Why use the leaf stage?
Leaf stage helps to identify when a paddock is ready to be grazed and indicates how well rotation length fits with current pasture growth conditions. In spring, using leaf stage will impact on the amount and quality of pasture grown later in the season. Further, good grazing management in spring increases tillering in perennial ryegrass.
The leaf stage takes into consideration:
Quantity and quality of pasture accumulated
- Grazing too late, increasing rotation length beyond the 3-leaf stage results in wastage as the first leaf begins to die. This dead material reduces pasture quality.
- Fast rotations where pastures are consistently grazed before the 2-leaf stage of regrowth will significantly reduce pasture growth and yield.
Tiller energy status and the ability for a pasture to recover after grazing
- Consistently grazing pastures before the 2-leaf stage significantly reduces pasture regrowth as it does not allow the plants reserves to be fully restored
How to incorporate leaf stage into grazing management?
- To determine the leaf stage of a perennial ryegrass pasture, collect 10 ryegrass tillers across the paddock. Ryegrass tillers are usually red/purple at the base.
- Compare each of the tillers with the picture below, if they are all between the two and three leaf stages then the paddock is ready to be grazed.
Assessing rotation length
Rotation length is a practical way to manage pasture growth and quality. Through rotation length we can manage leaf stage and through leaf stage we can evaluate if the rotation length is optimal.
Rotation length can be adjusted to different times of year and pasture situation.
- Increasing rotation length to graze pasture at the 3-leaf stage results in a yield advantage compared with grazing at the 2-leaf stage. For example, the yield advantage was measured to be 1.1 t DM/ha/year for Canterbury irrigated pastures.
- Slowing rotation length to graze closer to the 2 leaf stage can be necessary when you can’t see any bare ground through the pasture e.g. canopy closure or when you are trying to reduce growth rates to help manage a surplus.
- Grazing before the two leaf stage should not be done repeatedly or the plant will die. If pastures are consistently at canopy closure before the two leaf stage, re-assess the nitrogen fertiliser policy (nitrogen grows bigger leaves) or grazing intensity. High post grazing residuals result in canopy closure earlier in the regrowth cycle.
- Increasing rotation length to graze pasture after the three leaf stage reduces pasture quality as older leaves begin to die. However, grazing beyond the three leaf stage is a strategy to manage feed supply at key times of the year, such as transferring pasture from winter into early spring or spring into summer deficit periods.
Leaf appearance rates depend on soil temperature and moisture availability, with leaves taking longer to appear when it is cooler or when soil water is limited.
To determine rotation length
|Average temperature||13 - 16oC||18 - 20oC||14 - 20oC||10 - 13oC|
|Time taken for one leaf to fully grow||9 - 11 days||8 - 10 days||8 - 12 days||11 - 15 days|
|Average temperature||11 - 16oC||16 - 20oC||12 - 20oC||9 - 12oC|
|Time taken for one leaf to fully grow||9 - 13 days||8 - 11 days||8 - 14 days||12 - 16 days|
|Average temperature||9 - 16oC||16 - 19oC||10 - 18oC||7 - 10oC|
|Time taken for one leaf to fully grow||9 - 16 days||9 - 11 days||10 - 17 days||15 - 21 days|
|Bay of Plenty|
|Average temperature||10 - 16oC||16 - 20oC||11 - 20oC||7 - 12oC|
|Time taken for one leaf to fully grow||9 - 15 days||8 - 11 days||8 – 16 days||12 - 21 days|
|Average temperature||10 - 16oC||14 - 18oC||10 - 18oC||8 - 10oC|
|Time taken for one leaf to fully grow||9 - 15 days||10 - 12 days||10 - 17 days||15 - 18 days|
|Lower North Island|
|Average temperature||10 - 16oC||14 - 20oC||10 - 18oC||8 - 10oC|
|Time taken for one leaf to fully grow||9 - 15 days||8 - 12 days||10 - 17 days||15 - 18 days|
|Top of South Island/Westland|
|Average temperature||10 - 16oC||14 - 18oC||10 - 18oC||7 - 9oC|
|Time taken for one leaf to fully grow||9 - 15 days||10 - 12 days||10 - 17 days||16 - 21 days|
|Average temperature||7 - 14oC||13 - 18oC||6 - 16oC||2 - 8oC|
|Time taken for one leaf to fully grow||10 - 21 days||10 - 13 days||11 - 28 days||18 - 72 days|
|Average temperature||7 - 13oC||13 - 18oC||6 - 15oC||2 - 8oC|
|Time taken for one leaf to fully grow||11 - 21 days||10 - 13 days||12 - 28 days||18 - 72 days|
The table presents approximate leaf appearance rates for different regions based on average temperatures and soil water availability of at least 40%.
- To determine the minimum rotation length (i.e. two leaf stage) multiply the time taken for one leaf to grow by two
- For the maximum rotation length multiply the time taken by three.
This can be used as a guide but it is important to determine the leaf stage of your own pastures using the ryegrass picture outlined above
Leaf stage should be used in combination with yield measurements and feed demand information
Rather than rigid adherence to a single leaf stage grazing target, grazing management must also consider needs such as pasture cover targets, feed demand requirements and pasture quality. For example, during periods of high growth rates in spring, lower stocked-farms may graze closer to the 2-leaf stage to control pastures covers and maintain pasture quality.