Irrigated wheat agronomy in northern cropping environments ‐ what's critical?

Call to action/take home messages

  • The most important decision to consider when growing an irrigated wheat crop is whether it really needs to be fully irrigated. Deficit irrigation is often more profitable than full irrigation, and has the added bonus of being less likely to cause lodging.
  • Lodging can drastically reduce wheat yield and cause difficulties at harvest. A package of agronomic measures should be used to reduce lodging risk including variety choice, irrigation strategy, N application strategy, plant population and Plant Growth Regulators (PGRs).
  • Varieties respond differently to in-crop N application. Suntop, Wallup, Kennedy and LRPB Cobra often had higher yields when N was applied ‘in-crop’, but Mitch and LRPB Lancer did not. In-crop N application increased protein by 0.4% for most varieties and locations.
  • PGRs gave the biggest yield response (0.6 t/ha) on well irrigated paddocks with more than 120 kg/ha of nitrogen available at sowing, when lodging was severe. However, PGRs still improved yield by 0.32 t/ha on high sowing N paddocks when there was little or no lodging. PGRs had a negative effect on yield for some varieties in an experiment that was only partially irrigated and experienced lower yields in the region of 5.5 t/ha.
  • A guide to identifying lodging risk has been developed and is included in this paper. It is also detailed in Chapter 7 of the project publication ‘Better Irrigated Wheat Agronomy’ (Reference 1) which is available in hard copy here at the Goondiwindi Updates or from the authors. It can also be downloaded from the GRDC website at Better irrigated wheat agronomy North.
  • All varieties have advantages and disadvantages for irrigated wheat production so please choose carefully after consulting the ‘Better Irrigated Wheat Agronomy’ publication (Reference 1) and the QLD and NSW variety guides. LRPB Cobra and Dart are the two most lodging resistant varieties for QLD and NNSW, but can still lodge under extreme conditions.
  • Growers may achieve improved yield by using row spacings as narrow as 19cm (7.5 inches) compared to 28 or 38 cm (11 and 15 inches), but the results weren’t consistent across varieties and locations. Achieving a yield benefit from narrow row spacing was more likely when lodging was avoided.

Introduction

In 2008, many growers from irrigated farms in the northern region decided to take advantage of high wheat prices of over $400 per tonne, sowing large areas of irrigated wheat with the aim of fully irrigating the crop and producing yields of 7 or 8 t/ha. Unfortunately, widespread lodging at the end of that season caused large yield losses, which were conservatively estimated to have cost the industry more than $20 million in lost production.

At that time, little was known about growing irrigated wheat in the northern region. The GRDC subsequently invested in research with the CSIRO and several other collaborators, most recently through the ‘Better Irrigated Wheat Agronomy’ project led by CSIRO.

This paper summarises key findings from the Better Irrigated Wheat Agronomy project. However, we recommend that growers and agronomists involved in irrigated wheat production should read the full project results booklet to ensure they understand the full detail. The book is called: ‘Better Irrigated Wheat Agronomy: lessons from eight years of on-farm research and experiments in Queensland and northern New South Wales’.(Reference 1) and is available at the publications desk. A hard copy can also be obtained from Dr Allan Peake (CSIRO) or Matt Gardner (AMPS Research). It can also be downloaded from the GRDC website.

The book contains recommendations for:

  • whole-farm irrigation scheduling
  • agronomy to avoid lodging
  • the best varieties for irrigation
  • nitrogen application strategies
  • when to use plant growth regulators (PGRs) and other general agronomic techniques.

It is intended to be read as a companion to a pre-existing publication Irrigated Wheat – Best Practice Guidelines in Cotton Farming Systems’ (Reference 2). This publication covered topics such as disease management, irrigation scheduling for individual paddocks and establishing crops in cotton rotations. Readers may also benefit from consulting the Waterpak manual (Reference 3) for a broader understanding of irrigation practices.

When reading this paper, it is important to understand that growers wanting to try new techniques or varieties should do so on a small scale first, to ensure new techniques work for their specific situation. The results from our experiments may not apply to all individual farms due to seasonal and locational variation (i.e. farm management requirements, available moisture, crop rotational history etc.). Additionally, readers should be aware that these recommendations have been developed specifically for vertosol soil types and farms within the ‘old’ GRDC northern region (Queensland and northern NSW), and may not be applicable to other soil types or regions.

