The effect of stubble on nitrogen tie-up and supply

Take home messages

  • Cereal stubble should be thought of as a source of carbon (C) for microbes, not as a source of nitrogen (N) for crops. In no-till systems, only 1% to 6% of the N requirement of crops is derived from wheat stubble.
  • Nitrogen tie-up by cereal residue is not just a problem following incorporation — it occurs in surface-retained and standing-stubble systems.
  • Nitrogen tie-up in cropping soils is only a temporary constraint as the immobilised N will be released through microbial turnover, generally later in the crop season in spring.
  • Management of tie-up is reasonably straightforward — supply more N (5kg N for each t/ha of cereal residue) and supply it early to avoid impacts of N tie-up on crop yield and protein.
  • Deep-banding N can improve the N uptake, yield and protein of crops, especially in stubble-retained systems.

Background

In many Australian agricultural soils, carbon (C) availability is the most limiting constraint of microbial functions. Hence management of biologically available C is the key to improving biological functions including those involved in N mineralisation. Crop residues are one of the major sources of C for soil biota, therefore stubble retention can provide benefits through changes in soil physical, chemical and biological properties which influence C turnover, nutrient generation and subsequent availability of nutrients to crops. Although stubble retention benefits are expected to be realised in all soil types, the magnitude and nature of change in biological functions can vary depending on type and timing of stubble management and is influenced by soil type and environmental factors, such as rainfall.

Most dryland growers in Australia retain all, or most of their crop residues to protect the soil, retain soil moisture and maintain soil fertility in the long-term. However, a pro-active and flexible approach to stubble management that recognises and avoids situations in which stubble can reduce productivity or profitability makes sense, and has been promoted as part of the GRDC Stubble Initiative (Swan et al. 2017a). One such situation is where large amounts of retained stubble, especially high C:N ratio cereal stubble, ’ties-up’ soil N leading to N deficiency in the growing crop that may reduce yield.

The timing, extent and consequences of N tie-up are all driven by variable weather events (rainfall and temperature), as well as soil and stubble type, so quite different outcomes may occur from season to season and in different paddocks (Gupta, 2016). In this paper, we firstly review in simple terms the process of N tie-up (immobilisation) to understand the factors driving it. We then provide the results from a series of recent experiments in southern NSW and SA (both long-term and short-term) that serve to illustrate the process, and the ways in which the negative consequences can be avoided while maintaining the benefits of stubble.

N cycling processes and controlling factors

Nitrogen mineralised from soil organic matter (SOM) and crop residues makes a substantial contribution (approximately 50%) to crop N uptake (Angus and Grace, 2017, Gupta, 2016). The rate and timing of N mineralisation regulate plant available mineral N levels in soils and the release of mineral N in soil is regulated by the processes associated with microbial turnover (Figure 1). Microbial activities are also responsible for the conversion of fertiliser N into plant available forms.

The rate and timing of N mineralisation regulate plant available mineral N levels in soils and the release of mineral N in soil is regulated by the processes associated with microbial turnover.

Figure 1. Biological processes involved in N cycling that influence plant available N levels in soil. SOM – soil organic matter, DON – dissolved organic nitrogen, POM – particulate organic matter (Gupta, 2016).

The process of N tie-up and release (N-immobilisation and supply)

Growers always grow two crops – the above-ground crop (wheat, canola, lupins) is obvious, but the below-ground crop (the microbial biomass (MB)) is always growing as well, and like the above-ground crop, it needs water, warm temperatures and nutrients to grow (there is as much total nutrient in the microbes/ha as in the mature crop, and two-thirds are in the top 10cm of soil). There are two main differences between these two ’crops’ — firstly the microbes cannot get energy (C) from the sun like the above-ground plants, so they rely on crop residues as the source of energy (C). Secondly, they do not live as long as crops — they can grow, die and decompose again (turnover) much more quickly than the plants — maybe two to three cycles in one growing season of the plant.

The microbes are thus immobilising and then mineralising N as the energy sources available to them come and go. In a growing season, it is typical for the live microbial biomass to double by consuming C in residues and root exudates, but they also need mineral nutrients. Over the longer-term, the dead microbe bodies (containing C, N, phosphorus (P) and sulphur (S)) become the stable organic matter (humus) that slowly releases fertility to the soil. In the long-term, crop stubble provides a primary C-source to maintain that long-term fertility, but in the short-term, the low N content in the cereal stubble means microbes initially need to use the existing soil mineral N (including fertiliser N) to grow and compete with the plant for the soil N.

