For long term productivity and persistence of lucerne stands, best practice management is to rotational graze with a minimum period of at least 35 days recovery. This spell period is critical as lucerne relies on stored energy in its roots to regrow.
The lucerne plant won’t start putting energy for storage back into growth until after 15-20 days following a defoliation through cutting or grazing.
Actual grazing duration should be targeted between 5-7 days until all green leaf and soft stem is removed.
If the grazing period is too short, the crop will not be adequately utilised, and wastage occurs.
If the grazing period is too long, sheep for example, will actively graze new crown shoots once they have reached a grazeable height.
Remove remaining stubble and stems after grazing if stock pressure is low or uneaten. This allows better utilisation on next grazing or cuttings.
Different strategies and focus should be applied to lucerne stands in different seasons and climates. This includes shortening rotations to maximise yield and animal performance in spring and summer, while in autumn allowing approximately 50% flowering for root reserves to replenish for survival over winter for early spring production.
The focus for spring grazing is on stock performance, maximising live weight gains and yield.
A fundamental, yet unavoidable, reality of lucerne production is that the yield and quality are inversely related. This means that as yield increases, the quality of the stand generally declines and is often referred to as the “yield-quality trade-off”.
The timing of the grazing or harvest is a compromise between yield, quality and persistence. Grazing adds another level of complexity to this due to animal performance and health factors.
Researchers have proposed a relative forage yield and quality summary diagram showing the different stages of lucerne with different yield components and digestibility. As the yield of the crop increases through stages of maturity (vegetative to post-flower), stems make up the greater proportion of total yield and the digestibility of the stem material declines because of increased lignin content. The leaf yield contributes little to the total yield beyond the first flowering stage.
Basic principles in the yield-quality trade-off graph can relate directly to dryland lucerne grazing management. If rotation lengths are shortened and grazing occurs too early in the vegetative state, it may reduce the replenishment of root carbohydrates and affect regrowth and persistence. It has been well documented that frequent early grazings can reduce root size and stem height (Moot et al. 2003).
Even though it is high quality feed, grazing immature and actively growing ‘lush’ foliage can result in animal health issues. Grazing in the later stages of maturity can result in less digestible and nutritious feed and, in turn, result in poor animal performance. This is often observed through a high proportion of remnant stem, resulting in animals lacking adequate nutrition and losing condition.
In addition, extended grazing periods may result in new shoots from crown buds being grazed-off, or allows the regrowth of shoots to become more accessible to grazing animals that are high in protein and subsequently eaten by livestock leading to animal health issues.
Summer grazing period should focus on utilising the crop yield to maximise animal productivity.
The most limiting factor for dry matter yield through this period is directly related to the availability of moisture. The onset of drought conditions, or prolonged moisture stress periods during summer, has several implications which include reduction of dry matter production, reduced transpiration which can increase sward temperatures, accelerated phonological development and senescence and reduced quality. Drought-stressed crops can still accumulate nodes on basal buds after hard grazing during summer which will allow for a rapid response after rainfall. Therefore, spelling is critical following a grazing so that stock are removed to protect developing lucerne buds.
The autumn time is a critical period in the physiological process of lucerne growth. The objectives through this period should be to focus on managing the stand for persistence and production in the subsequent year rather than focus on animal performance.
If sowing a winter-active lucerne, grazing rotations should be lengthened.