What is “LER” and Why Are they on the Webber Chivell Text Messages ?
Recently you may have noticed that Webber Chivell has been publishing weekly “LER” figures for ryegrass on their text messages. LER stands for Leaf Emergence rate and can be used as a guide for the ideal rotation length for rye grass pastures. Aiming to graze ryegrass at the three-leaf stage over the winter period will maximise pasture growth, improve pasture persistence and density. This article explains how to use the weekly LER text information to guide your rotation.
Rotation Lengths
Ryegrass tillers have a maximum of three actively growing leaves on one tiller at a time. As the fourth leaf emerges, the oldest first leaf begins to decay, and therefore represents a waste of feed. (The only two exceptions to this are when 1. A ryegrass seedling first germinates ryegrass, where it can have up to five leaves and 2. When the ryegrass tillers become reproductive – hence we stop counting leaves in late spring). Over the winter period the ideal leaf stage to graze is at three leaves or before canopy closure. This is the point that ryegrass growth rates are the greatest. The LER is driven by temperature at the base of the ryegrass plant and soil moisture. As the weather begins to get colder the LER slows down. Over the June /July period the LER is typically around 20 days per leaf, therefore the ideal grazing rotation would be 3 leaves x 20 days (per leaf) = 60-day grazing rotation or 1/60th of the milking area per 24 hours.
Not All Leaves Are Created Equal.
Ryegrass leaves act like solar panels where they trap sunlight and create food energy. The first leaf to emerge after grazing is generated from the stored energy in the base of the grazed grass stem. Hence the first leaf to emerge is the smallest. As the priority of the ryegrass plant is to regrow the first leaf, root growth stops. Grazing at this stage will make the pasture more vulnerable to being pulled out by grazing cattle.
The Ideal residual height of a grazed is between 4 to 6 cm (between clumps) will ensure that there is sufficient energy reserves to boost the growth of the first leaf. If the pasture has been overgrazed, the first leaf will be tiny because of the reduced energy stores and the subsequent other leaves will also be smaller.
The second leaf is bigger than the first leaf and is focused on replacing the borrowed energy the first leaf used. The whoosh phase of growth occurs between the second and third leaf. In winter there is a 40% increase in leaf weight between the second and the third leaf. The increasing size of leaves is why over winter grazing at the three-leaf stage to maximise pasture growth is promoted.
In spring the difference in size between the second and third leaf disappears, so there is no benefit in waiting until three leaves before grazing, hence in spring two leaf grazing is recommended.
Grazing at the third leaf in autumn/ winter and second leaf in Spring will also improve pasture density. Daughter tillers grow from the base of the ryegrass plant and until they grow their own root systems etc, they depend on the energy reserves of the parent plant. Grazing at the correct leaf stage will allow the daughter tillers to become independent and this will improve overall pasture density and pasture production.
Impact of Soil Moisture and Nutrients
Soil moisture and available plant nutrients can impact the size of leaves/plant growth.  A paddock with less feed could still be at a more advanced leaf stage and therefore should be grazed a head of a paddock with more feed but less leaves. In these situations, the number of “feeds” per paddock will be reduced e.g. you might only get one feed out of the paddock instead of three or four and more supplements may need to be fed to compensate for the reduced pasture availability.
Nitrogen fertilizer can be used on ryegrass pastures to boost pasture yield and pasture will generally respond to nitrogen when soil temperatures are above 4°C, providing other nutrients are not limiting.
