Does it pay to irrigate a perennial pasture over summer?

By Country News on January 20, 2016

With temporary water prices sitting above $230 many farmers may be asking themselves, does it pay to irrigate perennial ryegrass pastures this summer? The decisions made now will not only have an effect on farms in summer but also for the coming 12 to 18 months.

During spring and autumn it makes sense to irrigate perennial pastures, because these conditions are ideal for ryegrass growth. Over the summer period, water-use efficiency tends to be poorer. This is due to lower in-season rainfall, higher evapo-transpiration and higher temperatures. However, the lower response rate does not mean summer irrigation is not suitable for individual farming businesses.

Irrigating perennial pastures over summer

Perennial ryegrass pastures can provide a valuable source of protein in the herd’s diet this season with lower availability of lucerne or vetch hay. Well managed, dense pastures have the potential of producing 4 tonnes DM/ha over the summer period and provide feed in early autumn.

If you plan to only water a portion of perennial pastures through summer, select the best performing paddocks. Often these paddocks are highly fertile, largely dominated by desired species and have minimal weed burden. Remember, pastures are only as productive as their most limiting factor. Poorer performing paddocks should be flagged for renovation in autumn , because they will not be as productive or profitable under summer irrigation.

Maximise your water usage by selecting paddocks which irrigate well. Paddocks with longer irrigation times or poor drainage have increased risk of scalding. Stretching the irrigation interval will not save water, it will only stress the plants and use more water at each irrigation, reducing pasture production and quality. 

Manage the grazing rotation to achieve the optimum balance between quantity and quality for the dominate species in the paddock. In perennial ryegrass pastures, aim to graze at the two to three leaf stage to a post grazing residual of 4-6 cm.

Dry off perennial ryegrass pastures over summer and restart in late summer/early autumn

Currently there is only anecdotal evidence, with no research results, on drying off pastures over summer. The idea is to reduce water usage and resow with pasture to be ready to graze within three to four weeks of watering in autumn. Some farmers succeed while others have been unable to restart their pastures. Those who have had succeeded have at some later stage failed to achieve a repeated good result, which has reduced production, delayed the start to the season as well as adding resowing costs of more than $400/ha.

There are a few factors thought to impact on pasture survival when dried off over the summer period:

-         The longer the time pastures are dried off for, the higher the chance the pastures will not come back at satisfactory pasture densities;

-        The conditions over drier, hotter summers are believed to reduce survival rates of ryegrass tillers;

-        Maintaining a residual of 4-6 cm has anecdotally been seen to be crucial to survival of the pasture sward;

-        A pasture with good density prior to drying off will potentially respond better then pastures with poorer tiller densities; and

-        Younger pastures are thought to be more successful than older pastures.

If you are considering drying off perennial ryegrass pastures and restarting them, consult people who have experience including agronomists. You will find some have not had success while others have. Carefully consider the benefits and risks in both watering pastures through summer and drying pastures off. Complete water budgets and financial budgets taking into account feed requirements for autumn and make the best decision for your farm.

DEDJTR offers a Weekly Irrigation Requirements Summary to help land managers make irrigation decisions. To receive this email service phone Robert O’Connor on 5482 1922 or email 

By- Sarah Brown, Dairy Extension Officer, DEDJTR Tatura



By Country News on January 20, 2016

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