We hope that this paper and the booklet are helpful to you, and we wish you good luck with your next irrigated wheat crop.

1. Water budgeting

Irrigated wheat growers need to decide if fully irrigating a wheat crop is the most profitable option for their situation. The alternative is known as deficit irrigation – the practice of irrigating with less than the crops maximum water requirement. Deficit irrigation allows growers to grow a larger area of wheat with the same amount of irrigation water in storage.

Deficit irrigation of a large crop area is associated with greater production risk, but can be the most profitable option in high rainfall environments and seasons when there are significant amounts of stored water in the soil profile.

Full irrigation of a smaller crop area has lower production risk, but also has lower potential profits in many cases. This strategy is more likely to be the most profitable option when rainfall and stored soil water is limited, and the cost of water is high.

A study published by CSIRO in 2016 (Reference 4) investigated whether full irrigation or deficit irrigation was more profitable for growers in Queensland and northern NSW. The study was conducted using the APSIM simulation model, which is widely used to investigate complex whole-farm questions such as this one. A range of whole-farm irrigation scenarios were investigated, but all strategies had access to the same amount of irrigation water (1300 megalitres) that was in storage at sowing, and 1000 hectares of land was available to be irrigated. The water was either used to fully irrigate a smaller area, or partially irrigate increasingly larger areas. The amount of irrigation applied per hectare therefore had to decrease as the irrigated crop area became larger.

A long-term climate data set was used to see if a particular strategy worked for different seasons (i.e. wet, dry or average), for three locations: Emerald, Goondiwindi and Gunnedah. A wheat price of $250 per tonne at the farm gate was assumed and two different water cost scenarios were compared, where low cost water was $40 /ML and expensive water was $120 /ML. The simulations were also conducted for two different amounts of stored soil water at sowing, either zero or 100mm.

The study used the concept of ‘risk efficiency' to determine the best strategy, rather than using a long-term average gross margin. Risk efficiency is the balance between risk and potential profit.For example,if you irrigate a large area with just a single furrow irrigation during the season, your risk is high because if in-crop rainfall is low, a high proportion of the water will be lost to evaporation and low yields will be the result. But if rainfall is high and the single furrow irrigation results in a yield of 5 t/ha, then it can be a very profitable decision. Risk efficiency balances risk and profit by assuming that growers require a 50% increase in profit (on average over many seasons) in exchange for twice as much production risk– i.e. it assumes growers will accept twice as many unprofitable seasons in exchange for achieving 50% more profit in the long term due to outstanding profits in the good seasons.

The results of the study are summarised in Table 1 and Table 2. The average growing season rainfall was 212 mm at Gunnedah, 174 mm at Goondiwindi and 100 mm at Emerald. Generally, they showed that in a dry, warm environment (Emerald), the most risk efficient strategy is one which applies more irrigation water to a smaller area of land. At Gunnedah, a cooler environment with higher and more reliable winter rainfall, the more profitable long-term strategy was to deficit irrigate, spreading water over a wider area.

As water became more expensive, concentrating the water on a smaller area was more likely to produce better profits in the long run. This may seem counter-intuitive, but it works out this way because larger areas of partially irrigated wheat are more likely to have greater amounts of ‘wasted’ water through evaporation. Smaller areas of fully irrigated wheat are also more likely to conserve water in the soil which is then available for the next crop, and this remaining stored water was valued at the same price as irrigation water in the CSIRO study.

Table 1. Number of furrow irrigations*# to achieve maximum risk-efficiency when stored soil water at sowing is zero. All strategies assume the same amount of irrigation water is held in storage at sowing, therefore a smaller area must be grown when more irrigations are applied.

Water cost

Gunnedah

Goondiwindi

Emerald

($40/ML)

Sowing* + 1-2 in-crop#

Sowing* + 1-2 in-crop#

Sowing* + 2-3 in-crop#

($120/ML)

Sowing* + 1-2 in-crop#

Sowing* + 2-3 in-crop#

Sowing* + 2-3 in-crop#

*Sowing irrigation assumed to be 1.7 ML/ha. #In-crop irrigations are assumed to be 1 ML/ha. Irrigation amounts are assumed added to root zone not including distribution and application losses, which vary between soil types and paddocks. Note: applying the greater number of irrigations to a smaller area reduces risk of crop failure in a dry season, but reduces potential profit in a high rainfall season.

