John Smith1, Mike Bell2
2 The University of Queensland, School of Agriculture and Food Sciences, Gatton, QLD, 4343
Lint yield of irrigated cotton is typically responsive to the application of fertiliser nitrogen (N). However, the applications of high rates of fertiliser N that exceed crop requirements result in unnecessarily low nitrogen recovery efficiency (NRE). Three field experiments with eight N application rates were established across overhead and flood-furrow irrigation systems to determine N response curves for lint yield in irrigated cotton. Lint yield was considered to be at its maximum where there was no further statistical increase from additional N application, this occurred between 145-245 kg/ha of total N supply (mineral N at planting + applied fertiliser N) with plant N uptake levels of 134-170 kg/ha. NRE was determined by dividing crop N uptake at defoliation by the total N supply. Where starting soil N levels were similar, overhead irrigation offered 34% higher NRE compared to flood. The NRE at maximum lint yield was 6-28% higher than that achieved using farm practice at each site.