printStock Journal Article - November 2024
Author: Emma Shattock, Elders
Grazing to manage ground cover is an important part of a sheep production system. While maintaining ground cover is important year-round, it comes into focus during summer and autumn when annual species are no longer growing and dead material is breaking down. Setting targets to maintain ground cover can lead to benefits for pasture recovery and erosion management, particularly in stubbles.
Ground cover is a term that describes and material on or above the soil surface. Plant material is the most important component of this and can be further classified as canopy (standing) or contact (on soil surface). Whether or not this material is attached to the soil also matters. For example, where wind erosion is a major concern, ground cover needs to be attached to the soil surface.
Maintaining a healthy level of ground cover can have many positive benefits. Perhaps the more obvious is its role in helping protect the soil from damage by raindrops and erosion from wind, water or traffic. Without protection, this erosion can lead to the loss of important nutrients and organic matter, cause quality issues in waterways and fill dams and creeks.
Pastures maintained with an adequate level of ground cover tend to recover faster. By slowing the movement of water across the soil surface, there is more time for the water to infiltrate the soil. The extra plant material can also increase the soil organic matter content and provide nutrients. This can increase biological activity, nutrient efficiencies and overall soil health, creating flow on effects for faster pasture recovery. With higher levels of ground cover, there can also be a reduction in the weeds that usually take advantage of bare ground for germination.
Setting targets is an important part of managing ground cover levels. A rough rule of thumb is to maintain a minimum of 70% ground cover in pasture paddocks, although this may need to be higher for steeper country and drainage lines. Exact targets will vary depending on factors like rainfall amount and intensity, soil type, slope and seasonality. The goal is to achieve a system where run-off is minimal and soil erosion is no greater than soil formation.
It is important to regularly monitor ground cover levels, particularly through summer and autumn. There are many photo guides available that can help when making an assessment.
Stubbles are often unique in terms of grazing and ground cover management. A minimum of 50% ground cover is recommended for managing wind erosion in stubbles, although this may be higher for lighter, more susceptible soils or where water erosion is also a concern. Studies have shown that standing stubble at least 10cm high can be twice as effective as loose, flat stubble in reducing wind erosion.
Grazing for short periods with high stocking rates can be useful to maximise grazing opportunities while keeping pressure on soil condition as lower.
Much of the nutritional value of a stubble comes from grain and green plant matter and sheep will graze these preferentially. Stubble stem and leaf material are high in fibre and poorly digestible, making them below the quality required for maintenance by a dry ewe.
It is important to assess the feed value of a stubble before putting sheep in, while checking for any large amounts of spilt grain that could pose an acidosis risk. Stubbles need to contain at least 40kg/ha of grain to maintain dry ewes or at least 100kg/ha for lambs. Once below these levels, supplementary feeding with high energy and high protein grains can be used to improve stubble utilisation until the target minimum ground cover threshold is reached.
Supplementation with vitamins and minerals that may be lacking in a stubble can help improve stubble utilisation and feed conversion. Consult your livestock advisor to find a supplement that best suits your situation.
By monitoring ground cover regularly and adjusting grazing pressure as needed, graziers have the ability to not only reduce soil erosion but also improve overall soil health and water utilisation. This creates a better environment for pasture recovery after a grazing period or following an opening rain. Ground cover targets should be tailored to each farm and paddock and can be simple to assess and monitor.