Canopy management and its relevance to shorter season cereal crops in northern NSW (GRDC Agribusiness extension project)

 
Author/s: By Peter McKenzie (AgVance Farming), Nick Poole (FAR), Ron Southwell (NSW DPI/EFS)
 
Keywords
Canopy management, black vertosols, nitrogen, population, timing, wheat, NDVI, biomass, Greenseeker.
 
At a glance
Nitrogen applied at planting or 50% at planting and 50% later at the early stem elongation stage (GS30-31) gave similar yield results.
Later single dose applications of nitrogen resulted in significant yield and biomass decline as opposed to a split nitrogen or up front strategy.
Higher plant populations with added nitrogen tended to be more productive.
 
Why do the trial?
The use of canopy management has been widely adopted in traditional cereal cropping regions with a winter dominant rainfall pattern.  Soils in these regions typically have low water holding capacity therefore growers are manipulating timing of nitrogen application as a risk management tool as well as a yield maximising strategy.
This trial was conducted to explore the viability of such a crop management system in shorter growing seasons, on high moisture holding black vertosol soils and a summer dominant rainfall environment of the northern cropping belt.   
The full trial included 2 wheat sites on the Liverpool Plains (extensive measurement and 1 basic measurement), 1 wheat site at Croppa Creek and 1 barley trial also located on the Liverpool Plains (both basic measurement).  Due to presentation constraints, this paper will deal with the results from the extensive measurement trial on the Liverpool Plains.
 
Treatments/how done/Was it a demonstration or replicated trial?
Trial design was a four replicate, randomized, small plot (2m x 8m).
Sowing date of trial: 28th June 2006.  Harvest Date 30th November 2006.
Sowing rate:  4 planting rates were used, aiming to establish 50, 100, 150 & 200 plants per square metre.  Actual populations were approx. 15-20% higher than targeted.
 
Crop(s) and variety(s): Wheat variety: Ventura.
Base fertiliser:  Starter Blend N9% : P16% : K0% : S17% : Zn1.5% applied at 70 kg/ha with the seed at planting.
 
7 different nitrogen timings were used in the trial (all N applied as urea):
Untreated control
100% N at planting (inter row banded) 110kgN/ha
100% N at GS30-31 (spread) 110 kgN/ha
100% N at GS 37-39 (spread) 110kgN/ha
50% N at planting (inter row banded) + 50% N at GS30-31 (spread) 55 + 55kgN/ha
50% N at planting (inter row banded) + 50% N at GS37-39 (spread) 55 + 55kgN/ha
50% N at GS30-31 (spread) + 50% N at GS 37-39 (spread) 55 + 55kgN/ha
 
All post applied nitrogen was ‘rained in’ using a centre pivot irrigator.
 
Measurements: Biomass (dry matter cuts + NDVI), tiller number, head number, green leaf retention, leaf area index, soil moisture level, yield, grain quality were all measured in this trial however not all results are mentioned due to page limitations.
What happened?
 
Biomass
Biomass was recorded using two methods; dry matter cuts and NDVI technology (Greenseeker).  NDVI proved to be an effective method of predicting dry matter yield mimicking the results achieved through dry matter cuts.  
 
i)  Nitrogen timing interaction and its influence on dry matter production.
There was a significant increase in dry matter associated with the application of nitrogen in this trial, irrespective of nitrogen timing (Fig. 1). Of those strategies tested, there was a dry matter decline associated with later nitrogen timing compared to the seedbed timing however, this decline was only significant with single dose application at GS 37-39.
 
Figure 1.  Effect of Nitrogen Treatment on Crop Biomass at GS 99 (Please Click Here)
 
 
 
 
 
 
NB - Quadrat size: 0.36m2
 
ii) Interaction of plant density and nitrogen timing on NDVI (Greenseeker).
There was a significant (P<0.05) interaction between nitrogen treatment and plant density (Fig.
 
iii). When N was not applied as in the control the NDVI was similar over the four planting populations but where N was applied (eg. seedbed and 50% seedbed/50% GS31) increasing the plant population increased the size of the canopy as measured by NDVI.
 

