The oil palm empty fruit bunch (EFB) is one of the major waste products of the oil palm industry and is currently used as an organic mulch in young and mature oil palm plantations. A field experiment was set up to monitor EFB decomposition and N and K release for a period of 10 months with the EFB placed in single or double layers stacked along mature oil palm interrows with and without inorganic N and K fertilizers. The quantity of EFB applied was 37.5 t ha^-1 applied in a single layer and 75 t ha^-1 applied in a double layer. N was applied as ammonium sulphate and K as muriate of potash at three rates of 0, 3.5 and 7.0 kg fertilizers palm^-1 yr^-1. The frequency of fertilizer application was once and three times per year. Random samplings of EFB were taken from the single layer, and from the top and bottom layer of the double layer treatment and dry weights, N and K concentrations determined.

The EFB dry matter loss followed an exponential model. There was a 50% loss in dry matter in the initial three months and 70% dry matter loss after eight months. The single layer EFB decomposed faster than the double layer top or bottom. Addition of inorganic N fertilizer enhanced significantly dry matter loss in the single layer EFB. Inorganic K fertilizer application did not significantly affect EFB decomposition for all treatments. Release of EFB-N was not detected during the 10-month period of the study. Release of EFB-K was very rapid during the initial stages of decomposition, with 90% of it released after six months of decomposition. At 10 months, more than 99% of EFB-K and been released.