Managing Perennial Pastures

Many factors contribute to perennial pasture productivity but as a pasture manager, the factors under your control are soil fertility and plant density. 

Soil testing is essential during summer/early autumn so that adequate amounts of phosphorous can be applied to maximize productivity of perennial grass pastures which are highly responsive to this nutrient.

In late autumn plant density targets are 

  • perennial ryegrass – at least 60 plants/m2but 100 plants m2 is ideal
  • phalaris, tall fescue and cocksfoot – 20 plants/m2

However, the size of the perennial grass plants is also important, even if apparently “dead”. This is called basal cover, or the area covered by live or dormant plant material – either tillers (perennial ryegrass, cocksfoot) or buds (phalaris or tall fescue).  

Target basal cover in late autumn is

  • minimum of 30%
  • ideally 50% or higher – up to 100% 

Basal cover is the key to perennial pasture grass productivity because early winter pasture production (kg/ha DM/day) will approximately double for each additional 20% of the ground covered with either a growing leaf or an active bud.

How to maintain high basal cover?

Basal cover is managed by rotational grazing during summer and autumn. During summer and autumn perennial grass pastures should only be grazed once every 35-60 days to allow enough time for buds and dormant tillers to fully replenish root carbohydrate reserves during the dry time of the year. 

Continuous or frequent grazing of any green leaf re-growth during summer will severely weaken the pasture, reduce basal cover and then significantly reduce winter pasture production.

Grazing over summer/autumn to achieve a 35-60 day spell is best managed by using large mobs and high grazing pressure, for example 30-50 dse/ha for 15-20 days. This can be achieved with a 4-paddock rotation.  

During summer/autumn perennial grass pastures should not be grazed below 800 -1000 kg/ha dry matter (1-2 cm height). Perennial grass pastures can be grazed very short (to 1cm) if they are spelled for upto 60 days following the grazing and if 70% ground cover is maintained. 

Big mobs 30-50 + dse/ha with short grazing periods (15-20 days) are the best way of maintaining 70-100%  ground cover. 

At the “break” dry perennial grass pastures should be no higher than 1 cm to maximise sub clover germination but with at least 70 % ground cover to minimize soil and fertiliser movement off the paddock and minimize bare areas where capeweed and geranium will readily germinate.

Once the season breaks, perennial grass pastures should not be grazed until there are 2-3 leaves per tiller/bud, but they should always be grazed before the oldest (third-forth) leaf dies. Ideal grazing time will be between 20 and 40 days after the break. This time is best determined by counting the number of leaves on 10-20 tillers in a paddock

This period of deferred grazing following the break will significantly increase winter pasture growth – up to double that achieved under set stocking/continuous grazing.

Further increases in winter pasture production can be achieved by applying

  • Gibberellic acid in early winter
  • Nitrogen fertiliser in early winter
  • A mix of gibberellic acid and liquid nitrogen in early winter

The MLA Pasture Paramedic Tool is an objective method of assessing your perennial grass pastures.