Losses of nitrogen fertiliser under oil palm in Papua New Guinea: 2. Nitrogen transformations and leaching, and a residence time model*
Murom Banabas A B C , David R. Scotter B and Max A. Turner BA Papua New Guinea Oil Palm Research Association, PO Box 28, Popondetta, Papua New Guinea.
B Institute of Natural Resources, Massey University, Palmerston North, New Zealand.
C Corresponding author. Email: murom.banabas@pnp.pngopra.org.pg
Australian Journal of Soil Research 46(4) 340-347 https://doi.org/10.1071/SR07174
Submitted: 1 November 2007 Accepted: 28 April 2008 Published: 23 June 2008
Abstract
Nitrogen fertiliser is an expensive input to oil palm in Papua New Guinea, and prone to leaching due to the about 3000 mm/year of rainfall. Transfer function theory is used to describe this leaching, and to devise ways of reducing it. Four variants of a leaching experiment were conducted at 2 sites to parameterise and check the theory. The experiment involved the application of ammonium chloride to an area of 25 m2, and then from 6 days to 5 months later taking soil samples at 200-mm intervals down to 2 m depth and analysing them for chloride, ammonium, and nitrate. Background concentrations were obtained by contemporaneous sampling nearby. In one variant of the experiment 353 mm of rain in 6 days moved nearly half the applied nitrogen to below 400 mm depth. Nitrification was rapid, with ammonium half-lives ranging from 2 to 16 days once the soil was wet. The theory is used to demonstrate how the fertiliser residence time in the root-zone can be increased by applying it in certain months and about 2 m from the trunk where there is less throughfall.
Additional keywords: transfer functions, stochastic convective flow.
Acknowledgments
The European Union funded the work (Stabex 4.22). Dr Michael Webb provided useful discussion during the planning stages, and Dr Neil Macgregor assisted with the nitrification studies. Competent and dedicated technical support was provided by Papua New Guinea Oil Palm Research Association staff in the field, and by Massey University Institute of Natural Resources staff in the laboratory. An anonymous referee provided some useful criticism.
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