Trials look to answer nitrogen questions
GroundCover™ Issue: 135 July - August | Author: Alistair Lawson
Mid-row banding (MRB) nitrogen fertiliser in-season is showing promise as an alternative practice to top-dressing, offering the potential to improve yields and crop nitrogen use efficiency.
Trials conducted by Agriculture Victoria in 2016 and 2017, as part of a bilateral research agreement with the GRDC, compared MRB with other options for in-season application of nitrogen fertiliser.
Potential benefits of MRB include increased yields and/or grain protein, a reduction in nitrogen losses through volatilisation, slowing the nitrification of ammonium – possibly reducing other losses – and increasing root growth surrounding the fertiliser band to improve crop uptake of applied nitrogen.
The trials, conducted in the Wimmera and Mallee regions of Victoria, have tested two rates (25 kilograms of nitrogen per hectare and 50kg/ha) using the following application methods:
- mid-row banded: nitrogen placed at 35 to 50 millimetres depth into every second inter-row using a twin disc opener;
- mid-row surface: nitrogen placed on the surface of every second inter-row;
- streaming spray: nitrogen applied using streaming nozzles spaced evenly across the plot;
- flat-fan spray: nitrogen applied using air-induction nozzles to produce extra-coarse droplets; and
- top-dressed granular urea.
Agriculture Victoria regional research agronomist Ashley Wallace says in most cases MRB increased wheat yields and/or grain protein compared with where nitrogen was surface-applied.
“In 2016, MRB produced the highest average yield at both sites – Quambatook and Longerenong. However, this difference was only statistically significant at Quambatook,” he says.
“At Ultima in 2017 the mid-row surface and flat-fan treatments resulted in significant yield reductions of approximately 0.1 tonnes per hectare in absolute terms, while the mid-row banding treatment significantly increased protein compared to all other methods, by 0.5 to 1 per cent.
“At Longerenong in 2017, the streaming spray treatment resulted in the highest yield. However, this was not significant compared to plots that received no additional nitrogen fertiliser.”
In regard to nitrogen use efficiency, previous studies have shown that, on average, Australian grain crops take up 44 per cent of nitrogen applied in a season.
Mr Wallace says results from the 2016 trials indicated mid-row banding in-season has the potential to increase crop uptake of fertiliser nitrogen well beyond typical rates.
“At Quambatook in 2016, crop uptake increased from approximately 42 per cent of the nitrogen applied to 63 per cent, and at Longerenong this figure increased from approximately 54 per cent to 78 per cent when comparing mid-row banding to mid-row surface or streaming applications,” he says.
“By improving crop uptake of applied nitrogen, this also resulted in a significant reduction in nitrogen lost to the environment, shown by the proportion of applied nitrogen not present either in the soil or crop at harvest.”
Mr Wallace says one of the reasons growers might consider MRB nitrogen in-season is the potential to reduce losses of nitrogen as volatilised ammonia in situations where rainfall following the application is low.
While results to date are very encouraging, further verification of results will be undertaken in 2018. Mr Wallace says adoption of MRB in-season will require consideration of a range of practical and economic factors.
“This includes the ability to apply nitrogen inter-row at a given row spacing and stubble load, speed of operation, cost of capital and ongoing operating costs, as well as unforeseen impacts such as the potential for increased weed germination following inter-row soil disturbance,” he says.
GRDC Research Code DAV00143
0429 935 400
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