Microbial biomass in soil

Soil microbial biomass (MB) is a store-house for nutrients. Changes in the amount of MB due to management and seasonal variation can exert a significant impact on microbial immobilisation and net N mineralisation. In Australian agricultural soils, MB-C accounts for 1.5% to 3.0% of soil organic C and MB-N 2% to 5% of total N. The amount of MB varies with soil type and agro-ecological region (Table 1) and is influenced by crop rotation, tillage and stubble management practices that influence microbial populations and the quantity and quality of residues. The MB-C:N ratio generally varies between 6.5 and 9.0 and a wide MB-C:N ratio is shown to be associated with cereal crop residues and rhizosphere soils. Due to the short turnover time of MB in Australian soils, it may only act as a short-term reservoir for nutrients and as a biocatalyst for SOM cycling and N release, in particular in-crop N mineralisation.

As microbial turnover and the associated N mineralisation-immobilisation balance is influenced by seasonal conditions, estimation of N supply potential at the beginning of a crop season should include the amount of N in MB and the N that can be mineralised from SOM and crop residues (Gupta 2016, McBeath et al. 2015a). In addition, management practices that increase the size of the MB pool and modulate its turnover could assist with the synchronisation of N mineralisation to crop demand. For example, higher N mineralisation after a legume crop is related to higher MB, whereas greater microbial turnover after canola also contributes to higher N mineralisation (Gupta, 2016).

Table 1. Amount of microbial biomass C and N supply and immobilisation potentials in the surface 0cm to 10cm of agricultural soils from the different cropping regions of Australia (Gupta 2016).

Location

Soil type

MB-C
(kg C/ha)

N immobilisation potential&
(kg N/ha)

N supply potential$
(kg N/ha)

Rutherglen, VIC

Red brown earth

350 - 700

25 - 50

30 - 100

Horsham, VIC

Sandy loam

140 - 230

12 - 24

10 - 16

Horsham, VIC

Clay

546 - 819

39 - 59

52 - 72

Waikerie/Karoonda, SA

Sand and sandy loam

150 - 300

15 - 25

10 - 35

Streaky Bay, SA

Calcarosol - sandy loam

210 - 400

15 - 30

20 - 50

Minnipa, SA

Calcarosol - loam

560 - 710

40 - 51

42 - 56

Appila, SA

Loam

450 - 585

32 - 42

35 - 45

Leeton/Warialda, NSW

Clay

350 - 1000

25 - 60

25 - 75

Condobolin, NSW

Sandy loam

240 - 585

17 - 42

20 - 45

Kerrabee, NSW

Loam

420 - 525

30 - 40

35 - 50

Temora, NSW

Red earth

525 - 735

35 - 55

50 - 100

Millewa, NSW

Sandy loam

150 - 310

11 - 22

14 - 31

Wongan Hills, WA

Loamy sand

250 - 350

18 - 25

25 - 40

& N immobilisation potential is estimated assuming an average 50% increase of MB during a growing season.

$ N supply potential is calculated from N in MB plus N mineralisation measured in a laboratory aerobic-incubation assay.

A worst-case scenario

That simplified background helps to understand the process of immobilisation, when and why it happens, and how it might be avoided or minimised. Imagine a paddock on 5 April with 8t/ha of undecomposed standing wheat stubble from the previous crop after a dry summer. A 30mm storm wets the surface soil providing a sowing opportunity. Fearing the seeding equipment cannot handle the residue, but not wanting to lose the nutrients in the stubble by burning, the residue is mulched and incorporated into the soil. A canola crop is sown in mid-April with a small amount of N (to avoid seed burn) and further N application is delayed until buds are visible due to the dry subsoil.

So in this case, the cereal stubble (high C and low N — usually approximately 90:1) is well mixed through a warm, moist soil, giving the microbes maximum access to a big amount of C (energy),but not enough N (microbe bodies need a ratio of about 7:1). The microbes will need all of the available N in the stubble and the mineral N in the soil, and may even break down some existing organic N (humus) to obtain more N if they need it (so C is lost from the soil). The microbes will grow rapidly, so when the crop is sown, there will be little available mineral N - it is all ’tied-up’ by the microbes as they grow their population on the new energy supply. Some of the microbes are dying as well, but for a time more are growing than dying, so there is ’net immobilisation’.

