Since 1992, experiments to validate the Decision Support System CottonLOGIC have been conducted. These experiments have focused on insect management and have been located on commercial cotton farms in the upper and lower Namoi Valleys. During the 1998/99 and 1999/00 seasons experiments were conducted on commercial cotton farms within a wider range of regions (Table I). The reason for conducting experiments on commercial farms is to test the capabilities of CottonLOGIC in a range of environments that represent a commercial system in 1998, the NutriLOGIC module was incorporated into CottonLOGIC. This system informs the user of the need for nitrogen (N) fertiliser for a given field or cotton crop based on soil or petiole nitrate analysis. This paper presents the results of two years of validation and discusses the field performance of NutriLOGIC and the current limitations of its use.