and momentum between the ecosystem and the atmosphere. Those models can be applied, for example, to study the land cover and land use changes climate impacts considering not only the climate impacts through biogeochemical (CO2) emissions but also through the biophysical mechanisms (regulation of water and energy).
In this study, the ECOSMOS-Palm sub-model is presented, which simulates the growth and yield of oil palm through the structure of the ECOSMOS integrated simulator, which is based on the Agro-IBIS model (Foley et al., 1996; Kucharik and Brye, 2003). In addition, the sub-PFT scheme proposed by Fan et al. (2015) was used to implement phenology and carbon allocation to the plant pools (roots, trunk, leaves, and fruits). Thus, the objectives of this paper are (i) evaluate the oil palm crop sub-model implemented in the ECOSMOS model, (ii) to evaluate modeled crop carbon assimilation and energy balance through two micrometeorological flux tower measurements, and (iii) to investigate modeled crop yield in the major Brazilian producing region.
Section snippets
The ECOSMOS-Palm model
ECOSMOS is a biophysical growth model based on Agro-IBIS (Foley et al., 1996; Kucharik and Brye, 2003). Researchers from EMBRAPA (Brazilian Agricultural Research Company) have been improving the original model and implementing the most important crops in Brazil. One of the major changes in the ECOSMOS framework is that developers can add new a crop-PFT (plant functional type) as a module of the main program, and this crop module is linked with core model sub-routines that solves biophysical
Sensitivity analysis and calibration
The proposed sensitivity analysis framework was able to identify the most sensitive parameters to simulate energy and carbon fluxes. Fig. 3 presents the 33 parameters that significantly affect the simulation of at least one variable (H, LE, and NEE) on JAM site. NEE simulation was sensitive to the largest number of parameters, followed by H and LE (24, 18, and 10 parameters, respectively). For four parameters, the model was sensitive to simulate all variables simultaneously (H, LE, and NEE),
Climate dependence on oil palm carbon uptake efficiency
Previous studies have shown that oil palm achieves a high rate of photosynthesis compared to other C3 photosynthesis pathway plants, saturating at a PPFD (Photosynthetic Photon Fluence Density) of 1100 μmol m−2 s−1 (~240 W m−2 of PAR) in ~20 μmol-CO2 m−2 s−1 (Apichatmeta et al., 2017; Dufrene and Saugier, 1993). Also, the oil palm requires PAR of at least 230 MJ m−2 month−1 (Woittiez et al., 2017), which is commonly fulfilled in the equatorial region, where MOJ and site are located. On the
Conclusions
The new oil palm model presented proved to be able of simulating carbon and energy exchanges between the land surface and the atmosphere. The exception was the simulation of the sensible heat flux, which was affected by the lack of data on the soil's physical properties. In addition, the model was also able to simulate well the oil palm yield in the main producing region of Brazil. In general, the model better simulated the yield of plants from 12 to 25 years old and for varieties that showed
Declaration of Competing Interest
None.
Acknowledgement
This study was made possible thanks to the support of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, finance code 88882.437129/2019-01) and Agropalma SA. The Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, finance code 480210/2011-0), the Empresa Brasileira de Pesquisa Agropecuária (Embrapa), and Marborges Agroindústria SA also contributed to this study.
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