As the soil cools down after sowing, the ’turnover’ slows, and so is the time taken for more N to be released (mineralised) than consumed (immobilised) and net-mineralisation is delayed. Meanwhile, the relatively N-hungry canola crop is likely to become deficient in N as the rate of mineralisation in winter is low. This temporary N-deficiency, if not corrected or avoided, may or may not impact on yield depending on subsequent conditions.

Based on these simple principles, it is relatively easy to think of ways to reduce the impact of immobilisation in this scenario:

  1. The stubble load could be reduced by baling, grazing or burning (less C to tie up the N).
  2. If the stubble was from a legume or canola rather than cereal (crop sequence planning), it would have a lower C:N ratio and tie up less N.
  3. The stubble could be incorporated earlier (more time to move from immobilisation to mineralisation before the crop is sown).
  4. Nitrogen could be added during incorporation (to satisfy the microbes and speed up the ’turnover’).
  5. More N could be added with the following crop at sowing (to provide a new source of N to the crop and microbes), and this could be deep-banded (to keep the N away from the higher microbe population in the surface soil to give the crop an advantage).
  6. A different seeder could be used that can handle the higher residue without incorporation (less N-poor residue in the soil).
  7. A legume could be sown rather than canola (the legume can supply its own N, can emerge through retained residue and often thrives in cereal residue).

In modern farming systems, where stubble is retained on the surface and often standing in no-till, control-traffic systems, less is known about the potential for immobilisation. In GRDC-funded experiments as part of the Stubble Initiative (CSP187, CSP00174, MSF 00003, BWD00024), we have been investigating the dynamics of N in stubble-retained systems. Here we provide examples from recent GRDC-funded experiments in southern NSW, VIC and SA, and discuss the evidence for the impact of immobilisation and provide some practical tips to avoid the risks of N tie-up.

Cereal stubble is not a major source of N for crops – tracing N from previous cereal crop stubble

Studies at three sites in southern Australia (Temora, Horsham and Karoonda) have tracked the fate of N in wheat stubble to determine how valuable it is for succeeding wheat crops under Australian systems. Stubble labelled with 15N (a stable isotope that can be tracked in the soil) was used to track where the stubble N went. At Horsham (Figure 2), of the 32kg/ha of N contained in 4t/ha of wheat residue retained in 2014, only 0.85kg/ha N (2.5%) was taken up by the first crop (representing 3% of crop requirement) and 3.5kg/ha N (11%) was taken up by the second wheat crop (2.5% of crop requirement).

At Horsham, of the 32kg/ha of N contained in 4t/ha of wheat residue retained in 2014, only 0.85kg/ha N (2.5%) was taken up by the first crop (representing 3% of crop requirement) and 3.5kg/ha N (11%) was taken up by the second wheat crop (2.5% of crop requirement).

Figure 2. The fate of the N contained in retained wheat stubble over two years in successive wheat crops following the addition of 4t/ha of wheat stubble containing 32kg/ha N. The successive crops took up 2.5% (0.7-1kg N/ha) and 11% (3.5kg N/ha) of the N derived from the original stubblerepresenting only 3% and 2.5% of the crop’s requirements. Most of the stubble N remained in the soil (approximately 40%) or was lost (26%). MB – total amount of N (kg/ha) in the microbial biomass in the surface 10cm soil.

The majority of the N after two years remained in the SOM pool (13kg N/ha or 40%) and some remained as undecomposed stubble (20% or 6kg N/ha). Thus we can account for approx. 74% of the original stubble N in crop (6%), soil (40%) and stubble (20%) with 26% unaccounted (lost below 50cm and/or denitrified). In similar work carried out in the UK which persisted for four years, crop uptake was 6.6%, 3.5%, 2.2% and 2.2% over the four years (total of 14.5%), 55% remained in the soil to 70cm, and 29% was lost from the system (Hart et al. 1993). The main point is that the N in cereal stubble represented only 2.8% of crop requirements over two years (3% Year 1, 2.5% Year 2) and takes some time to be released through the organic pool into available forms and losses can occur during the process. Similarly, N in cereal stubble represented only 6% and 1.1% of crop requirements over two years at Temora (7.6% Year 1, 4.4% Year 2) and Karoonda (1.2% Year 1, 1.0% Year 2), respectively.

