Pasture Production & Irrigation

Pasture Production

Pasture growth rates on Tasmanian dairy farms is normally in the range of 6 and 11 tonnes of dry matter per hectare.

The table below summarises 10 years of data assembled by the Department of Primary Industries, Water and Environment (DPIWE) between 1986 and 1996.

In recent times there has been an increase in the use of both irrigation and nitrogen to increase pasture production:

• Irrigation Response - approximately 1 tonne dry matter per megalitre applied, or 3 to 4 tonnes of dry matter per hectare. Higher responses are possible.
• Nitrogen Response - approximately 10:1 eg 2 tonnes of drymatter per hectare for 200 kg N applied.

Efficient grazing management has the potential to further increase pasture production and utilisation. The Department of Primary Industries, Water and Environment (DPIWE) currently have programs in place with the stated goal of achieving increases in pasture production and utilisation. There is potential on most farms for at least a 10 per cent improvement in the short to medium term.

Growth rates measured on five farms assisted and monitored by DPIWE staff between 2002 to 2005 to demonstrate best practice (companion farms) recorded pasture utilisation figures of 9,100 to 13,500 kilograms of dry matter per hectare. Irrigation was used on several farms and applications of 100 to 280 kilograms on nitrogen per hectare.

Computer modelling carried out by Dr Richard Rawnsley (TIAR) using climate and soil data highlights the differences in pasture growth rates that occur between regions and between months.

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Climate & Irrigation - Farm Irrigation

Around two thirds of Tasmanian dairy farms are irrigated. In the higher rainfall areas in the far north west and on King Island the proportion of irrigated farms is less than 50 per cent. There is also a significant proportion of farms in the Deloraine area that are not irrigated.

Irrigation Water Requirements

The table below summarises estimated average irrigation requirements for a number of current and prospective dairy areas throughout the state. The calculations are based on Bureau of Meteorology average rainfall and pan evaporation (crop factor = 0.8). In calculating the total water requirements, an allowance has been made for an 80 per cent application efficiency (ie 20 per cent loss on application).

In determining total farm water requirements allowance needs to be made for the fact that rainfall in a dry year might be 25 to 30 per cent lower than average.

Soil types also have a large bearing on the requirement for irrigation. Dairy farms on King Island and in the far north west on swamp soils are commonly not irrigated.

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Irrigation Availability

Whereas water availability for irrigation in the mainland states is likely to be cut back in future years there are still prospects for increased irrigation in Tasmania.

The total area under irrigation in Tasmania has risen from around 40,000 hectares in 1985 to around 70,000 hectares currently, with an increase in irrigated dairying being one of the main reasons for the overall increase. Irrigated pasture (mainly for dairy farming) makes up 40 to 45 per cent of the total area irrigated in the state and perhaps 55 to 60 per cent of total irrigation water used.

The total licensed water allocation for irrigation in Tasmania has increased greatly over the past 15 to 20 years. Most of that increase has been in the form of water taken into on-farm storage as distinct from direct take from rivers and streams.

The availability of water for irrigation has been identified by the state government and farmer and industry bodies as a key factor in the maintenance of current agricultural output, and the potential for expansion.

The Water Management Act 1999 provides for the preparation of catchment water management plans, which are currently being progressed. These provide for environmental flow, and are a vehicle for integrating the priorities for use of water on a catchment scale. The Act also allows for the transferability of water licences separate from the transfer of land.

The Department of Primary Industries Water and Environment has developed guidelines for the issuing of new water allocations into storage during the winter. There is a moratorium on the issue of licences for direct-take from rivers and streams during the summer.

While most irrigation water schemes in the State are privately owned and operated, the Tasmanian Government is involved in several schemes via the Rivers & Waters Supply Commission:

1. South East Irrigation Scheme - irrigation water supplied along the Coal River from the Craigbourne Dam to Richmond, and by pipeline to Cambridge. Approximately 3,000 ML used annually. No dairy farms included.
2. Cressy-Longford Scheme - in the central north of the state. Irrigation water supplied by channels from the Poatinna power station tailrace. Approximately 10,000 ML used annually. Mainly for annual crops but some dairy farm usage.
3. Winnaleah Irrigation Scheme - in the north east of the state. Irrigation water provided by pipeline (under pressure) to farms in the Winnaleah area. Approximately 3,000 to 4,000 ML used annually, with around two thirds for dairy pastures.

The annual cost for water from the Cressy Longford Scheme varies from around $38 to $55 per megalitre. The cost of water from the Winnaleah Scheme varies from around $46 to $53 per megalitre.

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Meander Irrigation Scheme

The state government is currently undertaking a 43,000 megalitre dam construction project on the Meander River near Deloraine in the central north. When complete it will be able to supply an additional 24,000 megalitres of irrigation water.

From June 2007 the capital cost of a water right is $1,000 per megalitre. In addition there is an annual charge of $35 per megalitre with $7 per megalitre refunded if the water is not used.

There will also be a spot price option for irrigators not wanting to purchase a water right. For 2007-08 the price has been set at $140 per megalitre for water ordered prior to the irrigation season and $220 per megalitre for water ordered during the irrigation season.

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