Dormancy — the key to more drought-resilient cocksfoot
The dry spring and summer of 2015–16 saw many dryland pastures fail to grow and persist across Tasmania. Results from studies within the Tasmanian Institute of Agriculture (TIA) Herbage Development Program (HDP) have supported this on-farm anecdotal evidence, with large losses of plant populations and the ability of the trial swards to persist and remain productive.
Long-term persistence is a key selection trait for many cultivars developed through the HDP, with many regional evaluation sites across Tasmanian showing HDP species and cultivars persisting for 10 years or longer.
One valuable perennial grass that has shown fantastic persistence in tough conditions is cocksfoot. Cocksfoot is generally hardier and more robust than perennial ryegrass, tolerating lower pH and drier conditions.
Cocksfoot cultivar variability
As with other grass species, there is a range of naturally-occurring cocksfoot cultivars or varieties. Commercially-available cocksfoot varieties fall into three main categories, Continental, Mediterranean (or Hispanic) and Intermediate.
Unlike Continental and Intermediate cocksfoots, Mediterranean cocksfoots, can enter a long period of dormancy when conditions become dry, particularly during summer.
This dormancy increases the plant’s long-term persistence, but still allows the plant to maximise production when significant summer rainfall events break the dormancy mechanism an, the pasture returns with competitive, high-quality and productive growth. This dormancy mechanism ensures plant survival and saves the great expense of regularly renewing pastures following dry periods.
The likelihood of a plant becoming dormant, and the time for which it can remain dormant, is determined by the category into which a variety fits. The three categories of cocksfoot are:
- Summer active (Continental)
- Summer dormant (Mediterranean / Hispanic)
- Summer active with low levels of dormancy (Intermediate)
Summer-active varieties, as described, grow actively during summer. These plants grow as temperatures rise, but require moderate soil moisture levels to persist. These varieties typically originate from Continental Europe and include Megatas* (bred through the HDP). Other commercially-available summer-active varieties include Savvy*, Greenly, Kara and Wana.
Mediterranean or Hispanic varities are also known as summer-dormant cocksfoots. Declining soil moisture induces these plants into dormancy, particularly during summer, but also during drought conditions. Dormancy is broken by high rainfall events (>25mm) when the temperatures start to decline during late summer/early autumn. The HDP has bred and released the successful Mediterranean cocksfoot culitivar: Uplands*. The only other Mediterranean cocksfoot currently marketed is Kasbah. Varieties from this category can remain dormant for much longer periods than the following Intermediate varieties.
Intermediate, as the name suggests, are intermediate in their growth pattern. They tend to have a year-round growth pattern and are hardier than the Continental types, but not as hardy as the Mediterranean types. This dormancy group includes: Porto, Yarck and Currie.
Figure 1: A visual interpretation on the activity, dormancy and rainfall requirements for some cocksfoots in Tasmania.
Selecting the right cocksfoot
Selecting the right cocksfoot is critical for maximising pasture and animal productivity. Factors to consider when selecting a cocksfoot variety include:
- annual rainfall (amount)
- annual rainfall pattern (winter vs summer dominance)
- production system(s)
Selecting the wrong cultivar can impact on pasture persistence and animal production. Selecting between cocksfoot cultivars is determined by the average length of the typical summer dry period and the extremity of summer temperatures.
Continental (summer-active) cultivars are better suited to properties with either access to irrigation or reliable and consistent summer rainfall.
Mediterranean or Hispanic (summer dormant) cultivars are best suited to regions with long periods of moisture stress or unpredictable rainfall, as experienced in the Midlands and Upper Derwent Valley regions of Tasmania. Dormancy is usually broken with decreasing temperatures and/or upon significant rainfall opportunities.
If sowing on a north-facing slope, Mediterranean cultivars are better suited as shown by HDP research. These slopes can have significantly higher temperatures, which impact the persistence of intermediate and summer-active types.
The HDP has a simple factsheet available outlining suitability of cocksfoot and other grass and legume species to rainfall and other growth constraints.
Adapted from an article written by Tony Butler, TIA with support from Bob Reid, Tasglobal Seeds and Eric Hall.
For more information contact:
Tony Butler, TIA
M: 04 07 912 761