Does grazing canola have a fit in the high rainfall zone?

| Date: 09 Feb 2011

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Results
Seasonal conditions
2010 provided an opportunity to test the tolerance of canola to grazing under severe growing conditions. Three of the five sites (at Lake Bolac and Werneth) were severely waterlogged at grazing. Two trials at Inverleigh experienced much less severe conditions. At all sites the canola plants were grazed briefly (approximately 5 days each) but severely, removing all the leaves and some of the stem. While grazing would not be recommended under these waterlogged conditions or degree of leaf removal, defoliation and trampling by the animals enabled the worse case results to be measured.
The severity of the conditions were reflected in the lower yields even from the non grazed canola at Lake Bolac and Werneth compared to the less challenging conditions at Inverleigh (Table 1). This was especially evident for the later sowing date (Table 2).

Table 1. Grain yield (t/ha) at Inverleigh (favourable conditions) and Lake Bolac (challenging conditions) sown in mid May

 

Variety
Inverleigh
(sown May 15)
Lake Bolac
(sown May 20)
Hyola 571 (CF)
1.97
1.17
46Y78 (CF)
1.76
1.53
46Y20 (RR)
1.73
0.99
Jardee (TT)
1.71
0.69
Marlin (TT)
0.68
0.35
Table 2. Grain yield (t/ha) at Inverleigh (favourable conditions) and Lake Bolac (challenging conditions) sowing in mid June 

 

Variety
Inverleigh
(sown June 15)
Lake Bolac
(sown June 18)
46Y78 (CF)
2.42
0.31
Jardee (TT)
2.23
0.11
Marlin (TT)
2.16
0.05
Hyola 571 (CF)
1.77
0.32
46Y20 (RR)
1.75
0.50
Grain yield due to grazing
 
Grazing had a significant impact on grain yield where the sowing time was later and the more severe waterlogging was encountered during grazing and in the post grazing recovery period (table 3 & 4).
Table 3. Grain yield (t/ha) at Inverleigh (favourable conditions) with and without grazing 
Treatment
Inverleigh 1
(sown May 15)
Inverleigh 1
(sown June 15)
Inverleigh 2
(sown June 15)
Ungrazed
1.94
2.05
1.12
Grazed
1.62
1.74
0.58
LSD p<0.05
Not significant
0.30
 
Table 4. Grain yield (t/ha) at Lake Bolac (challenging conditions) with and without grazing 
Treatment
Lake Bolac 1
(sown May 15)
Lake Bolac 1
(sown June 15)
Lake Bolac 2
(sown May 20)
Ungrazed
1.02
0.27
1.16
Grazed
0.26
0.10
0.10
LSD p<0.05
0.18
0.27
 
The comparative yield of all varieties in shown, indicating the impact of grazing and sowing time (figure 1).
 
 
 
 
Note on how to interpret Figure 1. The graph compares the grain yield of grazed and ungrazed canola. The black diagonal line indicates the position on the graph where the yield of the grazed and ungrazed canola is the same (i.e. no yield loss due to grazing). Each dot on the map represents the yield of an individual canola variety where half the canola has been grazed and the other half left ungrazed. Any dots above the black diagonal line indicate grazing has increased yield compared to no grazing. A dot below the line indicates grazing has reduced yield compared to no grazing. The further the dot is along the horizontal (ungrazed) axis the greater the ungrazed yield. The higher up the vertical (grazed) axis, the greater the grazed yield. So a dot in the bottom right hand corner of the graph would indicate a high ungrazed yield but a low grazed yield (i.e. grazing severely reduced yield). A dot in the bottom left hand coner indicates low ungrazed and low grazed yield (i.e. a poor variety even when ungrazed). Ideally we want varieties that are on or above the black vertical line and in the top right hand corner of the graph.   
 

