Sowing and seeding

Crop suitability and profitable crop production depends on:

• sowing window timing
• soil temperature and moisture
• choosing the most suitable variety for your soil.

Understanding your sowing windows

Different varieties of seeds have specific sowing times due to their response to day length or their vernalisation (need for cold temperature to induce reproduction) requirement, it may also be a mixture of the two. The ideal sowing dates for each variety are focused on grain recovery.

Keep your business goals in mind when deciding on optimum sowing times.

It is important to understand that the recommended sowing windows are calculated to ensure the variety will flower and fill grain during the period where frost and heat stress risk is at its lowest.

This ideal flowering period changes from region to region, hence why some areas can sow one variety earlier than others. Sowing a variety outside its recommended planting window significantly increase the risk of:

• yield loss due to frost damage, if sown too early
• heat stress, if sown too late. 

To determine the ideal window for your area, resources like Australian CliMate are useful in mapping climate trends from over the last 50 years and determining where risk is lowest. Suggested parameters are:

• risk of 10%
• heat stress as >30°C
• cold stress <0°C
• what year you would like to access data from e.g. since 1950.

Measuring your soil temperature and moisture

Soil temperature can have a major impact on germination and seedling survival. Consider that:

• soil temperatures should be below 25 degrees
• heavy, dark clays will absorb and store heat longer than lighter soil types
• good stubble cover and available soil moisture will reduce soil temperatures
• soil temperatures can increase if there is a late heatwave and this is not uncommon in February.

Soil temperature should be measured at 9am at sowing depth over 3 days.

Good soil moisture is always important when sowing but even more so if going early. Consider that:

• if there is limited moisture, soil will be more likely to dry out from the sowing process and therefore seed will either not germinate or partially germinate, then die
• higher ambient temperatures early in the season will increase the drying out process
• high temperatures will also increase established seedlings need to transpire, which will mean they may run out of moisture quickly.

Selecting the right variety

The physiology of a variety is what causes it to move from vegetative to reproductive maturity. These physiologies include:

• vernalisation
• photoperiod
• day degrees.

Varieties are not strictly controlled by one driver, but a varying combination where a one of the above may have more control over maturity than the others.

Variety physiology

Growers need to consider these drivers when planning their sowing at regular times and manage their risk, if wanting to sow early, by understanding the growing habits of different varieties.

Growers need to keep in mind other characteristics that are important to cropping systems, for example grain quality. Make time to discuss this with your local agronomist and identify varieties which best fit your situation.

Vernalisation

Vernalisation is a plant's requirement to be exposed to a cumulative number of cold temperatures before flowering. 

Generally, this occurs when exposed to temperatures below 12°C. 

Varieties with vernalisation requirements can be sown earlier than others as they won’t race ahead if conditions suddenly turn warm as they would still need to meet their cold requirement.

Photoperiod

Photoperiod refers to a plant's response to a change in day length. 

A short day (less than 10 hours of light) will deter flowering in varieties with a strong photoperiod response while a long day (over 14 hours) will accelerate a variety to flower. 

This is why some varieties, with a strong photoperiod response, are known to finish quicker.

Day degrees

A day degree is the maximum temperature minus the minimum temperature of one day. 

Day degrees refers to the accumulated number of degrees that a plant has been exposed to over a certain number of days. In varieties where there is a limited vernalisation or photoperiod response, temperature is the main driver. 

For example, the Gregory variety is known to flower after roughly 1500-day degrees. Hence maturity can fluctuate from season to season depending on whether the conditions in the season are warmer or cooler than usual.

Grazing management

Maturity can be managed in dual-purpose varieties to an extent with grazing management. However, this is not as reliable as the other physiological drivers as maturity can only be delayed by 1 or 2 weeks at the most. This is also assuming crops are evenly grazed across a whole paddock.