Figure 2.  Interaction of Plant Density and Nitrogen Treatment as Measured by Greenseeker at GS 31 (Please Click Here)
 
 
 
 
N.B. At the time of NDVI assessment nitrogen application at GS31 and GS39 had not been applied
 
Yield
i) Influence of plant population on yield (t/ha)
Plant populations ranging from 65 – 220 plants/m2 showed no significant difference in yield, despite significant differences in crop structure (tillers/m2 and ear number/m2). This would indicate that there was considerable compensation in other crop yield components, such as grain size and or grain number per ear to make up for the lower ear number recorded in the lower plant populations.
 
ii) Influence of nitrogen timing on grain yield (t/ha)
There was a significant increase in yield associated with the application of nitrogen in this trial, irrespective of nitrogen timing. Of those strategies tested, there was a significant yield decline associated with later nitrogen timing compared to the seedbed timing, however this decline was most pronounced with single dose application. There was a significant interaction with whether nitrogen was applied as a single dose or split into two doses, since the sharp decline in yield associated with moving nitrogen from GS31 to GS39, as a single dose (3.31 t/ha down to 2.30 t/ha), was not recorded when the nitrogen dose was split, with 50% of the nitrogen at sowing. In addition, the benefit of splitting the nitrogen dose was only observed with nitrogen timings that incorporated the later GS39 application, with early seedbed nitrogen applications or GS31 timings, there was no benefit to splitting the dose over single applications.
iii) Plant population nitrogen timing interaction and its influence on yield
 
 

Figure 3. Influence of nitrogen timing on final yield cv Ventura (mean of all plant populations) (Please Click Here)
 
LSD (0.42 t/ha within plant population otherwise 0.53 t/ha)

Nitrogen timing
There was a significant interaction between plant population and the response to later nitrogen timings, since with nitrogen strategies that employed later timings there was a tendency for yields to decline with higher plant population whilst with earlier timed nitrogen not only were yields overall higher but there was a trend for higher plant populations to be more productive.  This trend was apparent in both single and split dose approaches.
 
Water relationships
At flowering the volumetric moisture was 6.5 mm greater in the seedbed/GS31 application treatment compared to the seedbed application over all plant populations with the greatest difference in the 150/m2 population.  Thus there was more water available for the crop to finish.  
Despite the delay in water use where N was applied as a split application this treatment and the N applied at planting had similar grain yield and protein.  This is most likely a consequence of irrigation (22 mm) and rainfall (56 mm) after flowering.
 
Making it Commercial Practice
Based on only one seasons results it is difficult to justify changes to on farm practices.  The current technology exists to make changing to a 50% at plant and  50% later risk management strategy viable in a variable winter crop climate however; reliable weather prediction to aide the incorporation of nitrogen is a major inhibiting factor for many growers.   Development of soil injection systems for nitrogen application would make this risk management strategy in the production system highly affective.
   
Other Factors to be Considered
Considering the dry conditions and the relatively low rainfall received during the trial it remains to be seen if these interactions continue into a higher yielding season.  The length of growing season particularly on the Liverpool Plains has the ability to extend the crop growth period significantly therefore the results achieved in 2006 need to be continued across a number of seasons.
   
Sponsors
GRDC Agribusiness Extension Project.  AgVance Farming would like to thank GRDC for their contribution in 2006 and for continuing the support for this work on a paddock scale in 2007.

Acknowledgements
We would like to thank Mick Bradfield, Hugh Simpson and Doug Makim for providing trial sites for this work.  Also Giles Butler, Anthony Mitchell (NSW DPI/EFS) & Alan Bowring (AgVance Farming) for their extensive work in organising and collecting information during the trial.
 
For further details contact
Peter McKenzieon 0428 474 860 or pmckenzie.agvance@bigpond.com
 
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