Are responses to nitrogen fertiliser predictable under similar conditions?

Much attention in nutrient-management research, development and extension (RD&E) has recently focused on improving nitrogen-use efficiency (NUE) in sugarcane production in Australia. Although these activities provide potential solutions to nitrogen (N) management issues facing the Australian industry, they appear to have resulted in perceptions that yield responses to applied N on particular soils and in particular circumstances are precise and highly predictable. This paper reports on an investigation aimed at questioning the validity of these perceptions using the results of two trials with different rates of N conducted on similar soils in the same region during the same seasons and covering the same ratoon crops. The trial results indicated that, although sugarcane yields may be similar across sites and crops, differences in optimum N rates occurred due to differences in soil properties and seasonal rainfall patterns. Although the SIX EASY STEPS N guidelines for the two trial sites remain appropriate, actual N rates determined for the sites were variable. This suggests that, although the SIX EASY STEPS N guidelines remain appropriate for circumstances in general, the inherent and associated variability needs to be recognised. The N guidelines are therefore neither precise nor highly predictable for specific circumstances. This is particularly important, if growers and/or their advisors were to consider reducing N rates below the SIX EASY STEPS guidelines. Key words Sugarcane, yield response, nitrogen management, soil type, climatic conditions