Effect of N and K Fertilizers on Nutrient Leaching and Groundwater Quality under Mature Oil Palm in Sabah during the Monsoon Period

Abstract

Abstract: Problem statement: The oil palms are mainly grown in the humid tropics with high rainfall. Soluble Nitrogen (N) and Potassium (K) fertilizers are commonly required by the oil palm plantations to maximize palm productivity due to the highly weathered soils with low fertility. Thus, leaching losses of N and K nutrients may be unavoidable and these nutrients may move further downward and eventually cause groundwater pollution. This study reports the leaching of N and K nutrients in a mature oil palm field as affected by fertilizer rates and soil depths and its effect on groundwater quality during the monsoon period in Tawau, Sabah. Approach: The sources of N and K fertilizer were Ammonium Chloride (AC) and Muriate of Potash (MOP), respectively. Soil water samplers were installed at depths of 30, 60 and 120 cm in four fertilizer treatments, namely, N0P0K0 (Control plot, no N and K), N0P2K1 (K1 = 4.5 kg MOP palm−1 year−1), N1P2K1 (N1 = 3.75 AC kg palm−1 year−1) and N1P2K0. Three replications were used in the experiment. Monitoring wells were installed in the above treatment plots and in another treatment, N2P2K1 (N2 = 7.5 kg AC palm−1 year−1) to investigate the effect of excessive N rate on groundwater quality. Samplings were done at 15 day intervals for a duration of 150 days from October 2008-February 2009 to cover the entire monsoon period in Sabah. Water samples were analyzed for NH4-N by automated phenate method, NO3-N + NO2-N and NO2-N by