Nutrient response efficiency, soil greenhouse gas fluxes, and nutrient leaching losses from a large-scale oil palm plantation under conventional and reduced management practices

Abstract

The area of oil palm plantations has expanded rapidly in the tropics over the past few decades due to the high demand for palm oil and the considerable economic benefits. Oil palm is playing a vital role in the global vegetable oil supply and regional economic development.However, the conventional management with high fertilization rates and herbicide application from oil palm plantations brings various environmental concerns. Reduced fertilization with mechanical weeding is one of the proposed practical alternatives to conventional management, which has the potential to improve multiple ecosystem functions without sacrificing production and profit. A field full factorial oil palm management experiment (OPMX) with two fertilization rates (conventional and reduced fertilization, equal to nutrients exported via fruit harvest) and two weeding methods (herbicide and mechanical) was conducted since 2016 in a 15-year-old, large-scale oil palm plantation in Jambi, Indonesia. This thesis consists of three studies that were conducted during 3-4 years of the OPMX experiment. The main objectives were to assess differences in yield and nutrient response efficiency (study 1), soil greenhouse gas (GHG) fluxes (study 2), and nutrient leaching losses (study 3) between conventional management (conventional fertilization with herbicide weeding) and reduced management (reduced fertilization with mechanical weeding) in this mature large-scale oil palm plantation.In the first study, the oil palm fruit yield, soil net N cycling rates, and soil mineral N stocks were measured. Nitrogen response efficiency (NRE), partial factor productivity of applied P (PFPP) and K (PFPK) fertilizer, and profit were calculated. The results showed that yield and soil net N cycling rates were comparable between conventional and reduced management. Reduced fertilization decreased soil mineral N stocks in 50-150 cm depth interval. Compared to conventional management, reduced fertilization with mechanical weeding increased NRE by 68%, PFPP by 200%, PFPK by 22%, and profit by 15%.In the second study, soil CO 2 , N 2 O, and CH 4 fluxes were measured monthly for one year from three management zones, and global warming potential was calculated in this oil palm plantation. We found that soil GHG fluxes did not differ between conventional and reduced management practices. Annual soil GHG fluxes were 5.