Oil palm management experimentResults from Phase 1 have shown that a major reason why oil palm is currently an attractive land-use option is because of its reliance on inputs such as herbicides and fertilizers instead of labour. Unfortunately, the economic benefits are in strong contrast with most ecosystem function indicators and together with rubber monocultures, oil palm ranks lowest on indictors, such as naturalness, species richness of plants and animals, carbon stocks and nutrient leaching losses (Clough et al., 2016; see also Dislich et al. 2015). Since the current trend is that land uses supporting multiple ecosystem functions are replaced by more oil palm and rubber monocultures, it is necessary to evaluate alternatives to offset the negative impact of oil palm expansion on ecosystem services. One of these approaches is, besides the B11 Enrichment experiment, the oil palm management experiment which was set up in 2017.
Since current fertilizer application practices result in high leaching losses of nutrients (Kurniawan et al., 2016; https://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0028-8706-8) leading to poor ground water quality, and weed control is often done through application of herbicides. Therefore, the overall goal of this experiment is to evaluate whether alternatives to current oil palm nutrient and weed management can contribute to reducing the negative impact of this land-use system on ecosystem services while maintaining current production levels.
The management experiment is situated in a large oil palm plantation of PTPN VI, a state-owned company, where also the meteorological tower is established (A03). The experiment started in 2017 and will continue at least until end of 2019. The experimental design is a 2 x 2 factorial experiment with four replicates. Treatments are (1) conventional fertilizer rate vs. moderate fertilization rate (i.e., at compensation level) and (2) conventional weed control (by herbicides) vs. mechanical weed control (by weed whacking). The 16 experimental plots each span 50 x 50 m and the minimum distance between plots is 50 m. The plots are laid out in the same way as the core plots.
Project Group A investigates palm water use (A02), climate variables (A03), soil carbon and nutrient stocks as well as nutrient turnover and losses and free-living nitrogen fixation (A04, A05). Project Group B focuses on plant and animal diversity as well as soil food web structure (prokaryotes - B02, terrestrial plants - B06, oil palm root health - B07, soil decomposers - B08, insect pollinators and flying vertebrates - B09 and oribatid mites - B13). The Central Tasks Project Z01 monitors oil palm yield and growth, as well as canopy gap fraction. 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, C04 and C07 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.