Summer dormancy - the key to persistent perennial pastures in low rainfall areas

Kate Bryne, AusWest Seeds, Central West NSW

What is summer dormancy?


A plant which expresses the summer dormancy trait does not grow or grows a very minimal amount after rainfall during the summer months (Norton, 2011). These plants have the ability to shut down and avoid the hot, dry stresses of summer and recover after late summer and early autumn rains. Varieties with the trait often originate from the Mediterranean basin where the climate is typically wet in winter and dry in summer. While these plants are dormant in summer and provide very little forage during this time, they provided large amounts of dry matter production during the autumn, winter and spring. The summer dormant trait is present in some varieties of cocksfoot, tall fescue and phalaris.
Planting the most suitable species for your soil type and rainfall will ensure you get the most out of your new pasture. Uplands Hispanic cocksfoot is well suited to light sandy loam soils with low rainfall, while phalaris and tall fescues such as Flecha, are more suited to heavier soils and like slightly more rainfall.

Summer dormant species grow considerable amounts of dry matter during the autumn, winter and spring. As the pasture is performing its best during the winter months, it can out compete any winter weeds which may normally be problematic, thus reducing the need for herbicides.

Like all grass pastures, using a winter growing legume such as a clover or medic will provide nitrogen which will feed the grass and provide quality feed for grazing stock. Using a winter active grass with the legumes helps to minimise animal health issues such as red gut and bloat, while still providing a high quality diet. Including a lucerne in the pasture mix will also benefit the system for a number of reasons. Lucerne grows rapidly during the warmer months, and due to its deep tap root, it can persist in environments with little summer rainfall as it can access water deep in the soil profile which most pasture species cannot reach. The disadvantage of a summer dormant perennial grass is they cannot utilise out of season rainfall events. This normally results in summer weeds infesting the pasture. Including lucerne in these pasture systems provides ground cover and also allows high quality plants to capitalise on any summer rainfall which will help overcome any potential weed infestations.
Will’s property is predominantly on light sandy loam soils and only receives 350mm annually. In 2015, Will was looking for a pasture which would improve their pasture biomass in paddocks and persist in the harsh Hillston environment. With the assistance of Frank McRae, our AusWest Seeds Product Development manager, Will decided Uplands cocksfoot mixed with medics, clovers and lucerne would be a good fit. Will was happy to discover the pasture mix “works really well in providing year-round, high quality feed for our livestock”. The clovers and medics feed the Uplands cocksfoot in the winter providing bulk winter feed while the lucerne carries the stock over summer. This is a perfect example of how summer dormant perennial grasses can be used in a low rainfall pasture system, as up until cocksfoot was included in his pasture mix, he could not find a perennial grass which could persist and perform in his region and soil type.


References:

Norton, M. (2011). Summer dormancy in temperate forage plants .
Norton, M., Volaire, F., & Lelievre, F. (2006). Summer dormancy in Festuca arundinacea Schreb.; the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars. Australian Journal of Agricultural Research, 57, 1267-1277.
Summer dorm_Jan18
Mixed pasture at Will Storrier's farm in Hillston NSW
In low rainfall areas, summer dormancy is a key trait to ensure optimal survival and persistence of perennial grass pastures. Other plants which do not express the summer dormancy trait, respond to summer rainfall and if there is no follow up rain, these plants can die and are lost from the pasture sward . Past research supports this and shows during drought periods, grasses with the summer dormancy trait have much better survival over extended dry periods than other grasses without the trait. For example, Flecha tall fescue, a Mediterranean type with the dormancy trait, had 30% more survival over a 2 year period than cv. Demeter tall fescue, a continental type without the summer dormancy trait (Norton, Volaire, & Lelievre, 2006).

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