Table 2. Number of furrow irrigations# to achieve maximum risk-efficiency when stored soil water is 100 mm and no irrigation is required at sowing. All strategies assume the same amount of irrigation water is held in storage at sowing, therefore a smaller area must be grown when more irrigations are applied.

Water cost

Gunnedah

Goondiwindi

Emerald

($40/ML)

1 in-crop#

1 – 2 in-crop#

3 – 4 in-crop#

($120/ML)

1 - 2 in-crop#

1 – 2 in-crop#

3 – 4 in-crop#

#Irrigation applications assumed to be 1 ML/ha. This irrigation amount is assumed added to the crop root zone and does not include distribution and application losses, which vary between soil types and paddocks. Note: applying the greater number of irrigations to a smaller area reduces risk of crop failure in a dry season, but reduces potential profit in a high rainfall season.

2. Irrigating for maximum yield

Without going to the full detail contained in the project book, the following points briefly describe the key aspects of irrigating when a grower has decided to irrigate for maximum yield:

  • Stored soil water is critical to irrigated crops. Growers need to understand their soil plant available water capacity (PAWC) and how this impacts on their irrigation strategy, and monitor soil water during the season.
  • Irrigating early in the season can ‘bank’ stored water in the soil, which helps avoid stress late in the season when crop water use can be as high as 7mm per day.
  • Season water budget should allow for 50-100mm of water to remain in the soil profile at the end of the season in order to minimise late season water stress. This will be in addition to the 4.5-5.5 ML/ha typically needed for an 8t/ha wheat crop. And remember, irrigation losses are not included in the 4.5-5.5 ML/ha water requirement, so the required stored irrigation water at the beginning of the season can be closer to 7-10 ML/ha depending on storage, distribution and application efficiency.
  • Sow different varieties in a way that allows them to be irrigated separately if necessary. This allows you to change irrigation strategy on one variety if it lodges, or has different maturity to the other.
  • Avoid irrigating when storms or strong winds are forecast, to reduce the risk of lodging.
  • Remember that maximising yield may not maximise profit (see section 1).

3. Understanding and avoiding lodging

Lodging occurs when wheat crops ‘fall over’, and is caused by many factors including tall varieties, high yield potential, a thick canopy, wind, rain and wet soil. The average yield loss caused by lodging in 2008 was 1.7 t/ha, with the worst lodged paddock losing over 4 t/ha.

Lodging can affect yield and gross margins in many ways, including; physiological disruptions of crops close to flowering, increased risk of canopy diseases, increased risk of grain sprouting and shattering, decreased grain recovery and slower harvesting.

Lodging risk varies between seasons due to variations in yield potential and the intensity and frequency of storms, wind and rain. When aiming to achieve high wheat yields it is important to understand that lodging risk can never be completely eliminated. Extreme storms can occur that can cause lodging even in the most lodging resistant crops. On the other hand, it is possible for high lodging-risk strategies to ‘get lucky’ and avoid lodging in years when favourable weather is experienced during grain filling.

There are several management strategies that can be used to reduce lodging risk, primarily by controlling how the plant grows and acts as a lever. Dense early-season biomass (i.e. thick, lush, large leaves at the end of tillering) increases lodging risk by increasing shading of the stem base and soil surface. This increased shading has been shown to reduce both the strength of the stem and the spread of surface roots. Therefore, reducing biomass during tillering reduces lodging risk.

