2006 Nitrogen Trial


Summary
This trial aimed to determine if any benefit could be derived from in-crop deep N testing.  Unfortunately, only 65mm of in-crop rain was received, with only 3mm occurring after topdressing.  As a result, no yield data was obtained from the trial site.  However, it is hoped to repeat the trial next year, in addition to sampling the 2006 trial site to examine residual fertiliser levels.


Trial Aims and Design
Split applications of nitrogen (N) between sowing and topdressing have several agronomic and risk management advantages. Agronomically, this method supplies some N under the ground at sowing (least loss to the environment) and some at a time when plant demand is highest (topdressing).  Furthermore, due to lower starter fertiliser rates at sowing, this method makes the sowing process more efficient and timely. Split applications enable growers to maximise profits in variable climates by reducing up-front fertiliser costs and matching inputs to crop demand.

Peak N requirement for cereals generally occurs at Zadocks 31-39. At this time N use is at its highest efficiency. Determining if soil N levels are adequate at this time requires significant planning and some guesswork.  It is often determined by N budgeting at sowing, with some crude allowances made for mineralisation, plant available water, plant root depth and estimated N availability from pre-sowing soil tests at depth, to name just a few. This project aimed to investigate the use and timing of in-crop deep N testing to assist in decision making for application rates and timing of topdressing to maximise potential crop yield and quality (protein).

This field trial aimed to demonstrate to growers the relationship between in-crop deep N levels and application of topdressed N and their effect on potential yield, protein and gross margin.  The trial design is demonstrated below:

Starting Rate

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Topdress Rate

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Topdress Rate

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The trial was a randomised plot design replicated three times across the trial area.  The plots that did not receive any urea at sowing are designated in shades of blue.  Those that were pre-drilled with 50kg urea are represented by the orange/red areas.  Topdressing then occurred at three different rates - 0kg/ha, 50kg/ha and 100kg/ha - within those starting rate plots.  The darker the shade of colour, the greater the rate.  Therefore, it can be seen that the three plots of the darkest blue colour represent a pre-drilling rate of 0kg/ha and a topdressing rate of 100kg/ha.  The plot areas are one width of the airseeder (12 metres) and run the length of the paddock (approximately 1,200m), giving plot areas of approximately 1.4ha.

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IMAG Home Page Summary of IMAG-GRDC Projects 2006 Nitrogen Trial 2006 Disc versus Tine Machine 2006 Precision Planting for Disease Management

A summary of the main aspects of the trial are as follows:

Paddock History: Wheat in 2005, Canola in 2004 and pasture prior to that.  Sampling of stubble indicated low levels of Crown Rot and no detectable Common Root Rot, minimising interference from these pathogens.
Date Trial Area First Deep-N Tested: 26 June 2006
Date Sown: 9 July 2006
Variety: Lang at 50kg/ha.  Crown Rot - 5, Common Root Rot - 6, Stripe Rust - 5, Yellow Leaf Spot - 4, Root Lesion Nematode - 4; NSW DPI ratings.  In short, Lang has a good tolerance to most likely problems, therefore less potential impact on the trial.
Starter Fertiliser: 100kg/ha MAP.  50kg/ha urea pre-drilled on appropriate plots.
Equipment Used: 12m NDF precision seeder with disc and tine delivery assemblies, pulled by a 285hp John Deere tractor.  MAP was placed using the tine, followed by the seed sown with the disc.  For more information, visit www.ndf.com.au.
Date Plots Deep-N Tested: 6 September 2006
Date Topdressed: 9 September 2006
In-Crop Spraying: 12 September - 1L/ha MCPA LVE 500, 5g/ha Ally 600, 100mL/100L Wetter 1000 at 50L/ha

The rainfall received at the site is as follows:

1 July 0.4 4 August 7.0 4 September 2.0 The total amount of rain received from 1 December 2005 to 30 June 2006 was 116mm.  Let's use some very broad assumptions, such as all fallow moisture was stored with 40% efficiency, and the crop converted available moisture at an efficiency of 15kg/mm.  Using the French-Schultz model and an evapo-transpiration loss of 110mm, we would expect the crop to essentially have no yield^.  This corresponds to the fact no yield was obtained off the trial area.
3 July 0.8 6 August 0.2 7 September 4.0
10 July 0.2 25 August 4.0 8 September 0.2
15-19 July 26.2 26 August 0.2 10 September 3.0
23-26 July 11.6 31 August 3.0 19-22 October 1.2
TOTAL 39.2mm 14.4mm 10.4mm
TOTAL IN-CROP RAIN RECEIVED = 64.8mm
^ French-Schultz model: (in-crop rain + available fallow moisture - 110) x 15kg/ha/mm ÷ 1,000 = expected yield in t/ha
                                      (64.8 + (116 x 40%) - 110) x 15 ÷ 1000 =  0.02t/ha

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Results
The entire trial area was extensively sampled on 9 July, using a pneumatic soil corer to take soil samples to 90cm.  12 cores were taken over the trial site, and the samples homogenised and subsampled.  Results were sent to SoilTec Laboratories (a NATA accredited facility) and nitrate levels calculated.  A reading of 9.2mg/kg was returned, which equates to 116kg/ha of available N (assuming a soil bulk density of 1.4).  This was higher than anticipated and higher than desired for a trial attempting to examine differences in N levels.  It is thought that the warm, moist conditions in the spring of 2005 created conditions conducive to high nitrate production.

The second set of samples was collected on 6 September 2006 (mid-tillering), with 6 cores taken per treatment area.  The results are as follows:
 
TREATMENT Rep 1 (kg/ha N) Rep 2 (kg/ha N) Rep 3 (kg/ha N) Average
0kg/ha at sowing 63 139 103 102kg/ha N
50kg/ha at sowing 112 88 111 104ka/ha N

Obviously, there is no significant difference between the treatments, and the total available N is slightly less than the starting quantity.  As can be seen from the rainfall chart above, only 3mm of rain fell after the application of urea on 9 September.  This is unlikely to be enough to prevent large losses through volatilisation (lost as a gas to the atmosphere) and certainly not enough to get significant quantities to the root zone.  There was no yield harvested off the area and so no comparison between the trial strips can be made.  This is a trial we will be aiming to repeat in 2007, again with the assistance again of the GRDC, on a new site.

However, extra testing of the 2006 site was done to see how much residual N was available in 2007, and if there were any differences between the test strips.  These results can be found in the 2007 results.