Strategies and tactics to extend whole-farm water-use efficiency - sow on-time or early (VIC data)

Authors:

James Hunt¹, John Kirkegaard¹, Julianne Lilley¹, Susie Sprague¹, Tony Swan¹, Brad Rheinheimer¹,

Tracey Wylie², Nick Poole², Dannielle McMillan³, Alison Frischke³, Annieka Paridaen⁴, Ed Hilsdon⁴, Gina Kreeck⁴, Paul Breust⁵ and Tony Pratt⁵,

¹CSIRO Sustainable Agriculture Flagship, ²FAR Australia, ³BCG, ⁴SFS, ⁵FarmLink Research

Take home messages

• Maximise wheat WUE by ensuring as much crop flowers during the optimal period as possible – sow on time or early!
• Early sown, slow maturing varieties (winter and spring) yield as well as or better than faster maturing varieties sown later.
• Including an early sown variety in a cropping program can greatly increase whole-farm yield.

Introduction

The dry autumn and frosty spring of 2013 continues the pattern of the last 17 years, and is likely to continue into the future (Cai et al. 2012). Getting wheat to flower during the optimal period in a given environment is a huge driver of yield and water use efficiency, particularly with the recent pattern of late frosts, early heat and dry autumns making this very difficult to achieve. The majority of current wheat varieties need to be sown in the first half of May in order to flower during the optimal period for yield in most environments, which unfortunately coincides with the period of recent rainfall decline.

Growers wishing to maximise farm water-use efficiency need to adopt strategies that will allow them to get as much of their wheat crop as possible flowering during the optimal period in their environment. This means having the varieties, rotations, equipment and level of organisation required to take advantage of any sowing opportunity that arises from late summer onward. This article reports results from several experiments conducted across southern Australia investigating the potential for earlier sowing to increase wheat yields in the face of autumn rainfall decline.

Optimal flowering periods

Every production environment has an optimal period in which wheat crops need to flower in order for yield and water-use efficiency to be maximised (Figure 1). This period is defined by an optimal balance between temperature, radiation and water availability, and also decreasing frost risk and increasing heat risk. Optimal flowering periods vary for different locations e.g. the optimal flowering period for the northern Mallee is at the start of September, whilst in SW Victoria it is at the end of October. Growers and advisers should have a firm understanding of the optimal flowering period in their environment, and how to achieve it from different sowing dates with different varieties.

Figure 1. The relationship between flowering time and yield at Kerang and Lake Bolac – optimal flowering periods are highlighted by light and dark grey boxes. Curves are derived from APSIM from 120 years of climate and with a yield reduction for frost and extreme heat events. Optimal flowering periods are mid-September at Kerang, and late October at Lake Bolac. 

The key challenge for growers wanting to maximise whole-farm yield and WUE is to have as much of their wheat crop as possible flowering during the optimal period. This has become increasingly difficult for three reasons;

1. Autumn rainfall has declined significantly in the last 17 years as a direct consequence of anthropogenic climate change.
2. Recently released varieties for most environments have a very narrow range of maturities and unstable flowering times and only flower during the optimal period if sown between late April and late May.
3. Farm sizes and cropping programs are getting bigger.

For these reasons, growers increasingly need to be able to take advantage of whatever sowing opportunities they can get, and there are three strategies that can be employed in order to ensure as much wheat crop as possible flowers during the optimal period.

1. Sow winter wheats from late February through to April.
2. Sow slower maturing spring wheats from mid-April to early May.
3. Sow mid-fast wheats from late-April onward, including dry sowing if the break has not arrived by this time.

Currently most growers are comfortable with the third strategy, and this has been the principal adaption to the drying autumns. However, there is great potential for the first two strategies to complement May sowing and further increase farm yield.