Techniques used to avoid lodging include:

  • Choose lodging resistant varieties.
  • Do not increase plant populations for irrigated wheat production. Plant populations similar to those used in rainfed wheat production (i.e. 100 plants / m2) are adequate to produce maximum wheat yield in most irrigated situations. Higher populations are more at risk of lodging but could sometimes be appropriate if the sowing date has been substantially delayed, or when sowing N is low enough to use in-crop N application to reduce lodging risk.
  • Apply less nitrogen at sowing and more during the growing season according to plant demand (see section 4). This reduces canopy density at the end of tillering, which is related to an increased risk of lodging.
  • If you can’t avoid sowing irrigated wheat on a high-nitrogen soil, consider reducing irrigation during tillering to prevent overly-dense canopy growth. Increased water availability will increase nitrogen availability to the crop, so the desire to maintain a full profile of moisture early in the season may need to be compromised in high nitrogen fields.
  • Apply plant growth regulators (PGRs) at the correct growth stage. Results from the project show that PGR’s can reduce lodging risk and often have a positive impact on yield even when no lodging occurs. See section 5 for more detail.
  • Late sowing can reduce lodging by reducing yield potential but is not foolproof, because late sown crops face greater exposure to spring storms than an early sown crop.
  • Partial irrigation is less susceptible to lodging than full irrigation, because crops with yield potential of less than 6 t/ha are unlikely to lodge. However, partially irrigated crops can still lodge if rainfall is greater than average especially if the crop has high soil N reserves at sowing. Therefore lodging reduction measures should still be considered for partially irrigated crops.

There is no ‘silver bullet’ to prevent lodging. Lodging risk varies between seasons because yield potential varies between seasons, but also due to variation in the occurrence, intensity and frequency of storms, wind and rain. A range of measures will work together to build a lodging resistant crop.

4. In-crop N application techniques

In-crop N application is one of several ‘canopy management’ techniques that minimises excess canopy growth and can reduce lodging risk. The main findings of our project were that:

  • Soil + fertiliser N at sowing should total approx. 30-70 kg/ha N in order to induce N stress and reduce canopy growth during tillering, although different soil types and locations may need slightly different targets in order to account for high soil fertility or cold temperatures.
  • In our experiments, crops needed approx. 200 kg/ha of soil + fertiliser N supplied at (or before) GS31 in order to reliably achieve high yields in different locations and seasons.
  • Varieties responded differently to in-crop N application. Suntop, Wallup, Kennedy and LRPB Cobra often had higher yields when N was applied in-crop, but Mitch and LRPB Lancer did not.
  • In-crop N application increased grain protein by 0.4% for most varieties and locations.
  • In-crop N application tended to reduce screenings and increase hectolitre weight, but this was not consistent for all varieties.
  • Lodging was not always reduced by in-crop N application, possibly because in-crop N application often increases yield potential which in turn increases lodging risk.

5. Plant growth regulators

We used a PGR mix of 1000 mL/ha chlormequat chloride and 200 mL/ha trinexapac-ethyl for all our PGR experiments. The mix was tested on a range of combinations of variety, sowing dates, N application strategies and row spacing, and the project found that:

  • The PGR mix gave the biggest yield response on well-irrigated paddocks with more than 120 kg N/ha available at sowing, with an average yield increase of 0.35 t/ha (Figure 1, Figure 2).
  • The largest yield responses were observed on heavily lodged fields with high sowing N (by 0.6 t/ha on average). However, yield was still improved (by 0.32 t/ha) on high sowing N paddocks with little or no lodging (Figure 2).
  • The PGR mix rarely improved yield on paddocks with low sowing N when in-crop N application was successfully implemented (Figure 1). However, lodging was reduced even more by combining in-crop N application with PGR application, and this may be beneficial in high lodging risk seasons.
  • Grain protein tended to be higher and screenings tended to be lower when the PGR mix was applied. Hectolitre weight had a slight tendency to be lower when the PGR mix was applied.
  • PGRs can decrease yield in partially irrigated or rainfed crops.
  • PGRs didn’t always reduce lodging, and should be used in conjunction with other lodging control measures.

Figure 1 is a set of three pie graphs which show the proportion of PGR trial plot comparisons resulting in a statistically significant yield increase or decrease for well irrigated paddocks with (a) all N applied at sowing, (b) 120-150 kg/ha N at sowing with the remainder applied ‘in-crop’, and (c) low sowing N (50-80 kg/ha N applied at sowing) followed by in-crop N application.

