A healthy pasture has four to five million tillers per hectare. However, we know that many farmers, particularly in the Upper North Island, are struggling to maintain this density. The drive to maximise animal production, combined with a drier and hotter climate and insect pressure, is placing the ryegrass plant under greater stress during late spring and summer, reducing pasture persistence.

Ryegrass pasture recovery using deferred grazing (foreground) compared with control treatment (adjacent plot in background).

In March 2018, DairyNZ started a plot-scale trial at Scott Farm, near Hamilton, to look at ways of recovering perennial ryegrass populations through grazing management. Through our discussions with a group of Waikato dairy farmers, we identified two management interventions:

DairyNZ scientist, Wendy Griffiths.

1. Extending the spring grazing rotation.
2. Deferred grazing of pasture in spring and summer.
   
   These are being compared with two other management interventions:
   
   
3. Autumn undersowing.
4. Current best practice spring and summer management.

Over the next year and beyond, our research team will track tiller populations to see if there’s a lasting benefit from deferred grazing. We’ll quantify the costs involved, particularly the feed lost during deferral and the reduced energy density when paddocks are re-opened.

We’ll also be seeking to better understand the potential pitfalls of this practice. There are two key questions we’ll aim to answer:

• Does the endophyte transmit from seed to seedling after sitting on a warm soil surface over summer?
• Does the mulch effect that retains moisture contribute to damaging insect populations?

Results from this trial will be published in an Inside Dairy edition next year.

How to use deferred grazing

We recommend you follow these steps:

1. Identify poor-performing paddocks.
2. Close paddocks in line with flowering date:
   • early October for mid-heading cultivars.
   • early November for late-heading cultivars.
3. Re-open paddocks to grazing in:
   • mid- to late January for mid-heading cultivars.
   • late February for late-heading cultivars.
4. Before grazing, check the ground for evidence of seed shed and stomp on the ryegrass plants, which may have lodged, to check that seed will shed with cow traffic.
5. Leave some residual after grazing and consider mowing to 7cm to 8cm to provide a mulch layer for conserving soil moisture.

By adopting these guidelines, you’ll capitalise on perennial ryegrass cultivar flowering patterns and ensure there’s enough recovery time for a paddock to re-enter the farm’s rotation.

This article was originally published in the Upper North Island and Lower North Island editions of Inside Dairy September 2019