Achieving optimal flowering periods – experiments 2013

February-March rainfall has not declined over the past 17 years, and in some areas it has increased (Hunt and Kirkegaard 2011). This rain can be used in lieu of the traditional autumn break to establish crops, but winter wheats are required to achieve this. Winter wheats have a vernalisation or cold requirement which means they will not develop beyond tillering until they have been exposed to a certain duration of low temperatures (~4-18 C). This gives them a very stable flowering date from a broad range of sowing dates (Figure 2). They can even be sown in summer, and not flower until the optimal flowering period in spring. They are often only thought of as ‘dual purpose’ (grain and graze) varieties, and have been undervalued as grain-only varieties, particularly in drier areas of the country. Unfortunately, Australian breeding programs stopped selecting for milling quality winter wheats early last decade. There are very few cultivars available, particularly for medium-low rainfall zones with alkaline soils. Commercial breeding companies have now resumed selection for winter wheats, and it is likely that they will play a greater role in our future farming systems as modern, adapted varieties are released.

Figure 2.  Flowering date of three wheat cultivars from sowings between March and June at Wagga Wagga in 2006 (GRDC, 2011).  EGA Wedgetail (―) is a winter wheat with a moderate photoperiod requirement, EGA Eaglehawk (∙∙∙∙) is a very slow maturing spring wheat with a strong photoperiod requirement and Janz (– –) is a mid-fast spring wheat with a minor photoperiod requirement (adapted from GRDC Southern Region Time of Sowing Fact Sheet using data from Peter Martin, NSW DPI).

Sowing winter wheats on summer rain

The Curyo district north of Birchip received 50 mm of rain in mid-February 2013. As part of their Grain and Graze II project, BCG took the initiative and planted an experiment (sown 26 February, 2013) which consisted of a range of winter wheat varieties from various sources planted on a chick-pea stubble. The farmer’s paddock (Kord wheat sown 18 May) provided the experimental control.

The winter lines emerged successfully and survived one of the hottest and driest autumns on record. When rains finally came at the end of May, they regenerated rapidly and were able to flower during the optimal period for that environment (Table 1). Yields of the highest yielding lines (Table 2) were equivalent to that of the farmer’s paddock sown in May (3.6 t/ha), despite most of the winter varieties having been released over a decade ago, and having no adaptation to the Mallee environment (CCN, salt or boron resistance).

Table 1. Growth stage of different varieties assessed on 12 September 2013. Mid-September is the optimal anthesis (flowering) period for wheat in the southern Mallee

All lines produced useful amounts of forage for early grazing (0.2-0.5 t/ha), however grazing reduced yield across all varieties by an average of 0.3 t/ha (main effect P<0.001, LSD (p=0.05) = 0.1). See BCG 2013 Season Research Results for more details of this trial.

Whilst this experiment really pushes the boundaries of what is possible with winter wheats, yield of winter wheats is probably maximised if sown from early April onward. Temperatures are too hot during March for wheat to use water efficiently, and sowing this early is only an advantage if it is intended that crops be grazed, or the break ends up being very late.

This experiment really shows the possibilities which winter wheats could afford our modern farming systems, provided breeding companies could release modern, adapted lines. SW and NE Victoria are relatively lucky in that they have reasonably well adapted but aging winter varieties available (Wedgetail and Whistler in NE Vic, Revenue in SW Vic). NW Victoria is not so lucky.

Sowing opportunities – take them as they arise

In regions such as southern NSW, which is lucky to have adapted winter wheats (Wedgetail, Whistler, Wylah) and slow maturing spring wheats (Eaglehawk, Bolac, Lancer) available, it has been repeatedly shown that there is a clear yield benefit from planting slower maturing varieties early (see GRDC update articles 2013). This was again the case in 2013, as demonstrated by a CSIRO and Kalyx trial comparing the grazing potential and grain recovery of winter and spring wheats sown at different times and with different grazing regimes. The experiment was located at Iandra north of Young on the SW slopes of southern NSW (571 mm median annual rainfall with equiseasonal distribution). The site received 81 mm of rain from 24 February to 1 March 2013, which was followed by 14 mm on 23 March which made for ideal sowing conditions for a winter wheat (Wedgetail) on 26 March. Another 13 mm fell on 29 March, and the crop emerged well and grew rapidly.