Figure 1. Comparison of grain yield for grazed and ungrazed canola at Inverleigh, Lake Bolac and Werneth (traditional and late sowing times)

Three varieties were able to recover from grazing and still produce a ‘commercial’ grain yield equivalent to no grazing. These were 46Y78, Jardee and 46Y20. Variety 46Y20 and Hyola 502 also produced equivalent grain yield to no grazing, but yields were lower than ideal. However the late sowing (mid June) may explain the lower yield. These results were all achieved at the Inverleigh site, where water logging conditions were less severe. At the more severely waterlogged sites, a significant loss in grain yield was measured due to grazing.
To put these results into perspective, the experimental lines also were compromised by the severe waterlogged conditions (Figure 2).

Figure 2. Comparison of grain yield for grazed and ungrazed experimental canola lines at Inverleigh and Lake Bolac (traditional and late sowing times)

DM available for grazing

There was large variability in the dry matter produced by the different canola varieties (Figure 3). The hybrid varieties, sown in mid May were able to produce valuable quantities of drymatter for grazing. As expected late sowing reduced the amount of drymatter available.


Figure 3. Drymatter available for grazing at Inverleigh and Lake Bolac (traditional and late sowing times)

 

 

 

 

Canola plants recovered after heavy grazing at Inverleigh unlike Lake Bolac where heavy grazing in combination with severe waterlogging greatly reduced plant numbers (Table 3).  
Table 3. Viable plants at flowering with and without grazing under challenging climatic conditions (Lake Bolac)  
Variety
Ungrazed
(pl/m2)
Grazed
(pl/m2)
Marlin (TT)
50
7
Lightning (TT)
68
6
Jardee (TT)
42
18
Tumby (TT)
56
5
46Y83 (CF)
75
10
46Y78 (CF)
93
15
Hyola 571(CF)
67
20
46Y20 (RR)
76
27
Hyola 502 (RR)
23
22
 
High drymatter production and recovery from grazing
Only three commercial varieties grew large quantities of drymatter for grazing and were able to withstand grazing and not compromise yield (Figure 4). These were Hyola 502, 46Y78 and Jardee.   One experimental line also achieved high drymatter production and yield after grazing (CBI306).

Figure 4. Drymatter available for grazing and impact on grain yield by grazing (Inverleigh, Werneth and Lake Bolac, traditional and late sowing times)

 

 

Weed control
 
A critical aspect of grazing canola is the interaction with various herbicides. The lengthy withholding period of some herbicides excludes potential grazing eg triazine herbicides have a 15 week with-holding period if used pre emergent and 6 weeks post emergent, Intervix®  used with Clearfield® technology has a 5 week withholding period when used post emergent.  Roundup® used on Roundup Ready canola has a 7 day withholding period.
Two of the three varieties that showed promise for grazing were either triazine tolerant or Clearfields varieties. This may limit the opportunity for grazing.  
 
 
 
Impact on weeds and soil structure from grazing
 
It is premature to draw any conclusions about the impact of grazing on weed populations and soil structure. 2010 provided extreme conditions to ‘damage’ the soil and while significant pugging was visually evident, further testing is required to fully appreciate the long term effects. 
Preliminary observations on weed populations do not indicate any significant increase in the number of weeds due to grazing. However observations would suggest the removal of the canola canopy, coupled with a slow canopy recovery reduces competition which promotes weed growth especially toad rush.
 
Conclusion
 
These results are only the first year of a four year testing regime. Varieties were sown later than ideal if you wanted to maximise drymatter production and grazing was severe and conducted under unfavourable conditions. Not surprisingly yield suffered with most varieties. Nevertheless it provides an ‘extreme end’ of the grazing regime.   Future trials will examine the impact of grazing when sown earlier and with less severe grazing conditions and levels of defoliation.
As a comparison, no significant yield loss was measured on adjacent cereal crops grazed at a similar time to the canola. This would suggest the canola may be more sensitive to unfavourable grazing conditions than cereals. Factors which we would see as unfavourable at this stage would include:
  • Late sown canola
  • Water logged conditions at grazing or in the post grazing recovery period
  • Complete defoliation of the plants
  • Incorrect paddock selection - Low nutrient availability or poor seed bed preparation.
  • Incorrect variety selection that have poor vigour eg non hybrid TT’s.
  • High weed populations
 
Contact details:
 
Grain and Graze, Southern Victoria
 
Cam Nicholson nicon@pipeline.com.au