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 4218 IREC Farmers' Newsletter No. 196 — Summer 2016 nitrogen was applied up-front and the shorter irrigation deficit was used (Figure 1). Maize grain yield was strongly influenced by poor establishment in three bays, which was caused by very wet conditions as a result of rain shortly after planting following pre-irrigation of the field. This meant that three of the eight bays were not harvested as part of the trial, eliminating the second replicate in all but one treatment and precluding any statistical analysis of grain yield. For the bays that were harvested, grain yield was higher with more frequent irrigation or shorter deficit, i.e. 10.1 t/ha with 30 kPa deficit, compared with standard practice deficit, i.e. 8.7 t/ha with 45 kPa deficit. A grain yield of 11.1 t/ha was achieved using the ‘up-front’ nitrogen management strategy compared with 8.8 t/ha with the ‘split’ strategy. Soil moisture monitoring during the experiment highlighted some issues regarding the suitability of the standard irrigation practice for the soil type at the site. Although it is only one year’s data, it appears that the short irrigation deficit treatment may better suit the red clay loam soil at the site. Matric potential measurements at the 30 and 45 cm soil depths showed that from the end of January until harvest, the irrigation applications in the standard treatment were not refilling the soil water profile (Figure 2 and Figure 3). Given this result, it is considered more likely that yield was limited in the standard treatment by water stress during the season rather than the short irrigation deficit treatment providing a higher grain yield. Management to lift yield It is important to note that this is only the first year of a three-year trial and that the results from the 2015–16 season were strongly affected by wet soils at establishment. Despite these problems, there was as improvement in crop nitrogen uptake and grain yield when 75% of the predicted crop fertiliser nitrogen requirement was applied up-front, compared with only 40% applied up-front. This result provided the project with some confidence to continue investigation into the impact of these nitrogen management strategies in irrigated maize production. The result from the irrigation treatment highlighted the importance of soil moisture monitoring. Upon first inspection it appears that crop nitrogen uptake and grain yield benefit from a shorter irrigation deficit. However, monitoring of the soil moisture status showed that the irrigation application in the standard treatment of the experiment was not applying enough water and this resulted in a reduction in crop nitrogen uptake and grain yield due to water stress. During the 2016–17 season, new tools such as multi-spectral and thermal imagery will also be used to more precisely assess the temporal and spatial variability within bays caused by the irrigation and nitrogen treatments applied. Acknowledgements The project is supported by funding from the Australian Government Department of Agriculture and Water Resources as part of its Rural R&D for Profit Programme, the Cotton Research and Development Corporation and the Rural Industries Research and Development Corporation. The contribution of Mr Ray Thornton for the time and effort in conducting the trial and Rubicon for water monitoring is gratefully acknowledged. Contact details John Smith Research Officer, Irrigation M: 0472 060 597 E: [email protected] 0 40 80 120 160 200 28-Nov-15 12-Dec-15 26-Dec-15 9-Jan-16 23-Jan-16 6-Feb-16 20-Feb-16 5-Mar-16 19-Mar-16 2-Apr-16 16-Apr-16 Matric potential (kPa) Average of 45 cm depths 30 kPa 45 kPa 0 40 80 120 160 200 28-Nov-15 12-Dec-15 26-Dec-15 9-Jan-16 23-Jan-16 6-Feb-16 20-Feb-16 5-Mar-16 19-Mar-16 2-Apr-16 16-Apr-16 Matric potential (kPa) Average of 30 cm depths 30 kPa 45 kPa Figure 2. Average matric potential at 30 cm depth for the two irrigation treatments. The short deficit (30 kPa) irrigation treatment is the solid blue line and the standard irrigation deficit (45 kPa) is the dashed yellow line. Figure 3. Average matric potential at 45cm depth for the two irrigation treatments. The short deficit (30 kPa) irrigation treatment is the solid blue line and the standard irrigation deficit (45 kPa) is the dashed yellow line. Figure 1. The interaction between irrigation management (standard and short irrigation deficit) and nitrogen management (up-front and split) in maize. Applying more nitrogen upfront with a shorter irrigation frequency significantly increased crop nitrogen uptake in the 2015–16 season. 0 50 100 150 200 250 standard short irrigation deficit standard short irrigation deficit Up-front 75/25 Split 40/60 Crop nitrogen uptake (kg N/ha) Up-front 75/25 Split 40/60 Crop nitrogen uptake (kg N/ha) Average of 30cm depths Average of 45cm depths Matric potential (kPa) Matric potential (kPa)