Can stubble really reduce yield significantly in no-till systems — and is N tie-up a factor?

Harden long-term site

In a long-term study at Harden (28 years), the average wheat yield has been reduced by 0.3t/ha in stubble retained vs stubble burnt treatments, but the negative impacts of stubble were greater in wetter seasons (Figure 3). Nitrogen tie-up may be implicated in wetter years, due to higher crop demand for N and increased losses due to leaching or denitrification. However, significant differences in the starting soil mineral N pre-sowing were rarely found. For many years, we were not convinced N tie-up was an issue (though there were insufficient measurements to confirm it).

In a long-term study at Harden (28 years), the average wheat yield has been reduced by 0.3t/ha in stubble retained vs stubble burnt treatments, but the negative impacts of stubble were greater in wetter seasons.

Figure 3. Effect of retained stubble on wheat yieldis worse in wetter seasonsat the Harden(circles) and Wagga Wagga (squares) long-term tillage sites. Open symbols where difference between retain and burnt was not significant (NS), solid where significant (S).

In 2017, two different experiments in sub-plots at Harden were implemented to investigate the potential role of N tie-up in the growth and yield penalties associated with stubble. A crop of wheat (cv. Scepter) was sown on 5 May following a sequence of lupin-canola-wheat in the previous years. In both the stubble-retained and stubble-burnt treatments, we compared the 100kg N/ha surface applied with 100kg/N deep-banded below the seed. The pre-sowing N to 1.6m was 166kg N/ha in retained and 191kg N/ha in burnt, but was not significantly different.

Deep-banding the N fertiliser had no impact on crop biomass or N% at GS30, but increased both the biomass and N content of the tissue at anthesis, more in the stubble retained than in burnt stubble (Table 2). Retaining stubble decreased biomass overall, but not tissue N. Nitrogen uptake (kg/ha) at anthesis was significantly increased by deep-banding in both stubble treatments, however the increase was substantially higher in the stubble-retained treatment than in the burnt treatment (38kg N/ha compared with15kg N/ha).

The overall impact of deep-banding on yield persisted at harvest, but there was neither effect nor interaction with stubble retention, presumably due to other interactions with water availability. However, the fact that deep-banding N has had a bigger impact in the stubble-retained treatment provides evidence of an N-related growth limitation related to retained stubble. Its appearance at anthesis, and not earlier, presumably reflects the high starting soil N levels which were adequate to support early growth, but the cold dry winter generated N deficiencies as the crop entered the rapid stem elongation phase. The increased protein content related to both burning and deep-banding and its independence from yield suggest an N deficiency effect throughout the growing season generated by stubble retention.

Table 2. Effect of surface-applied and deep-banded N on wheat response in stubble-burnt and stubble-retained treatments at Harden in 2017.

Treatment

Anthesis

Harvest (@12.5%)

Stubble

100 N

Biomass
(t/ha)

Tissue N
(%)

N Uptake
(kg N/ha)

Yield
(t/ha)

Protein
(%)

Retain

Surface

8.1

1.1

91

4.5

9.3

Deep

9.1

1.4

129

5.1

10.2

Burn

Surface

8.9

1.2

104

4.5

10.3

Deep

9.5

1.3

119

5.0

10.8

LSD (P<0.05)

Stubble

0.6

ns

ns

ns

0.8

N

0.2

0.1

8

0.2

0.4

Stubble x N

0.6

0.2

12

ns

ns

Temora site

At Temora, a nine year experiment managed using no-till, controlled traffic, inter-row sowing (spear-point/press-wheels on 305mm spacing) in a canola-wheat-wheat system investigated the effects of stubble burning and stubble grazing on soil water, N and crop growth (Hunt et al. 2016). In the stubble-retained treatment, stubble was left standing through summer, and fallow weeds were strictly controlled. Stubble was burnt in mid-late March and the crop sown each year in mid-late April. Nitrogen was managed using annual pre-sowing soil tests, whereby 5kg/ha N was applied at sowing and N was top-dressed at Z30 to attain 70% of maximum yield potential according to Yield ProphetÒ(Swan et al. 2017).

Burning

Retaining stubble rather than burning had no impact on the yield of canola or the first wheat crop over the nine years, but consistently reduced the yield of the second wheat crop by an average of 0.5t/ha (Table 3). This yield penalty was associated with an overall significant reduction in pre-sowing soil mineral-N of 13kg/ha, while there was no significant difference in pre-sowing N for the first wheat crop.

