Western Australia
April 30, 2013
- Canola can be dry sown if the soil is really dry.
- Moisture in ‘dry’ soil can trigger premature germination, resulting in seedling death.
- If sowing into wet soil, make sure there is no ‘break’ between the surface moisture and sub-soil moisture, or there is sufficient shallow moisture to support the crop.
- If sowing dry, the maximum allowable rainfall on a dry soil is 5mm for sandy soils, 8mm for loams and 10mm for clay.
- If rain exceeds these limits, wait up to two days for evaporation – especially when conditions have not been warm and dry.
Canola can be successfully dry-sown or seeded into wet soil.
For these approaches to be successful, dry-sown crops need to be sown into really dry soil to avoid premature germination and ‘wet’ soils need to contain sufficient moisture to ensure the crop does not run out of water.
These are the key findings from two years of trials at Merredin and Kellerberrin that have shown dry-sowing or seeding into wet soil can maximise yields in different conditions, and that both carry risks of seed and seedling losses if conditions are not right.
Department of Agriculture and Food WA researcher Darshan Sharma told this year’s Agribusiness Crop Updates sowing canola into moisture provides the best results when rainfall connects moisture in the top 10cm of soil with subsoil moisture.
This scenario ensures sufficient moisture in the seedbed for good germination and adequate deeper moisture to support continuing growth.
When dry sowing canola, soil moisture should not be more than 30 per cent of plant available water capacity.
About 5mm of rain will take a dry sandy soil past this level and make it too damp for dry sowing.
A fall of about 8mm will take a loamy soil past the 30 per cent cut-off, while a dry clay soil can tolerate about 10mm of rain before becoming too damp for dry sowing.
Any rain above these levels should be allowed to evaporate before sowing to avoid having enough water in the soil to germinate the seed but not establish plants (a false break).
Calculating evaporation rates can be challenging. At the Kellerberrin trial site the daily evaporation rate in April 2011 was 5.4mm.
Moisture stress
Canola plant emergence increased with increased soil moisture in irrigated trials at Merredin in April 2011 and April 2012.
In plots exposed to early moisture stress, daily seedling loss in the first 15 days was about 2.8 per cent, compared to 0.8 per cent plant loss in trial crops not subjected to early dry conditions.
Plant losses also changed over time in moderately stressed treatments, with losses higher in crops sown after April 20.
Additional branching can offset plant losses, so a low population of early-sown canola can, in some cases, be sufficient to achieve maximum yield, especially in dry conditions, according to Dr Sharma’s research.
Non-wetting soils
In a trial on a non-wetting soil, small irrigations - replicating light falls of rain - proved insufficient to wet the seedbed thoroughly. Some seed remained dormant in the soil and did not germinate until the season break.
This germination pattern could buffer canola crops sown dry into non-wetting soils against a false break, but this requires further research, according to Dr Sharma.
NOTE: This research was carried out by DAFWA with support from the Grains Research and Development Corporation (GRDC) and Department of Agriculture, Fisheries and Forestry (DAFF) through the National Adaptation and Mitigation Initiative (NAMI), plus CSIRO, the WA No-Tillage Farmers Association and the Kellerberrin Demonstration Group.
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