Impacts of empty fruit bunch applications on soil organic carbon in an industrial oil palm plantation.

Extensive oil palm plantations have often resulted in the decrease of soil organic carbon (SOC). Several options exist to counter this, such as recycling empty fruit bunches (EFB) as a soil amendment. However, the extent to which EFB increase SOC has been disputed. Since EFB could also be used as a climate change mitigation tool, it is necessary to truly understand their impact on SOC. The investigation of the impact of nine EFB treatments (differing in frequency and application rates) on a 27-year-old large-scale experiment (Lampung, Sumatra, Indonesia) revealed that, while EFB impacts are heterogeneous throughout the plantation, they can positively affect total SOC and permanganate oxidisable carbon (POX-C) both at shallow and deep depths (measured up to 100 cm). POX-C was closely correlated to SOC, but showed significant increases compared to the untreated control in all treatments, while total SOC was only increased in a few treatments with small and frequent rates of EFB application. Overall, between 12 (±16) and 56 (±12) t ha-1 of carbon were sequestered under the harvesting path after 21 years. Focussing on the mineral nutrition value of the EFB, oil palm companies apply a rate of 60 t of EFB every second year for their commercial production, and the analysis of three commercial plots showed that the commercial rate only increased POX-C while it had no effect on the total SOC and SOC stocks. It seems obvious that a change of paradigm is necessary to consider EFB recycling as a new management perspective, where the potential for carbon sequestration becomes an important variable for climate change mitigation besides the initial objective of integrating EFB application into the fertiliser management plan of a plantation.

Replanting of first-cycle oil palm results in a second wave of biodiversity loss.

Conversion of forest to oil palm plantations results in a significant loss of biodiversity. Despite this, first-cycle oil palm plantations can sustain relatively high biodiversity compared to other crops. However, the long-term effects of oil palm agriculture on flora and fauna are unknown. Oil palm has a 25-year commercial lifespan before it must be replanted, due to reduced productivity and difficulty of harvesting. Loss of the complex vegetation structure of oil palm plantations during the replanting process will likely have impacts on the ecosystem at a local and landscape scale. However, the effect of replanting on biodiversity is poorly understood.Here, we investigate the effects of replanting oil palm on soil macrofauna communities. We assessed ordinal richness, abundance, and community composition of soil macrofauna in first- (25- to 27-year-old) and second-cycle oil palm (freshly cleared, 1-year-old, 3-year-old, and 7-year-old mature).Macrofauna abundance and richness drastically declined immediately after replanting. Macrofauna richness showed some recovery 7 years after replanting, but was still 19% lower than first-cycle oil palm. Macrofauna abundance recovered to similar levels to that of first-cycle oil palm plantations, 1 year after replanting. This was mainly due to high ant abundance, possibly due to the increased understory vegetation as herbicides are not used at this age. However, there were subsequent declines in macrofauna abundance 3 and 7 years after replanting, resulting in a 59% drop in macrofauna abundance compared to first-cycle levels. Furthermore, soil macrofauna community composition in all ages of second-cycle oil palm was different to first-cycle plantations, with decomposers suffering particular declines.After considerable biodiversity loss due to forest conversion for oil palm, belowground invertebrate communities suffer a second wave of biodiversity loss due to replanting. This is likely to have serious implications for soil invertebrate diversity and agricultural sustainability in oil palm landscapes, due to the vital ecosystem functions that soil macrofauna provide.