Research helps growers fine tune nitrogen management
Author: Sarah Jeffrey | Date: 21 Mar 2016
Research into the rate and timing impact of nitrogen (N) application in wheat promises to help growers across northern New South Wales and southern Queensland fine-tune their fertiliser strategies this season.
Trial work conducted by the Northern Grower Alliance (NGA) and funded by the Grains Research and Development Corporation (GRDC) during 2014 and 2015 evaluated the impact of application timing on N responses as well as the fit of `enhanced’ urea products.
NGA has been heavily involved in projects focussing on N application strategies in wheat in recent years, with the aim of assisting the management of high yielding, and frequently lower protein achieving, wheat varieties such as EGA Gregory.
The 2015 trial work involved six sites identified with low soil N which were planted to EGA Gregory with row spacings of 32cm and plot lengths of 9-12 metres.
Five N application approaches were evaluated using standard urea as the nitrogen source – N disc drilled pre-plant (late March/early April), N spread on soil surface (late March/early April), N spread immediately before sowing and incorporated by sowing with narrow point tynes, N spread immediately post sowing and N spread in-crop at GS30. The application rates were 50, 100 and 200kg N/hectare (the 200kg N/ha rate included to highlight the impact from an excess of nitrogen).
NGA chief executive Richard Daniel said the rate of N applied was the main factor impacting yield and grain quality – both positive and negative – in both 2014 and 2015.
“Grain protein levels increased with nitrogen rate at all sites over the two years, however yield responses were extremely variable with significantly increased yield at two sites but with yield reductions - from all rates of nitrogen applied - at three of the sites during the two seasons.
“Whilst grain protein levels still increased with the rate of N application at all sites in 2015, grain quality was significantly reduced (screenings and test weight) in response to increasing N rate at sites where yield losses occurred. Additional grain analysis has confirmed that the yield reductions were primarily due to a reduction in grain weight.
“In both years, the trial work also found that urea spread immediately post sowing, and with no physical incorporation, provided equivalent crop responses to the same rate of urea spread and incorporated by sowing.
“Unfortunately this also applied where yield losses due to excessive nitrogen occurred. However, it is important to note that all sites did record rainfall within four weeks of sowing, with the ‘driest’ sites still receiving between 7 and 25mm of rain within 16 to 25 days after planting.”
Although simply spreading urea pre-plant or PSPE without any incorporation is not being actively promoted, Mr Daniel said the results continued to support the N volatilisation results achieved by Dr Graeme Schwenke and indicated in-crop spreading may be less risky than previously thought in the northern grains region.
“Split application of urea at 50kg N/ha drilled pre-plant or incorporated by sowing followed by 50 kg N/ha spread in-crop at ~GS30 provided at least equivalent crop responses to urea at 100kg N/ha spread and incorporated by sowing,” Mr Daniel said.
He said the results confirmed that in-crop spreading (~July) was a useful tool to capture upsides in yield and grain quality when seasons were favourable.
However he cautioned that in-crop spreading in the northern grains region was unlikely to become a standard management practice because of the variable nature of late winter and spring rain events.
The trial work has been unable to show any significant benefit from polymer coated urea products compared to the equivalent rate of nitrogen applied as urea alone at any site across a range of application rates and timings.
For more information on the NGA trial work on N management in wheat, download a copy of Mr Daniel’s 2016 Update paper from the research and development section of the GRDC website here.
Richard Daniel, CEO, Northern Grower Alliance
07 4639 5344 / 0428 657 782
Sarah Jeffrey, Senior Consultant Cox Inall Communications
GRDC Project Code NGA00004