2013 R&D Results Compendium
Rotational impact of Mallee grain legume crops
on wheat
Ivan Mock, Dodgshun Medlin
Introduction
Inclusion of legume crops in the rotation has been associated with biological
processes including nitrogen fixation, disease suppression and potential for
improved weed control which combine to benefit subsequent crops. Production of legume crops in
Mallee environments has however been constrained by the demise of pasture legumes in crop
intensive rotations and inconsistent yields and therefore higher risks with grain legumes.
Two sites established in 2013 evaluated and demonstrated that appropriate grain legume crops can
be successfully grown in dryland Mallee environments when modern varieties and appropriate
agronomic systems, including inoculation with bradyrhizobia, are incorporated.
Both sites were re-sown to wheat in 2014 as a bioassay of the rotational benefits of the 2013 legume
crops. 2013 results have previously been reported (Mock, 2014) although 2013 legume yields are
included in this report to provide a context for 2014 wheat results.
Methodology
Sites were selected at Loxton (SA) and at Normanville (Vic) in Mallee paddocks where the landholder
had not had confidence to grow grain legumes for the previous 10 years. Six legume crops; vetch (cv.
Volga), lentil (cv. Flash), chickpea (cv. Genesis 90), faba bean (cv. Farah), field pea (cv. Twilight) and
lupin (cv. Mandelup) were sown in 2013 with and without the appropriate inoculum in randomised, 4
replicate plot trials. Granular and slurry inoculum treatments were applied to chickpeas while all other
crops had slurry only.
Both sites were resown to wheat (cv. Corack) in 2014 with nitrogen input limited to a sowing
application of 11.5 kg N/ha to assist in detecting any benefits from N fixation from the previous legume
treatments. Wheat was assessed for biomass production (NDVI), grain yield (plot harvester) and
quality (1000 grain weight and protein content).
Results
Grain yield results from the 2013 legume crops listed in table 1 demonstrate viable yields and the
importance of inoculation, especially for chickpea and lupin.
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2013 R&D Results Compendium
Table 1 Loxton and Normanville 2013 grain legume yield (t/ha) for each crop with and without inoculum and
percentage change between the two.
Crop
Chickpea
Chickpea (gran.)
Faba bean
Lentil
Lupin
Field pea
Vetch
Loxton yield (t/ha)
Inoculated Uninoculated
1.07
0.44
1.06
0.44
0.81
0.84
0.84
0.68
1.41
0.45
1.69
1.65
1.64
1.69
Change
%
58.8
58.1
-3.6
19.5
68.0
2.3
-3.0
Normanville yield (t/ha)
Inoculated Uninoculated
1.02
0.53
1.04
0.53
0.97
0.86
0.81
0.74
0.66
0.31
1.94
1.89
1.52
1.65
Change
%
48.0
49.0
13.8
9.1
53.9
2.7
-8.9
January – April rainfalls in 2014 were approximately twice the long term averages at both sites and
promoted mineralisation of residues from the 2013 legume crops. However soil analysis at sowing in
2014 had limited correlation to the 2013 treatments. Wheat biomass assessments using NDVI prior
to heading did replicate the grain legume yields (with the exception of lentil) although the magnitude
of variation was more condensed (table 2).
Table 2 Loxton (24/7) and Normanville (29/8) NDVI scores for wheat in 2014 sown on 2013 legume treatment
plots.
2013 Crop
Chickpea
Chickpea (gran.)
Faba bean
Lentil
Lupin
Field pea
Vetch
Lsd (P=0.05) crop
Inoc
crop x inoc
Loxton NDVI score
Inoculated Uninoculated
0.52
0.49
0.51
0.49
0.56
0.53
0.55
0.56
0.51
0.50
0.54
0.52
0.57
0.56
0.033
ns
ns
Change
Normanville NDVI score
%
Inoculated Uninoculated
7.55
0.52
0.45
3.92
0.51
0.45
5.36
0.53
0.50
-3.64
0.53
0.55
3.92
0.50
0.48
3.70
0.54
0.51
1.75
0.53
0.55
0.036
0.019
0.051
Change
%
12.84
12.42
5.21
-3.76
2.53
5.09
-5.25
At harvest, estimates of frost damage in plots at Loxton were as high as 50% in the first replicate which
was subsequently discarded from analysis. Damage estimates on the other replicates did not exceed
25% and a correction factor used to compensate for the severity in each plot. Grain yields for both
sites are presented in table 3.
