Summary

This research demonstrated that dry sowing can still produce high yields, even when establishment is low. Early dry sowing of wheat and canola did not reduce yield in field trials, despite lower and more variable establishment. For canola, sowing at a time to allow emergence during late April to mid-May generally produced the highest yields. Wheat yield was less affected by sowing time. Sowing deeper than recommended into dry soil reduced establishment and yield, particularly in canola, while increasing sowing rates by 50 per cent did not reliably improve yield. Pot trials showed that wheat and canola seed remained viable in dry soil for six to eight weeks. Wheat and canola required approximately 15 to 20mm of rainfall for reliable emergence from two to three centimetres, depending on soil type.

Background

Dry sowing is now widely used by growers to meet the demands of a large cropping program and establish all crops within an appropriate window. However, there is still uncertainty about crop establishment when soil moisture is limited and if there are any potential impacts on grain yield.

This project examined whether changing sowing depth or seeding rate could improve establishment under dry conditions. It also investigated how much rainfall was required for emergence and how long seed could remain viable in dry soil.

Research Aims

The core objectives of the project were to:

• Describe how soil moisture affects crop establishment across different soil types
• Determine how sowing rate and depth can be used to optimise establishment under marginal soil moisture.
• Examine the potential of remote sensing to identify variation in seedbed moisture.
• Improve dry-sowing guidelines and help growers assess establishment risk.

In The Field

Field experiments were conducted during 2023 and 2024 at Hart, Giles Corner and two sites near Bute. Wheat and canola were sown at different times, sowing depths and sowing rates to assess establishment and grain yield. Lentil was also included at Hart in 2023.

Pot trials with wheat and canola examined how much water was required for emergence and whether seed could remain viable in dry soil for extended periods.

Modelling was used to quantify the yield penalty of delayed emergence from dry sowing at Hart in 2023. Long term weather data was used to examine the probabilities of receiving sufficient rainfall for emergence.

The project also used drone and satellite imagery to examine within-paddock variation in soil type, crop establishment, growth and yield.

Results

Across the field trials, wheat sown in late-April averaged establishment of 67 per cent and a yield of 4.0t/ha. For canola, establishment averaged 60 per cent and yield was 2.8t/ha. Canola showed a particularly strong response to earlier sowing. Some early-sown wheat suffered frost damage, highlighting the need to match variety maturity with the expected emergence date.

Deep sowing reduced establishment from 75-80 per cent to 55-60 per cent in wheat and canola. Average wheat yield reduced from 3.9t/ha at the standard depth to 3.6t/ha when sown deep. The effect was larger in canola, where yield reduced from 2.0t/ha at standard depth to 0.9t/ha with deep sowing.

On loam and clay-loam soils, the results support using the recommended sowing depth rather than placing seed deeper in an attempt to find moisture. On sandy soils, shallow sowing reduced emergence and yield.

Increasing the sowing rate by 50 per cent had no effect on average yields. Wheat yielded 3.9t/ha at both standard and higher sowing rates, while canola averaged 2.2t/ha at both sowing rates.

Pot and field trials showed wheat and canola seed could remain viable in dry soil for up to six to eight weeks. About 15-20 mm of rainfall was required for emergence from two to three centimetres, depending on soil type. A relationship between soil matric potential – how hard it is for a plant to draw water from the soil – and seedling emergence was established for canola and wheat that was consistent across loamy soils from Hart, Giles Corner and Bute.

Modelling estimated that dry sowing could delay emergence by up to 20 days between April and mid-May. This delay had a predicted yield penalty of up to 0.5t/ha in canola and 1t/ha in wheat compared with crops that emerged without delay.
Historical modelling showed the probability of establishment from dry sowing was only 10-20 per cent in April but increased to 20-60 per cent by late May.

Variability in soil types also affected crop establishment. At Giles Corner, a dry start in 2024 caused more problems with establishment and early-growth on grey soil than red soil.