Abstract Sugarcane crop residues (‘trash’) have the potential to supply nitrogen (N) to crops when they are retained on the soil surface after harvest. Farmers should account for the contribution of this N to crop requirements in order to avoid over-fertilisation. In very wet tropical locations, the climate may increase the rate of trash decomposition as well as the amount of N lost from the soil–plant system due to leaching or denitrification. A field experiment was conducted on Hydrosol and Ferrosol soils in the wet tropics of northern Australia using 15 N-labelled trash either applied to the soil surface or incorporated. Labelled urea fertiliser was also applied with unlabelled sur- face trash. The objective of the experiment was to investigate the contribution of trash to crop N nutri- tion in wet tropical climates, the timing of N miner- alisation from trash, and the retention of trash N in contrasting soils. Less than 6% of the N in trash was recovered in the first crop and the recovery was not affected by trash incorporation. Around 6% of the N in fertiliser was also recovered in the first crop, which was less than previously measured in temperate areas (20–40%). Leaf samples taken at the end of the sec- ond crop contined 2–3% of N from trash and fertilizer applied at the beginning of the experiment. Although most N was recovered in the 0–1.5 m soil layer there was some evidence of movement of N below this depth. The results showed that trash supplies N slowly and in small amounts to the succeeding crop in wet tropics sugarcane growing areas regardless of trash placement (on the soil surface or incorporated) or soil type, and so N mineralisation from a single trash blanket is not important for sugarcane produc- tion in the wet tropics. Keywords Crop residue Æ 15 N Æ Mineralisation Æ Soil organic matter Æ Decomposition Æ Mulch Æ Ammonium Æ Leaching Æ Incorporation Introduction Sugarcane crops typically obtain only 20–40% of the nitrogen (N) they require from fertiliser, and as much as 60% of fertiliser N may be lost from the soil–crop system (Vallis et al. 1996) through leaching, runoff and denitrification. While some fertiliser N remaining in the soil is likely to be used E. A. Meier Æ P. J. Thorburn Level 3, Queensland Biosciences Precinct, CSIRO Sustainable Ecosystems, 306 Carmody Road, St Lucia Qld 4067, Australia M. K. Wegener Æ K. E. Basford Æ E. A. Meier (&) The University of Queensland, Brisbane Qld 4072, Australia e-mail: elizabeth.meier@csiro.au Tel.: +61-7-3214-2316 Fax: +61-7-3214-2308 Nutr Cycl Agroecosyst (2006) 75:101–114 DOI 10.1007/s10705-006-9015-0 123 ORIGINAL PAPER The availability of nitrogen from sugarcane trash on contrasting soils in the wet tropics of North Queensland Elizabeth A. Meier Æ Peter J. Thorburn Æ Malcolm K. Wegener Æ Kaye E. Basford Received: 28 October 2005 / Accepted: 10 March 2006 / Published online: 9 May 2006 Ó Springer Science+Business Media, Inc. 2006