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2013 R&D Results Compendium
Table 3 Loxton and Normanville wheat grain yield (t/ha) in 2014 on each 2013 crop with and without inoculum
and percentage change between the two.
2013 Crop
Loxton yield (t/ha)
Change Normanville yield (t/ha) Change
Inoculated Uninoculated
%
Inoculated Uninoculated
%
Chickpea
1.49*
1.58
-5.76
3.50
3.10
11.43
Chickpea (gran.)
1.61
1.58
1.80
3.50
3.10
11.36
Faba bean
1.73
1.77
-2.55
3.66
3.55
2.95
Lentil
1.58
1.69
-6.44
3.63
3.68
-1.46
Lupin
1.54
1.46
4.94
3.45
3.20
7.33
Field pea
1.71
1.69
1.35
3.65
3.58
1.95
Vetch
1.65
1.61
2.54
3.65
3.65
0.14
Lsd (P=0.05) crop
0.136
0.112
Inoc
ns
0.06
crop x inoc
ns
0.159
*Low wheat yield on inoculated chickpea treatment may be an anomaly resulting from frost damage
Where chickpea and lupin crops had been inoculated in 2013, the wheat protein in 2014 was 0.3-0.7
% more that where no inoculum was applied (Table 4).
Table 4 Loxton and Normanville wheat grain protein (%) in 2014 on each 2013 crop with and without inoculum
and percentage change between the two.
2013 Crop
Chickpea
Chickpea (gran.)
Faba bean
Lentil
Lupin
Field pea
Vetch
Loxton protein (%)
Inoculated Uninoculated
9.8
9.1
9.2
9.1
10.2
9.6
10.0
10.0
9.9
9.6
10.3
10.1
10.2
9.9
Change
%
7.1
1.1
5.9
0.0
3.0
1.9
2.9
Normanville protein (%)
Inoculated Uninoculated
8.5
8.0
8.3
8.0
8.9
8.8
8.6
8.5
8.6
8.2
8.7
8.7
8.4
8.6
Change
%
5.9
3.6
1.1
1.2
4.7
0.0
-2.4
Discussion
Wheat response to the previous grain legume treatment showed a similar trend at both sites when
biomass assessments were made although there was more variation between sites at harvest,
presumably due to the impact of frost at Loxton. It was apparent that grain legume crop selection and
inoculum application also impacted on the following wheat crops vegetative production, grain yield
and protein content. Notable examples are Chickpea and lupin crops which produced poorly without
inoculum and also had less wheat biomass, yield and grain protein compared to where inoculum was
applied.
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2013 R&D Results Compendium
Implications for commercial practice
•
•
•
The impact of legume crop selection on the following wheat yield and quality was relatively
small (particularly at the non-frosted site) compared to differences between legume crop
yields the previous year. Profitability of the legume crop is therefore paramount for its
selection for inclusion in the rotation.
Most grain legume crops benefit from inoculum application and benefits will continue into
the following wheat crop.
Soil nitrogen analysis at sowing was a poor predictor of wheat response although low wheat
protein indicates that substantial fertiliser N is required in addition to fixation by a successful
legume crop.
Acknowledgements
This work was funded by Dodgshun Medlin, Normanville Farm Advancement Group, Caring for Our
Country and the GRDC.
Thankyou to staff who contributed to this project, in particular Shannon Blandthorn, Nick McNamara,
Brett Barker, Brian Hassett, Rebecca Hope and Richard Saunders.
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