Figure 1. Proportion of PGR trial plot comparisons resulting in a statistically significant yield increase or decrease for well irrigated paddocks with (a) all N applied at sowing, (b) 120-150 kg/ha N at sowing with the remainder applied ‘in-crop’, and (c) low sowing N (50-80 kg/ha N applied at sowing) followed by in-crop N application.

Figure 2 is a column graph which shows the yield benefit gained by using the best practice PGR mix on well irrigated fields with high sowing N (greater than 120 kg N/ha), for a range of lodging event severity.

Figure 2. The yield benefit gained by using the best practice PGR mix on well irrigated fields with high sowing N (greater than 120 kg N/ha), for a range of lodging event severity.

6. Identification of lodging risk during the season

A lodging risk identification guide has been developed to assist growers and agronomists in understanding which paddocks are most at risk of lodging (see chapter 7 of the project results booklet). It is particularly useful when the last crop was a legume, or when soil tests haven’t been taken (or were taken a long time before sowing). The process is summarised as follows:

  • a) Use N deficient or N-rich strips in the field to create a visual indicator of paddock fertility. Different N zones will be obvious in a low fertility field where the added N will make a big difference to crop growth. On the other hand, they won’t look any different in a high N field because young crops don’t need a lot of N. In a field where large quantities of fertiliser are being applied at sowing (i.e. 100-200 kg/ha N), this involves leaving a strip where no fertiliser is applied. In a field where no fertiliser is applied, it means applying fertiliser (approximately 50 kg/ha N) to a test strip.
  • b) At GS30-31, visually assess the two N zones and compare to the pictures in Table 3 to see whether the field is high, medium or low in fertility. A large difference between the two N zones means the field is low in fertility, whereas if there is no difference the field is highly fertile. Alternatively, a hand-held Greenseeker can be used to quantify lodging risk. Using the following equation and Table 3, Greenseeker (or NDVI) readings can be compared for N zones and used to calculate an NDVI response index.

Equation NDVI reading (N rich area) divided by NDVI reading (N deficient area) equals NDVI response index

  • c) Use the paddock fertility rating in conjunction with the lodging risk calculator (Figure 3) to determine likely lodging risk for the agronomic management and climate forecast. Add up the scores in parentheses () for each factor applicable to your situation, and relate the score the interpretation notes at the bottom of Figure 3.

Table 3. Different lodging risk scenarios based on Normalised Difference Vegetative Index (NDVI) response index from N rich or strips with no additional N applied, seen at GS30-31 in paddock scenarios with different fertility.

Table 3 is a table showing different lodging risk scenarios based on Normalised Difference Vegetative Index (NDVI) response index from N rich or strips with no additional N applied, seen at GS30-31 in paddock scenarios with different fertility. The table compares photos from nitrogen rich zones to ones with no nitrogen added.

Figure 3 is a lodging risk calculator for fully-irrigated wheat fields

Figure 3. Lodging risk calculator for fully-irrigated wheat fields

7. Best varieties for irrigation

Extensive variety testing was conducted at Spring Ridge, Narrabri, Emerald, Gatton and Brookstead from 2012-2016. The results of the lodging screening experiments have been used to update the Queensland and NSW Variety Guide lodging ratings, and reported in previous GRDC update papers (Reference 5,6,7). The results were too numerous to fully reproduce even in the project booklet, which contains yield, protein, screenings and hectolitre weight data for selected varieties in the last three years of experiments (Reference 1). We have summarised findings on the best varieties in Table 4 of this paper. LRPB Cobra and LRPB Dart are the two most lodging resistant varieties, but both of these varieties can still lodge under extreme lodging conditions.

All varieties have advantages and disadvantages for irrigated wheat production, so choose varieties carefully. Please consult QLD and NSW variety guides to fully evaluate variety suitability.

Note: the most lodging resistant varieties may not achieve the highest quality grades (e.g. APH, Durum) and growers need to balance their desire to avoid lodging against the potential gross margins of higher quality varieties with less lodging resistance.

Table 4. Recommended wheat varieties for irrigation in Queensland and northern NSW. Readers are advised to also consider additional variety attributes (particularly disease susceptibility) as contained in the QLD and NSW wheat variety guides before choosing a wheat variety

Maximum quality class

Variety

Lodging rating

Notes

APH

LRPB Dart

R-MR

LRPB Dart is particularly quick maturing and has a slightly lower yield potential. Tended to have lower HLW (hectolitre weight) and higher screenings than other quick varieties. Excellent lodging resistance, a good choice for paddocks with extremely high N levels.

