Abstracts

John Smith¹, Mike Bell²

¹ NSW Department of Primary Industries, 2198 Irrigation Way East, Yanco, NSW, 2703, www.industry.nsw.gov.au, john.smith@dpi.nsw.gov.au

² The University of Queensland, School of Agriculture and Food Sciences, Gatton, QLD, 4343

Abstract

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 (N_RE).  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.  N_RE 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 N_RE compared to flood.  The N_RE at maximum lint yield was 6-28% higher than that achieved using farm practice at each site.