Table 3. Effect of stubble burning on grain yields at Temora in Phase 1 and Phase 2. Crops in italics are canola and bold are the second wheat crops. * shows where significantly different (P<0.05).

Phase

Treatment

2009

2010

2011

2012

2013

2014

2015

2016

2017

Phase 1

Retain

1.7

4.2

4.6

4.4

0.7

3.8

4.1

3.2

3.7

Burn

1.7

4.0

4.6

5.0*

1.0

3.8

4.6*

3.2

3.2

Phase 2

Retain

-

6.3

3.4

4.5

2.0

2.0

5.5

5.2

2.1

Burn

-

6.2

3.5

4.8

3.4*

2.0

5.3

5.7*

2.4

Deep N placement

In an adjacent experiment at Temora in the wet year of 2016, deep N placement improved the growth, N uptake and yield of an N-deficient wheat crop, but this occurred in both the stubble-retained and the stubble-removed treatments and there was no interaction suggesting N availability was not reduced under stubble retention (Table 4). However, we believe the level of N loss due to waterlogging in the wet winter and the significant overall N deficiency may have masked these effects, which were more obvious at Harden in 2017.

Table 4. Effect of deep banding vs surface applied N (122kg N/ha as urea) at seeding at Temora NSW in 2016 (starting soil N, 58kg/ha). The crop captured more N early in the season which increased biomass and yield in a very wet season (data mean of three stubble treatments). *indicates significant differences (P<0.01). (Data source: Kirkegaard et al., CSIRO Stubble Initiative 2016, CSP00186).

Treatments

Z30

Anthesis

Grain Yield
(t/ha)

Biomass
(t/ha)

N
(%)

N-uptake
(kg/ha)

Biomass
(t/ha)

N
(%)

N-uptake
(kg/ha)

Surface

1.4

3.8

51

7.8

1.3

103

4.0

Deep

1.4

4.4*

60

9.2*

1.5*

136*

5.2*

Karoonda long-term site

At Karoonda, five years of experiments on a dune-swale soil system (at Lowaldie, north east of Karoonda, SA), in a no-till stubble retained continuous cropping system, the application of all the N fertiliser at seeding time has consistently produced the highest cereal crop yields (on average 4% to 10%) demonstrating the importance of early N fertiliser in these soils where immobilisation is likely to be proportionally more important (Table 5). Continuous wheat crops were sown in May of 2010 to 2014 (following opening rains of at least 20mm with fertiliser treatments of (i) nil fertiliser inputs, (ii) low fertiliser inputs (9kg N/ha at sowing), (iii) higher N inputs at sowing (40kg N/ha with 10kg P/ha), and (iv) higher N inputs split (9kg N/ha at sowing and 31kg N/ha first node with 10kg P/ha at sowing). The N inputs split treatment received the second application of N at an earlier stage in 2013 and 2014, applied at early tillering. There was a notable absence of significant response to the management strategies imposed over the five years of experimentation on the swale soil (including a lack of difference between nil and plus N fertiliser — data not shown) (Table 5). The difference between supplying extra N in fertiliser at sowing compared with in-season was less consistent, especially on the swale. In general, the best yields were achieved with the extra fertiliser N applied at sowing and in some instances, there was a penalty for delaying to an in-season application (Table 5). The season type did not appear to drive the effectiveness of the in-season N application and in all cases, the in-season N was applied with impending rainfall. Generally, sandy soils with lower organic matter have lower N supply potential, hence the imbalance between mineralisation to immobilisation plays an important role in early season N nutrition of a cereal crop.

Table 5. Wheat yield (t/ha) in response to time of fertiliser application and season (2010-2014) on different soil types in a dune-swale system in the Mallee region of SA (McBeath et al. 2015b).

Fertiliser Treatment

2010

2011

2012

2013

2014

Average

Swale

High N upfront

4.3

3.4

3.2

1.3

3.0

3.04 (4.1%*)

High N split

4.0

3.3

2.9

1.4

3.0

2.8

Mid-slope

High N upfront

3.2

3.8

2.4

1.8

3.5

2.94 (7.3%)

High N split

3.1

3.6

1.7

1.8

3.5

2.74

Dune

High N upfront

2.0

2.9

1.5

1.6

2.1

2.02 (9.8%)

High N split

2.0

2.5

1.3

1.6

1.8

1.84

Note: Within a season and soil, yield values in response to fertiliser strategies that are significantly different (P < 0.05) are shown in bold. * Values in brackets indicate percentage higher than ‘High N split’ application.