Wallup

MR

Yields well at cooler locations and has high N recovery which allows it to achieve high protein concentrations as well as yield. Generally had lower screenings than most varieties of similar maturity but did have very low HLW at Spring Ridge in 2015 in a hot dry finish to the season. Wallup has short, upright stems that some growers prefer to use on wide row spacing, because it allows easier sowing of a double-crop in the inter-row spacing. Has sometimes lodged when sown early in the sowing window, so we recommend mid-window sowing for Wallup.

Suntop

Excellent yield potential across a range of environments, tillers prolifically. Does tend to have lower protein which is partly due to its higher yielding ability. N recovery is not as good as LRPB Spitfire or Wallup.

LRPB Crusader

Similar to LRPB Dart with slightly more lodging susceptibility and a higher HLW on average. Achieved a QLD record irrigated yield of 8.2 t/ha at Brookstead in 2011.

LRPB Spitfire

MR-MS

Only included in the final two years of field experiments but was consistently high yielding with the highest protein and N uptake of the quick maturing varieties, and high HLW as well.

LRPB Lancer

Borderline ‘MS’ lodging rating, very high tillering ability. Recommended only for partial irrigation due to its higher lodging susceptibility. The best long-season option for APH quality, but lower yielding than non-APH long-season varieties

Kennedy

Yields well in warmer environments such as Central Queensland and Lockyer Valley. Low tillering type, tends to have slightly lower screenings than some other quick varieties.

Durum

EGA Bellaroi

MR-MS

Similar yield potential to Caparoi, high grain quality. Has slightly higher N recovery but lower HLW than Caparoi.

Caparoi

Similar yield potential to EGA Bellaroi, high grain quality. Has slightly lower N recovery but higher HLW than EGA Bellaroi.

DBA Aurora

MS

Newly released varieties for which we only generated limited data. DBA Aurora has higher yield potential than most Durum varieties, but tends to have lower grain protein. DBA Lillaroi is rated by regional agronomists as having exceptional grain quality, similar to EGA Bellaroi.

DBA Lillaroi

Other

LRPB Cobra

R-MR

Excellent yield potential and lodging resistance, has high levels of N recovery. Had highest yield but also the highest level of screenings at Spring Ridge in 2015 in a hot, dry finish.

Livingston

MR

Performs particularly well at Narrabri, and also had high yield at Spring Ridge in 2015 under later water stress. High N recovery rates.

Mitch

Good yield potential especially in partially irrigated situations, but does tend to have higher level of screenings in these situations. Tillers prolifically, lower N recovery than LRPB Cobra or LRPB Trojan.

Sentinel 3R

Longer season type with excellent yield potential and high levels of N recovery. Good lodging resistance. The highest yielding variety at Spring Ridge in 2014.

LRPB Trojan

MR–MS

Excellent yield potential but less lodging resistance than LRPB Cobra.

Trojan was the highest yielding variety in several experiments.

R-MR: resistant to moderately resistant to lodging
MR: moderately resistant to lodging
MR-MS: moderately resistant to moderately susceptible to lodging
MS: moderately susceptible to lodging
APH: Australian Prime Hard (standards set by Wheat Quality Australia)
HLW: Hectolitre weight

8. Best sowing date for irrigated wheat

Sowing date is known to have a big impact on yield in dryland wheat cropping, with earlier sown crops likely to have higher yields as long as frost damage is avoided. However, in high yielding wheat production regions such as Europe and New Zealand, early sowing is known to cause increased lodging risk. One of the aims of our project was to determine whether sowing later could be used to decrease the risk of lodging, without reducing yield.

