Oil palm management experiment (EFForTS - OPMX)

Results from Phase 1 have shown that a major reason why oil palm is currently an attractive land-use option is because of its large productivity due to fertilizer and herbicide inputs as well as large profit (Grass et al. 2020). Unfortunately, the economic benefits are in stark contrast with most ecosystem function indicators, such as naturalness, species richness of plants and animals, carbon stocks, nutrient leaching losses and greenhouse gas fluxes (Clough et al. 2016, Meijide et al. 2020). As current trend is that land uses supporting multiple ecosystem functions are replaced by oil palm monocultures (Grass et al. 2020), it is necessary to evaluate alternative management strategies in oil palm production to offset the negative impacts of oil palm expansion on ecosystem functions without sacrificing profit. One of these approaches is, besides the B11 Enrichment experiment (EFForTS - BEE), the oil palm management experiment (OPMX) which started in November 2016.

Fig. 1. The oil palm management experiment of EFForTS at PTPN IV, Jambi, Indonesia.

Current fertilization regimes result in high leaching losses of nutrients (Formaglio et al. 2020, Kurniawan et al. 2018), reducing ground water quality, whereas herbicide weed control reduces group richness of soil macro and meso fauna and community metabolism (Darras et al. 2019). Thus, the overall goal of OPMX is to look for practical solutions, namely reduced fertilization equal to nutrients exported by fruit harvest and mechanical weeding (brush cutter), which can easily be implemented by plantation owners and workers, with the aim to reduce these negative impacts on ecosystem functions while maintaining current production levels and profit.

Fig. 2. The experimental design of the oil palm management experiment of EFForTS at PTPN IV, Jambi, Indonesia.

The OPMX is situated in a large oil palm plantation of PTPN VI, a state-owned company, where also the meteorological tower is established (A03). This ongoing OPMX will continue at least until end of 2022. The experimental design is a 2 x 2 factorial experiment with two fertilization rates and two weeding methods. The treatments are: conventional fertilization rate‒herbicide, conventional fertilization rate‒mechanical weeding, reduced fertilization rate‒herbicide, and reduced fertilization rate‒mechanical weeding. Each treatment is represented by a 50 m x 50 m plot, assigned randomly within a block with 4 replicate blocks. The 16 experimental plots have a minimum distance 50 m between plots. The conventional fertilization rates are based on rates common to large-scale plantations on Acrisol soils in Jambi province (260 kg N ha-1 yr-1, 50 kg P ha-1 yr-1, and 220 kg K ha-1 yr-1) whereas the reduced rates are based on the nutrient exports by harvest (136 kg N ha-1 yr-1, 17 kg P ha-1 yr-1, and 187 kg K kg ha-1 yr-1). All treatments receive the same rates of lime (426 kg dolomite ha-1 yr-1) and micronutrients (142 kg micro-mag ha-1 yr-1 with 0.5 % B2O3, 0.5 % CuO, 0.25 % Fe2O3, 0.15 % ZnO, 0.1 % MnO and 18 % MgO), as these are the common practices in large-scale plantations on acidic Acrisol soils. Herbicide weed control applies 1.5 L glyphosate ha-1 yr-1 (split in four applications in a year) to the palm circle, and 0.75 L ha-1 yr-1 (split in two applications in a year) to the inter-row. Mechanical weeding uses a brush cutter in the same areas and frequencies. The mechanical weeding removed only the aboveground biomass, allowing fast ground cover regeneration, while the herbicide eradicated above- and belowground vegetation parts, resulting to slow regeneration of ground cover.

The plots are laid out in the same way as the core plots.

Fig. 3. Illustration of hypothetical ecosystem functions for two treatments.

Project Group A investigates palm water use (A02), climate variables (A03), nutrient response, retention, leaching and greenhouse gases A05). Project Group B focuses on plant and animal diversity as well as soil food web structure (plant diversity - B06, belowground invertebrates - B08, insect pollinators and flying vertebrates - B09. C12 evaluates the ecological-economic optimization, and the Central Tasks Project Z01 provides scientific support (monitoring of oil palm yield and growth, and canopy gap fraction).

Results will be disseminated and incorporated into Teacher education for society: Making EFForTS knowledge available for Indonesia by the Project Ö (Public Relations).

The experimental data will be compared and combined with the plot level data from the household survey carried out in Project Group C to also integrate human decision and welfare perspectives. A07, B10 and C11 contribute to the integration of the results into the overall aims of the CRC. This will allow evaluation of ecological and socioeconomic functions of oil palm management in unprecedented detail including detection of trade-offs and win-win situations.

Fig. 4. Integrated activities of sub-projects into the OPMX.