Post-sowing N tie-up by retained stubble

The evidence emerging from these studies suggests that even where cereal crop residues are retained on the soil surface (either standing or partially standing) and not incorporated, significant N immobilisation can be detected pre-sowing in some seasons. The extent to which differences emerge is related to seasonal conditions (wet, warm conditions) and to the time period between stubble treatment (burning or grazing) and soil sampling to allow differences to develop. However, even where soil N levels at sowing are similar between retained and burnt treatments (which may result from the fact that burning is done quite late), ongoing N immobilisation post sowing by the microbes growing in-crop is likely to reduce the N available to crops in retained stubble as compared to those in burnt stubble, especially during the early crop growth period. At the Horsham site, based on the amount of MB, an 8t/ha stubble load could cause 40kg to 60kg N/ha of N tie-up depending upon seasonal conditions.

Conclusions

In stubble-retained systems, cereal stubble contributes only a small percentage (1% to 6%) of the N requirement for a following cereal crop, hence it should mainly be considered as a source of C for soil microorganisms. Our studies have confirmed a risk of N tie-up by surface-retained and standing cereal residues which may occur in-season, in addition to during the summer fallow, and so may not be picked up in pre-sowing soil mineral N measurements. Yield penalties from retained residues, especially to successive cereal crops, could be reduced by reducing the stubble load or by applying more N (approximately 5kg N per t/ha of cereal residue) and applying it earlier to the following crop. However, it is important to note that stubble provides the much needed C source to soil microorganisms in Australian agricultural soils.

Deep placement of the N improved N capture by crops irrespective of stubble management, but was especially effective in stubble-retained situations. Although N tie-up is a temporary issue, it could be potentially costly as early N supply is important for plant nutrition and health. In summary, N tie-up is an easily managed issue for growers with suitable attention to the management of stubble and N fertiliser.

Useful resources

Maintaining profitable farming systems with retained stubble

References

Angus J., Grace P (2017). ‘Nitrogen balance in Australia and nitrogen use efficiency on Australian farms’. Soil Research 55 (6) pp 435-450.

Gupta VVSR (2016). Factors affecting Nitrogen supply from soils and stubbles. GRDC Research Update held in Adelaide during 9-10th February, Adelaide SA.

Hart PBS et al. (1993). The availability of the nitrogen in crop residues of winter wheat to subsequent crops. Journal of Agricultural Science 121, 355-362.

Hunt JR et al. (2016). Sheep grazing on crop residues do not reduce crop yields in no-till, controlled traffic farming systems in an equi-seasonal rainfall environment. Field Crops Research 196, 22-32

McBeath TM et al. (2015a). Break Crop Effects on Wheat Production across Soils and Seasons in a Semi-Arid Environment. Crop and Pasture Science. 66: 566-579.

McBeath TM et al. (2015b). Managing nitrogen nutrition under intensive cropping in low rainfall environments, Australian Agronomy Conference, Hobart, Tasmania.

Swan AD et al. (2017). The effect of grazing and burning stubbles on wheat yield and soil mineral nitrogen in a canola-wheat-wheat crop sequence in SNSW.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC — the author would like to thank them for their continued support. We would especially like to thank Darryl Moore (Horsham), the Coleman family (Temora), the O’Connor family (Harden) and the Loller family (Karoonda) for the long-term use of their land for these experiments. We also acknowledge the expert technical assistance provided by CSIRO staff (Steve Szarvas, Stasia Kroker, Bill Davoren, Willie Shoobridge, Brad Rheinheimer, Mel Bullock, John Graham), BCG staff (Claire Browne) and FarmLink Research (Paul Breust, Tony Pratt, Colin Fritsch) who managed and measured the experiments. Funding was provided through GRDC projects CSP00174, CSP00186, MSF00003, BWD00024 and CSP00186.

Contact details

Vadakattu Gupta
CSIRO Agriculture and Food, Waite campus, SA 5064
0427790538
Gupta.Vadakattu@csiro.au

GRDC Project Code: CSP186, CSP174, MSF0003, BWD00024,