From 2014 to 2016 we tested six of the highest yielding irrigated varieties for yield and lodging on an early and late sowing date, at Emerald, Gatton, Narrabri and Spring Ridge. The varieties were LRPB Cobra, LRPB Trojan, Kennedy, EGA Bellaroi, Caparoi and Suntop. The first sowing date was between the 13th and 19th of May for all experiments except Narrabri in 2015 where it was delayed until 25th May due to operational difficulties. The second sowing date was eight days later at Gatton, two weeks later for Emerald and Narrabri, and three weeks later at Spring Ridge. Results of the experiments are summarised as follows:

  • Earlier sowing increased yields by 0.4 t/ha on average with yield gains over 1 t/ha experienced in two experiments. However, significant yield decreases were associated with early sowing in two other experiments. No frosts were experienced at flowering during these trials, and earlier sowing obviously increases frost risk as well.
  • Later sowing did not guarantee less lodging. Later sown crops can experience storms at earlier crop stages that are more susceptible to lodging damage.
  • Irrigated crops can take longer to reach flowering than dryland crops especially in dry seasons or regions, which means they can be sown slightly earlier and still flower at the same time as dryland crops.
  • Longer season varieties are typically sown early but tend to be highly lodging susceptible, and growers should reconsider growing such varieties under irrigation.

9. Optimum row spacing for irrigated wheat

Many dryland growers now sow wheat with a row spacing as wide as 38 cm (15 inches), however the project team was often asked if a narrower row spacing can maximise yield in irrigated wheat fields.

To examine this question, we conducted several row spacing experiments in the final three years of the project at Spring Ridge and Gatton. Alternative row spacings were tested with different agronomic regimes (PGRs and the in-crop N application strategy) on a small number of varieties. Due to experimental limitations, only 25 and 38 cm (10 and 15 inch) row spacings were compared at Gatton, while 19, 28 and 38 cm (7.5, 11 and 15 inch) row spacings were compared at Spring Ridge. The plant population was always 100 plants /m2, which meant that in the narrow-row crops the in-row plant population was lower (i.e. there were less plants per linear metre of row compared to the wider row spacing, but the same number of plants overall). The results showed that:

  • Growers may get inconsistent results from narrow row spacing in irrigated wheat production.
  • No yield benefit was gained by using the 25 cm row spacing when compared to the 38 cm row spacing at Gatton, a warmer short season environment that achieved lower yields. It is possible that 19 cm wide rows could have improved yields at Gatton if they had been tested.
  • When lodging was minimal, the 19 cm row spacing yielded 0.7 t/ha more than the 38 cm row spacing at Spring Ridge (Figure 4).
  • When lodging was severe and PGRs were applied, an increase of 0.4 t/ha was achieved using the 19 cm row spacing at Spring Ridge for five out of six varieties.
  • When lodging was severe and PGRs were not applied at Spring Ridge, the narrow row spacing caused a yield increase or decrease depending on the variety.
  • These results were obtained using a plant population of approx. 100 plants /m2. Growers should be aware that a higher plant population would increase lodging risk and could cause different outcomes.

Figure 4 is two column graphs (a) and (b) which show yield of alternative row spacing treatments at Spring Ridge in 2015 and 2016 when lodging was negligible (a) Average of long season varieties (Mitch  and LRPB Lancer ) sown on the early sowing date, (b), average of quicker maturing varieties (EGA Bellaroi , LRPB Cobra , Suntop , LRPB Trojan ) sown on the later sowing date.

Figure 4. Yield of alternative row spacing treatments at Spring Ridge in 2015 and 2016 when lodging was negligible (a) Average of long season varieties (Mitch and LRPB Lancer) sown on the early sowing date, (b), average of quicker maturing varieties (EGA Bellaroi, LRPB Cobra, Suntop, LRPB Trojan) sown on the later sowing date.

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. Funding from the Australian Federal Government and CSIRO is also gratefully acknowledged.

Northern region growers & agronomists are gratefully acknowledged for hosting experiments on farms and assisting with on-farm demonstration trials. In particular we would like to thank Greg Giblett, Derek Gunn, Angus Murchison, Gus Hamilton, Greg Hamilton, Tim Richards, Jamie Street, Peter Haslem, Jim Hunt, Hamish and Fraser Bligh, Drew Penberthy, Paul Castor, Jeremy Dawson, Graham Spackman, Jamie Iker, Josh Bell, Phil Lockwood, Steve Madden, Peter McKenzie, Bede Omara, Russel Wood, Ed Offner and Trevor Philp. These gentlemen assisted with field monitoring and farm visits and/or answered numerous questions to assist in constructing simulation scenarios that were relevant to growers of the northern grains region. Feedback from John Lacy, Dr Andrew Fletcher (CSIRO) and Douglas Lush (DAFQ) on the final draft of this best practice guide was also gratefully appreciated.