Like most of SE Australia, April was very dry and no further significant rain fell until mid May. Bolac was planted in its ideal window on 23 April, but into marginal seed-bed moisture, and only 30% of the crop emerged at this time. Gregory was sown dry on 8 May, and it and the remaining Bolac only emerged following 8 mm rain on 14 May. Winter was wet, but spring was dry, frosty and hot and the site received 280 mm for the growing season. The site was located on a hill and so largely avoided the black frost of 18 October which devastated crops in the region.

The yields very clearly show the benefit of using slower maturing wheats (winter and slow maturing spring) to take advantage of any establishment opportunity that arises early in the season (Table 3). Wedgetail and Bolac both had a 0.9 t/ha yield advantage over main season Gregory.

Needless to say, the Wedgetail also provided significantly more forage (2.6 t/ha) than both the spring wheats (0.8 t/ha for Bolac and 0.4 t/ha for Gregory), however grazing reduced yield. This (and the BCG data above) debunks a common misconception that winter wheats are only dual purpose varieties and have to be grazed in order to manage their canopy and achieve good yields. Winter wheats can be highly flexible grain-only varieties in their own right, and a very important tool for managing climate variability.

Table 3. Crop yields from four treatments at the CSIRO and Kalyx experiment at Iandra, NSW comparing grazing potential and grain recovery of winter and spring wheats sown at different times and with different grazing regimes

Early sowing in the HRZ

Early sowing has huge potential in the high rainfall zone of SW Victoria, as it overcomes many of the constraints of that environment e.g. water logging and damage by invertebrate pests. It also creates crops capable of achieving the high yield potentials which are frequently on offer.

As part of GRDCs new early sowing project, SFS, FAR Australia and CSIRO set up an experiment at Inverleigh in 2013 to investigate the potential for early sowing in SW Victoria. Constrained by the dry autumn, they used 15 mm of irrigation applied via drippers to press-wheel furrows to establish each time of sowing. Winter and spring were very favourable at this site (water limited yield potential was 8.2 t/ha), and Yield Prophet® was used to match N inputs to yield potential (300 kg/ha N applied in total). The trial was planted on pea-hay stubble, but there was significant take-all observed in the trial. Septoria tritici was also present despite in-furrow flutriafol and three foliar applications of fungicide.

Despite the disease pressure, yields were exceptional with the highest yields (>9 t/ha) coming from slow maturing red wheat varieties Revenue (winter) and Beaufort (slow maturing spring) sown at the end of April (Table 4). Defoliating Revenue at Z30 (to simulate grazing) increased yield such that it out-yielded Beaufort (Table 5). There is some evidence that this could have been related to the effect of grazing on severity of Septoria tritici. Grazing increased yield of Revenue by 3.3 t/ha in a section of the trial that inadvertently missed one of the foliar fungicides (and was excluded from the other analyses)!

Forrest was the highest yielding milling wheat, particularly at the early times of sowing. Due to the very kind spring experience at this location, overall there was very little effect of sowing time on yield. However even the latest time of sowing (10 May) is still considered ‘early’ in SW Victoria. The results could have been very different had a more hostile spring (e.g. 2009) been experienced.

Table 4. Yield results from the experiment conducted by SFS, FAR Australia and CSIRO at Inverleigh in 2013. Results analysed with take-all score as a co-variate

Table 5. Yield and take-all scores for Revenue (with different agronomy treatments intended to maximise yield of early sown crops) and Beaufort. There was no significant main effect of time of sowing or interaction with these treatments, and values are combined means from 26 March and 8 April sowing. Yield results were analysed with take-all score as a co-variate

* more early N to promote dry matter growth and recovery

A word on frost

The black frost of 18 October 2013 was financially and psychologically devastating to growers across southern NSW and Victoria who were affected. However, one learning from the catastrophe was that delaying sowing (or flowering) is not an effective way of managing frost risk. This was starkly illustrated by a grower (who shall remain nameless!) on the south west slopes of NSW who mixed up his seed silos and planted Spitfire on 22 April and Bolac in May. This generated a very broad range of flowering dates from ‘too early’ to ‘too late’, but all crops were equally affected.

