The science behind grazing at the third leaf stage

By hitting the right leaf stage, you can grow 10-15% more grass to substitute the costs on inputs.

Grazing ryegrass at the right leaf stage is crucial for maximising pasture yield and maintaining long-term pasture health. And aiming to graze as close to the third leaf stage as possible enhances the quality of the forage and encourages a sustainable growth cycle that supports what your herd need now and into the future. Here’s how!

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How does leaf stage affect pasture quality and growth?

Once ryegrass has been grazed, there’s only a little “solar panel” area left for regrowth, so it has to pull energy stored in the roots and stem. This energy is in the form of sugar which gets used up after grazing because the plant uses it to grow new leaves (2).

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When you graze before the second leaf, it doesn’t give the plant a chance to replenish the roots and the stem, meaning that you might be sacrificing the long term persistence of the pasture. Over time, consistently grazing before the second leaf stage decreases the density of the pasture, the dry matter yield on subsequent rounds, and the soil health.

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“In support of this, anecdotal feedback from farmers on rotation lengths of less than 20 days for a significant period over the spring and early summer, is that their pastures were not persisting and had ‘thinned’ out after 3 or 4 years. The implications of this decline in productivity and persistence are significant, with greater costs in re-grassing, and more supplement purchased.”

— Clarke, Donaghy, and Casey 2021

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On the other hand, grazing after the third leaf stage drops the quality and digestibility of the pasture. At this stage, the plant starts diverting its energy to reproductive growth, the protein content of the plant starts to decrease while the fibre content increases—making the grass less nutritionally valuable.

The reason why we always encourage farmers to graze as close to the leaf stage as possible is because you can expect:

• Increased pasture production
• Reduced supplement costs
• Reduced need for fertiliser inputs
• Improved pasture persistence

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“Simple calculations indicated 10% to 15% more grass was grown when the grazing rotation was extended to be continually closer to the 2.5- to 3-leaf stage.”

— Clarke, Donaghy, and Casey 2021

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Fun fact: Did you know that most farmers don’t hit the third leaf stage?

It’s common to over-estimate and graze before the third leaf stage, especially with the addition of nitrogen which greatly affects the size of the leaves, but not the leaf emergence rate. A 2014 study stated that

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“49% of measured paddocks were grazed too soon based on leaf stage”

— McCarthy et al, 2014

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How do you determine leaf stage?

Start with finding the remnant leaf on the tiller. The remnant leaf is the youngest leaf on the tiller that was grazed and it has a blunt tip at the end caused by the bite. To get the leaf stage, only count the leaves above the remnant leaf—the reason why we don’t count the remnant leaf is because the focus on our prediction is to understand the growth cycle of your pastures.

To get an accurate average leaf stage for your paddock, you need to pull at least 10 tillers. You should see a large amount of variation in leaf stages in a single paddock (this is normal!). A single paddock grazed can have a range of up to 1.5 leaf stages.

Just a note that it can be hard to accurately measure leaf stage in a paddock past the third leaf stage or when canopy closure has occurred because leaves will start to die off and decompose on the ground.

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What leaf stage should I be aiming for?

There are lots of variables that can complicate leaf stage, here are some of the most common scenarios:

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Nitrogen and Canopy Closure

Adding nitrogen results in large, fast growing leaves; but you should know that nitrogen does not affect the rate at which leaves emerge. So it’s possible to have high covers with low leaf stage when using nitrogen.

Halter’s studies show that with the addition of nitrogen, it’s common to see 3000 kgDM/ha covers at second leaf stage or 4000 kgDM/ha covers at 2.5 leaf stage. We were able to verify this by manually pulling (lots and lots of) tillers.

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Waiting for pasture to hit the third leaf stage might not be possible in these cases if the paddock is approaching canopy closure. Canopy closure happens when ryegrass grows so dense and tall that sunlight is unable to reach the soil, leading to the stem and lower leaves being starved of light.

It’s important to graze your pasture near or before canopy closure even if your pasture is not at the desired third leaf stage. This is because sunlight needs to reach the base in order to

1. stimulate new leaf growth
2. keep lower leaves and the stem green and high quality

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To maintain pasture longevity, it’s important to consider the factors that can lead to high covers at a low leaf stage. This can include your nitrogen strategy, chosen round length, amount of supplement, or area in rotation. Adjustments to your pasture management may help avoid the negative effects of repeated grazing before the second leaf stage.

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Winter and low temperatures

In the winter, ryegrass will have shorter and smaller leaves because there isn’t enough heat to enable full leaf growth. With less shade, smaller leaves create a higher light environment. This is why winter growth is often considered to be very good quality/high energy feed.

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Ultimately, do what’s right for your farm and the season you’re in

Even though we (and the science!) recommend that you graze at the 2.5 to 3 leaf stage for the health of the pasture, this isn’t always feasible. It’s always going to be a trade off between leaf stage and other important factors like cow demand, health and condition, and what’s happening with the environment.

During winter and early spring in dairy farming, your focus likely shifts from leaf stage to getting enough pasture cover and cow condition for calving. Often, you might need the pasture to grow past the 3rd leaf stage.

In late spring, the emphasis goes back to grazing at the 2.5 to 3rd leaf stage, balancing high-quality pasture for peak milk production with effective surplus management.

Later in the year, farmers will bank feed in late autumn, letting pasture go past the third leaf stage in order to have enough in spring to meet upcoming demands.

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Overcoming the Barriers with Halter

The two biggest challenge with leaf stages are knowing what to count on the tiller (remnant leaves and daughter tillers make counting difficult and unreliable), and even with expert-level understanding, going into paddocks and pulling tillers, counting leaves, and record keeping is a very time-consuming process.

The Halter app gives farmers real-time predictions of the leaf stage in every paddock and gives full-farm leaf emergence rate data so that they can proactively set their round length to hit the third leaf stage. If you’re a Halter farmer, reach out to your customer success representative to learn more about how to make the most out of your pasture insights!

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References

1. Clarke, Brian, Danny Donaghy, and Marie Casey. 2021. “Working with Dairy Farmers to Improve Their Pasture Management Skills through Better Understanding the Principles of Ryegrass Growth.” NZGA: Research and Practice Series 17. https://www.nzgajournal.org.nz/index.php/rps/article/view/3462 (November 23, 2023).
2. Donaghy, D. J., L. R. Turner, and K. A. Adamczewski. 2008. “Effect of Defoliation Management on Water‐Soluble Carbohydrate Energy Reserves, Dry Matter Yields, and Herbage Quality of Tall Fescue.” Agronomy Journal 100(1): 122–27.
3. Fulkerson, W. J., and D. J. Donaghy. 2001. “Plant-Soluble Carbohydrate Reserves and Senescence - Key Criteria for Developing an Effective Grazing Management System for Ryegrass-Based Pastures: A Review.” Australian Journal of Experimental Agriculture 41(2): 261.
4. Mccarthy, S. et al. 2014. “Opportunities to Improve Grazing Management.” Proceedings of the New Zealand Grassland Association 76: 75–80.
   Rawnsley RP, Langworthy AD, Pembleton KG, Turner LR, Corkrey R, Donaghy DJ. 2014. “Quantifying the interactions between grazing interval, grazing intensity, and nitrogen on the yield and growth rate of dryland and irrigated perennial ryegrass”. Crop and Pasture Science 65: 735-746. https://doi.org/10.1071/CP13453
5. Ong CK, Marshall C. 1979. Growth and survival of severely-shaded tillers in Lolium perenne L. Annals of Botany 43: 147-155. https://doi.org/10.1093/ oxfordjournals.aob.a085619