Power of understanding heading date on-farm

The heading date on farm is an important piece of the puzzle to ensure pasture supply meets demand in spring and stagger the dates that paddocks go to seed.

Understanding plant growth and lifecycles is essential for good pasture management. Knowing a plant’s heading date is an important piece of the pasture management puzzle to ensure pasture supply meets demand in spring.

Agricom defines the heading date as the point when 50% of plants in a ryegrass cultivar have fully emerged seedheads. This date is relative to the industry standard cultivar Nui whose heading date is considered ‘Day 0’.

Day 0 is typically referred to as the 22 October, however due to climatic and latitude differences across New Zealand, this is not the case for all regions. For example in recent years, Day 0 for Palmerston North has occurred between 9-14 November. 

Why is heading date important?

For dairy farmers, understanding heading date means being able to:

Tailor the pasture supply curve to match demand in spring

Aligning pasture growth and animal demand is vital for reaching the balance date more quickly. The selection of heading dates can be used as a tool to ensure there is enough early spring growth to support peak production and mating while having enough late spring pastures that maintain pasture quality. 

Predict when paddocks will ‘flush’

A paddock’s ‘spring flush’ can be predicted by the heading date of the cultivar. This flush marks the onset of reproductive development, leading to increased spring growth independent of climatic conditions and nutrient status. It typically begins six weeks prior to a cultivar’s heading date. Understanding this allows us to identify paddocks that will require quicker grazing rotations and can be managed with longer rotations.

Prevent seedhead emergence

By selecting cultivars with different heading dates on farm, we can stagger the dates that paddocks go to seed. This helps manage seedhead emergence throughout spring, assisting in the maintenance of pasture quality.

Integrating different heading dates on-farm

Strategically selecting cultivars with varying heading dates ensures that your entire farm doesn’t go to seed simultaneously. This approach helps distribute spring growth more evenly throughout the season.

A general recommendation is to plant 30% of the farm with early or mid-heading ryegrasses to boost early spring growth, while the remaining area is planted with late to extremely late heading ryegrasses for improved late spring and summer feed quality. A good rule of thumb is to put earlier flowering cultivars on country that dries out earlier to match the plant’s growth profile with the available moisture. 

Aftermath heading (AMH)

It is also important to consider the aftermath heading trait (AMH), which refers to the amount of seedheads that are produced after the initial primary seeding event.

Cultivars that continue to produce large numbers of seedheads after the initial seeding event tend to be harder to manage through the summer months, requiring more time and effort for paddock topping. Cultivars such as Reason, Legion and Three⁶⁰ diploid perennial ryegrass and the tetraploid perennial ryegrass Align demonstrate significant advancements in reducing AMH, resulting in pastures that are leafier and easier to manage for summer quality.