Further evidence of this was provided by a CSIRO experiment in a frost-prone site south of Temora. The experiment was dry-sown on 23 April, but only emerged following rain on 8 May. It included varieties with a broad range of maturities, and flowering extended for a fortnight from ‘too early’ until ‘too late’. Air temperature fell to -3.6°C on the morning of 18 October, and despite all varieties suffering ~60% frost damage, yield still very clearly declined with flowering date (Figure 3). Varieties which flowered on time (or early!) yielded the most. 

Figure 3. Relationship between flowering time and yield at a CSIRO experiment at Temora in 2013. The optimal flowering period in this environment is the first week of October

To have had crops flower after the 18 October frost would have required delaying sowing with main season wheats well into July, which in the majority of years is guaranteed to result in poor yields. Delaying sowing past the optimal date for a given variety is not an effective way of managing frost risk, and historically has probably cost more yield than frost itself.

There are more successful ways to manage frost risk than delaying sowing. Another result from a different experiment at the same Temora site (funded through the GRDC stubble initiative and run in conjunction with FarmLink Research) comparing grazed, burnt and retained stubbles clearly demonstrated the insulating effect of stubble on the soil surface during frost events, and resultant increase in frost damage (Table 6). A similar yield result was observed in 2012, but whilst stubble retained treatments appeared visually to have more frost damage, frost scores showed no significant difference. These trials show the potential of burning stubbles in frost prone sites to reduce the risk of damage.

Table 6. Grain yield and frost damage for different stubble treatments applied prior to sowing at the FarmLink and CSIRO stubble initiative site at Temora

Another observation from the 18 October frost and previous events was the strong effect of elevation. This means that frost is able to be managed spatially, and on the SW slopes, farms zoned according to how frost-prone the different regions are, were able to avoid the worst of the damage. Frost sensitive crops are not planted in low lying or frost prone paddocks, and only pasture, hay crops, dual-purpose wheat or barley are grown in these areas.

The last obvious way to manage frost risk is through enterprise diversity. Farms in frost-prone areas should maintain enterprises not exposed to frost risk. These could be off-farm investments, or on-farm enterprises such as livestock or hay.

Putting it into practice

Growers wishing to sow early in 2014 need to get themselves in a position to take advantage of early sowing opportunities should they arise? Early-sown wheat needs weed and disease free paddocks; a double break (e.g. pulse/legume pasture/hay crop followed by a canola crop) is an ideal set-up for early sown wheat, particularly in higher rainfall areas.

Growers also need to have a good idea of what their optimal flowering period is, and how to achieve it from different sowing dates with a range of varieties most suited to their environment. If growers keep 2-3 varieties (one winter and one or two spring wheats), they are able to take advantage of any sowing opportunity that may arise over a three month period (Table 7). It does require growers to be tactical in how much of each variety they grow in a given year, but the potential yield benefits well outweigh the logistical hassles.

Table 7. Wheat maturity groups, sowing windows to achieve optimal flowering windows and examples of best-bet varieties within groups for different regions in Victoria

Early sown crops do require different management to later sown crops. In SW Victoria Septoria tritici is a very serious pathogen of early sown crops, and it is recommended that flutriafol in-furrow and earlier foliar sprays are used when sowing early. Barley Yellow Dwarf Virus can be a threat in all environments, and it is recommended that seed be treated with imidicloprid, or crops closely monitored for aphid infestation and sprayed accordingly.

Nitrogen inputs should be deferred until Z30 to avoid excessive early growth (unless grazing), and if initial soil N is high, sowing rates should be reduced. Yield effects of grazing are variable; sometimes positive and sometimes negative, but the effect size is rarely more than 0.5 t/ha if grazed in the safe window (prior to Z30). It is certainly not necessary to graze early sown crops to maximise grain production, but they can offer significant amounts of forage at a time when feed can be scarce.

References

Cai W, Cowan T, Thatcher M (2012) Rainfall reductions over Southern Hemisphere semi-arid regions: the role of subtropical dry zone expansion. Nature Scientific Reports 2.

Hunt JR, Kirkegaard JA (2011) Re-evaluating the contribution of summer fallow rain to wheat yield in southern Australia. Crop & Pasture Science 62, 915-929.

Contact details

02 6246 5066

james.hunt@csiro.au