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Assessing your pasture
Published 9 February 10
How the Grass Plant Grows
To maximise the production from grazed grass it is necessary to ensure the optimum production and intake of the most palatable, highest feed value grass. Grass naturally wants to grow a seed head, but this will reduce sward palatability and digestibility, so grazing systems need to prevent this happening if grass quality and quantity are to be maintained. Effective systems graze the plant at the point where it is growing fastest with the highest ratio of leaf to stem. The plant grows fastest between the emergence of the second and third leaves, when sunlight capture is maximised. The amount of grass grown is 25-30% more with the third leaf present than with just two. The fastest growing paddock on-farm has three leaves. A clump of ryegrass is made up of tillers. Each tiller has its own independent roots. They reproduce by budding off daughter tillers at the base, which build up new clumps. Buds are your future sward density.
Grass is a living plant in a continuous cycle of growing and dying, so a ryegrass tiller only has three live green leaves at any time. Water and fertiliser will influence the size of those leaves. Grass has a central leaf pushed up from the growing point at the base of the tiller; a second leaf, collecting sun and producing sugars; and a third leaf doing the same. The oldest leaf will die as the newest leaf takes its place, so the plant will only ever have three living leaves.
A new leaf takes a minimum of six days to appear in spring. But depending on the temperature this will be extended to 30 or 40 days in winter. This can be influenced by soil moisture in extreme cases.
Therefore, in spring when it is taking six days for a new leaf to appear, three leaves will appear in 18 days, so the pasture will be ready to graze 18 days after grazing or cutting. When new leaves appear at
a slower rate, the optimum time between grazings will be longer. However, the plant also wants to reproduce, so it aims to grow reproductive tillers which put all their energy into producing a seed head.
This is influenced by:
- Day length,
- Temperature - with a ryegrass typically requiring an air temperature of about 10 degrees C for a week,
- Grass variety.
A reproductive tiller becomes fibrous and suppresses the daughter tillers at the bottom. When managing a grazing sward we need to understand this and manage grass to resist reproduction and to maximise grazing potential.