33 IREC Farmers' Newsletter No. 198 — Spring 2017 three defoliations compared with two in the standard and long deficit treatments (i.e. 14 or 19 day irrigation schedules). There was a yield increase with 270 kg N/ha compared with 180 kg N/ha but there was no interaction between irrigation and nitrogen rate for yield. The data highlights that in the 2016–17 season, short irrigation deficits optimised cotton yield but needed to be carefully balanced against crop production costs, fertiliser and chemical use that reduce efficiencies, risk associated with delayed harvest date, and cotton prices. With flexible water control that is now be available in automated systems, further efficiencies may be achieved by applying short deficits at critical growth periods such as flowering and boll filling, and longer deficits at other times. Further testing with such scenarios will be considered in the 2017–18 season. 0 2 4 6 8 10 12 Short 180 Short 270 Standard 180 Standard 270 Long 180 Long 270 Figure 2. Cotton lint yield from the different irrigation x nitrogen treatments at Darlington Point, 2016–17. Table 1. Management and maturity of different irrigation deficit x nitrogen treatments at Darlington Point, 2016–17. Irrigation x fertiliser strategy No. of pix No. of defoliations 60% open boll date Harvest date Short 180 N 3 3 25 Apr 2017 30 May 2017 Short 270 N 3 3 27 Apr 2017 30 May 2017 Standard 180 N 3 2 21 Apr 2017 11 May 2017 Standard 270 N 3 2 24 Apr 2017 11 May 2017 Long 180 N 3 2 18 Apr 2017 4 May 2017 Long 270 N 3 2 17 Apr 2017 4 May 2017 Irrigation strategy x nitrogen management Bales/ha Figure 1. Continuous logging of soil tension (kPa) illustrates the three irrigation schedules imposed on cotton at Darlington Point, 2016–17. Soil tension (kPA) 0 -20 -40 -60 -80 -100 3 Jan 2017 17 Jan 2017 31 Jan 2017 14 Feb 2017 28 Feb 2017 14 Mar 2017 28 Mar 2017 11 Apr 2017 25 Apr 2017