Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 427 IREC Farmers' Newsletter No. 196 — Summer 2016 Nitrogen (N) was applied as urea in single or split applications. The treatments were at the following rates: • 247 kg N/ha + 0 • 147 kg N/ha + 0 • 147 kg N/ha + 100 kg N/ha • 0 + 247 kg N/ha • Zero (control). Split application treatments were side-dressed with urea 10 December (first square). Nitrogen levels were monitored in crop with four petiole tests. A comprehensive soil test was done pre-season with no soil nutrient problems found at the site. Pre-season soil nitrogen tests were taken in August to a depth of 60 cm. Nutrilogic (available on the Cottassist website) was then used to determine fertiliser rates. The Nutrilogic program provides a nitrogen rate recommendation for optimal crop nutrition based on soil test results, soil type and any soil constraints such as compaction. Soil samples were taken from treatments throughout the season to help provide a calibration for a potential soil mineralisation test for the cotton industry. The irrigation water applied for the first two irrigations was monitored for nitrogen levels using nitrate test strips. The crop was picked 26 April 2016 and yielded two modules in each replicate. Modules were weighed using the CSD bale trailer. Gin turnout percentages from the Auscott gin at Hay were applied to individual modules. Samples from modules were tested for quality factors at Australian Classing Services at Narrabri. Seed samples were also tested for nitrogen levels. Statistical analysis was carried out by Oliver Knox, University of New England and technical input was provided by Chris Dowling, Back Paddock. Yield results The zero strips were visible throughout the season with shorter bushes and less leaf material (see picture), so it was surprising to see that the zero strips yielded up to 88 % of the highest yield (Figure 1). Previous nitrogen work has reported that 60–70% of nitrogen used by the crop is contributed by the soil. This highlights that soil mineralisation is key for a successful season so maintaining a large soil organic nitrogen pool is critical to maintaining production. Access to this nitrogen pool can be compromised by soil constraints such as compaction and sodicity, therefore overcoming these problems results in more efficient production. The yield results showed that the 247 + 0 and 0 + 247 treatments were significantly different to the other treatments (Figure 1). These treatments yielded half a bale better than the split application. Split application however is the most common application method in the industry and is used by over 90% of growers. It is a risk management strategy that avoids having large amounts of fertiliser nitrogen vulnerable to losses from waterlogging events, such as large rainfall events occurring after an irrigation. Over the three years of trials there has been a change in the cooperators’ attitude to nitrogen management, with the cooperators now comfortable to reduce total nitrogen application rates from around 350 kg N/ha back to around 250 kg N/ha in fallow fields. Their confidence is reinforced by a nitrogen rate trial at Warren in 2015–16 where there was no significant yield increase from nitrogen applications of 180 kg N/ha up to 400 kg N/ha (Figure 2). 11.04 11.7 12.09 12.47 12.54 10.0 10.5 11.0 11.5 12.0 12.5 13.0 Zero 147 + 0 147 + 100 247 + 0 0 + 247 Lint yield (b/ha) Nitrogen treatments (kg N/ha) Figure 1. Lint yield of nitrogen treatments at Benerembah, 2015–16 LSD = 0.3 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 180 240 280 320 360 400 Lint yield (b/ha) Nitrogen treatments (kg N/ha) Figure 2. Yield of nitrogen treatments at Warren, 2015–16 An aerial view of the trial site at Benerembah clearly shows the zero nitrogen treatments in the randomised and replicated layout. Zero treatment on the right (5 rows) and the 247 + 0 treatment on the left (5 rows) showing a difference in growth between treatments. Nitrogen treatments (kg N/ha) Nitrogen treatments (kg N/ha) Lint yield (b/ha) Lint yield (b/ha)