Establishment, Methods, Timings and Targets

What is inhibition in the germination process?

The process of water uptake by the seed

What moisture does cereal seed require to start germination?

18%

What is are the main components of a seed?

The embryo is found in the endosperm (granules of starch for energy) surrounded by the bran

What are the two main hormones involved in germination?

ABA = Absicisic Acid

GA = Gibberellic Acid

What does Absicisic Acid do?

It suppresses growth (leads to dormancy) unless broken down by oxygen

What is required to break down absicisic acid?

Oxygen (seed needs oxygen to germinate)

Where is absicisic acid found?

In the aleurone layer

What does Gibberellic acid do?

It promotes growth (germination)

Where is Gibberellic acid found?

In the scutellum

If GA > ABA, what happens?

Germination

If GA < ABA, what happens?

Dormancy

What happens once there is excess GA within the seed once ABA has been degraded by oxygen?

Hydrolactic enzymes (amylace, glucanase, lipase and protease) start to break down starch in the endosperm which releases sugars to allow the embryo to grow

What factors influence seed vigour?

• Variety

• Storage period (longer periods degrade seed)

• Heat during grain drying

• Grain size (smaller = fewer starch reserves)

• Seed treatment

How does low vigour seed vary depending on the conditions it is grown in?

It will still establish well in warm, moist, early drilled conditions (similar level to high vigour seed), however in damp, cold, later drilled conditions it will perform much worse compared to high vigour seed

How does heat have an impact on crop establishment?

Warmer temperatures will increase the speed of chemical reactions (up to a point) and so germination will occur quicker if other conditions are met (moisture and oxygen)

How can rainfall impact inhibition?

Excess water (waterlogging) can reduce oxygen levels and therefore respiration, meaning inhibition takes longer to occur as there is less oxygen to break down the absicisic acid

Why is excess rainfall when temperatures are lower more of a problem for establishment?

Later drilled crops when temperatures are lower are more prone to waterlogging as less water will evaporate and so respiration (oxygen) is limited for a longer period

Which crop is most sensitive to waterlogging and how long will the seed survive before 100% seedling death?

After germination but before establishment, WW seed will survive only 16 days before 100% seedling death (population will be impacted after just 6 days depending on soil type)

What is the optimum temperature for cereal seed germination?

20 to 24 degrees

What is the thermal time (day degrees) from inhibition to emergence in cereals?

150 day degrees

When does soil temperature at 15cm peak during the calendar year?

In August then gradually declines through to February

How long does it take to reach 150 day degrees if a crop is drilled in mid September?

7 days

How long does it take to reach 150 day degrees if a crop is drilled in mid December?

28 days

How does soil temperature impact crop establishment?

Lower soil temperature = lower establishment (25% reduction when drilling from November onwards instead of early September)

Why do sandy soils have a much higher establishment rate than clay soils?

• Friable over a much wider range of soil moisture

• More likely to provide good seed to soil contact

• Smaller amount of water required to stimulate inhibition

• Lower strength allows unrestricted root and shoot growth

Why do clay soils have a much lower establishment rate than sandy soils?

• Poor sed to soil contact as only friable over a very narrow range of soil moisture

• Require a much higher water content to start inhibition

• Not free draining

Which 4 environmental factors influence crop establishment?

• Rainfall

• Waterlogging

• Temperature

• Soil Texture

Why does wheat straw left on the surface after harvest cause an issue in the following cereal crop?

It releases allelopathic chemicals which affect seedling growth (deter germination as chemicals signal there are other plants within that area) - known as autotoxicity

Why is WB and WO less vulnerable to slug damage than WW?

They have an extra seed coat and so are more protected

How many seedlings can each slug kill before emergence?

50

Why does WW following oats have a higher establishment rate than if following potatoes or beans?

The WW is drilled earlier

Why should drilling be avoided from December to February?

The higher seed rate, increased risk and low yield potential dont make it viable

Why does increasing the seed rate with later drilling still result in poor establishment?

The allelopathic chemicals released from the seed deter germination due to competition

What is the seed rate for WW within the optimum period (first half of October)?

300 seeds/m² - aiming for 500 to 600 ears at harvest

What is the risk with increasing the seed rate when drilling later?

It results in plants will less tillers that are more prone to lodging (high risk)

What is the ideal drilling depth for successful establishment?

30mm to 70mm (>70mm and first leaf emerges beneath surface or worse, soil restricts plants from emerging)

How much does establishment decrease with every additional 100 seeds/m²?

It is reduced by 2.6% for every additional 100