Assessing pastures following rain

Recent rainfall events, although by no means drought breaking, have led to a flush of green feed across the Coonamble and Warrumbungle region.

Many producers have got some oats or winter wheat in the ground and with the forecast of warm days, and the hope of follow-up rain, we might see a better winter than 2018.

Our pastures have really done it tough over the last two years, sporadic rainfall events have led to some growth, which in most cases, has been quickly grazed by stock or kangaroos. Most of our native and introduced perennial pastures are tolerant to drought. They run out of moisture, then go dormant holding energy in their root reserves, which they use to grow leaves once it rains. The leaves are like solar panels, they capture light and turn it into energy which the plant then uses to grow more leaves, produce seed and restock energy reserves ready for the next dry period.

Clover, medics and ryegrass

Image: Clover, medics and ryegrass will often fill in the gaps in perennial grass pastures. As will weeds such as saffron thistle!

If we graze plants too early following a rainfall event, we reduce the plants ability to capture energy to grow more leaves. Apart from reducing the amount of dry matter produced, we are also reducing the plants ability to store energy and therefore persist through the next dry period. Put simply, it is not the drought that kills plants, it is the depletion of energy through false breaks and then subsequent over grazing.

How well your pasture manages drought depends heavily on the species in your pasture. Pastures that are predominantly annual based will generally establish quickly as long as the seed bank has not been depleted by numerous false breaks or being vacuumed up by sheep. Hard seeded varieties of annual legumes will be much more likely to still be around than soft seeded varieties.

Native pastures normally handle drought well but the last two years may have reduced perennial grass populations. If this is the case, they may need to be managed so that new plants are recruited. Much of our native grass country has naturalised legumes and rye grass which may create ground cover quickly. Keep in mind, that weeds such as thistles and wild turnip may also try and fill some of the gaps so be mindful of weed control options.

Most of the tropical grasses recommended for our area are very resistant to drought. Rhodes grass is not as resistant as bambatsi, digit or consol lovegrass. Lucerne is not so tolerant to long term drought especially under high grazing pressure. The higher the winter activity, the less tolerant to both grazing and drought.

NSW Department of Primary Industries has developed some good guidelines on assessing pastures and making decisions on when to graze.

  • Paddocks with moderate to good density of desirable species but have been under severe stress from drought and grazing pressure should be a high priority to rest. These paddocks should be allowed to grow through to phase 3 growth (flowering, see figure 1) before they are grazed
  • Paddocks with moderate to good density of desirable species but have not been under severe stress from drought and heavy grazing could be grazed conservatively, with the aim to rest soon. Grazing would start once the plant have hit phase 2 growth (six leaves on each tiller)
  • Paddock where density is too thin for it to become a worthwhile pasture after a return to more normal conditions may be ear marked for cropping or re-sowing. In this case it may be used as sacrifice paddock. These are the paddocks you would graze first following the break Alternatively if you plan to let the paddock naturally thicken up, you would need to keep stock out and allow grasses to set seed. This practice will not work with Lucerne dominant pastures.

Simplified growth curve of pastureThere are a number of factors you need to take into account if you plan to renovate or crop old pasture paddocks. These include weed pressure, soil constraints and the ability to farm the paddock (spray or direct drill) due to slope, rocks and timber. Keep in mind that some native grass paddocks may fall under the land management code, speak to a Local Land Services Sustainable Land Management team member for more information.

Figure: Simplified growth curve of pasture (Source: The PROGRAZE Manual 8th Edition)

Discuss sowing options and get further advice with your local agronomist or LLS staff member as required.

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