Statistical support from Michael Mumford (DAFQ) was helpful, professional, and vital to the success of the project. Additionally, Douglas Lush and Don Baills at DAFQ offered support each year tracking down seed stocks for hard-to-find varieties. We also thank Geoff Moore (National Variety Trials), Jon Hunt and Rob Presser (Kalyx Australia), Pauline Twidale (Pacific Seeds), Longreach Plant Breeding, Australian Grains Technologies, Gururaj Kadkol (NSWDPI), and Jason Able (Durum Breeding Australia and University of Adelaide) for their assistance in sourcing seed, often at short notice.

Technical Support from Andy Hundt, CSIRO Narrabri was greatly appreciated, as was that of Steve Soderquist, Phil van Drie, Ryan Kearns, Greg Roberts and Terry Collins at CSIRO Gatton. Farm staff at the NSWDPI Breeza Research Station, the University of Sydney Plant Breeding Institute at Narrabri, and the DAFQ farms at Emerald and Kingsthorpe were also very helpful in conducting field experiments. The patient assistance of CSIRO Technical Staff in Toowoomba (John Lawrence and Ainsleigh Wixon) was also greatly appreciated.

Conclusion

Irrigators will grow irrigated wheat when commodity prices and water availability combine to make it an attractive proposition. Growers would benefit from growing a small area of wheat regularly to ensure they have seed of the best irrigated varieties on hand, and to keep their irrigated wheat agronomy skills up to date. We hope that this paper and the ‘Better Irrigated Wheat Agronomy’ publication will be a useful reference for many of the questions that arise when growing an irrigated wheat crop.

References

  1. Peake, A.S., Poole, N., Gardner, M., Bell, K.L., Das, B.T. (2017). Better irrigated wheat agronomy: Lessons from eight years of on-farm research and experiments in Queensland and Northern New South Wales. The Commonwealth Scientific and Industrial Research Organisation, ACT, Australia. ISBN 978-1-921779-49-7 (Print) ISBN 978-1-921779-50-3 (Online)
  2. Sykes, J (Ed.) (2012). Irrigated Wheat Best Practice Guidelines In Cotton Farming Systems. Cotton Catchment Communities CRC and the Grains Research and Development Corporation. ISBN: [978-0-9872308-1-2]
  3. Wigginton (Ed.) (2013). Waterpak – a guide for irrigation management in cotton and grain farming systems. Cotton Research and Development Corporation. ISBN: 1 921025 16 6.
  4. Peake, A.S., Carberry, P.S., Raine, S.R., Gett, V., Smith, R.J. (2016). An alternative approach to whole-farm deficit irrigation analysis: evaluating the risk-efficiency of wheat irrigation strategies in sub-tropical Australia. Agricultural Water Management 169, 61-76.
  5. Peake A.S., Gardner, M., Bell, K., Poole, N., (2016). The effect of sowing date, variety choice and N application timing on lodging risk and yield of irrigated wheat.In GRDC Northern Region Grains Research Updates, Goondiwindi, 1-2 March, 2016
  6. Peake A.S., Gardner, M., Bell, K., Poole, N., Fainges, J. (2015). Irrigated wheat agronomy x variety trials: 2014 trial update. In GRDC Northern Region Grains Research Updates, Goondiwindi, 3-4 March, 2015.
  7. Peake A.S., Gardner, M., Poole, N., Bell, K. (2014). Beyond 8 t/ha: varieties and agronomy for maximising irrigated wheat yields in the northern region. In: John Cameron (Ed), GRDC Adviser Updates 2014, Coonabarabran and Goondiwindi; 267-277.

Contact details

Dr Allan Peake
CSIRO Agriculture and Food, PO Box 102, Toowoomba, 4350
Ph: (07) 4571 3212
allan.peake@csiro.au

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.

GRDC Project code: CSA00039