Decomposition of oil palm empty fruit bunches in the field and mineralization of nitrogen

Abstract

Currently, most of the EFBs (empty fruit bunches) that come out of the mill as waste are used as an organic fertilizer for oil palms. An experiment was conducted to study the decomposition of EFBs applied single-layered or double-layered under oil palm field conditions, and to investigate the availability of N as a result of mineralization in 15 weeks period. The experiment was set up using lysimeters filled with topsoil of the area (an Oxisol). The EFB biomass had reduced to 50% of initial DM (dry matter) weight in 7.5 weeks in the double-layered and 8.5 weeks in the single-layered EFB. After 15 weeks only 32% and 29% of the EFB initial dry matter weights were left in the single-layered and double- layered, respectively. The C/N ratios had reduced from 57 to 31 in the single-layered and from 55 to 24 in the double-layered EFB. About 50% of the initial EFB N was left after 15 weeks. The total nitrogen in the soil had increased from 0.23% to 0.27% in the single-layered and 0.28% in the double-layered EFB. The soil pH increased by 2-3 units. However, very small amounts of mineral N were found in the leachate indicating that in the 15 week period little mineralized N was available for plant uptake. This was probably due to immobilization by microbes, retention by the EFBs together with moisture, and also lost through NH3 volatilization and denitrification.