2007 Nitrogen Trial
Summary
Difficult seasonal conditions have again made nitrogen extension work
difficult. Yield responses could not be ascertained as seasonal
conditions did not allow a harvest to occur. However, extra
sampling of the 2006 trial site revealed a trend (not significant) to
more residual N being present in strips sown with extra N at sowing
than those without. Furthermore, there was no difference between
the strips that were topedressed, highlighting the difficulties
associated with managing N vusing topdressing.
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. In
2006, we
aimed to investigate different topdressing rates at two different
starting applied N rates (0 and 50kg/ha urea). However, given the
drought in that season and reasonable soil moisture over the fallow
period, it was suspected that the starting N levels would be reasonably
high. Therefore no N was applied at sowing and there were 3
topdressing rates of 0, 60 and 120kg/ha urea laid out in alternating
strips. The topdressing occurred on 17 August and Table 1
illustrates the rainfall during the period.
A summary of the main aspects of the trial are as follows:
| Paddock History: |
Canola in 2006, wheat in 2005 and 2004
and canola in 2003. |
| Date Sown: |
16 July 2007 |
| Variety: |
Gregory at 50kg/ha.
Crown Rot
- 3, Common Root Rot - 6, Stripe Rust - 7, Yellow Leaf Spot - 3,
Root
Lesion Nematode - 7; NSW DPI ratings. |
| Starter Fertiliser: |
50kg/ha MAP |
| Equipment Used: |
12m NDF combodrill with
disc delivery assembly, pulled by a 285hp John Deere
tractor. MAP and the seed sown
with the disc. For more information, visit www.ndf.com.au.
|
| In-Crop Spraying: |
|
Table 1: Rainfall at the trial site (2007)
| 01-10 June |
91.2 |
21 July |
0.2 |
20 August |
3.0 |
| 11-20 June |
0.4 |
30 July |
0.2 |
21 August |
1.0 |
| 21-30 June |
30.4 |
03 August |
6.0 |
11 September |
0.4 |
| 01-10 July |
9.6 |
04 August |
7.0 |
28 September |
0.2 |
| 11-19 July |
1.2 |
08 August |
0.2 |
26 October
|
2.0 |
|
|
17 August |
3.0 |
30 October |
0.6 |
| TOTAL |
132.8mm |
|
|
TOTAL (sowing - end Oct) |
23.8mm
|
In order to salvage
some value out of the 2006 site, it was decided to conduct deep N testing on
each of the strips to determine if there was any differences between the
treatments with regard to carryover (or residual) N. The 2006 site had replicated strips, and the
all strips were sampled on 14 August 2007 and sent to Incitec Pivot for analysis.
Results
The 2007 trials were topdressed on the 17th of August, and so received the
only significant rain after sowing, but this was still only 3mm.
This had a twofold
effect. Firstly, the urea once again did
not receive sufficient rain for full incorporation and so most, if not all, was
lost to the atmosphere. Secondly,
the
lack of rain post application, in conjunction with the already dry
year, resulted in a crop failure and no yield data being available.
The 2006 trial site
produced the results found in Table 2.
It can be seen that there is a definite trend indicating the areas that
started with 50kg/ha urea applied at sowing had greater residual N than those
that did not receive the treatment.
However, the difference was not significant, due to the variability in
the samples.
Table 2: Residual N from 2006 trial site
| Topdressed Rate |
Starting Rate
0kg/ha urea |
Starting Rate
50kg/ha urea |
| 0kg/ha urea |
22 |
32 |
| 50kg/ha urea |
23 |
69 |
| 100kg/ha urea |
34 |
48 |
| Average |
26 |
50 |
It can also be seen that there is no trend with
regard to residual N and amount of topdressing.
This is to be expected when we consider that the 2006 site received only
one fall of rain in excess of 1mm/day in the 55 days after topdressing; i.e.
most of the N from topdressing may have volatolised. This highlights the inherent risks with
topdressing using volatile N sources such as urea. In this instance, there is no carryover
benefit to the following season which can sometimes occur if incorporation
occurs but poor seasonal conditions result in a low yielding crop.
