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 428 IREC Farmers' Newsletter No. 196 — Summer 2016 Petiole nitrogen results Petioles were tested in each of the treatments throughout the season. Adequate nitrogen levels should range from 20,000 to 40,000 mg/kg at 500 day degrees, 10,000 to 22,500 mg/kg at 1000 day degrees and decline to 2,500 to 10,000 mg/kg at 1500 day degrees. All of the treatments were in the adequate range through the season except the zero strips, which were always at a deficient level (Figure 3). Nitrogen fertiliser use efficiency Growers can monitor the nitrogen fertiliser use efficiency (NFUE) of their applied fertiliser with a simple calculation: NFUE = lint yield (kg/ha) ∕ applied nitrogen fertiliser (kg N/ha) To achieve the economic optimum nitrogen fertiliser rate, the yield/N fertiliser index should be between 13 and 18. If the index is greater than 18, insufficient nitrogen has been applied; if the index is well below 13, too much nitrogen has been applied. In the 2015–16 Benerembah trial, a NFUE of 11.5 was achieved, which is close to the target of 13. Nitrogen application rates could have been reduced by 30 kg N/ha to get to 13 kg lint/kg N. It is when NFUE drops into single figures that the index indicates something else in the system is reducing nitrogen efficiency. Applying more nitrogen than is required to satisfy the crop’s demand will not increase yield. Rather, growers need to assess their cropping system’s nitrogen use efficiency and determine if other factors such as irrigation management, layout and drainage times are inducing waterlogged conditions and are limiting efficient cotton production. Dowling (2016) outlines that NFUE should be benchmarked over a number of seasons as an indicator of crop performance, and to refine target yield and nitrogen application rates. Table 1 shows recommended nitrogen application rates to achieve industry target NFUE. Paddocks with a minor soil constraint would require 10% more applied nitrogen to achieve 11.7–13.0 kg lint/kg N; and paddocks with a moderate soil constraint would require 20% more applied nitrogen to achieve 10.4–11.7 kg lint/kg N. Constraints typically include soil characteristics and management practices that negatively impact nitrogen availability and efficiency, such as salinity, dispersion, sodicity, compaction and waterlogging. If these constraints are likely to lead to more than 20% yield penalty (a NFUE less than 10 kg lint/kg N), a longer-term program to overcome the constraint needs to be implemented rather than continuing to push yield against constraints with applied nitrogen. High nitrogen rates 0 5000 10000 15000 20000 25000 400 600 800 1000 1200 1400 1600 1800 Petiole nitrogen level (mg/kg) Day degrees Nitrogen treatment (kg N/ha) Zero Nitrogen treatment (kg N/ha) 147 + 0 Nitrogen treatment (kg N/ha) 147 + 100 Nitrogen treatment (kg N/ha) 247 + 0 Nitrogen treatment (kg N/ha) 0 + 247 Figure 3. Nitrogen levels of petioles of cotton plants at Benerembah, 2015–16 have the potential for higher nitrogen losses and can contribute to increasing the severity of some soil borne diseases, increased canopy management and defoliation costs. Plans for 2016–17 season The CottonInfo Regional Extension Officers will conduct more trials this coming season, with a focus on overcoming soil constraints and reducing variability in fields. Work will continue on quantifying soil mineralisation rates through the growing season. A trial looking at pix management is also being planned. Further information Kieran O’Keeffe M: 0427 207 406 E: [email protected] Further reading www.cottassist.com.au/NutriLOGIC/About.aspx Dowling. C, The Australian Cotton Grower, ‘How much N is enough for 15+ bales’?, June–July 2016, pp 32–34. Dowling. C, Impact of changes in variety and management on cotton N dynamics in SoilMate CotNPlan model, SoilMate Technical Bulletin #SMM-01, July 2016. Macdonald. B, Chang Y, Nadelko T, The Australian Cotton Grower, ‘Where does the nitrogen fertiliser end up’?, June–July 2016, pp 36–38. Table 1. Applied nitrogen rate range based on industry target of minimum NFUE of 13 kg lint/kg applied nitrogen (par) and two levels of yield constraint for irrigated cotton production (Dowling 2016) Yield target Applied nitrogen rate (kg N/ha) bales/ha kg/ha (lint) Par (13 kg lint/kg N) Minor soil constraint (11.7–13 kg lint/kg N) Moderate soil constraint (10.4–11.7 kg lint/kg N) 9 2043 157 173 189 10 2270 175 192 210 11 2497 192 211 230 12 2724 210 230 251 13 2951 227 250 272 14 3178 244 269 293 15 3405 262 288 314 16 3632 279 307 335 17 3859 297 327 356 18 4086 314 346 377 Day degrees Petiole nitrogen level (mg/kg)