Experiments fine-tune early sowing strategies
GroundCover™ Issue: 109 | Author: Dr James Hunt, Dr John Kirkegaard
Recent research is examining early sowing strategies to cope with drying autumns
Getting wheat to flower during the optimal period for a given location is a huge driver of yield and water use efficiency (WUE).
This is particularly so with the recent pattern of dry autumns and late frosts.
Most current wheat varieties need to be sown in the first half of May to flower during the optimal period for yield in most environments, but this now coincides with a period of declining rainfall.
This article reports on several experiments that have investigated the potential for earlier sowing to counter dry autumns.
Optimal flowering periods
Every production environment has an optimal period in which wheat crops need to flower for maximum WUE and yield. This period is defined by an optimal balance between temperature, radiation and water availability, and decreasing frost risk and increasing heat risk.
The key challenge for maximising whole-farm yield and WUE is to have as much of the wheat crop as possible flowering during this optimal period, but there are hurdles:
- autumn rainfall has declined significantly in the past 17 years;
- most recently released varieties have a narrow range of maturities and flowering times and only flower during the optimal period if sown between late April and late May;
- farm sizes and cropping programs are bigger; and
- growers and advisers need to know the optimal flowering period in their environment, and how to achieve it with different sowing dates and varieties.
Given the above, there are three strategies that can be employed:
- sow winter wheats from late February through to April;
- sow mid-fast wheats from late April onward – including dry sowing if the break has not arrived by this time. This is already becoming the principal adaption to the drying autumns.
Winter wheats option
As February–March rainfall has not declined, it is this rain that can be used instead of relying on the traditional autumn break. Winter wheats offer particular flexibility because they will not develop beyond tillering until they have been exposed to a certain duration of low temperatures (vernalisation). This gives them a stable flowering date from a broad range of sowing dates.
They can be sown even in summer and still not flower until the optimal flowering period in spring.
Because they are often thought of as only grain-and-graze varieties, winter wheats have been undervalued as grain-only varieties. Unfortunately, Australian breeding programs stopped selecting for milling-quality winter wheats more than 10 years ago. However, the broader climate-management potential of winter wheats was demonstrated in experiments in 2013 as part of the BCG Grain & Graze 2 project.
The Curyo district north of Birchip, Victoria, received 50 millimetres of rain in mid-February. BCG planted an experiment (sown 26 February 2013) comprising a range of winter wheat varieties. The grower’s paddock (Kord CL Plus wheat, sown 18 May) provided the experimental control.
The winter lines emerged 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.
Yields of the highest-yielding lines were equivalent to that of the grower’s paddock sown in May (3.6 tonnes per hectare) despite most of the winter varieties having been released over a decade ago, and having no adaptation to the Mallee environment (lacking cereal cyst nematode, salt and boron resistance).
All lines produced useful amounts of forage for early grazing (0.2 to 0.5t/ha) although grazing reduced yields by an average of 0.3t/ha. The experiment pushed the limits of what is considered possible with winter wheats. Normally you would expect to have to sow from early April to maximise yields.
In regions such as southern New South Wales, it has been repeatedly shown that there is a yield benefit from planting slower-maturing varieties early. This was again demonstrated in 2013 by a CSIRO and Kalyx trial, which compared the grazing potential and grain recovery of winter and spring wheats sown at different times and with different grazing regimes.
The site near Greenethorpe, NSW, received 81mm of rain from 24 February to 1 March, followed by 14mm on 23 March, which provided ideal sowing conditions for a winter wheat (EGA Wedgetail) on 26 March. Another 13mm fell on 29 March, and the crop emerged well and grew rapidly.
April was dry and no further rain fell until mid-May. Bolac was planted in its ideal window on 23 April, but into marginal seedbed moisture, and only 30 per cent of the crop emerged at this time. EGA Gregory was sown dry on 8 May, and both it and the remaining BolacA emerged following 8mm rain on 14 May.
Winter was wet, but spring was dry, frosty and hot. The site received 280mm for the growing season. The yields 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 1). EGA Wedgetail and Bolac both had a 0.6 to 0.9t/ha yield advantage over main-season EGA Gregory.
The EGA Wedgetail also provided significantly more forage (2.6t/ha) than both the spring wheats (0.8t/ha for Bolac and 0.4t/ha for EGA Gregory). This debunks a common misconception that winter wheats have to be grazed to manage their canopy and achieve good yields.
Putting into practice
Growers wishing to sow early in 2014 need to be ready to take advantage of early sowing opportunities if they arise. This means being prepared with weed and disease-free paddocks and knowing your area’s optimal flowering period and how to achieve it with different sowing dates and a range of varieties.
Early sown crops also require different management. In higher-rainfall regions, Septoria tritici is a serious pathogen of early sown crops, and it is recommended that in-furrow flutriafol 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 imidacloprid or that crops are closely monitored for aphid infestation. Wheat streak mosaic virus is a serious threat in the higher-rainfall zones of southern NSW.
If planning to graze crops, higher seeding rates and up-front nitrogen application will maximise early dry-matter production. If crops are not to be grazed, then nitrogen fertiliser should be deferred until after GS30 to avoid excessive early growth, and if initial soil nitrogen is high, sowing rates should be reduced (to 50 to 80 plants per square metre).
More information:Dr James Hunt,
02 6246 5066,
GRDC Project Code BWD00018, CSP00178, CSP00160
Region National, North, South, West